U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2008–1177

Yellow-billed Cuckoo Distribution, Abundance, 

and Habitat Use Along the Lower Colorado River 

and its Tributaries, 2007 Annual Report
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Funded by the Bureau of Reclamation 

Yellow-billed Cuckoo Distribution, Abundance, 

and Habitat Use Along the Lower Colorado River 

and Its Tributaries, 2007 Annual Report 

By Matthew J. Johnson, Scott L. Durst, Christopher M. Calvo, Laura Stewart, 

Mark K. Sogge, Geoffrey Bland, and Terry Arundel 

Open-File Report 2008-1177 

U.S. Department of the Interior 

U.S. Geological Survey 
U.S. Department of the Interior 

DIRK KEMPTHORNE, Secretary 

U.S. Geological Survey 

Mark D. Myers, Director 

U.S. Geological Survey, Reston, Virginia 2008 

For product and ordering information: 

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not imply endorsement by the U.S. Government. 

Although this report is in the public domain, permission must be secured from the 

individual copyright owners to reproduce any copyrighted material contained within 

this report. 

Cover: Picture of Yellow-billed Cuckoo (© Bob Steele/VIREO). 

Suggested citation: 

Johnson, Matthew J., Durst, Scott L., Calvo, Christopher M., Stewart, Laura, Sogge, 

Mark K., Bland, Geoffrey, and Arundel, Terry, 2008, Yellow-billed Cuckoo distribution, 

abundance, and habitat use along the lower Colorado River and its tributaries, 2007 

Annual Report: U.S. Geological Survey Open-File Report 2008-1177, 274 p. 

[http://pubs.usgs.gov/of/2008/1177/].

ii
Contents 

Executive Summary.............................................................................................................1

Chapter 1. Introduction ........................................................................................................3

The Lower Colorado River Multi-Species Conservation Program.................................3

Yellow-billed Cuckoo Breeding Biology, Habitat, Distribution, and Status..................4

Breeding Biology .......................................................................................................4

Habitat Requirements.................................................................................................5

Historic Abundance, General Breeding Distribution, and Current Conservation 

Status in the Western United States..................................................................5

Historic Population Status Along the Lower Colorado River....................................7

2006 USGS LCR MSCP Yellow-billed Cuckoo Research........................................8

LCR MSCP Yellow-billed Cuckoo Project Objectives ..................................................9

Document Organization ................................................................................................10

Chapter 2: Yellow-Billed Cuckoo Breeding Surveys.......................................................11

Survey Location and Selection of Study Sites ..............................................................11

Study Site Descriptions.................................................................................................14

Pahranagat National Wildlife Refuge, NV (White River Drainage)........................14

Overton Wildlife Management Area, NV (Muddy River).......................................15

Grand Canyon National Park/Lake Mead National Recreation Area, AZ 

(Colorado River and Lake Mead)...................................................................16

Havasu National Wildlife Refuge, AZ (Colorado River) ........................................17

Bill Williams River National Wildlife Refuge, AZ (Bill Williams River) ..............19

Ahakhav Tribal Preserve (Colorado River) (Elevation 94m; 308ft)........................22

Cibola National Wildlife Refuge, AZ (Colorado River)..........................................22

Picacho State Recreation Area, CA (Colorado River) 

(Elevation 52 m; 171 ft)..................................................................................23

Imperial National Wildlife Refuge, AZ and CA (Colorado River)..........................24

Mittry Lake State Wildlife Management Area/Pratt Restoration Area, AZ 

(Colorado River) (Elevation 52 m; 171 ft) .....................................................24

Gila–Colorado River Confluence Area, AZ (Gila and Colorado Rivers) ................24

Yuma West Wetlands, AZ (Colorado River) (Elevation 36 m; 118 ft) ...................25

Limitrophe Division, AZ (Colorado River) .............................................................25

Quigley Pond Wildlife Management Area, AZ (Gila River) (Elevation 67 m; 220 

ft).....................................................................................................................26

Survey Methods ............................................................................................................26

Survey Site Classifications.......................................................................................28

Supplemental Follow-up Surveys ............................................................................28

Nest Searching and Monitoring................................................................................28

Spatial Data ..............................................................................................................29

Results...........................................................................................................................29

Yellow-billed Cuckoo Formal and Follow-up Detections, 2007 .............................29

Grand Canyon National Park/Lake Mead National Recreation Area, AZ 

(Colorado River and Lake Mead)...................................................................33

Yellow-billed Cuckoo Breeding Activity ................................................................42

Nest Monitoring .......................................................................................................43

Discussion .....................................................................................................................44

Other Riparian Bird Detections.....................................................................................46

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Chapter 3: Survey Methodology........................................................................................51

Methods.........................................................................................................................52

Results...........................................................................................................................53

Discussion .....................................................................................................................57

Chapter 4. Habitat Vegetation Characteristics...................................................................59

Methods.........................................................................................................................60

Vegetation Sampling Design....................................................................................60

Vegetation Measures and Measurement Techniques ...............................................62

Results...........................................................................................................................63

Yellow-billed Cuckoo Vegetation by Occupancy Status.........................................63

Yellow-billed Cuckoo Vegetation by Geographic Area ..........................................69

Yellow-billed Cuckoo Vegetation at Bill Williams River NWR Sites ....................76

Discussion .....................................................................................................................81

Vegetation by Cuckoo Occupancy Status ................................................................81

Vegetation by Geographic Area...............................................................................82

Vegetation among Occupied Sites at Bill Williams River NWR.............................83

Chapter 5. Microclimate Characteristics............................................................................85

Methods.........................................................................................................................85

Temperature and Relative Humidity........................................................................86

Soil Moisture ............................................................................................................87

Results...........................................................................................................................88

Temperature and Relative Humidity by Yellow-billed Cuckoo 

Occupancy Status............................................................................................88

Temperature and Relative Humidity by Geographic Area.......................................89

Temperature and Relative Humidity at Bill Williams River 

NWR Study Sites............................................................................................90

Microclimate and Canopy Cover .............................................................................91

Soil Moisture ............................................................................................................92

Discussion .....................................................................................................................94

Chapter 6. Management and Research Considerations......................................................97

Yellow-billed Cuckoo Presence/Absence Surveys .......................................................97

Evaluation of Survey Protocol for Yellow-Billed Cuckoos..........................................97

Evaluating Survey Protocol ..........................................................................................98

Estimating Detection Probability ..................................................................................98

Habitat Vegetation Characteristics................................................................................99

Microclimate .................................................................................................................99

Identifying Core Yellow-billed Cuckoo Breeding Habitat .........................................100

Using Occupancy Patterns to Identify Core Yellow-billed Cuckoo 

Habitat...........................................................................................................101

Methods for Yellow-billed Cuckoo Follow-up Visits............................................101

Identifying Yellow-billed Cuckoo Habitat Model Variables......................................102

Chapter 7. 2006-2007 LCR MSCP Yellow-billed Cuckoo Research Summary .............105

Yellow-Billed Cuckoo Presence/Absence Surveys ....................................................105

Variation in Yellow-billed Cuckoo Detections, Occupied Sites and Habitat .............108

Yellow-billed Cuckoo Breeding Verification .............................................................110

Survey Methodology Evaluation ................................................................................111

Habitat Vegetation Characteristics..............................................................................111

Microclimate Characteristics ......................................................................................112

iv
Other Riparian Bird Detections...................................................................................113

What Have We Learned? ............................................................................................113

Acknowledgments.......................................................................................................114

References Cited .........................................................................................................115

Appendixes 1–6 ...............................................................................................................125

Appendix 1. Summary of Yellow-billed Cuckoo Detections by Survey 

Period, 2007.......................................................................................................127

Appendix 2. Narrative Descriptions of Each Yellow-billed Cuckoo 

Detection in the Lower Colorado River Watershed, 2007 ................................129

Appendix 3. Incidental Yellow-billed Cuckoo Observations in the 

Lower Colorado River Watershed, 2007...........................................................165

Appendix 4. Aerial Photographs of Yellow-billed Cuckoo Survey 

Points and Detections According to Survey Period, 2007 ................................167

Appendix 5. Habitat photos of yellow-billed cuckoo survey areas 

and sites in the lower Colorado River Watershed, 2007 ...................................235

Appendix 6. List of Other Bird Species Observed During 

Yellow-billed Cuckoo Surveys in the Lower Colorado River Watershed ........253

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1

 

Yellow-billed Cuckoo Distribution, Abundance, 

and Habitat Use Along the Lower Colorado River 

and Its Tributaries, 2007 Annual Report 

By Matthew J. Johnson, Scott L. Durst, Christopher M. Calvo, Laura Stewart, 

Mark K. Sogge, Geoffrey Bland, and Terry Arundel1

Executive Summary 

This 2007 annual report details the second season of a 2-year study documenting 

western yellow-billed cuckoo (Coccyzus americanus occidentalis) distribution, 

abundance, and habitat use throughout the Lower Colorado River Multi-Species 

Conservation Program boundary area. We conducted cuckoo surveys at 40 sites within 14 

areas, between 11 June and 9 September 2007. The 169 surveys across all sites yielded 

163 yellow-billed cuckoo detections. Cuckoos were detected at 25 of the 40 sites, 

primarily at the Bill Williams River National Wildlife Refuge (NWR) study area (n = 139 

detections; 85 percent of all detections). Detections declined slightly through the cuckoo 

breeding season, with most detections occurring in the first and second survey periods (n 

= 92; 54 percent). We detected breeding activity only at the Bill Williams River NWR, 

where we confirmed 27 breeding events, including two nesting observations. However, 

the breeding status of most detected birds was unknown. 

We used playback broadcast recordings to survey for yellow-billed cuckoos. 

Compared to simple point counts or surveys, this method increases the number of 

detections of this secretive, elusive species. It has long been suspected that cuckoos have 

a fairly low response rate, and that the standard survey method of using broadcast 

recordings might fail to detect all birds present in an area. In 2007, we found that the 

majority (84 percent) of cuckoo detections were solicited through broadcast at all study 

sites. The number of solicited detections was highest during the first survey period and 

declined as the breeding season progressed, while the number of unsolicited detections 

(cuckoos heard calling before broadcast was initiated) remained fairly constant through 

the first, second, and third survey periods. The majority (66 percent) of cuckoo 

detections, solicited or unsolicited, were aural, 23 percent were both heard and seen, and 

11 percent were visual detections only. We also found that 50 percent of all responses by 

cuckoos were evenly split between the first and second broadcasts at sites with >10 

detections, while 45 percent of responses occurred after a single broadcast at the sites 

with <10 detections. 

We refined our collection of vegetation data in 2007 and found that across the 

entire study area the dominant tree species were tamarisk (Tamarix spp.), willow (Salix

1

 Department of the Interior, U.S. Geological Survey, Southwest Biological Science Center, Flagstaff, Ariz. 
spp.), and cottonwood (Populus spp.). The smallest size class (<8 cm diameter at breast 

height) trees were the most common and were dominated by tamarisk, but cottonwood 

and willows were well represented in the larger size classes. Sites that were occupied by 

yellow-billed cuckoos generally had higher canopies, denser cover in the upper layers of 

the canopy, and sparse shrub layers compared to unoccupied sites that consistently had 

higher densities of woody species. As most occupied sites were within the Bill Williams 

River NWR and most unoccupied sites were at Grand Canyon National Park/Lake Mead 

National Recreation Area, vegetation characteristics at these study areas drove the cuckoo 

distribution patterns we observed in 2007. However, there was a range of habitat 

conditions in locations that were used by yellow-billed cuckoos across the entire lower 

Colorado River Multi-Species Conservation Program study area. 

We measured microclimate variables (temperature, relative humidity, soil 

moisture) at occupied and unoccupied sites, and found that, across the entire study area, 

occupied sites were consistently cooler during the day and more humid during the day 

and night compared to unoccupied sites, but that soil moisture did not differ between 

occupied and unoccupied sites. While most cuckoo detections occurred at Bill Williams 

River NWR, with generally cooler and more humid conditions, cuckoos were also 

detected at study areas that had hotter and dryer microclimate conditions. We did not find 

any relationship of canopy cover characteristics to temperature or soil moisture, 

suggesting that more complicated factors are involved in determining microclimate 

regime, possibly including canopy height, dominant tree species, proximity to water, the 

nature of surrounding habitat, or other variables. Although microclimate conditions might 

play a significant role in cuckoo habitat selection or breeding ecology, the factors 

underlying microclimate conditions in riparian patches are not currently fully understood. 

2
Chapter 1. Introduction 

The Lower Colorado River Multi-Species Conservation 

Program 

The Lower Colorado River Multi-Species Conservation Program (LCR MSCP 

2004) is a coordinated, comprehensive, long-term, multi-agency effort to conserve native 

species, work towards the recovery of endangered species, and protect and maintain 

wildlife habitat on the lower Colorado River. The LCR MSCP’s purposes are to (1) 

protect the lower Colorado River environment while ensuring the certainty of existing 

river water and power operations, (2) address the needs of threatened and endangered 

wildlife under the Endangered Species Act (ESA), and (3) circumvent federal and state 

listing of additional species from the lower Colorado River. The MSCP covers areas up 

to and including the full-pool elevations of Lakes Mead, Mohave, and Havasu, and the 

historical floodplain of the Colorado River from Lake Mead to the United States–Mexico 

Southerly International Boundary, a distance of about 400 river miles. Conservation 

measures currently focus on the area from Hoover Dam to the border, but might include 

the Grand Canyon in the future. 

The LCR MSCP Habitat Conservation Plan (HCP) measures are designed to meet 

the biological goals for 26 covered species, including the western yellow-billed cuckoo 

(Coccyzus americanus occidentalis). On 25 July 2001, the U.S. Fish and Wildlife Service 

(USFWS) found that the western yellow-billed cuckoo (i.e., populations west of the crest 

of the Rocky Mountains) represents a distinct population segment and warrants 

protection under the Endangered Species Act as “threatened,” but that listing of the 

cuckoo was precluded by other higher priority listing actions. Thus, it became a 

Candidate Species under the Endangered Species Act (USFWS 2002). The HCP requires 

the Bureau of Reclamation (‘Reclamation’) to restore 5,940 acres of cottonwood 

(Populus spp.) – willow (Salix spp.) riparian forest, including 4,050 acres specifically for 

the yellow-billed cuckoo. The Science Strategy is designed to provide Reclamation with 

a science-based process for ensuring that relevant new information generated over the 50-

year term of the LCR MSCP (2004) is used to guide implementation of HCP 

conservation measures. The restoration goals are to create native cottonwood-willow 

riparian forest that promotes yellow-billed cuckoo conservation and recovery. 

Additionally, Reclamation plans to establish a standardized survey protocol, and to 

monitor yellow-billed cuckoos at each restoration site and along the entire lower 

Colorado River to evaluate long-term trends and the effects of HCP conservation 

measures. 

Specifically, the LCR MSCP conservation measures relative to breeding yellowbilled cuckoos include the following: 

1. Conduct surveys and research, as appropriate, to collect information necessary to 

better define the yellow-billed cuckoo’s breeding habitat requirements, and to 

design and manage fully functioning habitats. 

2. Monitor and adaptively manage created habitat and evaluate the habitat needs of 

yellow-billed cuckoos. Reconstructed habitats covered under the MSCP will be 

3
managed to maintain their functions as habitat over the term of the LCR MSCP 

(2004). Created habitat will be monitored and adaptively managed over time to 

determine which types and frequency of management activities that might be 

required to maintain created cottonwood-willow and honey mesquite (Prosopis

spp.) as habitat for yellow-billed cuckoos. 

3. Create 1,639 ha (4,050 acres) of yellow-billed cuckoo habitat. Of the 2,404 ha 

(5,940 acres) of created cottonwood-willow, at least 1,639 ha (4,050 acres) will be 

designed to provide breeding and migration habitat for cuckoos along the lower 

Colorado River. A total of 1,093 ha (2,700 acres) will be designed and managed 

to provide habitat for both yellow-billed cuckoos and southwestern willow 

flycatchers (Empidonax traillii extimus); 546 ha (1,350 acres) will be restored 

specifically for the cuckoo. 

Yellow-billed Cuckoo Breeding Biology, Habitat, 

Distribution, and Status 

Breeding Biology 

The yellow-billed cuckoo (Coccyzus americanus) is a Neotropical migrant that 

summers in northern Mexico, the United States, and southern Canada from early June 

through early September, and winters primarily in South America (Hughes 1999). 

Cuckoos begin arriving in Arizona in late May and in California in late May–early June 

(Bent 1940, Hughes 1999). Nesting activities usually take place between late June and 

late July, but can begin as early as late May, and continue through late September 

(Hughes 1999, Laymon et al. 1997, Halterman 2003). Nesting peaks in mid-June through 

August, later than most co-occurring bird species. The timing of nesting can be 

influenced by an abundance of cicadas, katydids, caterpillars, and other large prey items, 

which are the bulk of the species’ diet (Hamilton and Hamilton 1965, Rosenberg et al. 

1982, Hughes 1999). 

Nest building takes 1–2 days. Incubation begins as soon as the first egg is laid, 

and lasts for 11 days (Hughes 1999). Clutch size in western populations averages just 

over two eggs, but ranges up to four (Laymon et al. 1997). Both adults incubate the eggs 

and brood the young, and approximately one-third of nests have a third adult assisting 

with care of the young. Eggs hatch asynchronously, and nestlings are fed large food 

items, such as katydids (Tettigoniidae), tree frogs (Hylidae), large caterpillars 

(Lepidoptera), and cicadas (Cicadidae) (Laymon et al. 1997). After fledging at 5–7 days, 

young are dependent on the adults for approximately 3 weeks (Laymon and Halterman 

1985). The number of broods reared per breeding season is unclear. Western populations 

were thought to raise a single-brood (Hamilton and Hamilton 1965, Hughes 1999), but 

recent observations indicate that at least some individuals double-brood (M. Halterman, 

pers. comm.). Although it is not possible to differentiate between the sexes of cuckoos in 

the field, it is possible to identify second-year birds (one-year-olds) from older birds by 

their yellow orbital skin (Pyle et al. 1997). 

Cuckoos do not exhibit classic territorial behavior, and the behaviors and 

vocalizations of unpaired birds are unknown (Hughes 1999, Laymon et al. 1997, 

Halterman 2002). Cuckoos can move broadly throughout riparian and adjacent 

vegetation, especially early in the season and post-breeding. Such cuckoos might be 

4
foraging or evaluating potential breeding sites for the current or subsequent breeding 

seasons. Similarly, migrating cuckoos can be found in habitats that might not have the 

same vegetation types or characteristics as those in which they breed. As a result, 

cuckoos are sometimes detected in non-riparian vegetation or within riparian vegetation 

that is not suitable for breeding. Thus, not every location at which a cuckoo is detected 

during the summer months can be considered as breeding habitat. The level of adult yearto-year breeding site fidelity is not well known, but is likely relatively low, based on 

large yearly fluctuations in cuckoo detections at some sites. These natural history traits 

complicate survey efforts and our ability to determine and characterize breeding habitat. 

Habitat Requirements 

Western yellow-billed cuckoos are thought to require structurally complex 

riparian vegetation with tall trees and a dense woody vegetative understory (Halterman 

1991, Hughes 1999). They breed in large blocks of riparian vegetation, particularly 

woodlands with cottonwoods and willows (Ehrlich et al. 1988, USFWS 2002). Nesting 

cuckoos along the Sacramento River in California were estimated to need riparian habitat 

patches ranging from 10 to 40 ha (Gaines 1974, Laymon et al. 1997, Halterman 1991). In 

California, dense riparian understory foliage appears to be an important factor in nest site 

selection, while cottonwood trees are an important component of foraging habitat 

(Laymon et al. 1997, USFWS 2002). In the West, cuckoos nest almost exclusively close 

to water and many researchers have hypothesized that the species might be restricted to 

moist river bottoms because of humidity requirements for successful breeding (Hamilton 

and Hamilton 1965, Rosenberg et al. 1991). Much of what is known about yellow-billed 

cuckoo habitat use in Arizona is the result of surveys conducted in 1998 and 1999 by 

both the Arizona Game and Fish Department (AGFD) and the U.S. Geological Survey 

(Corman and Magill 2000). The AGFD-USGS surveys show that cuckoo detection rates 

were highest in cottonwood-willow-ash (Fraxinus spp.) and mesquite bosque–hackberry 

(Celtis spp.) habitats. Yellow-billed cuckoos were much less common in Arizona 

sycamore (Platanus wrightii)—cottonwood habitat, sycamore-alder (Alnus spp.) habitat, 

and areas with more than 75 percent tamarisk cover. 

Historic Abundance, General Breeding Distribution, and Current Conservation 

Status in the Western United States 

Western yellow-billed cuckoos have historically bred in riparian areas from 

western Washington to northern Mexico, including Oregon, southwestern Idaho, 

California, Nevada, Utah, western Colorado, Arizona, New Mexico, and western Texas 

(American Ornithologists’ Union 1983, 1998). Although analysis of population trends is 

difficult because quantitative data, including historic population estimates, are generally 

lacking, rough extrapolations of historic and current information suggest that the yellowbilled cuckoo’s habitat distribution, range, and population numbers have declined 

substantially across much of the western United States over the past 50 years (USFWS 

1985, USFWS 2002). Cuckoo populations have suffered severe range contractions during 

the last 80 years, and the species has been extirpated from British Columbia, Washington, 

Oregon, and possibly Nevada (Hughes 1999). Currently, western populations of the 

yellow-billed cuckoo breed in localized areas of California, Arizona, New Mexico, 

extreme western Texas, Sonora, Chihuahua, and south irregularly to Zacatecas, Mexico 

(Howell and Webb 1995, Russell and Monson 1998, Hughes 1999). Local breeding is 

5
irregular in Utah (J. Parrish pers. comm., Johnson and O’Brien 1998) and western 

Colorado (Kingery 1998). The yellow-billed cuckoos found in California, southern 

Nevada, Arizona, and New Mexico west of the Pecos River are western yellow-billed 

cuckoos; we use the two names interchangeably when discussing any yellow-billed 

cuckoo west of the crest of the Rocky Mountains. 

Yellow-billed cuckoo populations have declined throughout the species’ range 

(Hughes 1999); western populations, in particular, have decreased and suffered range 

reductions during the last 80 years (Laymon and Halterman 1987a, Hughes 1999). In 

1986, a petition was filed to establish the western yellow-billed cuckoo as endangered in 

the states of California, Washington, Oregon, Idaho, and Nevada (Manolis et al. 1986). 

The published 12-month finding determined that the petitioned action was not warranted, 

because the petitioned area did not encompass either a distinct subspecies or a distinct 

population segment. Another petition was filed, resulting in a 25 July 2001 finding by the 

USFWS that the western yellow-billed cuckoo (i.e., populations west of the continental 

divide) represents a distinct population segment and warrants protection under the 

Endangered Species Act as “threatened,” but that listing of the cuckoo was precluded by 

other higher priority listing actions. Thus, it became a Candidate Species under the 

Endangered Species Act; it is a species for which the Fish and Wildlife Service “has 

sufficient information on their biological status and threats to propose them as 

endangered or threatened under the ESA, but for which development of the proposed 

listing regulation is precluded by other higher priority listing activities” (USFWS 2002). 

Candidate species receive no statutory protection under the ESA. However, the Fish and 

Wildlife Service “encourages the formation of partnerships to conserve these species 

because they are by definition species that may warrant future protection under the ESA” 

(USFWS 2002). 

Probable factors believed to have contributed to population declines in the West 

are the loss, fragmentation, and alteration of native riparian breeding habitat, the possible 

loss of wintering habitat, and pesticide use on breeding and wintering grounds (Gaines 

and Laymon 1984, Franzreb 1987, Laymon and Halterman 1987a, Hughes 1999). Local 

extinctions and low colonization rates also might have contributed to the declines 

(Laymon and Halterman 1989). Populations might also be further limited by food 

availability for the young, therefore cuckoos might not nest if the food supply at the 

breeding grounds, which is likely affected by drought conditions (Newton 1980, Durst 

2004, Scott et al. 2004), is inadequate (Veit and Petersen 1993). 

The early literature documents dozens of locations in California where the species 

was reported and/or collected historically, sometimes in apparent abundance, but has not 

been found subsequently (Gaines 1974, Gaines and Laymon 1984, Hughes 1999). During 

the late 19th century, the California breeding population was estimated to be at least 

15,000 pairs (Hughes 1999). However, Gaines (1974) believed that predevelopment 

cuckoo populations in California were even greater than implied by the early literature, 

due to the species’ inconspicuous behavior and the fact that large tracts of floodplain 

riparian habitat had already been lost to development before the first records and before 

accounts of the species began appearing in the literature. Grinnell (1915) described 

yellow-billed cuckoos as a common breeder, widely distributed in suitable river bottom 

habitats, but by 1940 the cuckoo populations were reduced due to declines in the amount 

and suitability of habitat (Grinnell and Miller 1944, Small 1994). Many modern 

investigators have concluded that there was a catastrophic decline of the cuckoo in 

California following the start of the major era of development, beginning about the mid6
1800s (Gaines and Laymon 1984, Laymon and Halterman 1987b, Launer et al. 1990). 

The species was listed as threatened in California in 1971, and was listed as endangered 

in 1987. Statewide surveys in 1986–87 found that only three areas in California supported 

more than about five breeding pairs on a regular basis: the Sacramento River between 

Colusa and Red Bluff, the South Fork of the Kern River, and the lower Colorado River 

(Laymon and Halterman 1987a). 

In Arizona, the yellow-billed cuckoo was once considered a fairly common 

breeding species within riparian forests dominated by cottonwood, willow, and/or 

mesquite throughout the state (Stephens 1903, Swarth 1905, 1914, Visher 1910, Phillips 

et al. 1964, Corman and Magill 2000). A 1977 statewide Arizona survey of habitat 

thought to be suitable for cuckoos found an estimated total of 205–214 pairs, with more 

than half of these along the lower Colorado River (Gaines and Laymon 1984). Past 

estimates suggested that fewer than 200 pairs remained in 1986 (Layman and Halterman 

1987a), and that fewer than 50 pairs were present five years later (Ehrlich et al. 1992). 

Prompted by continued concern regarding severe population declines, habitat loss, and 

the lack of statewide data, the USFWS initiated yellow-billed cuckoo surveys in 1998 and 

1999. Cuckoos were documented along 25 drainages; an estimated 73 pairs were detected 

in 1998 and 172 pairs in 1999. The primary concentrations in Arizona were along the 

major drainages of the Agua Fria, San Pedro, and Verde Rivers, Cienega and Sonoita 

Creeks, and the Bill Williams River tributary within the lower Colorado River region 

(Corman and Magill 2000, Johnson et al. 2006a). The Arizona Game and Fish 

Department has designated the yellow-billed cuckoo as a Wildlife of Special Concern in 

Arizona, and the U.S. Forest Service Regional Forester designated it a Sensitive Species 

on National Forests within Arizona and New Mexico (Region 3) (AGFD 2002). In 

addition, it is considered likely to become an endangered species throughout all or a 

significant portion of its range on the Navajo Nation if action is not taken (Navajo Nation 

2005). 

Until recently, there were few details about cuckoo distribution and abundance in 

Nevada. From 2000 to 2004, the Nevada Division of Wildlife (NDOW) coordinated 

surveys at selected riparian areas in southern Nevada, with results varying greatly by year 

and site. For example, detections at Warm Springs Ranch and Moapa NWR varied from 

19 individuals (4 pairs and 11 single cuckoos) in 2001 (Furtek et al 2002) to just a single 

bird in 2003 (Braden et al. 2005a) and in 2004 (Braden et al. 2005b). The number of 

detections at Mormon Mesa Littlefield North and Mesquite Bridge also varied: there were 

8 in 2000, 6–10 in 2001, 0 in 2002, and 1 in 2003 (Braden et al. 2005a). From 2000 

through 2002, the Southern Sierra Research Station (SSRS) also surveyed four sites in 

southern Nevada: Clover Creek at Caliente, Upper Pahranagat Lake, the Virgin River at 

Littlefield, and Meadow Valley Wash from river miles 39 to 57. SSRS detected one 

cuckoo pair at Pahranagat and one individual at Littlefield in 2000 (Halterman 2001), and 

four pairs and five single cuckoos in 2001 (Halterman 2002); SSRS and NDOW detected 

one or two pairs in 2002 (Halterman 2003). The Nevada Natural Heritage Program ranks 

the western yellow-billed cuckoo as critically imperiled (Nevada Natural Heritage 

Program 2004) 

Historic Population Status Along the Lower Colorado River 

Yellow-billed cuckoos were once considered abundant throughout the riparian 

floodplain along the lower Colorado River. Grinnell and Miller (1944) cited only 

7
Stephen’s (1903) observations of several cuckoos near Needles in 1902. Surveys in midJune 1964 along the lower Colorado River near Laguna Dam indicated that the density of 

yellow-billed cuckoos was similar to, and possibly higher than, that on the San Pedro 

River in southeastern Arizona (Hamilton and Hamilton 1965). 

A substantial population of cuckoos was detected north of Laguna Dam during the 

1960s and 1970s, suggesting that the Colorado River above Laguna Dam might have 

been the last stronghold for the yellow-billed cuckoo in California (Gaines and Laymon 

1984). Four to twelve cuckoos per season were reported from 1964 to 1975 near Laguna 

Dam in June and July (Gaines and Laymon 1984). Then, using species-specific protocols, 

Gaines (1977) detected 65 cuckoos along the lower Colorado River on the California side 

of the river. During surveys in the 1970s and 1980s a dramatic decline of the species was 

noted along the lower Colorado River. In both Arizona and California, the lower 

Colorado River and its tributaries supported an estimated 180–240 pairs in 1976–77, a 

number that had declined by an estimated 80–90 percent by 1986 (Laymon and 

Halterman 1987a). Rosenberg et al. (1991) estimated a decline of 93 percent along the 

lower Colorado River between 1976 and 1986, coinciding with habitat loss from high 

water levels of long duration in 1983–84 and 1986 (Laymon and Halterman 1987b, 

Ohmart et al. 1988, Rosenberg et al. 1991). In 1998, no pairs were found in the parts of 

California west of the Colorado River that had been occupied in 1976–77 (Halterman 

1998). Losses have been greatest at lower elevations, below 900 m (3000 ft) along the 

lower Colorado River and its major tributaries, which have been strongly affected by 

upstream dams, flow alterations, channel modifications, and clearing of land for 

agriculture (Groschupf 1987). 

The Bill Williams River National Wildlife Refuge (NWR), a tributary of the 

lower Colorado River, has had the largest known population of yellow-billed cuckoos 

since the 1960s. The refuge consists primarily of riparian habitat along the Bill Williams 

River from Lake Havasu upstream to Planet Ranch, approximately 16 km (10 miles). The 

riparian habitat is dominated by a cottonwood-willow overstory with a dense understory 

of cottonwood, willow, and tamarisk. The Bill Williams River NWR riparian habitat is 

the most continuous, unfragmented habitat of its kind in the lower Colorado River Basin. 

The Bill Williams River NWR cuckoo population was surveyed in 1993, 1994, 

and 1997–2004 (Halterman and Laymon 1994, 1995; Halterman 1998, 2001, 2002, 2003, 

2004). Despite repeated surveys, trends in abundance were difficult to detect from these 

survey results because the amount of survey effort varied annually and, prior to 2001, 

survey results were given in terms of estimated numbers of pairs rather than numbers of 

detections. Estimated pairs ranged from 28 to 30 in 1993, 26 in 1994, 12 in 1997, and 6 to 

9 in 1999. A total of 11 nests were found when combining nests from 1993, 1994, and 

1997. Then starting in 2001, results were reported as numbers of detections, which varied 

annually: 78 in 2001, 34 in 2002, and 42 in 2003. 

2006 USGS LCR MSCP Yellow-billed Cuckoo Research 

In 2006, under the Lower Colorado River Multi-Species Conservation Program 

(LCR MSCP), the USGS initiated a 2-year study documenting western yellow-billed 

cuckoo (C.a. occidentalis) distribution, abundance, and habitat use throughout the LCR 

MSCP boundary area (Johnson et al. 2007). Yellow-billed cuckoos were surveyed at 55 

sites within 17 areas. The 243 visits across all sites yielded 180 yellow-billed cuckoo 

detections. Cuckoos were detected at 27 of the 55 sites, primarily at the Bill Williams 

8
River National Wildlife Refuge sites (n = 117 detections) and the Grand Canyon National 

Park–Lake Mead National Recreation Area delta sites (n = 29 detections). In 2006, the 

majority (72 percent) of cuckoo detections were solicited through a broadcast at all study 

sites. The number of solicited detections peaked during the first half of July and then 

declined as the breeding season progressed, while the number of unsolicited detections 

(cuckoos heard calling before broadcast was initiated) remained fairly constant. Cuckoos 

in areas with the largest populations had the highest rate of vocalizations before a 

broadcast or after the first broadcast (first of five broadcasts). In contrast, more than half 

the responses at sites with fewer cuckoos (<10 detections per site) first occurred after 

three or more broadcast recordings. 

During the first year of this research, preliminary analysis of vegetation data 

(Johnson et al. 2007) from yellow-billed cuckoo occupied and unoccupied sites focused 

on general patterns in the distribution and abundance of woody species. Tamarisk was the 

most common tree, due to the abundance of small (<8 cm dbh) plants. Occupied sites 

tended to have higher average canopy cover, attributable to higher average cover of the 

mid and low canopy. The dominant canopy at occupied sites most often consisted of 

cottonwood or willow trees. When densities of trees in different size classes were 

compared between occupied and unoccupied sites, cuckoos did not use areas with the 

highest density of small trees (<8 cm dbh), but used areas with lower densities of small 

trees and larger native trees. This study also measured microclimate variables 

(temperature, relative humidity, soil moisture) at occupied and unoccupied sites. 

Microclimate measurements at Grand Canyon NP–Lake Mead NRA and Bill Williams 

River NWR showed that locations occupied by yellow-billed cuckoos were slightly 

cooler and more humid than unoccupied sites. On average, soil moisture was slightly 

higher at occupied cuckoo locations. 

LCR MSCP Yellow-billed Cuckoo Project Objectives 

The objectives of this project, initiated in 2006 as part of the LCR MSCP, were to 

document the distribution, abundance, and habitat use of yellow-billed cuckoos in 

riparian areas of the lower Colorado River, and to provide information relevant to the 

Habitat Conservation Plan measures. Yellow-billed cuckoo surveys provide information 

on their status and distribution, and establish baseline data that can be used for continued 

monitoring of cuckoo populations and riparian vegetation under the MSCP. There are 

four specific project objectives. 

1. Conduct comprehensive, repeatable surveys in all potentially suitable habitat types 

within the LCR MSCP project boundary. This work contributes to baseline 

information on yellow-billed cuckoo populations within these areas. All other avian 

species encountered within riparian habitats are also recorded. 

2. Evaluate the effectiveness of the current yellow-billed cuckoo breeding season survey 

protocol (Halterman et al. 2006) and refine it to use over the term of the MSCP. 

3. Determine breeding habitat selection and preferences in the areas of concern. This 

includes comparing habitat characteristics between occupied and unoccupied sites to 

identify factors that might influence habitat selection by breeding cuckoos. 

4. Identify core yellow-billed cuckoo breeding habitat to use as a basis for future habitat 

expansion through restoration efforts. 

9
Document Organization 

This document is organized into six chapters. Chapter 2 (Yellow-billed Cuckoo 

Breeding Surveys) describes the effort and results of the yellow-billed cuckoo surveys 

and breeding activity during the 2007 breeding season. Chapter 3 (Survey Methods) 

provides descriptive information about how cuckoos responded to our survey methods. It 

also poses hypotheses and questions that might prove useful in further optimizing the 

cuckoo survey protocol. Chapter 4 (Yellow-billed Cuckoo Habitat Vegetation) describes 

the riparian vegetation sampling design, provides results on vegetation characteristics in 

the study areas, and compares characteristics of occupied and unoccupied sites. Chapter 5 

(Microclimate Analysis) describes the design and results of microclimate sampling in 

occupied and unoccupied patches of riparian habitat. Chapter 6 (Management and 

Research Considerations) describes the options for moving forward with cuckoo 

presence/absence surveys, yellow-billed cuckoo survey methods, and vegetation and 

microclimate measurements in order to provide information needed to guide conservation 

efforts such as (1) restoring cuckoo habitat along the lower Colorado River, (2) 

identifying core cuckoo breeding habitat, and (3) identifying potential breeding habitat. 

10
Chapter 2: Yellow-Billed Cuckoo Breeding Surveys

The Lower Colorado River Multi-Species Conservation Plan of 2004 calls for the 

identification of areas used by yellow-billed cuckoos via survey and the collection of 

information necessary to better define the species’ habitat requirements. This information 

will then be used to design and maintain riparian habitat suitable for yellow-billed 

cuckoos in the LCR MSCP planning area, which should help reduce the likelihood of 

future federal listing of this species. This project was initiated in the spring of 2006, and 

standardized cuckoo surveys were conducted throughout the breeding seasons in 2006 

and 2007. The purpose of this chapter is to document the results of the 2007 surveys. 

Survey Location and Selection of Study Sites 

The MSCP boundary covers areas up to and including the full-pool elevations of 

Lake Mead, Lake Mohave, Lake Havasu, and the historical floodplain of the Colorado 

River from Lake Mead to the United States–Mexico Southerly International Boundary, a 

distance of about 644 river km (400 river miles). In order to determine the current 

yellow-billed cuckoo breeding range within the lower Colorado River Basin, we 

examined historic detection sites (Gaines 1977, Gaines and Laymon 1984, Halterman and 

Laymon 1994, 1995; Halterman 1998, 2001, 2002, 2003, 2004) and our previous survey 

efforts in 2005 and 2006 (Johnson et al. 2006b, and Johnson et al. 2007), which included 

sites along the Gila River near Yuma, Arizona, the Muddy River in Southern Nevada, 

and Pahranagat National Wildlife Refuge in the White Water River drainage, Nevada 

(Figure 2.1). 

Specific yellow-billed cuckoo survey sites were initially selected using the ‘look 

see’ method. This approach, which was employed during previous AGFD-UAGA 

surveys, calls for identification of suitable habitats before conducting surveys (see Bibby 

et al. 1992). It relies on prior knowledge of possible habitat preferences, expert opinion, 

and knowledge of the basic biology of the species in question (Halterman et al. 2006). 

We also selected sites based on historical detections collected in 2005 (Johnson et al. 

2006b), which is a preferred method for surveying rare birds (Dawson 1981) when the 

goal is detection of all occurrences of a species within constraints such as time. Most of 

our survey sites were identified using these methods prior to the 2006 field season. In 

2007, we added three survey sites. Big Horn Draw at Lake Mead NWR was surveyed due 

to its habitat growth from 2006 to 2007, and Teepee Trail as well as North Burn at the 

Bill Williams River NWR was added to better encompass some of the wider portions of 

the riparian habitat that exists there. 

In 2007 we discontinued conducting some portions of surveys previously done in 

2006 at Pahranagat NWR, Littlefield Bridge, Mesquite Bridge, Lake Mohave, and 

Imperial NWR Paradise sites, and many areas along the Gila River (Gila River sites at 

Hwy. 95, Gila River Welton site and the Gila River Ligurta Site). The decision to 

discontinue surveying these areas was based on our evaluation of the current habitat 

conditions, lack of cuckoo detections in 2005 and 2006, and consultation with the Bureau 

of Reclamation. Finally, some sites at the Bill Williams River NWR were split from one 

survey site into two or more sites for logistical purposes, mainly their immense length. 

For example, Cave Wash was split into portions of Cottonwood Patch and Honeycomb 

Bend. Many of our yellow-billed cuckoo survey areas overlap with southwestern willow 

11
Figure 2.1. Yellow-billed cuckoo survey areas along the Muddy River, Nevada, and 

lower Colorado, Bill Williams, and Gila Rivers in Arizona and California, 2007. 

12
flycatcher surveys areas, which have their own established site names (Table 2.1). Some 

of cuckoo surveys encompass a much larger area than do the flycatcher areas they are 

named after; in a few cases they do not overlap at all. 

Table 2.1. Yellow-billed cuckoo (YBCU) and southwestern willow flycatcher (SWIFL) 

2007 sites names in the lower Colorado River watershed along the Muddy, Virgin, and 

White Rivers in Nevada, and the Colorado, Bill Williams, and Gila Rivers in Arizona and 

California. 

YBCU 2007 Site Name SWIFL 2007 Site Name

Pahranagat NWR-Pahranagat North Pahranagat North 

Pahranagat NWR-Pahranagat South Pahranagat South 

Overton WMA-Honeybee Pond Overton WMA to the south 

Overton WMA-Overton Wildlife Overton WMA 

Grand Canyon NP/Lake Mead NRA-RM 274.5 RM 274.5N 

Grand Canyon NP/Lake Mead NRA-Cuckoo Beach Kowlp Corner, RM 286N, Twin Coves 

Grand Canyon NP/Lake Mead NRA-Iceberg Ridge Bradley Bay 

Grand Canyon NP/Lake Mead NRA-Chuckwalla Cove Chuckwalla Cove 

Grand Canyon NP/Lake Mead NRA-Big Horn Draw NA 

Havasu NWR-Pintail Slough NA 

Havasu NWR-North Dike NA 

Havasu NWR-Topock Marsh Restoration NA 

Havasu NWR-Topock Tamarisk NA 

Bill Williams River NWR-Teepee Trail NA 

Bill Williams River NWR-Cottonwood Patch Site 8 

Bill Williams River NWR-Cave Wash Site 8 

Bill Williams River NWR-Honeycomb Bend Site 8 

Bill Williams River NWR-Mineral Wash Beaver Pond, Site 8 

Bill Williams River NWR-Big Bend Mineral Wash & Beaver Pond 

Bill Williams River NWR-Gibraltar Rock None, but near Site 5 

Bill Williams River NRA-Sandy Wash Site 5 

Bill Williams River NWR-Fox Wash Site 5 

Bill Williams River NWR-Mosquito Flats Site 3 & Site 5 

Bill Williams River NWR-Saguaro Slot Site 1, Site 2, Site 3, Site 4, Site 11 

Bill Williams River NWR-North Burn NA 

Bill Williams River NWR-Bill Williams River Marsh Site 1, Site 2, Site 4, Site 11 

Ahakhav Tribal Preserve-CRIT Restoration NA 

Cibola NWR-Cibola North Restoration NA 

13
Table 2.1. Yellow-billed cuckoo (YBCU) and southwestern willow flycatcher (SWIFL) 

2007 sites names in the lower Colorado River watershed along the Muddy, Virgin, and 

White Rivers in Nevada, and the Colorado, Bill Williams, and Gila Rivers in Arizona and 

California.—Continued 

YBCU 2007 Site Name SWIFL 2007 Site Name

Cibola NWR-Cibola Nature Trail Restoration Cibola Nature Trail 

Cibola NWR-Cibola Eucalyptus Restoration NA 

Cibola NWR-Cibola South Restoration NA 

Picacho SRA Picacho NW 

Imperial NWR-Imperial South Restoration Imperial Nursery, Nursery NW 

Mittry Lake WMA/Pratt Restoration Mittry South 

Gila/Colorado River Confluence-Colorado Confluence Gila Confluence North, Gila Confluence 

Gila/Colorado River Confluence-Gila Confluence Gila Confluence North, Gila Confluence 

Yuma West Wetlands NA 

Limitrophe Division-Limitrophe Division North Morelos Dam 

Limitrophe Division-Limitrophe Division South Gadsden, Hunters Hole 

Gila River/Quigley Pond WMA NA 

Study Site Descriptions

A site is a discrete location—typically one or more distinct habitat patches—that 

is surveyed for yellow-billed cuckoos. We use survey area to mean the entire area that 

encompasses one or more sites. Therefore, a survey area such as the Bill Williams River 

NWR may contain multiple sites, such as Sandy Wash. The survey area and descriptions 

are listed below beginning with the most upstream locations and progressing 

downstream; this is true both within the entire study area and for each side drainage. 

Additional details on each site and the associated surveys and detections are presented in 

Appendix 2, Appendix 4 and Appendix 5. 

Pahranagat National Wildlife Refuge, NV (White River Drainage) 

The entire Pahranagat National Wildlife Refuge encompasses 2,177 ha (5,380 

acres) in southern Nevada, approximately 132 km (82 miles) northwest of Las Vegas 

(Figure 2.1; Appendix 4). All surveys were conducted at the upper Pahranagat Lake, the 

only site in the refuge with appropriate cuckoo habitat. The habitat consists of patches of 

native willow and cottonwood at the inflow and outflow of upper Pahranagat Lake, which 

is fed by Pahranagat Springs just north of the lake. The upland habitat adjacent to the lake 

is Mohave Desert consisting of creosote (Larrea tridentate) and desert scrub. We divided 

this area into two survey sites covering: (1) the northern lake shore, and (2) southern lake 

shore which also included potential cuckoo habitat that follows U.S. Highway 93 to the 

south. In 2006, we surveyed the entire lake perimeter. In 2007, we excluded the 

Pahranagat East and West sites because of they lacked suitable cuckoo habitat. 

14
Pahranagat North (Elevation 1,026 m; 3,366 ft) 

The north end of upper Pahranagat Lake supports the best quality cuckoo habitat 

(Appendixes 4 and 5). It consists of large Fremont cottonwood (Populus fremontii) and 

Goodding’s willow (Salix gooddingii) trees. The height of the relatively closed canopy is 

15–18 m (49–59 ft). The understory consists of forbs and grasses, with little apparent tree 

recruitment. In 2007, standing water was not present within this site, and in September, 

the lake receded considerably from the site. This site is surrounded by marsh along the 

lake’s edge, which consists mainly of lizard tail (Yerba manza). 

Pahranagat South (Elevation 1,020 m; 3,346 ft) 

Pahranagat South consists of a relatively small stringer of Goodding’s willow, 

coyote willow (Salix exigua), and Fremont cottonwood lining a developed channel that 

carries the outflow from upper Pahranagat Lake (Appendixes 4 and 5). Canopy height is 

16–18 m (52–59 ft). The site is bordered by open marsh on the lake side. Tamarisk and 

Russian-olive (Elaeagnus angustifolia) form a sparse understory. Standing water was not 

present within this site in 2007. The upland habitat adjacent to this site is creosote and 

desert scrub. There are extensive trails and campsites in and around this site that impact 

the riparian vegetation. The riparian habitat follows both sides of U.S. Highway 93 and 

becomes sparser away from the lake. 

Overton Wildlife Management Area, NV (Muddy River) 

The Overton Wildlife Management Area (WMA) consists of 7,146 ha (17,657 

acres) located at the inflow of the Muddy River into the Overton Arm of Lake Mead 

(Figure 2.1; Appendix 4). The study area consists of seasonally flooded marshes, dense 

tamarisk, willow patches, scattered mesquite thickets, and isolated stringers of Fremont 

cottonwood. There are agricultural fields and ponds throughout the wildlife management 

area that are managed for waterfowl. Numerous roads cross the refuge, allowing for easy 

access to all sites. We surveyed two survey sites within Overton WMA in 2007 but 

excluded the 2006 sites of Overton North and Overton Tamarisk because of unsuitable 

cuckoo habitat. 

Honey Bee Pond (Elevation 375 m; 1,230 ft) 

This is the largest pond in the Wildlife Management Area (Appendixes 4 and 5). 

The site consists of tamarisk, Fremont cottonwood, coyote willow, and a few scattered 

California fan palms (Washingtonia filifera). Canopy height is 4–6 m (13–19 ft). The 

understory is comprised of baccharis (Baccharis spp.), tamarisk, and giant reed (Arundo 

donax). In 2007, standing water was present within this site, and the banks of the pond 

overflowed in July. A dense stand of tamarisk surrounds the pond area. 

Overton Wildlife (Elevation 371 m; 1,217 ft) 

This is a small isolated site with a multi-layered canopy that consists of coyote 

willow and tamarisk, as well as a re-vegetation site that consists of dense even-aged 

coyote willow 

(Appendixes 4 and 5). Canopy height is 6–8 m (19–26 ft). The understory consists of 

young willow, tamarisk, and arrowweed (Pluchea sericea). A canal divides the site, and, 

15
in July, the canal flooded resulting in standing water within the site. Most of the site is 

surrounded by dense monoculture tamarisk. 

Grand Canyon National Park/Lake Mead National Recreation Area, AZ (Colorado 

River and Lake Mead) 

Since 1997, deposited sediments had been exposed by declining water levels 

where the Colorado River emerges from the Grand Canyon and flows into the northern 

end of Lake Mead (Figure 2.1; Appendix 4). Where these deposited sediments occurred, 

adequate habitat for yellow-billed cuckoos had developed. In 2006, yellow-billed 

cuckoos occupied and bred in these sites. However, since 2000, a 31-m (102 ft) drop in 

lake levels has lowered the water table and stressed the vegetation at these sites. Over a 

one year period (May 2006–May 2007) there was a 4.5 m (15 ft) drop in lake levels. 

Riparian habitat consisting of willow, tamarisk, and baccharis that developed on those 

deposited sediments, is now almost all dead due to the lack of water and erosion, all 

caused from the declining lake level. In 2007, we observed tamarisk and some willow 

recruitment along the river’s edge. This area is divided into five sites, one new site (Big 

Horn Draw) that developed into adequate cuckoo habitat in 2007, RM274.5, Cuckoo 

Beach, Iceberg Ridge and Chuckwalla Cove. In 2007, we excluded the Spencer Canyon 

site because of unsuitable cuckoo habitat. 

RM 274.5 (Elevation 360 m; 1,181 ft) 

RM 274.5 is approximately 19 km (11.8 miles) upstream from the Cuckoo Beach 

site, and consists mainly of dense Goodding’s willow and tamarisk with sparse patches of 

cattail marsh (Typhus spp.; Appendixes 4 and 5). Canopy height is 8–10 m (26–32 ft). 

The understory is consists of young tamarisk, baccharis, and young Goodding’s willow, 

with an average height of 2 m (6.5 ft). Standing water was present during all surveys in 

2007 due to the large number of seeps and creeks. The site is bordered by dense tamarisk, 

desert upland, and steep canyon walls. In 2007, we extended this survey area upstream 

along the river’s edge approximately 800 m compared to our 2006 surveys. 

Cuckoo Beach (Elevation 340 m; 1,115 ft) 

Cuckoo Beach is approximately 1.5 km (0.9 miles) upstream from the Iceberg 

Ridge site, and lies on both sides of the river (Appendixes 4 and 5). It consists of 

stringers of Gooding’s willow 8-12 m (26-39 ft) in height, extending inland 

approximately 60 m (197 ft). Tamarisk (canopy height is 6–8 m (20–26 ft) is dominant 

toward the back of the site (away from the river), where there are also sand dunes and 

desert scrub. The understory consists of tamarisk and Goodding’s willows, 1-1.5 m (3 ft) 

tall. In 2007, standing water was not present within this site. The adjacent habitat is desert 

upland. By July of 2007, approximately 50 percent of the Goodding’s willow had died. 

By August, 100 percent had died downstream on the river left portion of the site. Though 

some young Goodding’s willow still exists on the upstream right portion of the site, 90 

percent of the overstory was dying by August. Also, 100 percent of the marsh vegetation 

was dry and dying by July. Soil band erosion was evident all along the river’s edge. In 

2007, we also documented cattle at this site. 

16
Iceberg Ridge (Elevation 345 m; 1,132 ft) 

Iceberg Ridge is a crescent-shaped patch within a cove approximately 300 m (984 

ft) upstream from Chuckwalla Cove on river left (Appendixes 4 and 5). This site consists 

of small stringers of Goodding’s willow and tamarisk. The upstream portion is sparsely 

vegetated, with open spaces between the willow and tamarisk. The middle section 

consists of multi-aged Goodding’s willow. The downstream section is dense Goodding’s 

willow with a canopy of approximately 4–5 m (13–16 ft) tall, although a majority of the 

upper canopy (>5 m; 16 ft) is dead or dying. In 2007 there was no standing water at this 

site. The marsh vegetation consisting of reeds (Phragmites spp.) and cattails that thrived 

in 2006 had died by July 2007. The site is bordered by desert upland habitat, and thick 

tamarisk. In July of 2007, 60 percent of the Goodding’s willow was dead at this site. By 

August, 80 percent was dead. Tamarisk recruitment was documented all along the edge 

of the river at this site. 

Chuckwalla Cove (Elevation 340 m; 1,115 ft) 

Chuckwalla Cove is the first large delta site upstream from Lake Mead NRA 

proper, located on river right approximately 14.5 km (9 miles) from the South Cove boat 

ramp (Appendixes 4 and 5). Suitable yellow-billed cuckoo habitat consisting of large 

patches of Goodding’s willow and tamarisk had developed in exposed sediment, low 

water areas over the past six years. The habitat is spread throughout the entire floodplain, 

for approximately 250 m (820 ft) perpendicular to the river’s edge. The Goodding’s 

willow at this site are found in stringers that extend perpendicular to the river. Canopy 

height is 8–10 m (26–33 ft). The understory is comprised of young tamarisk, 1 m (3 ft) 

tall. In 2007, standing water was not present within this site. The adjacent habitat is desert 

upland. In 2007, we found high mortality rates (60 percent in August) of Goodding’s 

willow due to the drop in lake levels. Willow recruitment was non-existent, yet tamarisk 

recruitment was high. 

Big Horn Draw (Elevation 340m, 1,115 ft) 

Big Horn Draw is a small site, located 500 m (1640 ft) downstream from 

Chuckwalla Cove, approximately 14 km (8.7 miles) from the South Cove boat ramp 

(Appendixes 4 and 5). In 2006, we noted that this site could potentially develop into 

suitable cuckoo habitat. In 2007, we surveyed this site three times, but did not conduct a 

fourth survey because the majority of the Goodding’s Willow had died by August due to 

the drop in lake levels. The habitat consisted of a stringer of mixed Goodding’s willow 

and tamarisk along the river’s edge, approximately 500 m (1640 ft) long, and 30 m (98 ft) 

wide. Canopy height is 4-5 m (13-16 ft). The understory is dominated by young tamarisk, 

1 m (3 ft) tall. There was marsh vegetation near the back (away from the river) and in the 

middle of the site that consisted of reeds (Phragmites spp.) and cattails, but this dried up 

by July. In 2007, there was no standing water at this site. This patch backs up to the steep 

Iceberg Ridge wall consisting of desert upland habitat. 

Havasu National Wildlife Refuge, AZ (Colorado River) 

The Havasu National Wildlife Refuge is 15,181 ha (37,515 acres), including 

approximately 45 river km (28 river miles) of the Colorado River (Figure 2.1 ; Appendix 

4). Topock Marsh is an old marsh within the existing river meander, covering 

17
approximately 1619 ha (4000 acres) of the refuge, and is where most of the riparian 

habitat in the refuge exists. It is maintained through a dike system established with the 

creation of the refuge. Topock Marsh presently consists of 40 percent of all backwater 

habitat on the entire Colorado River system. In 2007, we divided the Havasu National 

Wildlife Refuge area into four yellow-billed cuckoo survey sites, excluding two sites 

(Sacramento Wash and Havasu Tamarisk) from our 2006 survey because of lack of 

suitable cuckoo habitat. 

Pintail Slough (Elevation 135 m; 443 ft) 

Pintail Slough is a restoration site that consists of young Fremont cottonwood 

with a small area of large Fremont cottonwoods (Appendixes 4 and 5). The younger 

portion of the site is only four years old and lacks an understory or multi-layered canopy. 

Canopy height is 4–6 m (13–20 ft) in the young portion of the site and 12–15 m (39–9 ft) 

in the older section. The site is surrounded by tamarisk, arrowweed, four-wing saltbush 

(Atriplex canescens), and some mesquite. The site is bordered by old agricultural fields, 

dikes, and a grid of roads. In 2007, standing water was occasionally present within this 

site. 

North Dike (Elevation 137 m; 449 ft) 

The North Dike site is comprised of two restoration plots located about 300 m 

(984 ft) south of Pintail Slough. It consists of large Fremont cottonwoods with sparse 

mesquite along the edges of the plot (Appendixes 4 and 5). Canopy height is 8–10 m (26–

33 ft). The understory consists of forbs and grasses. The smaller younger plot is mainly 

Fremont cottonwood and sparse mesquite, 1–2 m (3–6 ft) tall, with an understory of tall 

grasses. There was intermittent standing water within this site in 2007 and occasional 

water in the surrounding canals. There is also a large patch of tamarisk and arrowweed 

surrounding the site, and old agricultural fields and roads bordering each plot. 

Topock Marsh Restoration (Elevation 136 m; 446 ft) 

The Topock Marsh restoration site is adjacent to the Colorado River, consisting of 

five-year-old Fremont cottonwoods intermixed with two-year-old Fremont cottonwoods 

and Goodding’s willow planted in rows, with a small dense mesquite restoration plot 

adjacent to the site (Appendixes 4 and 5). Canopy height is 5–7 m (16–23 ft). There was 

no standing water within this site in 2007. A large patch of tamarisk and arrowweed, 

agriculture fields, and roads surround the site. In late July, a large part of the northern 

side of the plot that borders the agriculture field was thinned extensively. 

Topock Tamarisk (Elevation 143 m; 469 ft) 

Topock Tamarisk is along the western end of Sacramento Wash, which is near I40 (Appendixes 4 and 5). This site consists of Athel tamarisk (Tamarix aphylla) with a 

dense overstory. There is no understory within this site, although there is a thick duff 

layer and many downed trees and branches. A small stringer of tall cottonwoods runs 

along a dirt road that borders the site. Canopy height is 10-13 m (33–43) ft). In 2007, 

standing water was present at this site during late July and August due to the flooding of 

Sacramento Wash. The site is surrounded by a large patch of young monotypic tamarisk, 

arrowweed, and creosote. 

18
Bill Williams River National Wildlife Refuge, AZ (Bill Williams River) 

The Bill Williams River, a tributary of the Colorado River, runs 64 km (40 miles) 

from Alamo Dam to the confluence of the Colorado River. Alamo Lake, which is behind 

Alamo Dam, is fed by the Big Sandy and Santa Maria Rivers. Bill Williams River 

National Wildlife Refuge is a 2,489 ha (6,150 acres) area that stretches from Cave Wash 

downstream to the Colorado River–Bill Williams River confluence, a distance of 

approximately 16 km (10 miles) (Figure 2.1; Appendix 4). Bill Williams River NWR is a 

unique riparian system that consists of sandy washes, marsh, and riparian areas that offer 

some of the last naturally occurring large cottonwood-willow stands along the lower 

Colorado River. The entire riparian area and the floodplain are flanked by Sonoran desert 

upland habitat. 

We divided the Bill Williams River NWR into thirteen cuckoo survey sites. We 

chose most of the sites (see below) in 2006 based on historic survey routes where 

cuckoos had been detected from 1994, 1995, 1998, and 2001–03 (Halterman and Laymon 

1994, Halterman and Laymon 1995, Halterman 1998, 2001, 2002, 2003). We also added 

survey routes that connected each site within the refuge riparian system. In 2007, we 

added two sites that we did not cover in 2006; North Burn and Teepee Trail. For 

logistical purposes, we split one of our longer survey routes (Cave Wash) into three 

shorter survey routes; Cottonwood Patch, Cave Wash, and Honeycomb Bend. 

Survey site descriptions are listed below beginning with the most upstream 

locations and progressing downstream. 

Teepee Trail (Elevation 180 m; 590 ft) 

Teepee Trail is located on the northeastern edge of the refuge (Appendixes 4 and 

5). The site consists of a small strip of suitable habitat 600 m (1969 ft) long. Teepee Trail 

is approximately 1.5 kilometers (0.93 mi) from the nearest surface water and is not 

contiguous with other cuckoo habitat within the refuge. The understory of this site is 

dominated by dense tamarisk while the overstory is made up of Fremont cottonwood and, 

to a lesser extent, Goodding’s willow. Canopy height is 6 to 8 m (19 to 26 ft). There is no 

standing water within this site. The site is surrounded by a combination of sparse 

tamarisk and fallow fields to the south and by Sonoran Desert upland to the north. 

Cave Wash (Elevation 175 m; 574 ft) 

Cave Wash is located in the eastern portion of the refuge (Appendixes 4 and 5). 

The site is a wide floodplain, with the western portion consisting of young Goodding’s 

willows and Fremont cottonwoods along the river’s edge. The eastern portion of the site 

is made up of large Fremont cottonwoods farther from the water. The riparian patches 

within the floodplain are well developed with very little understory. The vegetation at this 

site is extremely thick in some places. Canopy height is 8–10 m (26–33 ft) in the western 

part of the site and up to 18 m (59 ft) in the eastern part. The river is braided at this site 

allowing thick riparian patches and standing water to alternate with dry, sandy washes 

away from the main river channel. This site is surrounded by Sonoran Desert upland. In 

2006, this site also covered Honeycomb Bend and Cottonwood Patch sites, but was split 

in 2007 for logistical purposes. 

19
Cottonwood Patch (Elevation 181m; 593 ft) 

Cottonwood Patch is the eastern portion of the 2006 Cave Wash survey 

(Appendixes 4 and 5). The site consists of a lush but thin stringer of Fremont 

cottonwoods. The canopy is 8-10 m (26-33 ft) and consists of Fremont cottonwood. The 

understory is sparse, consisting of tamarisk and some small Fremont cottonwoods. 

Cottonwood Patch is located within 30 m (98 ft) of the Bill Williams River, but the river 

runs underground in this part of the refuge. A small puddle is the only surface water near 

Cottonwood Patch. The site is surrounded by Sonoran Desert upland. 

Honeycomb Bend (Elevation 171 m; 561ft) 

This site is the western arm of the 2006 Cave Wash survey. It consists of multilayered, uneven aged Goodding’s willow and Fremont cottonwoods that line both banks 

of the river (Appendixes 4 and 5). The Bill Williams River flows at the surface in this site 

and has a wide floodplain, which allows some patches of riparian vegetation to grow 

away from the main channel. The understory consists mainly of tamarisk of variable 

density. Canopy height is 8–15 m (26-49 ft), depending on the individual stand. It is 

surrounding by Sonoran Desert upland to the north and south. 

Mineral Wash (Elevation 160 m; 525 ft) 

Mineral Wash has dense, mature riparian vegetation lining both banks 

(Appendixes 4 and 5). The vegetation is dominated by native species, but also contains an 

exotic component. There are many patches with multi-layered, uneven-aged Fremont 

cottonwood and Goodding’s willow stands with a dense understory of Goodding’s 

willow, tamarisk, mesquite, and other shrubs. Historical flooding is evident in this section 

of the river. Canopy height is 12–14 m (39–46 ft). The river is heavily braided here, 

causing riparian patches to be thicker, with standing water away from the main river 

channel. This site is surrounded by Sonoran Desert upland. 

Big Bend (Elevation 165 m; 541ft) 

Big Bend is a large bend in the Bill Williams River that winds through Bill 

Williams River Canyon (Appendixes 4 and 5). The canyon varies in width throughout the 

site and patchy dense riparian vegetation lines the riverbanks throughout. The vegetation 

is dominated by native species, but also has braided tamarisk throughout. There are many 

patches with multi-layered uneven-aged Fremont cottonwood and Goodding’s willow 

stands with a dense understory of tamarisk. Bulrush (Scirpus spp.) lines the riverbank 

throughout much of the site. Canopy height is 10–14 m (33–46 ft). The river flowed 

through Big Bend during all surveys in 2007. This site is surrounded by sandy deltas and 

contains extensive patches of mesquite that extend into the canyon floodplain. There are 

strips of young willow and cottonwood in areas where the sandy uplands have flooded. 

This site is surrounded by Sonoran Desert upland. 

Gibraltar Rock (Elevation 145 m; 476 ft) 

Gibraltar Rock consists of a large sandy floodplain with large areas of cobble. 

This washed-out section of the river is straddled at either end by two lush riparian patches 

consisting of mature and young Fremont cottonwoods, and young Goodding’s willow 

20
(Appendixes 4 and 5). There are tamarisk stringers throughout the site and thicker 

tamarisk extending into the upland desert habitat. Canopy height is 10–12 m (33–39 ft). 

The river flowed through the eastern third of the site during 2007. The site is surrounded 

by Sonoran Desert upland. 

Sandy Wash (Elevation 146 m; 473 ft) 

The Sandy Wash site has lush riparian habitat on either side of dry, sandy braids 

of several river washes. Within this site, the river runs against a cliff face on the northern 

side of the patch, away from the main part of the riparian habitat (Appendixes 4 and 5). 

The patches consist of large Fremont cottonwoods and Goodding’s willows, with a thick 

understory dominated by tamarisk, younger Fremont cottonwood and Goodding’s 

willow. Canopy height is 12–14 m (39–46 ft). The river washes did not flow during any 

surveys in 2007, but a stagnant pool in the river bed stayed wet throughout. The site is 

surrounded by mesquite and palo verde (Parkinsonia microphylla) to the south and by 

Sonoran Desert upland to the north. 

Fox Wash (Elevation 145 m; 476 ft) 

Fox Wash is located on the northern edge of the western portion of the refuge 

(Appendixes 4 and 5). It is extremely diverse, consisting of a dry river bed and desert 

washes lined with tamarisk stringers, burnt tamarisk, and downed wood. There is a 

unique section of large Fremont cottonwood and Goodding’s willow with very little 

understory, leaving it very open except for widely dispersed young tamarisk. Canopy 

height is 12–14 m (39–46 ft). There were pools of standing water within this site 

intermittently during 2007. The site is surrounded by patches of mesquite and blue palo 

verde to the south and by Sonoran Desert upland to the north. 

Mosquito Flats (Elevation 140 m; 459 ft) 

Mosquito Flats borders the refuge’s broadest riparian area ,which is 

approximately 600 m (1968 ft) wide (Appendixes 4 and 5). We focused our surveys on 

the southern edge of the site. The patch consists of native and exotic vegetation in 

multiple stages of growth. Large Fremont cottonwood and Goodding’s willow are present 

throughout the site. Canopy height is 12–14 m (39–46 ft). Some areas of the site have a 

relatively open understory while other areas contain very dense tamarisk or Goodding’s 

willow. There was intermittent standing water within this site during 2007. Mosquito 

Flats is bordered by large patches of mesquite, blue palo verde, and arrowweed. 

Saguaro Slot (Elevation 135 m; 443 ft) 

Saguaro Slot is an extremely dense site with both native and exotic vegetation, 

roughly 100 m (328 ft) away from the river at its farthest edge (Appendixes 4 and 5). The 

overstory includes many large Goodding’s willows and limited Fremont cottonwoods. 

The understory is made up of many thick clumps of small-diameter tamarisk and dense 

stands of small Goodding’s willow. There are numerous downed logs and a thick 

decomposing layer of duff. Canopy height within the site is 12–14 m (39–46 ft). There 

were pools of standing water during all 2007 surveys. The site is surrounded by a dense 

mesquite thicket. 

21
North Burn (Elevation 151 m; 495 ft) 

The North Burn site is located on the northern edge of the wide riparian patch, its 

southern border is the Mosquito Flats site (Appendixes 4 and 5). North Burn was not 

surveyed in 2006 due to inaccessibility, but became accessible due to vegetation clearing 

from a fire in late July 2006. There are numerous large Fremont cottonwoods and 

Goodding’s willow throughout the site. Canopy height is 12–14 m (39–46 ft). 

Goodding’s willow and tamarisk create a thick understory. A side channel of the river 

flows through the western portion of the site while the eastern portion is dry. The middle 

section of the site borders the area burned in 2006. The burn itself consists of large native 

trees that are mostly dead now with regenerating tamarisk. North Burn is surrounded by 

very dense mesquite and blue palo verde, to the north the site is bordered by Sonoran 

Desert upland. 

Bill Williams River Marsh (Elevation 133 m; 436 ft) 

Bill Williams River Marsh was accessed by boat by paddling from Lake Havasu 

to the confluence of the Bill Williams River, then continuing upriver approximately 1.6 

km (0.9 miles), to the beginning of the site (Appendixes 4 and 5). Habitat consists mainly 

of Fremont cottonwood and Goodding’s willow along the river’s edge and throughout the 

floodplain, with tamarisk and Goodding’s willow making up most of the understory. The 

understory is extremely dense in some areas due to the thick tamarisk. Canopy height is 

12–14 m (39–46 ft). Marsh vegetation is abundant along the banks, and stagnant pools of 

water are present just beyond the river’s edge within the riparian area. The site is 

bordered to the south by Sonoran Desert. 

Ahakhav Tribal Preserve (Colorado River) (Elevation 94m; 308ft) 

The Ahakhav Tribal Preserve is located on the Colorado River Indian Tribes land, 

2 km (5 miles) south of Parker, AZ (Figure 2.1; Appendix 4). The preserve was 

established in 1995 and now encompasses 507 ha (1,253 acres) dedicated to the 

restoration of backwater and riparian habitat. 

The preserve is a revegetation site that consists of Fremont cottonwood, 

Goodding’s willow, and mesquite adjacent to the Colorado River (Appendixes 4 and 5). 

Trees were planted at different times to create a multi-layered structure. Additionally, 

stands of varying age and species composition, including some composed solely of 

mesquite, have been planted creating a mosaic of patches throughout the site. Canopy 

height is 12–14 m (39–46 ft). The understory is mostly sparse native trees. No standing 

water was present within the site in 2007, but it is regularly irrigated. The Preserve is 

surrounded by agricultural fields. 

Cibola National Wildlife Refuge, AZ (Colorado River) 

The Cibola National Wildlife Refuge (NWR) encompasses 6,729 ha (16,627 

acres) in the floodplain of the lower Colorado River (Figure 2.1; Appendix 4). The 

primary flow of the river through the refuge is via a canalized section constructed in the 

late 1960s, while the original river channel forms the western boundary of the refuge at 

the California border. Approximately 809 ha (2000 acres) of the refuge is farmed for 

migratory waterfowl and 318 ha (785 acres) consists of Sonoran Desert. Most of the 

alluvial river bottom is dominated by tamarisk, mesquite, and arrowweed. Survey sites 

22
were located at riparian restoration plots planted within the past 10–15 years. Two fires 

occurred on the refuge during the 2006 field season, the first on 17 July and the second 

on 10 August. In 2007, we noted recruitment of arrowweed and tamarisk in these burned 

areas. No fires occurred in 2007. We surveyed four sites at Cibola National Wildlife 

Refuge in 2007. Two sites (Cibola Cross River, Cibola East Side) surveyed in 2006 were 

not surveyed in 2007 due to lack of suitable cuckoo habitat. 

Cibola North Restoration (Elevation 68 m; 223 ft) 

The Cibola North Restoration site consists of young (2–3 years old) Freemont 

cottonwoods and is approximately 500 m (1640 ft) north of the Cibola Nature Trail site 

(Appendixes 4 and 5). The site was planted in an abandoned agricultural field. Canopy 

height is 4–6 m (13–20 ft). In 2007, standing water was not present within the site. It is 

bordered by agriculture lands, with a paved road on the north side. 

Cibola Nature Trail Restoration (Elevation 74 m; 243 ft) 

The Cibola Nature Trail Restoration site was planted in 1999. It is dominated by 

cottonwood planted in a horseshoe-shaped ring: The north section is dominated by a 

lower canopy of willow and the south section is dominated by mesquite with a tall grass 

understory (Appendixes 4 and 5). A public nature trail passes through the site. Canopy 

height is 10–12 m (33–39 ft). The Colorado River is approximately 2 km (1.2 miles) 

away. Refuge staff periodically irrigated the site in 2007. Therefore, standing water was 

present in the north part of the horseshoe-shaped ring. The site is surrounded by 

agriculture fields. 

Cibola Eucalyptus Restoration (Elevation 71 m; 233 ft) 

The Cibola Eucalyptus Restoration site consists of eucalyptus trees, but also 

contains numerous Freemont cottonwoods (Appendixes 4 and 5). Other tree species 

present include tamarisk, mesquite, and palo verde. A refuge levee road bisects the site, 

which extends for 1 km (3.3 ft) north-south. Canopy height is 10–12 m (33–39 ft). The 

Colorado River lies 100 m (328 ft) to the east and in 2007 there was no standing water 

within this site. It is bordered by dense stands of tamarisk, mesquite, and arrowweed. 

Cibola South Restoration (Elevation 62 m; 203 ft) 

The Cibola South Restoration site has an open understory and is dominated by 

rows of planted cottonwoods interspersed with willow (Appendixes 4 and 5). This site 

lies about 300 m (984 ft) west of the Colorado River and is irrigated by refuge staff. 

Canopy height is 10–15 m (33–49 ft). In 2007, standing water was not present within this 

site. The site is bordered by tamarisk and dense stands of mesquite. 

Picacho State Recreation Area, CA (Colorado River) (Elevation 52 m; 171 ft) 

The Picacho State Recreation Area is 46 ha (120 acre) located on the California 

side of the Colorado River, within the Imperial National Wildlife Refuge (Figure 2.1; 

Appendixes 4 and 5). Most of the recreation area is dominated by desert scrub and 

washes, and includes restored riparian vegetation adjacent to the headquarters and the 

river. The canopy is dominated by large Fremont cottonwoods, with scattered 

23
Goodding’s willow. The understory is composed of Goodding’s willow, mesquite, palo 

verde, and arrowweed. The riparian area surrounding the study area consists almost 

entirely of tamarisk. Canopy height is 12–14 m (39–46 ft). In 2006, there was no 

evidence of standing water within this study area. This entire area is surrounded by desert 

upland habitat. 

Imperial National Wildlife Refuge, AZ and CA (Colorado River) 

The Imperial National Wildlife Refuge encompasses 10,428 ha (25,768 acres), 

including an unchannelized 50-km (31-mile) stretch of the Colorado River (Figure 2.1; 

Appendix 4). The refuge borders Cibola NWR to the south. It is dominated by desert 

ridges and riparian vegetation along the Colorado River. Native riparian vegetation is 

rare, and most of the habitat is dominated by tamarisk and reeds (Phragmites spp.). In 

2007, we surveyed for yellow-billed cuckoos at the Imperial South Restoration site; the 

Imperial Paradise site was surveyed in 2006, but not in 2007 due to lack of adequate 

cuckoo habitat. 

Imperial South Restoration (Elevation 56 m; 184 ft) 

The Imperial South Restoration site was planted in 1993 (Appendixes 4 and 5). 

The canopy is dominated by Fremont cottonwoods, with Goodding’s willow, mesquite, 

and arrowweed as the understory. The canopy is 12–14 m (39–46 ft) tall. The Colorado 

River lies 200 m (656 ft) to the west, and the refuge staff periodically flooded this site. 

However, in 2007 there was no evidence of standing water within this site. Marsh habitat 

occurs to the north and east of the site. To the south and west, additional habitat 

restoration is currently being constructed to benefit riparian vegetation and native fish. 

The entire site is a matrix of marsh vegetation, roads, and stringers of cottonwoods, 

ponds, and waterways. Upland desert with mesquite borders the site. 

Mittry Lake State Wildlife Management Area/Pratt Restoration Area, AZ (Colorado 

River) (Elevation 52 m; 171 ft) 

The Mittry Lake State Wildlife Management Area consists of the Pratt 

Restoration Area and the adjacent Betty’s Kitchen, a small recreation site managed by the 

Bureau of Land Management (Figure 2.1; Appendixes 4 and 5). The Pratt Restoration 

Site is dominated by a tall canopy of Freemont cottonwood (12–14 m; 39–46 ft) and 

Goodding’s willow. Most of the site has an open understory covered by leaf litter. The 

southern part of the site is dominated by a dense baccharis and scattered young Freemont 

cottonwoods. Betty’s Kitchen is dominated by 8–10 m (26–33 ft) tall Athel tamarisk and 

large mesquite trees 8 m (26 ft) tall. The rest of the survey area is open water or marsh. In 

2007, there was evidence of standing water within the Pratt Restoration site during the 

month of July. This entire site is surrounded by agriculture fields and Sonoran Desert 

upland habitat. 

Gila–Colorado River Confluence Area, AZ (Gila and Colorado Rivers) 

This study area is located 10 km (6.2 miles) east of Yuma and is managed by the 

Bureau of Land Management (Figure 2.1; Appendix 4). The riparian habitat in this area is 

dominated by tamarisk and is mainly bordered by agriculture. The habitat at the 

24
confluence and upriver from the confluence was surveyed for cuckoos. This area was 

divided into two survey sites, the Colorado River Confluence site and the Gila River site. 

Colorado River (Elevation 39 m; 128 ft) 

Within this site, we surveyed suitable riparian habitat along the north side of the 

river from kayaks (Appendixes 4 and 5). Thin stringers of Fremont cottonwood and 

Goodding’s willow occur close to the river; habitat north of the river’s edge is not 

suitable for cuckoos. Canopy height is 8–10 m (26–33 ft). Near the Gila–Colorado 

confluence, the riparian habitat transitions into a citrus orchard. On the south side of the 

river a thin belt of riparian vegetation exists between the river and the agricultural fields, 

which is almost entirely tamarisk. In 2007, there was no evidence of standing water 

within this site. 

Gila River (Elevation 39 m; 128 ft) 

The Gila River site is dominated by tamarisk (Appendixes 4 and 5), but also 

includes small patches of Fremont cottonwood and coyote willow. The site is largely 

unsuitable habitat. Canopy height within the site is 8–10 m (26–33 ft). There is riparian 

vegetation close to the river, but much of what remains is marginal with broad expanses 

of tamarisk and arrowweed in between native habitat. Canopy height is 8–10 m (26–33 

ft). In 2007, there was no evidence of standing water within this site. Agricultural fields 

border the Gila River on the north and south sides of the river. In late August of 2006, 

one of the best remaining patches within this site consisted of native Fremont 

cottonwoods, but was altered by a local farmer using heavy machinery. In 2007, the 

majority of those trees have now died. 

Yuma West Wetlands, AZ (Colorado River) (Elevation 36 m; 118 ft) 

This site is surrounded by urban development on the southeast edge of Yuma, AZ 

(Figure 2.1; Appendixes 4 and 5). It is managed by the city of Yuma, Bureau of 

Reclamation, and Cocopah (Kwapa) Indian Tribe. Most of the wetland is a riparian 

restoration plot that borders the Colorado River on one side and a levee on the other. The 

vegetation is composed of Fremont cottonwood, Goodding’s willow, and mesquite that 

are approximately 8–10 years old. Canopy height is 8–10 m (26–33 ft). Management 

activities at the study area include regular irrigation and exotic species removal. There 

was evidence of standing water within this study area in 2007. The southern edge of the 

park is bordered by a railroad right-of-way; the northern edge is bordered by a housing 

park, Interstate 10, and a large expanse of low desert scrub. This is the second year we 

have completed full yellow-billed cuckoo surveys at this study area. 

Limitrophe Division, AZ (Colorado River) 

The Limitrophe Division survey area starts at the International Border near 

Morales Dam and extend to San Luis, Arizona, at the International Border with Mexico 

(Figure 2.1; Appendix 4). We only surveyed the riparian habitat on the east side of the 

river (United States side). The habitat is enclosed by a series of tightly controlled gates 

and is actively patrolled by border security personnel. We requested permission to enter 

the study area from the Border Patrol prior to each survey. Agricultural fields border the 

25
riparian habitat on both sides the Colorado River. The Limitrophe Division area was 

divided into two sites, Limitrophe North Site and Limitrophe South. 

Limitrophe Division North (Elevation 36 m; 118 ft) 

This site starts at the International Border below Morales Dam and extends to the 

northern border of the Cocopah Indian Tribal lands (Appendixes 4 and 5). The riparian 

habitat transitions from Fremont cottonwood and Goodding’s willow to tamarisk. In 

some places the site is dominated by arrowweed. Canopy height is 4–10 m (13–33 ft). In 

2007, there was no evidence of standing water within this site. During June 2007, a fire 

burned 10 ha of the established survey route. There are agricultural fields adjacent to the 

site. 

Limitrophe Division South (Elevation 33 m; 108 ft) 

This site starts at the southern border of the Cocopah Indian Tribal lands and 

continues to San Luis, AZ, the Southerly International Border with Mexico (Appendixes 

4 and 5). The habitat transitions frequently between dense exotic/native vegetation and 

sparse scrub. Limitrophe Division South has two main patches of suitable riparian habitat 

that are separated by more than 2 km (1.2 miles) of sparse scrub dominated by 

arrowweed. The southern patch is a mix of Freemont cottonwood, Goodding’s Willow, 

and marsh, while the northern patch consists of Freemont cottonwood, tamarisk, and 

Goodding’s Willow. No marsh exists within this section. Canopy height is 4–10 m (13–

33 ft). In 2007, there was no evidence of standing water within this site. There are 

agricultural fields surrounding the site. 

Quigley Pond Wildlife Management Area, AZ (Gila River) (Elevation 67 m; 220 ft) 

The Quigley Pond Wildlife Management Area is located in the Gila River 

floodplain approximately 6 km (4 miles) south of the U.S. Highway 8 at the Tacna exit 

(Figure 2.1; Appendixes 4 and 5). It is managed by the Arizona Game & Fish 

Department. The site includes a restoration plot dominated by Fremont cottonwood with 

a small number of Goodding’s willow in the understory. Adjacent to the restoration plot 

is a larger section of mixed native-exotic habitat with a canopy of mostly young Fremont 

cottonwood and Goodding’s willow, and a dense understory of arrowweed. 

Approximately 500 m (1640 ft) to the north is the Gila River and an area mostly 

dominated by tamarisk. Canopy height is 8–14 m (26–46 ft). The Arizona Game & Fish 

Department irrigates the restoration site and in 2007 there was standing water within this 

site. The surrounding landscape consists of agricultural fields. 

Survey Methods 

Surveys for presence/absence of cuckoos were conducted following established 

methods (Laymon 1998a, 1998b; Halterman et al. 2006; Johnson et al. 2006b) that 

involve a minimum of four surveys distributed among four defined survey periods 

between 10 June and 15 September (Table 2.2). Surveys at each site were staggered at 

least 10 days apart to assure visits throughout the potential breeding season and to 

increase the likelihood of detecting nesting cuckoos. If cuckoos were detected during the 

fourth survey period, which might indicate that cuckoos were still breeding at that site, a 

fifth survey was conducted. 

26
Table 2.2. Number of official surveys and yellow-billed cuckoo survey detections per 

survey period in 2007 at sites in the lower Colorado River watershed along the Muddy, 

Virgin, and White Rivers in Nevada, and the Colorado, Bill Williams, and Gila Rivers in 

Arizona and California. 

Survey Period Survey Dates No. of Surveys 

(n = 169) 

Detections 

(n = 163) 

1 6/11–6/28 40 48 

2 7/1–7/18 41 44 

3 7/25–8/11 40 39 

4 8/13–9/5* 38 27 

5 9/5–9/9 10 5 

*There was a 15 point survey at Topock Tamarisk during the 4th survey period that couldn’t be conducted 

until 9/5. 

We used a taped recording of the yellow-billed cuckoo’s kowlp call (Hughes 

1999) during surveys. Broadcast equipment was capable of projecting this call at least 

100 m (328 ft) with a minimum of distortion. Surveys were conducted from half an hour 

before sunrise until 11:00 a.m., and were terminated if shade temperatures exceeded 41°C 

(110°F) or during steady rainfall. One transect (i.e., a series of points from which the tape 

was broadcast) was established through the habitat for every 200 m (656 ft) of habitat 

width. No cuckoos have been detected nesting in patches 2 ha (5 acres) or smaller in 

Arizona or California (Corman and Magill 2000, Halterman et al. 2006), thus we did not 

survey patches smaller than this size. We did not always conduct surveys from within the 

habitat because the playback vocalizations are broadcast loudly enough to cover a large 

area (i.e. 100 m). We selected survey points that were no more than 15 m (49 ft) from the 

habitat edge and not surrounded by dense vegetation in order to more easily detect 

cuckoos that responded by flying closer, but did not vocalize. In some cases, we surveyed 

small narrow stringers of habitat, steep banks, and backwater sloughs playing the tape 

from a boat. We bypassed areas of unsuitable habitat (e.g., a monoculture of young 

tamarisk or an extensive cobble bar) between patches if the unsuitable habitat was at least 

300 m (984 ft) in extent. 

At each survey point, we started by remaining quiet for one minute to acclimate to 

the ambient noise and to listen for spontaneously calling cuckoos. If no cuckoos were 

heard in this one-minute period, the surveyor then played the kowlp call once, followed 

by one minute of silence to listen for a response. If no detections occurred, this broadcastlisten sequence was repeated up to an additional four times. If there was no detection at a 

given point, the surveyor moved 100 m (328 ft) along the transect and repeated the 

broadcast-listen protocol. If a cuckoo was detected at the survey point, the surveyor 

moved 300 m (984 ft) before resuming survey broadcasts to reduce the probability of redetecting or attracting the same individual. 

We recorded Universal Transverse Mercator (UTM) coordinates (using Global 

Positioning System [GPS] units), GPS accuracy, estimated number of individual cuckoos 

detected, and estimated distance and direction (i.e., the compass bearing) from the 

surveyor to the detected cuckoo at all survey points. At each survey site, we also recorded 

the UTM coordinates of the survey site boundaries (including start and stop points), and 

provided a description of the habitat and surrounding area. 

27
When a yellow-billed cuckoo was detected, the surveyor briefly attempted to 

determine the number and breeding status of the individuals present by making direct 

behavioral observations and by nest searching. All behaviors were recorded including the 

cuckoo’s use of the habitat patch, interactions between individuals, types of 

vocalizations, and any breeding behavior. After the survey was completed, the surveyor 

went back to where birds were detected and tried to determine the number cuckoo 

detected and their breeding status. 

Survey Site Classifications 

Based on survey results across all four visits, sites were classified as either 

occupied (a yellow-billed cuckoo had been detected at a site during at least two survey 

periods) or unoccupied. The presence of a cuckoo at a site does not necessarily equate to 

pairing and breeding at that location. Breeding was considered “confirmed” only if an 

active cuckoo nest was found, copulation was observed, and/or recently fledged young 

were seen. The detection of multiple cuckoos during one or more surveys or of cuckoos 

carrying food or nesting material was suggestive of pairing and breeding, but was not 

considered confirmation.

Supplemental Follow-up Surveys 

Varying numbers of supplemental visits were made to areas with yellow-billed 

cuckoo survey detections. The purpose of these supplemental visits was to more fully 

ascertain yellow-billed cuckoo use of site. Supplemental visits also provided additional 

opportunities to observe breeding behavior and search for nests. When making a 

supplemental visit, observers did not follow survey protocol and used vocalization 

broadcasts sparingly (when birds were not being detected). The observers mainly focused 

on the areas within a site where cuckoos were previously detected or at the sites with the 

highest likelihood for cuckoo presence and breeding activity. Supplemental follow-up 

visits differed from surveys in that observers filled out detection information for every 

location a cuckoo was observed at, even if that meant recording the same individual 

multiple times. For example, if a cuckoo was seen on river right then flew to river left, 

then it was counted as one detection if the observer could positively determine it was the 

same bird. This allowed us to determine exactly which areas cuckoos were detected in 

within a given site. The same data were taken for supplemental survey detections as were 

taken for formal survey detections. For each supplemental visit, we also recorded start 

and stop UTMs for the portion of the site we visited that day. 

Nest Searching and Monitoring 

Nest searching was conducted by one of three methods: (1) keying in on the 

densest area of cuckoo activity: (2) using several observers to triangulate on cuckoo 

vocalizations; (3) or by searching every tree within a 100-m (328-ft) radius of a detection 

(Martin and Geupel 1993). When a nest was located, observers took a GPS reading from 

approximately 10 m (33 ft) away to minimize disturbance; a reading was later taken 

directly beneath the nest once it became inactive. Nests were checked every 2-7 days, 

depending on the stage of the nest when first found. When checking a nest, the nest was 

first observed from a distance of 20 m (66 ft) to ascertain its stage. Contents were 

checked only if an adult was not on the nest and only if the nest was in the incubation or 

28
early nestling stage, at which time we documented the number of eggs and nestlings 

along with their estimated age. If the nest was found to be empty, the area was searched 

for fledglings or signs of predation (Rourke et al. 1999). Inactive nests continued to be 

checked in order to search for fledglings. Vegetation measurements were taken at each 

nest after it became inactive. 

Spatial Data 

From orthorectified color aerial photography provided by the Bureau of 

Reclamation, we produced digital orthophoto quarter quads (DOQQs) to create aerial 

maps of study sites (Appendix 4). These maps were overlain with survey points (the 

coordinate point from which a broadcast survey was conducted), survey detections (the 

coordinate point at which the surveyor estimated the cuckoo to be located), supplemental 

visit detections, and locations of breeding activity. The GIS themes are projected in UTM 

Zone 11 north; the datums are NAD 1983 (horizontal) and NGVD 1929 (vertical), and 

the spheroid is GRS 1980. The software used to compile the maps, in meters, was 

ArcView GIS Version 3.3 (ESRI Corp.). 

Results 

Yellow-billed Cuckoo Formal and Follow-up Detections, 2007 

During the 2007 field season, we surveyed 40 sites between 11 June and 9 

September for a total of 312 official survey hours. The 169 individual surveys resulted in 

a total of 163 yellow-billed cuckoo detections at 25 of our 40 sites (62.5 percent). The 

vast majority of detections were at Bill Williams River NWR (n = 139; 85 percent; 

Figure 2.2; Appendix 2). Fifteen sites (37.5 percent) were classified as occupied, 

including twelve of the thirteen sites at the Bill Williams River NWR (Table 2.3). 

Official survey detections declined with each survey period, with 48 detections during the 

first period and 44, 39, 27, and 5 detections in the second through fifth survey periods, 

respectively (Figure 2.3). We also had 93 supplemental surveys (follow-up surveys) over 

the same time period, mainly in the Bill Williams River NWR. The 204 hours spent on 

these visits resulted in 253 additional cuckoo detections. 

29
Geographic Area

Pahranagat NWR

Overton WMA

Grand Canyon NP - Lake Mead NRA

Havasu NWR

Bill Williams River NWR

CRIT Reservation

Cibola NWR

Picacho SRA

Imperial NWR

Pratt Restoration

Yuma West Wetlands

Limitrophe

Gila-Colorado Confulence

Quigley Pond

Detections

0

20

40

60

80

100

120

140

160

Survey period 1

Survey period 2

Survey period 3

Survey period 4

Survey period 5

Figure 2.2. Summary of yellow-billed cuckoo detections by survey period and 

geographic area within the LCR MSCP boundary area, 2007. Results are only from formal 

surveys. 

Table 2.3. Number of yellow-billed cuckoos detected at each survey site during each 

survey period within the LCR MSCP boundary area, 2007. * = occupied site, NS = no 

survey. 

Survey Site Name Survey 1 Survey 2 Survey 3 Survey 4 Survey 5 

Pahranagat NWR 

Pahranagat South NS 0 0 0 NS 

Pahranagat North 0 0 0 0 NS 

Overton WMA 

Honeybee Pond 0 0 0 0 NS 

Overton Wildlife 0 0 0 0 NS 

Grand Canyon NP/Lake Mead NRA 

River Mile 274 0 0 0 0 NS 

Cuckoo Beach 0 0 0 0 NS 

Iceberg Ridge 0 0 0 0 NS 

Chuckwalla Cove 0 0 0 0 NS 

Big Horn Draw 0 0 0 NS NS 

30
Table 2.3. Number of yellow-billed cuckoos detected at each survey site during each 

survey period within the LCR MSCP boundary area, 2007. * = occupied site, NS = no 

survey.—Continued 

Survey Site Name Survey 1 Survey 2 Survey 3 Survey 4 Survey 5 

Havasu NWR 

Pintail Slough 0 1 0 0 NS 

North Dike 0 1 0 NS NS 

Topock Marsh Rest. 1 0 0 0 NS 

Topock Tamarisk 0 0 0 0 NS 

Bill Williams River NWR 

Teepee Trail 0 0 1 0 NS 

Cottonwood Patch* 3 3 2 0 NS 

Cave Wash* 2 3 3 3 0 

Honeycomb Bend* 5 3 2 1 0 

Mineral Wash* 13 7 5 2 0 

Big Bend* 4 7 2 6 1 

Gibraltar Rock* 4 4 0 1 0 

Sandy Wash* 0 3 6 3 2 

Fox Wash* 0 1 1 0 NS 

Mosquito Flats* 0 3 6 4 2 

Saguaro Slot* 0 2 4 2 0 

North Burn* 0 1 2 2 0 

Bill Williams Marsh* 1 0 4 3 0 

Ahakhav Tribal Preserve 

Ahakhav Tribal Preserve 2 0 0 0 NS 

Cibola NWR 

North Restoration 0 0 1 0 NS 

Nature Trail Restoration 2 0 0 0 NS 

Eucalyptus Restoration 0 2 0 0 NS 

South Restoration* 1 1 0 0 NS 

Picacho SRA 

Picacho SRA 0 0 0 0 NS 

Imperial NWR 

Imperial South 

Restoration* 2 1 0 0 NS 

Mittry Lake WMA 

Pratt Restoration 0 0 0 0 NS 

Gila/Colorado Confluence 

Colorado Confluence 2 0 0 0 NS 

Gila Confluence 0 0 0 0 NS 

Yuma West Wetlands 

Yuma West Wetlands 0 0 0 0 NS 

Limitrophe Division 

Limitrophe Div. North 0 0 0 0 NS 

Limitrophe Div. South 2 0 0 0 NS 

Quigley Pond WMA* 

Quigley Pond WMA* 4 1 0 0 NS 

31
0

10

20

30

40

50

60

6/11 - 6/30 7/1 - 7/21 7/22 - 8/11 8/12 - 9/4 9/5 - 9/9

Date Interval

Number of Cuckoo Detections

Figure 2.3. Summary of yellow-billed cuckoo detections by survey period within the LCR 

MSCP boundary area, 2007. Results are only from formal surveys. 

Survey area and site results are listed below starting with the most upstream 

locations and proceeding downstream; for both the entire study area and within each side 

drainage. Additional details on each survey area and site and supplemental follow-up 

survey detections are presented in Appendixes 2 and Appendixes 4. 

Pahranagat National Wildlife Refuge, NV (White River Drainage) 

We conducted seven surveys at Pahranagat NWR in 2007 (Table 2.4). We had no 

yellow-billed cuckoo detections and, therefore no follow-up surveys were performed. 

Yellow-billed cuckoos were detected in 2000 at Pahranagat NWR (Halterman 2001) and 

in 2006 we had one yellow-billed cuckoo detection at Pahranagat North. This bird was 

unpaired and no further detections occurred at the refuge (Johnson et al 2007). 

Table 2.4. Dates (2007) for yellow-billed cuckoo surveys conducted at Pahranagat 

National Wildlife Refuge, NV. 

Site Name Survey Period 

1 

Survey Period 

2 

Survey Period 

3 

Survey Period 

4 

 Survey Period 

5 

Pahranagat North 6/27 7/17 7/30 8/26 no survey 

Pahranagat South no survey 7/17 7/30 8/26 no survey 

Overton Wildlife Management Area, NV (Muddy River) 

We conducted eight cuckoo surveys at Overton WMA in 2007 (Table 2.5). In 

2007, no yellow-billed cuckoos were detected and, therefore no follow-up surveys were 

performed. Cuckoos were detected at Overton WMA at the Honey Bee Pond site in 2000 

and 2002 (McKernan and Braden 2001, Rathbun and Braden 2003). In 2006, there were 

seven yellow-billed cuckoo detections; four at Honeybee Pond and three at the Overton 

Wildlife site. Both sites were confirmed occupied in 2006, but breeding was not 

confirmed at either site (Johnson et al. 2007). 

32
Table 2.5. Dates (2007) for yellow-billed cuckoo surveys conducted at Overton Wildlife 

Management Area, NV. 

Site Name Survey Period 

1 

Survey Period 

2 

Survey Period 

3 

Survey Period 

4 

 Survey Period 

5 

Honeybee Pond 6/26 7/18 7/29 8/27 no survey 

Overton Wildlife 6/16 7/12 8/10 8/22 no survey 

Grand Canyon National Park/Lake Mead National Recreation Area, AZ (Colorado 

River and Lake Mead) 

In 2007, we completed 19 yellow-billed cuckoo surveys (Table 2.6) and six 

supplemental follow-up surveys (Table 2.7) at five Grand Canyon/Lake Mead sites. No 

yellow-billed cuckoos were detected in 2007. We completed follow-up surveys at this 

survey area because we had 29 yellow-billed cuckoo detections in 2006 (RM 274.5 = 1 

cuckoo; Cuckoo Beach = 10 cuckoos; Iceberg Ridge = 3 cuckoos; and Chuckwalla Cove 

= 15 cuckoos; Johnson et al. 2007). We also confirmed breeding at Chuckwalla Cove in 

2006. 

Table 2.6. Dates (2007) for yellow-billed cuckoo surveys in Grand Canyon National Park 

and Lake Mead National Recreation Area, AZ. 

Site Name Survey Period 

1 

Survey Period 

2 

Survey Period 

3 

Survey Period 

4 

 Survey 

Period 5 

RM 274.5 6/17 7/13 8/9 8/23 no survey 

Cuckoo Beach 6/16 7/12 8/10 8/22 no survey 

Iceberg Ridge 6/15 7/11 8/8 8/22 no survey 

Chuckwalla Cove 6/15 7/12 8/8 8/22 no survey 

Big Horn Draw 6/15 7/12 8/8 no survey no survey 

Table 2.7. Dates (2007) for yellow-billed cuckoo follow-up surveys at Grand Canyon 

National Park and Lake Mead National Recreation Area, AZ. 

Site Name Survey Period 

1 

Survey Period 

2 

Survey Period 

3 

Survey Period 

4 

 Survey Period 

5 

RM 274.5 no survey no survey no survey no survey no survey 

Cuckoo Beach 6/28, 6/29 no survey no survey no survey no survey 

Iceberg Ridge 6/28, 6/29 no survey no survey no survey no survey 

Chuckwalla Cove 6/28, 6/29 no survey no survey no survey no survey 

Big Horn Draw no survey no survey no survey no survey no survey 

Havasu National Wildlife Refuge, AZ (Colorado River) 

We conducted 16 yellow-billed cuckoo surveys in 2007 (Table 2.8) and four 

follow-up surveys (Table 2.9) at four sites within the Havasu National Wildlife Refuge, 

AZ. 

33
Table 2.8. Dates (2007) for yellow-billed cuckoo surveys at the Havasu National Wildlife 

Refuge, AZ. 

Site Name Survey Period 

1 

Survey Period 

2 

Survey Period 

3 

Survey Period 

4 

 Survey 

Period 5 

Pintail Slough 6/19 7/10 7/28 no survey no survey 

North Dike 6/11 7/3 7/25 8/15 no survey 

Topock Marsh Rest. 6/12 7/9 7/26 8/14 no survey 

Topock Tamarisk 6/13, 6/28 7/12 7/31 9/5 no survey 

Table 2.9. Dates (2007) for follow-up surveys at Havasu National Wildlife Refuge, AZ. 

Site Name Survey Period 

1 

Survey Period 

2 

Survey Period 

3 

Survey Period 

4 

 Survey Period 

5 

Pintail Slough no survey 7/10 no survey no survey no survey 

North Dike no survey 7/3 no survey no survey no survey 

Topock Marsh Rest. 

no survey no survey 7/26, 7/27 no survey no survey 

Topock Tamarisk no survey no survey no survey no survey no survey 

Yellow-billed cuckoos were detected at Pintail Slough, North Dike, and Topock 

Marsh Restoration (Table 2.10). Pintail Slough and North Dike were classified as 

occupied sites with cuckoos being detected during two survey periods. The Topock 

Marsh Restoration site was classified unoccupied as we did not have detections during 

multiple surveys. The two cuckoos detected at North Dike during survey period two were 

seen concurrently and heard counter calling. Breeding was unconfirmed for all cuckoos 

detected at Havasu NWR. See Appendix 2 for a detailed description of each yellow-billed 

cuckoo detection. 

In 2006, a single yellow-billed cuckoo was detected at the Pintail Slough site 

during the first survey period, the site was classified as unconfirmed and no cuckoos were 

detected during later surveys (Johnson et al. 2007). 

Table 2.10. Yellow-billed cuckoo detections in 2007 at Havasu National Wildlife Refuge, 

AZ. Detections during cuckoo follow-up surveys are displayed in parenthesis. 

Site Name Survey 

Period 1 

Survey 

Period 2 

Survey 

Period 3 

Survey 

Period 4 

Survey 

Period 5 

 Total 

Detections 

Pintail Slough 0 (0) 1 0 0 no survey 1 

North Dike 1 0 (2) 1 0 no survey 2 (2) 

Topock Marsh Rest. 1 0 0 (7) 0 no survey 1 (7) 

Topock Tamarisk 0 0 0 0 no survey 0 

Total 2 (0) 0 (2) 0 (7) 0 no survey 4 (9) 

34
Bill Williams River National Wildlife Refuge, AZ (Bill Williams River) 

In 2007, we completed 62 formal yellow-billed cuckoo surveys and 83 follow-up 

surveys at 13 sites in the Bill Williams River NWR (Table 2.11, Table 2.12). 

Table 2.11. Dates (2007) for yellow-billed cuckoo surveys at the Bill Williams River 

National Wildlife Refuge, AZ. 

Site Name Survey 

Period 1 

Survey 

Period 2 

Survey 

Period 3 

Survey 

Period 4 

 Survey 

Period 5 

Teepee Trail 6/26 7/12 7/28 8/14 no survey 

Cottonwood Patch 6/26 7/12 7/28 8/14 no survey 

Cave Wash 6/26 7/12 7/25 8/14 9/5 

Honeycomb Bend 6/19 7/9 8/7 8/23 9/5 

Mineral Wash 6/18 7/2 7/30 8/13 9/6 

Big Bend 6/12 7/2 7/25 8/13 9/6 

Gibraltar Rock 6/13 7/3 7/26 8/15 9/6 

Sandy Wash 6/17 7/11 7/26 8/15 9/7 

Fox Wash 6/11 7/3 8/11 8/21 no survey 

Mosquito Flats 6/14 7/11 8/8 8/21 9/7 

Saguaro Slot 6/13 7/11 8/1 8/21 9/7 

North Burn 6/27 7/17 8/8 8/26 9/9 

Bill Williams Marsh 6/14 7/15 8/1 8/24 9/8 

Table 2.12. Dates (2007) of follow-up surveys Bill Williams River National Wildlife Refuge, 

AZ. 

Site Name Survey Period 

1 

Survey Period 

2 

Survey Period 

3 

Survey Period 

4 

 Survey Period 

5 

Teepee Trail no survey no survey no survey no survey no survey 

Cottonwood Patch 6/28 7/1, 7/14, 7/16, 

7/18 7/25, 7/28, 8/7 8/23 no survey 

Cave Wash 6/26 7/1, 7/12, 7/14, 

7/16, 7/18 7/25, 8/7 8/23 no survey 

Honeycomb Bend 6/20, 6/29 

7/3, 7/9, 7/10, 

7/12, 7/14, 

7/18 

8/7, 8/10 8/14, 8/23, 

8/27 no survey 

Mineral Wash 6/19, 6/29 7/10, 7/14 7/24, 7/30 8/13 no survey 

Big Bend 6/15, 6/20 7/14, 7/17 7/29, 8/7, 8/9 8/25 9/6 

Gibraltar Rock 6/15, 6/25, 

6/30 7/13, 7/16 7/29, 8/9 8/26 no survey 

Sandy Wash 6/13, 6/25 7/11, 7/15, 

7/17 7/26, 7/29, 8/8 

8/24, 8/26, 

8/27, 8/28, 

8/29 

no survey 

35
Table 2.12. Dates (2007) of follow-up surveys Bill Williams River National Wildlife 

Refuge, AZ.—Continued 

Site Name Survey Period 

1 

Survey Period 

2 

Survey Period 

3 

Survey Period 

4 

 Survey Period 

5 

Fox Wash no survey no survey 8/11 no survey no survey 

Mosquito Flats 6/17 no survey 8/8, 8/11 no survey no survey 

Saguaro Slot 6/27 7/15 no survey 8/21, 8/27, 

8/29 no survey 

North Burn no survey no survey no survey no survey no survey 

Bill Williams Marsh no survey no survey 8/24, 8/29 no survey no survey 

In 2007, formal yellow-billed cuckoo surveys resulted in 139 cuckoo detections; 

244 additional cuckoo detections occurred during follow-up surveys (Table 2.13). The 

Big Bend and Mineral Wash sites had the greatest number of detections, with at least one 

cuckoo detection at all sites within the refuge. All sites at Bill Williams River NWR 

except for Teepee Trail were classified as occupied. 

The Bill Williams River NWR was the only geographical area with confirmed 

breeding in 2007. Breeding activities were observed at seven sites (Cottonwood Patch, 

Cave Wash, Honeycomb Bend, Big Bend, Gibraltar Rock, Sandy Wash, and Bill 

Williams Marsh) and breeding was confirmed in each of these sites except Teepee Trail 

and in Bill Williams Marsh, where only a food carry was observed (Appendix 2). 

Tale 2.13. Yellow-billed cuckoo detections in 2007 at the Bill Williams River NWR. 

Detections during cuckoo follow-up surveys are displayed in parenthesis. 

Site Name Survey 

Period 1 

Survey 

Period 2 

Survey 

Period 3 

Survey 

Period 4 

Survey 

Period 5 

Total 

Detections 

Teepee Trail 0 0 1 0 no survey 1 

Cottonwood Patch 3 (4) 3 (8) 2 (1) 0 (0) no survey 8 (13) 

Cave Wash 2 (3) 3 (33) 3 (8) 3 (0) 0 11 (44) 

Honeycomb Bend 5 (9) 3 (6) 2 (5) 1 (4) 0 11 (24) 

Mineral Wash 13 (11) 7 (0) 5 (11) 2 (1) 0 27 (23) 

Big Bend 4 (7) 7 (14) 2 (5) 6 (16) 1(1) 20 (43) 

Gibraltar Rock 4 (11) 4 (19) 0 (2) 1 (0) 0 9 (32) 

Sandy Wash 0 (1) 3 (11) 6 (18) 3 (6) 2 14 (36) 

Fox Wash 0 1 1 (1) 0 no survey 2 (1) 

Mosquito Flats 0 (0) 3 6 (12) 4 2 15 (12) 

Saguaro Slot 0 (1) 2 (3) 4 2 (8) 0 8 (12) 

North Burn 0 1 2 2 0 5 

Bill Williams Marsh 1 0 4 3 (3) 0 8 (3) 

Total 32 (47) 37 (94) 38 (63) 27 (38) 5 (1) 139 (243) 

36
In 2006, there were 117 cuckoo detections within Bill Williams River NWR. The 

number of 2006 cuckoo detections at each site is as follows; Cave Wash = 21 cuckoo 

detections Mineral Wash = 15 cuckoos, Big Bend = 19 cuckoos, Gibraltar Rock = 8 

cuckoos, Sandy Wash = 14 cuckoos, Fox Wash = 1 cuckoo, Mosquito Flats = 17 cuckoo 

detections, Saguaro Slot = 10 cuckoos, and Bill Williams River Marsh = 12 cuckoo 

detections (Johnson et al. 2007). During the 2006 field season, we only had confirmed 

breeding at the Big Bend and Saguaro Slot sites, compared to confirmed breeding at 

seven sites within the refuge in 2007. 

Ahakhav Tribal Preserve—Colorado River Indian Tribes’ Land 

We conducted four survey visits at four sites within the Ahakhav Tribal Preserve 

(Table 2.14): no follow-up surveys were performed because of logistical constraints. 

Table 2.14. Dates (2007) for yellow-billed cuckoo surveys at the Ahakhav Tribal 

Preserve, AZ. 

Site Name Survey Period 

1 

Survey Period 

2 

Survey Period 

3 

Survey Period 

4 

 Survey 

Period 5 

Ahakhav Tribal Pres. 6/16 7/18 7/31 8/28 no survey 

During the 2007 breeding season we had two yellow-billed cuckoo detections 

(Table 2.15). Cuckoos were detected only during the first survey period, so Ahakhav 

Tribal Preserve was classified as unoccupied. We had two cuckoo detections during the 

same survey, but these detections were separate (not counter-calling) and did not indicate 

that these were paired birds. Breeding was not confirmed at Ahakhav Tribal Preserve. 

This was the first year complete yellow-billed cuckoo surveys (i.e., four surveys) were 

completed 

Table 2.15. Yellow-billed cuckoo detections in 2007 at Ahakhav Tribal Preserve, AZ. 

Site Name Survey 

Period 1 

Survey 

Period 2 

Survey 

Period 3 

Survey 

Period 4 

Survey 

Period 5 

Total 

Detections 

Ahakhav Tribal 

Pres. 2 0 0 0 no survey 2 

Cibola National Wildlife Refuge, AZ (Colorado River) 

We conducted 16 survey visits at four sites within Cibola NWR (Table 2.16); no 

follow-up surveys were completed because of logistical constraints. 

Table 2.16. Dates (2007) of yellow-billed cuckoo surveys at the Cibola National Wildlife 

Refuge, AZ. 

Site Name Survey Period 

1 

Survey Period 

2 

Survey Period 

3 

Survey Period 

4 

 Survey 

Period 5 

Cibola North Rest. 6/16 7/2 7/27 8/24 no survey 

Cibola Nature Trail 6/16 7/2 7/27 8/24 no survey 

Cibola South Rest. 6/16 7/2 7/27 8/24 no survey 

Cibola Eucalyptus 

Rest. 6/16 7/2 7/27 8/24 no survey 

37
During the 2007 breeding season, we had seven yellow-billed cuckoo detections 

(Table 2.17). Cuckoos were detected at all four sites, but only Cibola South Restoration 

was classified as occupied. We had two cuckoo detections during the same survey at the 

Cibola Nature Trail and at the Eucalyptus Restoration sites, but these detections were 

separate (not counter-calling) and did not indicate that these were paired birds. Breeding 

was not confirmed at any of the sites at Cibola NWR. 

Table 2.17. Yellow-billed cuckoo detections in 2007 at Cibola National Wildlife Refuge, 

AZ. 

Site Name Survey 

Period 1 

Survey 

Period 2 

Survey 

Period 3 

Survey 

Period 4 

Survey 

Period 5 

Total 

Detections 

Cibola North Rest. 0 0 1 0 no survey 1 

Cibola Nature Trail 2 0 0 0 no survey 2 

Cibola South Rest. 1 1 0 0 no survey 2 

Cibola Eucalyptus 

Rest. 0 2 0 0 no survey 2 

Total 3 3 1 0 no survey 7 

In 2005, two cuckoos were detected at the Cibola South Restoration site, and one 

was detected at the Cibola Cross River site (Johnson et al. 2006b). In 2006, we had 

yellow-billed cuckoo detections at two sites, Cibola Nature Trail Restoration and the 

Cibola South Restoration site (Johnson et al. 2007). The Cibola Nature Trail Restoration 

site was the only site classified as occupied, yet no breeding behavior was observed, and 

only one cuckoo was confirmed per detection. 

Picacho State Recreation Area, CA (Colorado River) 

We conducted four yellow-billed cuckoo surveys at Picacho State Recreation 

Area in 2007 with no yellow-billed cuckoo detections—thus, no follow-up surveys were 

performed (Table 2.18). 

Table 2.18. Dates (2007) for yellow-billed cuckoo surveys at the Picacho State 

Recreation Area, CA. 

Site Name Survey Period 

1 

Survey Period 

2 

Survey Period 

3 

Survey Period 

4 

 Survey 

Period 5 

Picacho SRA 6/27 7/18 8/1 8/28 no survey 

In 2006, a single yellow-billed cuckoo was detected during survey period three at 

Picacho State Recreation Area (Johnson et al. 2007). This cuckoo was only detected 

once, and responded eagerly to the broadcast. One cuckoo was also heard vocalizing in 

early July (second survey period) by a SWCA consulting firm Willow Flycatcher Project 

employee near where our individual cuckoo was detected. No breeding behavior was 

observed during either detection. 

38
Imperial National Wildlife Refuge, AZ (Colorado River) 

In 2007, we conducted four yellow-billed cuckoo surveys at Imperial NWR, but 

we had no follow-up surveys due to logistical constraints (Table 2.19). 

Table 2.19. Dates (2007) of yellow-billed cuckoo surveys at Imperial National Wildlife 

Refuge, AZ. 

Site Name Survey Period 

1 

Survey Period 

2 

Survey Period 

3 

Survey Period 

4 

 Survey 

Period 5 

Imperial South Rest. 6/27 7/18 7/31 8/28 no survey 

This site was classified as occupied because cuckoos were detected during two 

different survey periods; two detections in the first survey period and one in the second. 

No detections were confirmed after 18 July (Table 2.20). All detections were of 

individual birds and breeding was not confirmed. 

Table 2.20. Yellow-billed cuckoo detections in 2007 at Imperial National Wildlife Refuge, 

AZ. 

Site Name Survey 

Period 1 

Survey 

Period 2 

Survey 

Period 3 

Survey 

Period 4 

Survey 

Period 5 

Total 

Detections 

Imperial South 

Rest. 2 1 0 0 no survey 3 

In 2005, a single cuckoo was detected during two visits at the Imperial South 

Restoration site (Johnson et al. 2006b). In 2006, three cuckoos were detected at the 

Imperial South Restoration site (Johnson et al. 2007). These detections were of cuckoos 

vocalizing simultaneously in two different areas of the refuge and ,during a later followup survey, we observed a cuckoo carrying food, but breeding was not confirmed. 

Mittry Lake State Wildlife Management Area/Pratt Restoration Area, AZ (Colorado 

River) 

In 2007, we conducted four surveys at the Mittry Lake SWM/Pratt Restoration 

site. As no cuckoos were detected at this site, no follow-up visits were performed (Table 

2.21). During 2006, we had no cuckoo detections at this site, but in 2005 we detected one 

cuckoo during the second survey period (Johnson et al. 2006b, Johnson et al. 2007). 

Table 2.21. Dates (2007) of yellow-billed cuckoo surveys at Mittry Lake State WMA/Pratt 

Restoration Area. AZ. 

Site Name Survey Period 

1 

Survey Period 

2 

Survey Period 

3 

Survey Period 

4 

 Survey 

Period 5 

Pratt Restoration 6/11 7/3 7/26 8/15 no survey 

Gila–Colorado River Confluence, AZ (Gila and Colorado Rivers) 

In 2007, we conducted eight surveys at the Gila/Colorado Confluence sites, but 

due to logistical constraints no follow-up surveys performed (Table 2.22). 

39
Table 2.22. Dates (2007) of yellow-billed cuckoo surveys at the area of the Gila River–

Colorado River confluence, AZ. 

Site Name Survey Period 

1 

Survey Period 

2 

Survey Period 

3 

Survey Period 

4 

 Survey 

Period 5 

Colorado Confluence 6/26 7/12 8/11 8/27 no survey 

Gila Confluence 6/26 7/11 8/11 8/27 no survey 

We had two separate yellow-billed cuckoo detections at the Colorado Confluence 

site on river right during the first survey period (Table 2.23). No detections occurred here 

after 26 June. No cuckoos were detected at the Gila Confluence site. In 2007, the 

Colorado Confluence was classified as unoccupied and both birds (observed during same 

survey period) we observed along the Colorado River were unpaired. 

Table 2.23. Yellow-billed cuckoo detections in 2007at the Gila River-Colorado River 

confluence, AZ. 

Site Name Survey 

Period 1 

Survey 

Period 2 

Survey 

Period 3 

Survey 

Period 4 

Survey 

Period 5 

Total 

Detections 

Colorado 

Confluence 2 0 0 0 no survey 2 

Gila Confluence 0 0 0 0 no survey 0 

In 2006, we had two cuckoo detections at the Colorado Confluence site over two 

survey periods (Johnson et al. 2007). During the first visit, two counter-calling birds were 

confirmed in the same patch, but breeding was not confirmed. In 2005, cuckoos were also 

detected at this same site, but breeding also was not confirmed (Johnson et al. 2006b). 

Yuma West Wetlands, AZ (Colorado River) 

In 2007, we completed four surveys at the Yuma West Wetlands with no yellowbilled cuckoo detections (Table 2.24). In 2006, no cuckoos were detected at this site 

either (Johnson et al 2007). This restoration site is four years old and might not yet have 

the correct vegetation structure for cuckoo breeding needs. 

Table 2.24. Dates (2007) of yellow-billed cuckoo surveys at the area of the Yuma West 

Wetlands, AZ. 

Site Name Survey Period 

1 

Survey Period 

2 

Survey Period 

3 

Survey Period 

4 

 Survey 

Period 5 

Yuma West 

Wetlands 6/25 7/10 7/30 8/13 no survey 

Limitrophe Division, AZ (Colorado River) 

We completed eight yellow-billed cuckoo surveys at the Limitrophe Division sites 

in 2007 (Table 2.25). No follow-up surveys were completed due to logistical constraints. 

40
Table 2.25. Dates (2007) of yellow-billed cuckoo surveys at the Limitrophe Division, AZ. 

Site Name Survey Period 

1 

Survey Period 

2 

Survey Period 

3 

Survey Period 

4 

 Survey 

Period 5 

Limitrophe Div. 

North 6/14 7/11 7/29 8/26 no survey 

Limitrophe Div. 

South 6/13 7/13 7/28 8/25 no survey 

We had no cuckoo detections at the Limitrophe North site, but we had two cuckoo 

detections at the Limitrophe South site during the first survey period (Table 2.26). 

Breeding was not confirmed and this site was classified as unoccupied. 

Table 2.26. Yellow-billed cuckoo detections in 2007 at the Limitrophe Division, AZ. 

Site Name Survey 

Period 1 

Survey 

Period 2 

Survey 

Period 3 

Survey 

Period 4 

Survey 

Period 5 

Total 

Detections 

Limitrophe Div. 

North 0 0 0 0 no survey 0 

Limitrophe Div. 

South 2 0 0 0 no survey 2 

In 2005, we had six cuckoo detections at Limitrophe Division North and one 

detection at Limitrophe Division South (Johnson et al. 2006b). In 2006, six cuckoos were 

detected in the area, all at Limitrophe Division North (Johnson et al. 2007). The cuckoos 

detected near the Morelos Dam were detected during three surveys periods. 

Quigley Pond Wildlife Management Area, AZ (Gila River) 

In 2007, four surveys were conducted at Quigley Pond WMA with two follow-up 

surveys (Table 2.27). 

Table 2.27. Dates (2007) of yellow-billed cuckoo surveys at Quigley Pond WMA, AZ. 

Dates of cuckoo follow-up surveys are displayed in parenthesis. 

Site Name Survey Period 

1 

Survey Period 

2 

Survey Period 

3 

Survey Period 

4 

 Survey 

Period 5 

Quigley Pond 6/12 (6/13) 7/9 (7/10) 7/28 8/14 no survey 

We had four cuckoo detections during the first survey period and one detected in 

the second survey period (Table 2.28). We classified this site as occupied. All cuckoo 

detections at this site were of unpaired birds. 

Table 2.28. Yellow-billed cuckoo survey detections in 2007 at Quigley Pond WMA, AZ. 

Detections during cuckoo follow-up surveys are displayed in parenthesis. 

Site Name Survey 

Period 1 

Survey 

Period 2 

Survey 

Period 3 

Survey 

Period 4 

Survey 

Period 5 

Total 

Detections 

Quigley Pond 4 (0) 1(0) 0 0 no survey 5 

41
In 2005, we had eight yellow-billed cuckoo detections at this site. A pair was 

detected during one survey, with one cuckoo carrying nest material, but breeding was not 

confirmed (Johnson et al. 2006b). 

In 2006, we detected a single cuckoo during the first survey period (Johnson et al. 

2007). This cuckoo was seen foraging in a cotton field on the edge of the restoration area. 

Subsequent surveys yielded no further detections. 

Yellow-billed Cuckoo Breeding Activity 

Over the course of the 2007 field season, 27 breeding events were documented in 

7 of our 40 survey sites (17.5 percent). Detailed descriptions of these activities can be 

found in Appendix 2. All breeding activity in 2007 occurred in the Bill Williams River 

NWR (Figure 2.4). The majority (59 percent) of these events took place during the 

second survey period (1 July–21 July). We detected the lowest breeding activity in the 

first or fifth survey periods. The most common evidence of breeding activity was 

observations of food carrying, followed closely by detections of fledglings. 

Five

Four

Three

Two

One

Survey 

Period 

Type of Activity

Nest 

Building

Nests Fledglings Food Carries Copulations

12

10

8

6

4

2

0

Number 

of 

Activities

Figure 2.4. Number and survey period of each breeding activity at Bill Williams River 

NWR within the LCR MSCP boundary area, 2007. 

The number of food carries varied considerably throughout the breeding season, 

and was most evident (73 percent of observations) during the second survey period 

(Figure 2.4). Fledglings were found consistently in survey periods 2, 3, and 4. Three of 

these fledges were found within 15 m of a documented nest, the others were found 

several hundred meters from the nearest known nest. Two copulations were observed in 

2007, both in the second survey period. One other breeding activity was recorded during 

42
the first survey period in Honeycomb Bend when two adult cuckoos were observed 

placing leaves on a tree branch. 

The number of breeding activities varied between sites as well and Honeycomb 

Bend and Big Bend had by far the most observed activity (Figure 2.5). Food carries were 

documented at all our breeding sites and fledglings were found at five of the seven (72 

percent). Nests and copulations were less widespread; they were observed at respectively 

two of the seven (43 percent) and two of the seven (29 percent) breeding sites. 

0

1

2

3

4

5

6

7

8

9

Cottonwood

Patch

Cave Wash

Honeycomb

Bend

Big Bend

Gibraltar Rock

Sandy Wash

Bill Williams

Marsh

Survey Sites

Number of Activities

Other

Copulation

Food Carries

Fledglings

Nests

Figure 2.5. Number of type of breeding activities by survey site at Bill Williams River 

NWR within the LCR MSCP boundary area, 2007. 

Nest Monitoring 

We located two yellow-billed cuckoo nests in 2007. The success of each nest was 

unknown as fledging occurred between successive visits to the nest. Below, we will 

discuss in detail, the progression of each nest. 

Cottonwood Patch 

The Cottonwood Patch cuckoo nest was located along with an adult at the nest on 

14 July. The nest was constructed in a Fremont cottonwood (10 m tall; 32.8 ft) that was 

part of a stringer comprised of the same species. This stringer had little understory, but 

what was present consisted of Fremont cottonwood and tamarisk, with the canopy above 

the nest closed (Table 2.27). The nest was located within 20 m of a small puddle that was 

the only surface water in the area. On 16 July, a nestling was observed when an adult 

43
attempted to deliver a large, green prey item. We estimated the nestling’s age to be one 

day based on its black and somewhat slick appearance. On 18 July, we again saw an adult 

cuckoo and one nestling. During nest checks on 25 July, 7 August, and 23 August, no 

activity was observed at the nest. The outcome of the nest (i.e., whether the nestling 

successfully fledged) was unknown. 

Big Bend 

The Big Bend cuckoo nest was located on 13 August in a tamarisk (6.4 m tall; 

20.9 ft) close to the river (15 m; 49.2 ft). The overstory consisted of tamarisk and was 

heavily covered, while the understory was 50 percent covered (Table 2.29). A large 

Goodding’s willow was located adjacent to the nest tree. During our first visit, an adult 

cuckoo was on the nest and movement was seen inside the nest. On 14 August, a nestling 

was observed sitting on the rim of the nest. Its feathers were sheathed and streaks of skin 

were still visible around the bill. At this time, we estimated the nestling’s age to be 7-8 

days. On 22 August, the nestling was not present in the nest and no fledglings were 

observed. However, an adult cuckoo was seen carrying prey within 10 m (32.8 ft) of this 

nest. 

Vegetation measurements were taken at each nest after it became inactive. Percent 

cover measurements are shown in Table 2.29, and nest and substrate measurements for 

each nest are shown in Table 2.30. 

Table 2.29. Percent cover measurements of yellow-billed cuckoo nests at Bill Williams 

River NWR within the LCR MSCP, 2007. 

Nest ID % Overhead 

cover 

% Undernest cover % Side 

cover N 

% Side 

cover S 

% Side 

cover E 

% Side 

cover W 

CPNest1 45% 15% 5% 20% 18% 10% 

BBNest1 85% 50% 45% 40% 70% 80% 

Table 2.30. Yellow-billed cuckoo nest and substrate measurements at Bill Williams River 

NWR within the LCR MSCP, 2007. 

Nest ID UTM 

coordinates Substrate Substrate DBH (cm) 

Substrate 

height (m) 

Nest height 

(m) 

Distance to 

water (m) 

CPNest1 227747 E 

3794239 N 

Freemont 

cottonwood 15 10 1 16 

BBNest1 774359 E 

3795439 N Tamarisk 11 6.4 3.7 3 

Discussion 

Yellow-billed cuckoos have historically been considered a common breeding 

species within extensive riparian forests throughout the lower Colorado River Basin 

(Swarth 1905, Visher 1910, Phillips et al. 1964). In 1976, the estimated number of 

breeding cuckoo pairs along the lower Colorado River and its five tributaries was 846 

(Groschupf 1987). Later studies found a 93 percent decline along the lower Colorado 

River between 1976 and 1986 and an estimated 71 to 75 percent decline on the Bill 

Williams River delta during the same period (Rosenburg et al. 1991). 

44
Our 2007 yellow-billed cuckoo surveys included most areas that were historically 

surveyed throughout the lower Colorado River Basin. We had163 cuckoo detections, the 

majority (85 percent) of which were in the Bill Williams River NWR. The exact number 

of cuckoos present in our survey sites is not known as there was no way to tell whether 

detections on separate surveys represented the same or different individuals. Thus, the 

detections summarized above should not be interpreted as a count of the number of 

cuckoos present or as the number of birds breeding at a site. The Bill Williams River 

NWR continues to have the highest number of yellow-billed cuckoos. This area 

represents the largest swath and highest habitat quality of appropriate yellow-billed 

cuckoo habitat on the lower Colorado River. Because of differences in survey methods, 

specific areas surveyed, and probable differences in the criteria used to estimate the 

number of individuals, it is difficult to make direct comparisons between our results and 

estimates of cuckoo number from previous studies. 

However, we can compare the occupancy of yellow-billed cuckoos between our 

2006 and 2007 surveys, the two years we have conducted surveys within the lower 

Colorado River Multi-Species Conservation Program boundary. At the Grand 

Canyon/Lake Mead area and sites, we had three occupied sites in 2006 with confirmed 

breeding at the Chuckwalla Cove (Johnson et al. 2007). In 2007, we had zero yellowbilled cuckoo detections and therefore no occupied sites in this area. At Havasu National 

Wildlife Refuge in 2006, we had no occupied sites and only one cuckoo detection. In 

2007, we had one occupied site at the North Dike survey site within Havasu NWR and 

one cuckoo detection at Pintail Slough. Within the Bill Williams River NWR area, we 

had eight occupied sites in 2006 and confirmed breeding at two sites. In 2007, ten sites 

were designated as occupied within Bill Williams River NWR and we confirmed 

breeding at seven of those sites. At Cibola NWR, we had one designated occupied site in 

2006 Cibola Nature Trail Restoration and 2007 Cibola South Restoration site, we did not 

confirm breeding during either year. At Imperial NWR, Imperial South restoration was 

the only site designated occupied for both 2006 and 2007, breeding was not confirmed 

for either year, however in 2006 a pair was observed performing courtship. Among the 

Yuma, AZ sites, two sites were occupied in 2006 (Colorado/Gila Confluence and 

Limitrophe North), and in 2007, one site were designated occupied (Quigley Pond 

WMA). In 2005, Quigley Pond was designated occupied, where a pair was observed 

performing courtship. Breeding was not confirmed within any of the Yuma, AZ sites in 

either 2006 or 2007. With the exception of Bill Williams River NWR, there was 

substantial variation between sites and years in occupancy and breeding confirmation. 

There are a number of factors that might account for this variation. There were 

several patterns in our detections that reinforce the idea that cuckoos within the entire 

LCR MSCP study area can readily move between survey areas and sites. For example, 

the habitat at several sites where cuckoos were detected was far outside the range of 

normal within this region and was probably not suitable for nesting. We also had several 

sites with just single detection of a cuckoo. We believe the individuals found in such sites 

were likely non-breeding “wanderers,” migrants, or birds breeding elsewhere, but 

foraging within the patch it was detected in. 

Yearly variation is very obvious within the Grand Canyon NP/Lake Mead NRA 

area. In 2006 there were 29 yellow-billed cuckoo detections at the Grand Canyon NP/ 

Lake Mead NRA study area and three occupied sites (Cuckoo Beach, Iceberg Ridge, and 

Chuckwalla Cove); however, we did not detect any cuckoos at Grand Canyon NP/ Lake 

Mead NRA in 2007. During the cuckoo breeding season, the elevation of Lake Mead was 

45
approximately 4.5 m (15 ft) lower in 2007 compared to 2006 

(http://www.usbr.gov/lc/region/g4000/hourly/mead-elv.html) because of long-term 

drought conditions in the Colorado River watershed. The greatest impact to the riparian 

habitat that might be due to these declining lake levels is the dramatic increase in the 

proportion of snags we detected in vegetation sampling plots between the two years. In 

2006, snags made up 14 percent of the entire woody vegetation, but accounted for 46 

percent in 2007. However this apparent drought induced stress on the vegetation at Grand 

Canyon NP/Lake Mead NRA was not evident in soil moisture. In 2006, soil moisture 

ranged between 8–11 percent at unoccupied and occupied sites, respectively, but, in 

2007, soil moisture at Grand Canyon NP/Lake Mead NRA averaged 9 percent, identical 

to values at the Bill Williams River NWR that was densely occupied by yellow-billed 

cuckoos. 

Historically, sites within Grand Canyon NP/Lake Mead NRA have likely been 

exposed to periodic drought and disturbance; therefore, these sites may not be the most 

suitable locations for habitat restoration efforts. For this reason, continued long-term 

studies of yellow-billed cuckoo occupancy patterns should be conducted throughout the 

lower Colorado River. Information about occupancy patterns would be useful for 

identifying sites suitable for habitat restoration and capable of promoting eventual cuckoo 

occupancy. 

It is clear that there are challenges verifying yellow-billed cuckoo breeding at a 

site. Cuckoos are very secretive, difficult to detect, and move over large areas. Thus, 

verifying that cuckoos are breeding in a particular patch requires finding young, a nest, or 

copulating adult—all of which can sometimes present difficulties. This reality makes it 

safe to assume that we did not observe all breeding activities that occurred in 2006 or 

2007. For example, some repetitive activities like food carries were certainly missed. We 

are also aware that more nests were present in our study sites than just those we were able 

to locate. All fledglings were found in areas with high concentrations of cuckoo activity 

where nests were likely located, but only three fledglings were found in close 

proximately to a nest. Given this knowledge, the number of breeding activities recorded 

at a site should be interpreted as a minimum of breeding activity that occurred. However, 

all of our documented breeding activities took place at the Bill Williams River NWR, 

indicating that this area has more and/or better breeding habitat than the other survey 

locations. 

Other Riparian Bird Detections 

We detected and documented 160 additional species during our surveys in 2007, 

including local breeders and many Neotropical migrants (Table 2.31; Appendix 6). These 

species were observed before, during, or after our yellow-billed cuckoo surveys. Because 

the focus of our efforts was on detecting cuckoos, no effort was made to quantify 

abundance of these additional species, nor to track down and verify any species that were 

not readily identifiable or obvious to the surveyors. 

Of the 160 species detected, nine species were focal species under the Lower 

Colorado River Multi-Species Conservation Program (Table 2.32). The willow flycatcher 

(Empidonax traillii), Bell’s vireo (Vireo bellii), and yellow warbler (Dendroica petechia) 

were the most widespread species. 

46
Table 2.31. Number of bird species detected at each site and totaled by yellow-billed 

cuckoo survey area within the Lower Colorado River Multi-Species Conservation Program 

Area, 2007. 

YBCU-LCR-MCSB Survey Area/Site Name Number of Bird Species 

Pahranagat NWR 35 

Overton WMA 29 

Grand Canyon NP/Lake Mead NRA 39 

Havasu NWR 68 

Bill Williams River NWR 127 

Ahakhav Tribal Preserve 55 

Cibola NWR 46 

Picacho SRA 23 

Imperial NWR 17 

Mittry Lake WMA/Pratt Restoration 31 

Gila/Colorado River Confluence 42 

Yuma West Wetlands 38 

Limitrophe Division 62 

Quigley Pond WMA 31 

47
Table 2.32. Lower Colorado River Multi-Species Conservation Program focal bird 

species detected by LCR MSCP geographic area, 2007. 

LCR MSCP Geographic Area LCR MSCP Focal Species 

Pahranagat NWR Willow Flycatcher 

Yellow Warbler 

Overton WMA Willow Flycatcher 

Yellow Warbler 

Grand Canyon NP/Lake Mead NRA Willow Flycatcher 

Bell’s Vireo 

Summer Tanager 

Yellow Warbler 

Havasu NWR Gilded Flicker 

Bell’s Vireo 

Yellow Warbler 

Bill Williams River NWR Black Rail 

Least Bittern 

Gilded Flicker 

Willow Flycatcher 

Vermillion Flycatcher 

Ahakhav Tribal Preserve Bell’s Vireo 

Summer Tanager 

Yellow Warbler 

Willow Flycatcher 

Vermillion Flycatcher 

Yellow Warbler 

Cibola NWR Willow Flycatcher 

Bell’s Vireo 

Yellow Warbler 

Vermillion Flycatcher 

Picacho SRA Bell’s Vireo 

Imperial NWR Least Bittern 

Bell’s Vireo 

Summer Tanager 

Mittry Lake WMA Bell’s Vireo 

Gila/Colorado River Confluence Willow Flycatcher 

48
Table 2.32. Lower Colorado River Multi-Species Conservation Program focal bird 

species detected by LCR MSCP geographic area, 2007.—Continued 

LCR MSCP Geographic Area LCR MSCP Focal Species 

Yuma West Wetlands Bell’s Vireo 

Yellow Warbler 

Limitrophe Division Willow Flycatcher 

Vermillion Flycatcher 

Yellow Warbler 

Quigley Pond WMA Willow Flycatcher 

Vermillion Flycatcher 

Bell’s Vireo 

Yellow Warbler 

49
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50
Chapter 3: Survey Methodology 

The basic approach of this survey protocol—the use of broadcast vocalizations to 

elicit a response by resident yellow-billed cuckoos—was established in California in 

1965 (Hamilton and Hamilton 1965). Since then, the protocol has evolved as biologists 

have learned more about the cuckoo’s breeding biology and behavior (Gaines 1974; 

Gaines 1977; Gaines and Laymon 1984; Laymon and Halterman 1985, 1987a, 1987b, 

1989; Halterman 2005; Halterman et al. 2006). Refinements to the protocol have helped 

to maximize the likelihood of detecting cuckoos while minimizing survey time and costs. 

Although our current project was not intended to serve as a full evaluation and test of the 

cuckoo survey protocol, our results might be used to help further refine and develop 

specific experiments of the method that can be tested in the future. 

Tape broadcast survey techniques have proven advantageous in eliciting 

responses from many bird species, especially those that are secretive or nocturnal. It often 

increases the total number of birds seen or heard for a given species in comparison to a 

conventional census (Johnson et al. 1981), especially for species with low song activity 

(Robbins 1978). Broadcasting has also been helpful in estimating population size and 

investigating avian social behavior and territoriality. Broadcast surveys have been used 

primarily during the breeding season to study the presence and distribution of species 

(Glahn 1974, Griese et al. 1980, Sogge et al. 1997), but they also have been employed on 

wintering grounds (Koronkiewicz et al. 2006). However, the use of broadcast recordings 

can sometimes have unexpected consequences. Robbins (1978) found that the use of tape 

recordings during repeated visits over the breeding season can bias results, as birds might 

alter their habits or their territorial boundaries if they believe that there are competing 

conspecifics holding a territory nearby. Studies of the use of broadcast recordings to 

survey spotted owls (Strix occidentalis) suggest that, if surveyed too often, some 

individuals and/or species might become less responsive (Forsman et al. 1977). Also, the 

use of broadcast recordings can attract some individuals away from their territories, as in 

elegant trogons (Trogon elegans; Taylor 1978), resulting in inflated population density 

estimates. To date, we are not aware of any adverse impact of tape broadcast survey 

techniques to yellow-billed cuckoos or estimates of their population size. As with other 

monitoring techniques, an assumption of broadcast surveys techniques is a constant 

probability of detection over time and space (Pollock et al. 2002). Violation of this 

assumption can confound efforts to compare results among different areas or studies. 

The use of broadcast recordings in surveys of western yellow-billed cuckoos has 

increased the number of detections of this elusive and easily overlooked species 

(Hamilton and Hamilton 1965, Halterman et al. 2006). Cuckoos do not sing to defend 

territory and they vocalize relatively infrequently. Little is known about the functions of 

the cuckoo’s various calls, but the kowlp call might function as a spacing mechanism and 

as a means to communicate between mated individuals (Hughes 1999). Studies, mostly of 

eastern yellow-billed cuckoos (Coccyzus americanus americanus), have found that calls 

are most frequent during pair formation and nest building; calls continue through nesting, 

then become infrequent after the last young fledge (Hughes 1999). Unfortunately, little is 

known about whether frequency of vocalization is related to mating status (paired or 

51
unpaired) or to population density. Lack of this information complicates the interpretation 

of survey results. 

Assessing the use of broadcast recordings for surveys to determine the presence 

and distribution of yellow-billed cuckoos can be challenging, especially due to the 

difficulty in finding and following individuals. As with any field survey protocol, there is 

no way to be absolutely certain that an area with no detections is unoccupied. This might 

be a particular challenge with yellow-billed cuckoos, which we have long suspected have 

a fairly low response rate; the standard survey method of using broadcast recordings 

might fail to detect all birds present in an area. In fact, it has been observed that some 

individuals known to be present in the area sometimes do not respond to the recordings 

(Halterman 2004, Johnson et al. 2006b, Johnson et al. 2007). During a test of broadcast 

survey methods using adult cuckoos with radio transmitters, Halterman (2005) found that 

only 30 to 50 percent of radio-transmitted birds were detected when solicited through 

broadcast recordings. 

In our evaluation of the survey protocol in 2006, we found that the majority (72 

percent) of cuckoo detections were solicited through broadcast at all study sites. The 

number of solicited detections peaked during the first half of July and then declined as 

the breeding season progressed, while the number of unsolicited detections (cuckoos 

heard calling before broadcast was initiated) remained fairly constant. The majority (64 

percent) of cuckoo detections, solicited or unsolicited, were aural; 27 percent were both 

heard and seen and nine percent were visual detections only. We found that cuckoos in 

areas with the largest populations had the highest rate of vocalizations before the 

broadcast or after the first broadcast. In contrast, more than half the responses at sites 

with fewer cuckoos (with <10 detections per site) first occurred after three or more 

broadcast recordings. 

In 2007, we continued to examine the cuckoo survey protocol and specifically 

continued to collect baseline information that will be used to help refine the survey 

protocol, and to create experiments that can serve as the foundation for a full-scale 

evaluation and optimization of this survey technique. 

Methods 

To gain a better understanding of the efficacy of the yellow-billed cuckoo survey 

protocol, we continued to compare cuckoo responses to tape broadcasts among sites and 

within the breeding season. We summarized the number of broadcasts needed to solicit a 

response, how the cuckoos responded, and the cuckoo’s distance from survey points. We 

also summarized the number of cuckoo detections across survey periods to examine the 

minimum number of surveys needed to determine occupancy and breeding status of a 

site. 

Our survey method involved one minute of listening for spontaneously calling 

cuckoos, followed by five consecutive broadcasts of the cuckoo kowlp call spaced one 

minute apart. Broadcasts were ceased at a survey point once a cuckoo was detected. 

Cuckoo detections were categorized as either “unsolicited” if birds called before 

initiation of the broadcast or “solicited” if they occurred after a broadcast (i.e., in 

response to the broadcast). Cuckoo detections were also classified as “aural” if 

individuals were heard calling but were never seen, “visual” if birds were seen but not 

heard, or “both” if birds were heard and seen. See Chapter 2 for a complete description of 

the methods used to survey for yellow-billed cuckoos during this study. 

52
Results 

Almost 85 percent of solicited and 88 percent of unsolicited responses were at 

Bill Williams River NWR; the other solicited responses were Havasu NWR, Ahakhav 

Tribal Reserve, Cibola NWR, Imperial NWR, Gila/Colorado Confluence, Limitrophe 

Division and Quigley Pond WMA (Fig. 3.1). The other unsolicited responses occurred at 

Cibola NWR, Imperial NWR, and Gila/Colorado Confluence. 

0

10

20

30

40

50

60

70

80

90

100

110

120

Havasu NWR Bill Williams

River NWR

Ahakhav

Tribal

Preserve

Cibola NWR Imperial

NWR

Gila/Colorado

Confluence

Limitrophe

Division

Quigley Pond

Survey Area

Number of Cuckoo Detections

Solicited

Unsolicited

Figure 3.1. Number of unsolicited initial responses and post-broadcast responses by 

yellow-billed cuckoo in each geographical area. 

We found that 66 percent of all detections occurred before the third broadcast was 

played (Fig. 3.2). We also found that timing of initial responses differed slightly between 

areas with >10 detections (i.e., Bill Williams River NWR) and areas with <10 detections 

(i.e., Limitrophe Division; Fig. 3.3). Yellow-billed cuckoos responded more readily (in 

earlier surveys) to broadcasts in areas with lower overall detections (73 percent of 

detections) than in areas with higher overall detections (68 percent of detections; Fig. 

3.2). The actual density of cuckoos per area is unknown, but it appears that cuckoo’s 

respond more readily to playback broadcasts in areas with estimated lower densities than 

areas with higher densities. We also found that 50 percent of all initial responses were 

almost evenly split between the first and second broadcast at sites with >10 detections 

while 45 percent of responses occurred after a single broadcast at the areas with <10 

detections. 

53
0

5

10

15

20

25

30

Unsolicited One Two Three Four Five

Number of Broadcasts

Percentage of Initial Responses

Figure 3.2. Percentage of initial yellow-billed cuckoo responses to survey broadcasts, 

based on sequential order of broadcast (n = 163). All data collected within the LCR MSCP 

boundary area, 2007. 

0

5

10

15

20

25

30

35

40

45

50

Unsolicited One Two Three Four Five

Number of Broadcasts

Percentage of Initial Responses

Areas with >10 detections

Areas with <10 detections

Figure 3.3. Percentage of initial yellow-billed cuckoos responses to broadcasts at 

geographical areas with >10 detections (n = 139) and all areas with <10 detections (n = 24) 

based on sequential order of response. All data collected within the LCR MSCP boundary 

area, 2007. 

Solicited detections were highest in the month of June and declined throughout 

rest of the breeding season (Fig. 3.4). Contrastingly, unsolicited detections remained 

fairly constant through 11 August. After this time, no unsolicited survey detections 

occurred. The percentage of unsolicited initial responses was slightly higher in areas with 

>10 detections (17 percent) than in areas with <10 detections (13 percent). 

54
0

5

10

15

20

25

30

35

40

45

6/11 - 6/30 7/1 - 7/21 7/22 - 8/11 8/12 - 9/4 9/5 - 9/9

Date Interval

Number of Cuckoo Detections

Solicited

Unsolicited

Figure 3.4. Number of yellow-billed cuckoo detections (solicited vs. unsolicited) by time 

period, from 11 June to 9 September. All data collected within the LCR MSCP boundary 

area, 2007.

For the entire study area, the total number of cuckoo detections declined as the 

season progressed (Fig. 3.5). We saw the biggest drop in areas with <10 detections. 

Detections in these areas made up 16 percent of the total in the first survey period, 7 

percent in the second period and only 2 percent in the third. After this point, no detections 

were made in areas with apparent low populations (<10 detections). In contrast, 

detections at the areas with higher populations (>10 detections) remained fairly constant 

up until the third survey period, then decreasing later in the season. 

55
0

5

10

15

20

25

30

35

40

6/11 - 6/30 7/1 - 7/21 7/22 - 8/11 8/12 - 9/4 9/5 - 9/9

Date Interval

Number of Cuckoo Detections

Areas with >10 detections

Areas with <10 detections

Figure 3.5. Number of yellow-billed cuckoo detections by time period, from 11 June to 9 

September, in areas with >10 detections vs. areas with <10 detections. All data collected 

within the LCR MSCP boundary area, 2007.

Over the course of the breeding season, 66 percent of total survey detections were 

aural, 23 percent were both heard and seen, and 11 percent were visual only (Fig. 3.6). 

During the first survey period, the ratio of aural-only to visual-only and visual/aural 

detections was nearly even. However, during the second survey period, the cuckoos were 

seen less frequently and the proportion of visual detections declined. By the third survey 

period, aural-only detections were five times more prevalent than visual detections. 

0

10

20

30

40

50

60

70

80

90

6/11 - 6/30 7/1 - 7/21 7/22 - 8/11 8/12 - 9/4 9/5 - 9/9

Date Interval

Percentage of Cuckoo Detections

Aural 

Both

Visual

Figure 3.6. Percent of yellow-billed cuckoo aural, both aural and visual, and visual 

detections by time period, from 11 June to 9 September. All data collected within the LCR 

MSCP boundary area, 2007.

56
Almost 90 percent of initial cuckoo detections were within 100 m (328 ft) of the 

observer (Fig. 3.7) and only 1 percent were at distances greater than 200 m (656 ft). Twothirds of cuckoos were initially detected from less than 51 m (167 ft) away. 

0

5

10

15

20

25

30

35

0-25 26-50 51-100 101-200 >201

Distance (m)

Percentage of Cuckoo Detections

Figure 3.7. Percentage of yellow-billed cuckoos detected within categories of distance 

from the survey point. All data collected within the LCR MSCP boundary area, 2007. 

Discussion 

Results from our study indicate that the number of broadcasts required to elicit a 

response may be influenced by cuckoo abundance (nearest-neighbor distances), as has 

been found in other species (Penteriani et al. 2002). Birds were detected earlier when 

found in smaller populations than when in larger populations. Individuals in the former 

might be displaying a heightened reaction (responding after the first broadcast) to the 

presence of other cuckoos. 

In 2007, we also observed that over 13 percent of cuckoo detections across all 

sites were made after the fifth broadcast. Therefore, repeated broadcasts at each point, at 

least to the point of five, continues to increase the probability of a cuckoo being detected. 

It has been observed that birds might be less likely to vocalize in response to a 

broadcast after nesting has started (Sogge et al. 1997, Legare et al. 1999, Bogner and 

Baldassarre 2002). Laymon and Halterman (1985) found that yellow-billed cuckoos were 

fairly vocal during pair formation, nest building, and the nestling stage, and less vocal 

during incubation. However, Halterman (2005) found no noticeable decrease in 

vocalization frequency after nesting for two yellow-billed cuckoos that were tracked via 

telemetry throughout their nesting cycles. We found that the total number of detections 

peaked in late June, just before observed breeding activity peaked (See Chapter 2: 

Breeding Activity), then declined as the season progressed. However, across all sites 

there was declining trend in the mean timing of initial response, as one would expect if 

breeding stage does indeed affect responsiveness to the broadcast. Potentially, staggered 

breeding by individual cuckoos and the presence of non-breeders could produce this 

result. 

Yellow-billed cuckoos have been documented breeding in late August and even 

into September (Halterman 2002). Sites were confirmed as occupied by the end of the 

third survey period (see Chapter 2, Table 2.3). However, previous surveys at the Bill 

57
Williams River NWR detected several new pairs in mid-August (Halterman 2002, 

Johnson et al. 2007). Additionally, 22 percent of our observed breeding activities (n = 27) 

took place during the fourth survey period (August) and breeding activity was not 

observed at one of the seven breeding sites until the fourth survey period (See Chapter 2: 

Yellow-billed Cuckoo Breeding Surveys). This demonstrates the value of continuing 

surveys through August and even the first half of September to verify cuckoo occupancy. 

The survey protocol we utilized requires broadcasts to be conducted every 100 m 

(328 ft) on transects separated by 200 m (656 ft) of habitat. If a cuckoo is detected, the 

surveyor must move 300 m before conducting the next survey point. This protocol 

assumes that a yellow-billed cuckoo 100 m away will be able to hear the broadcast and 

respond, and that the response is heard by the observer. It also assumes that a cuckoo 

>300 m (984 ft) away will not respond to a broadcast. Halterman (2005) found that 

yellow-billed cuckoos called 14 percent of the time when a survey point was completed 

300 m (984 ft) away, but surveyors heard this response only 4 percent of the time. In 

2007, almost 90 percent of our detections were within 100 m (328 ft) of the survey point 

and no yellow-billed cuckoos were detected at a distance greater than 250 m (820 ft) 

from the survey point. This suggests the distances we currently utilize represent 

appropriate intervals for the spacing of survey points and transects. 

58
Chapter 4. Habitat Vegetation Characteristics 

To design an effective habitat restoration program under the Lower Colorado 

River Multi-Species Conservation Program, information is needed regarding yellowbilled cuckoo habitat requirements in this region. We currently know relatively little 

about the cuckoos’ specific breeding habitat requirements along the lower Colorado 

River. In the arid Southwest, yellow-billed cuckoos are primarily restricted to densely 

wooded rivers and streams and damp thickets with relatively high humidity (Corman and 

Wise-Gervais 2005, Johnson et al. 2007, Holmes et al. 2008). 

Western yellow-billed cuckoos generally breed in large blocks of riparian habitat, 

particularly woodlands with cottonwoods and willows (Ehrlich et al. 1988, USFWS 

2002). Nesting cuckoos along the Sacramento River in California were estimated to need 

riparian habitat patches ranging from 10–40 ha (25–100 acres) (Gaines 1974, Laymon et 

al. 1997, Halterman 1991). 

Within riparian patches in California, dense understory foliage appears to be an 

important factor in cuckoo nest site selection, while cottonwood trees are an important 

foraging habitat (Laymon et al. 1997, USFWS 2002). Cuckoo surveys in Arizona from 

1998 and 1999 (Corman and Magill 2000) found that occupancy rates (i.e., the 

percentage of sites surveyed that were occupied) were highest in cottonwood (Populus

spp.) -willow (Salix spp.) -ash (Fraxinus spp.) -mesquite (Prosopis spp.) habitat with less 

than 75 percent tamarisk (Tamarix spp.). Mesquite bosque-hackberry (Celtus spp.) 

habitat also had a relatively high occupancy rate. Yellow-billed Cuckoos were much less 

common in sycamore (Platanus spp.) -cottonwood (46 percent occupancy), sycamorealder (Alnus spp.; 33 percent occupancy), and habitats comprised of more than 75 percent 

tamarisk (33 percent occupancy). Surveys conducted by the Arizona Breeding Bird Atlas 

(Corman and Wise-Gervais 2005) found that 68 percent of the Yellow-billed Cuckoo 

observations were in lowland riparian woodlands, often containing a variable 

combination of Fremont cottonwood (Populus fremontii), willow, velvet ash (Fraxinus 

velutina), Arizona walnut (Juglans major), mesquite, and tamarisk. 

Our preliminary efforts to characterize the habitat vegetation characteristics in 

2006 (Johnson et al. 2007) were primarily focused on comparing occupied and 

unoccupied habitats within Grand Canyon NP/Lake Mead NRA, Bill Williams River 

NWR, and Cibola NWR. Across these study sites the dominant tree species were 

cottonwood, willow, and tamarisk. Tamarisk was the most common tree due to the 

abundance of trees in the smallest size class (<8 cm [<3.2 inches] diameter at breast 

height [DBH]) and variation among the different study sites was driven by these trees. In 

general we found that occupied sites had canopies dominated by cottonwood and willow, 

with greater total canopy cover compared to unoccupied sites due to the denser mid- and 

low strata layers. The habitats where we detected cuckoos in 2006 had lower total tree 

density, particularly of tamarisk in the smallest size class, compared to unoccupied 

habitats. Our objective in this chapter is to build upon last year’s work to refine the 

current knowledge of yellow-billed cuckoo habitat requirements specifically within the 

LCR MSCP study area by characterizing riparian habitat at the site-patch level. We 

sampled occupied and unoccupied sites within the entire study area in order to describe 

vegetation composition and structure, including characteristics of the canopy and the 

59
distribution and density of woody species based on the occupancy of status of sites from 

2007 and vegetation measurements made in 2007. 

Methods 

In 2007, we refined our characterization of vegetation based on results from our 

2006 pilot year and a review of sample designs and measurement techniques typically 

used in western riparian bird-habitat studies. Based on previous experience, yellow-billed 

cuckoo use fairly large areas (10–40 ha; 25–100 acres), are not territorial, are present in 

low numbers, and have nests that are difficult to locate (Gaines 1974, Laymon et al. 

1997, Halterman 1991, Johnson et al. 2007). We reviewed vegetation sampling designs 

and found that the majority of studies used point-based sampling associated with 

songbird territories or nest sites (e.g., James and Shugart 1970, Noon 1981, Strong and 

Bock 1990, Martin et al. 1997, Saab 1999, Powell and Steidl 2000, Miller et al. 2003). 

Therefore, we selected point-based sampling measures but sampled in a manner to 

characterize riparian habitat at the survey site-patch level rather than at the territory or 

nest scale. This provides more general and appropriately scaled information to guide 

riparian restoration efforts along the lower Colorado River. We based our evaluated 

measurement techniques on our understanding of cuckoo habitat use and the physical 

features that might be most important in characterizing breeding cuckoo habitat. Overall, 

we selected measures to provide data on vegetation composition and structure: the 

numbers and identities of plant species present in a sample site, and the relative 

abundance or importance of riparian woody species. We also documented general 

vegetation characteristics within sites by taking photographs at each vegetation plot 

(Appendix 5). Our measurement of vegetation characteristics covers multiple spatial 

scales. The smallest scale includes the 5 m and 11.3 m vegetation sampling plots located 

within survey site. The mean values of all vegetation sampling plots comprise the 

vegetation characteristics of what we refer to as the site/patch level—our survey sites. 

The total or mean values of all measurements at the site/patch level make up the 

vegetation characteristics of an entire study site/area, these are the large scale geographic 

area that we conducted this study along the lower Colorado River (Table 4.1). 

Vegetation Sampling Design 

During the 2007 study season, we were primarily interested in characterizing 

vegetation at the site-patch level and in comparing vegetation characteristics between 

occupied and unoccupied sites, among different geographic areas, and among survey sites 

within the Bill Williams River NWR. The entire survey region was stratified north to 

south from the Grand Canyon to the United States/Mexican International border (Table 

4.1). For the vegetation analyses presented in this chapter, we focused on the Grand 

Canyon NP/Lake Mead NRA, Havasu NWR, Bill Williams River NWR, Cibola NWR, 

and Yuma Restoration Sites. 

We attempted to sample vegetation plots in both occupied and unoccupied survey 

sites within each study area. Sites were categorized as occupied if cuckoos were detected 

during two or more survey periods, and unoccupied if cuckoos were detected during only 

one or no survey periods. We classified sites prior to the 2007 field season as occupied or 

unoccupied based on 2005 and 2006 yellow-billed cuckoo surveys (Johnson et al. 2006b, 

Johnson et al. 2007). However, yellow-billed cuckoo detections were not evenly 

distributed across the geographic extent of the study in 2007. Our vegetation sampling 

60
plots corresponded to microclimate and soil moisture sampling locations. So in 2007 

when we detected cuckoos at nearly all sites within the Bill Williams River NWR and at 

none of the sites with the Grand Canyon NP/Lake Mead NRA, we continued our 

vegetation sampling at the locations pre-established in our protocol, because data 

collection had already started for microclimate and soil moisture parameters. Most 

vegetation sampling plots in the Bill Williams River NWR in 2006 were also in occupied 

habitats (26 of 28 plots). At Grand Canyon NP/Lake Mead NRA in 2006 there were plots 

in both occupied and unoccupied habitats in contrast to 2007 when there were none. This 

sampling design resulted in 60 percent of all occupied and 55 percent of all unoccupied 

vegetation sampling plots being located in the Bill Williams River NWR and Grand 

Canyon NP/Lake Mead NRA, respectively. One result of this approach is that the data 

from the Bill Williams River NWR and Grand Canyon NP/Lake Mead NRA likely drove 

vegetation characteristics of occupied and unoccupied habitats, respectively. Because 

there were so few unoccupied sites within the Bill Williams River NWR we could not 

characterize unoccupied habitat within this otherwise heavily occupied study area. 

Table 4.1. Vegetation and microclimate study areas along the lower Colorado River and 

tributaries, 2007. Geographic areas marked with an asterisk (*) have been lumped 

together as “Yuma Restoration Sites” geographic area for comparative purposes. The 

number of randomly selected vegetation plots at occupied and unoccupied sites at each 

geographic study area is indicated. 

Study Areas Plots in Occupied Sites Plots in Unoccupied Sites 

Pahranagat NWR 0 0 

Overton WMA 0 0 

Grand Canyon NP/Lake Mead NRA 0 57 

Havasu NWR 10 10 

Bill Williams River NWR 62 0 

CRIT Reservation 0 0 

Cibola NWR 10 20 

Picacho SRA 0 0 

Imperial NWR* 10 0 

Pratt Restoration* 0 10 

Yuma West Wetlands* 0 6 

Limitrophe 0 0 

Gila/Colorado Rivers Confluence 0 0 

Quigley Pond* 12 0 

Total 104 103 

To identify sampling points we used orthorectified aerial photographs for each 

study site to identify habitat boundaries. We then created a numbered list of Geographic 

Information System (GIS)-generated random locations (Universal Transverse Mercator 

[UTM] coordinates) for each site. Sampling locations were assigned to these random 

61
UTM coordinates. These points were then located in the field using a handheld Global 

Positioning System (GPS) unit and, in cases where random UTM locations were 

inaccessible or located in inappropriate habitat, such as marsh, an alternate random 

location was selected by choosing the next point on the list for that site. In addition to 

randomly-placed sampling plots, plots were established at each yellow-billed cuckoo nest 

site when the nest became inactive (i.e., when the nest fails or the nestlings fledge and 

leave the area of the nest). 

Vegetation Measures and Measurement Techniques 

Characteristics of the Canopy 

We sampled vegetation characteristics for horizontal canopy cover and vertical 

stem density within both 5 m (16.5 ft) and 11.3 m (37.3 ft) radius plot (centered on the 

same point). The vegetation cover layers described below are meant to be flexible enough 

to describe a range of habitats of varying structural complexity. Cover was estimated as 

the vertical projection of vegetation from the ground, as viewed from above. We 

estimated cover and height measures for following horizontal vegetation strata from 

highest to lowest layer in the canopy: “high canopy,” was defined as only that portion of 

the canopy >5 m (16.5 ft) tall; we defined “canopy,” as the top-most continuous layer of 

the canopy (of any height), this is what we described as the main canopy layer; “subcanopy” layer was a distinct layer of cover below the main canopy; and we defined 

“shrub/saplings,” as the lowest distinct layer of vegetation closest to the ground. We 

describe the high canopy and canopy layers together as canopy overstory. We describe 

the cover of sub-canopy and shrub/sapling layer together as the understory. Average 

canopy height was measured for each canopy layer using a clinometer based on a point in 

the canopy that represented the estimated average height of that layer within the 11.3 m 

(37.3 ft) plot; lone trees that emerged far above the main canopy were not considered 

when estimating this average (although these trees did contribute to high canopy 

measurements). We used a spherical densiometer to measure cover at each layer covering 

the 11.3 m (37.3 ft) radius plot by averaging measurements at the four cardinal directions. 

Counts from the densiometer were converted, after the field season, using the formula: 

 

numberof covered dots

96 × 100 = percentcanopycover.

We also determined the dominant plant species in each stratum except the high 

canopy. A plant was defined as dominant if it accounted for at least 40 percent of the 

particular vegetation layer. Two plant species were considered co-dominant when each 

accounted for ≥40 percent of the high canopy. If no single plant species comprised ≥40 

percent of the high canopy, there were no dominant species. In some sites, only a single 

tree layer or shrub layer might be present. In others, one layer or another might be 

entirely absent from the site. 

Density of Woody Species 

To characterize the distribution and density of woody plant species, we counted 

the number of trees in four different DBH size classes: <8 cm (<3.2 inches), 8–23 cm 

(3.2–9.2 inches), 23–38 cm (9.2–15.2 inches), and >38 cm (15.2 inches). Hereafter, we 

62
describe these four size classes as smallest, small, large, and largest, respectively. We 

counted trees in the two smaller size classes within the 5-m (16.5 ft) radius plot and trees 

in the two larger size classes within the 11.3-m (37.3 ft) radius plot. We also counted the 

number of shrubs and saplings by species within the 5-m (16.5 ft) radius and the number 

of snags by species within the 11.3-m (37.3 ft) radius plot. We classified live vertical 

stems less than 1.4 m (4.6 ft) in height as shrubs/saplings and those greater than 1.4 m as 

trees. We present stem count by species for the main riparian tree species: Fremont 

cottonwood, Goodding’s willow, and tamarisk (plus honey mesquite within the Bill 

Williams River NWR sites). For summary purposes, we presented all tree, shrub/sapling, 

and snag species in total counts. For the two smaller tree size classes, we present the 

number of Fremont cottonwood, Goodding’s willow, and tamarisk (and include honey 

mesquite within the Bill Williams River NWR sites) in an effort to characterize potential 

recruitment of these species. All sampling plots were a fixed size; thus, mean abundance 

also represents the relative density of each area. 

Our analyses focused on comparing patterns in woody plant structure and density 

and the different canopy layers in occupied and unoccupied sites, among the different 

geographic study areas, and among sites within the Bill Williams River NWR. Vegetation 

sampling was conducted during August and September of 2007. 

Results 

Yellow-billed Cuckoo Vegetation by Occupancy Status 

There were 104 vegetation plots within occupied yellow-billed cuckoo sites and 

103 in unoccupied sites. Most of the occupied plots were within the Bill Williams River 

NWR (62 of 104; 60 percent), thus many of the patterns we observed in occupied sites 

were driven by the vegetation characteristics there. Most unoccupied plots were within 

Grand Canyon NP/Lake Mead NRA (57 of 103; 55 percent), so vegetation characteristics 

of unoccupied sites primarily reflect the habitat conditions there. 

Characteristics of the Canopy 

We detected several differences in the canopy cover and canopy plant species 

composition between occupied and unoccupied sites. Occupied sites had nearly twice the 

high canopy cover (canopy>5 m in height) compared to unoccupied sites (t205 = 5.0, 

p<0.0001; Fig 4.1). However, there was no difference between occupied and unoccupied 

sites in canopy cover (t205 = 0.1, p = 0.91; Fig. 4.1) or sub-canopy cover (t205 = 1.7, p = 

0.08; Fig 4.1). While the shrub/sapling canopy layer was sparse compared to the high 

canopy, canopy, and sub-canopy layers; cover in the shrub layer was over four times 

greater in unoccupied sites compared to occupied sites (t205 = - 4.1, p<0.001; Fig 4.1). 

Corresponding to the differences in high canopy cover between occupied and unoccupied 

sites, we also found that total tree height was 70 percent higher at occupied sites 

compared to unoccupied sites (t205 = 8.0; p<0.001; Fig. 4.2). In general, occupied sites 

appear to have more developed over-stories and sparser under-stories compared to 

unoccupied sites, indicating the possible importance of these layers to yellow-billed 

cuckoos. 

63
While we did not record the plant species making up the high canopy layer, most 

species taller than 5 m (16.5 ft) across the study area were native species (cottonwood 

and willow; Johnson et al. pers. obs.), so high canopy was likely dominated by natives. 

But in the canopy layer, plots in both occupied (77 percent) and unoccupied (74 percent) 

sites were dominated by native species such as Fremont cottonwood and Goodding’s 

willow. Tamarisk was the dominant canopy species at only a few occupied and 

unoccupied sites, 12 percent and 8 percent, respectively. At occupied sites the subcanopy was dominated by tamarisk (36 of 88 plots; 41 percent) or Goodding’s willow (25 

of 88 plots; 28 percent), while the sub-canopy of unoccupied sites was mostly tamarisk 

(41 of 70 plots; 59 percent). A shrub/sapling layer was relatively rare at occupied sites 

(17 of 104; 16 percent), but 76 percent of plots with a shrub/sapling canopy layer at 

occupied sites were dominated by arrowweed or seep willow. At unoccupied sites a 

shrub/sapling layer was more common (46 of 103; 45 percent) and most of these were 

dominated by tamarisk (63 percent). Based on these results, it appears that overstories 

made up of native Freemont cottonwood and Goodding’s willow with mixed willow 

tamarisk sub-canopies are widespread throughout the LCR MSCP area. Habitats 

occupied by cuckoos were less likely to have a shrub/sapling layer. If cuckoos were in a 

habitat with a dense shrub/sapling layer it was typically dominated by native species 

(arrowweed or seep willow); cuckoos do not appear to be found in habitats with dense 

tamarisk shrub/sapling layer. 

Strata Layer

High Canopy Cover

Canopy Layer

Sub Canopy

Shrub / Sapling

Mean Cover (%)

0

10

20

30

40

50

Occupied 

Unoccupied 

Figure 4.1. Percent cover at different layers in the canopy between occupied and 

unoccupied sites within the LCR MSCP boundary area, 2007. Error bars represent one 

standard error of the mean. 

64
Occupied Unoccupied

Mean Total Tree Height

0

5

10

15

20

Figure 4.2. Total tree height (in meters) for occupied and unoccupied sites within the 

LCR MSCP boundary area, 2007. Error bars represent one standard error of the mean. 

Density of Woody Species 

We detected many differences in the density and composition of woody species 

between occupied and unoccupied sites that corresponded to some characteristics of the 

canopy layers. The mean density of all stems (tree, shrubs/saplings, and snags combined) 

was over twice as great at sites unoccupied versus occupied (t205 = -3.0; p = 0.003; Fig 

4.3). Considering trees of all sizes and species and all shrub and sapling species, we 

found greater density at unoccupied sites (trees: t205 = -2.9, p = 0.004; shrubs/saplings: t205

= -2.9, p = 0.004; Fig 4.3); however, snag density was not significantly different between 

occupied and unoccupied sites (t205 = -1.6, p = 0.11; Fig 4.3). 

65
Stem Class

Total Stems Trees Shrubs / Saplings Snags

Mean Stem Count

0

100

200

300

400

Occupied 

Unoccupied 

Figure 4.3. Mean total stem count at occupied and unoccupied sites within the LCR MSCP 

boundary area, 2007. Trees with DBH <23 cm and shrubs and saplings were counted 

within the 5 m plot and trees >23 cm DBH and snags were counted within the 11.3 m plot. 

Error bars represent one standard error of the mean. 

We found that trees in the smallest size class accounted for 86 percent of total tree 

density in occupied sites and 94 percent at sites unoccupied, while trees in the large and 

largest size classes accounted for 6 percent of all trees at occupied sites and only<1 

percent at unoccupied sites. We found that unoccupied sites had more than twice the stem 

density of the smallest class trees (<8 cm DBH; 3.2 inches) as occupied sites (t205 = -3.0; p 

= 0.004; Fig. 4.4). The greater density of trees in the smallest size class in unoccupied 

sites is consistent with the greater cover of the shrub/sapling layer at unoccupied sites as 

these smaller trees likely to contribute to some of the understory cover. However, sites 

occupied by cuckoos had three times greater stem counts of trees in the large (23–38 cm 

DBH; 9.2–15.2 inches) and more than twice the density of trees in the largest (>38 cm 

DBH; 15.2 inches) size classes (large: t205 = 5.8; p<0.001; largest: t205 = 2.3; p = 0.02; Fig. 

4.4). The greater density of trees in these bigger size classes in occupied sites might 

correspond to differences in the characteristics of the high canopy between occupied and 

unoccupied sites. The stem density of small trees (8–23 cm DBH; 3.2–9.2 inches) was 

not different between occupied and unoccupied sites (t205 = -1.4, p = 0.17; Fig. 4.4). 

Although the occupancy status of sites is confounded by the distribution of 

vegetation sampling points among the different geographic areas, it appears that the 

density of trees in different size classes could be a useful predictor of yellow-billed 

cuckoo habitat use. We did not find cuckoos using sites with high density of the smallest 

trees (leading to dense understory cover) but we did detect cuckoos in sites with more 

trees in the large and largest size classes (likely with dense high canopies). Since most of 

the tree density occurred in the smallest and small classes trees, we presented the stem 

count of three common riparian tree species (cottonwood, willow and tamarisk) for only 

the smallest (<8 cm DBH; 3.2 inches) and small (8–23 cm DBH; 3.2–9.2 inches) tree size 

66
class. Also these young trees are the new recruits and thus likely indicate the future 

vegetation composition of a plot. For the smallest size class (<8 cm DBH; 3.2 inches), 

Freemont cottonwood stem count was higher in occupied sites (t205 = 2.2, p = 0.02; Fig. 

4.5), while Goodding’s willow and tamarisk were higher in unoccupied sites (willow: t205

= -2.5, p = 0.01; tamarisk: t205 = -2.8, p = 0.006; Fig. 4.5). 

Tree size class

smallest small large largest

Mean Stem Count

0

5

10

40

60

80

100

120

140

Occupied

Unoccupied

Figure 4.4. Total tree count by size class for occupied and unoccupied sites within the 

LCR MSCP boundary area, 2007. Note the break in the y-axis from 10–30. Trees in the 

smallest and small size classes were counted within the 5 m plot and tress in the large 

and largest size classes were counted within the 11.3 m plot. Error bars represent one 

standard error of the mean. 

In the small size class (8–23 cm DBH; 3.2–9.2 inches), Freemont cottonwood 

stem count was over twice as high in unoccupied sites (t205 = -2.3, p = 0.02; Fig. 4.6), 

willow density was the same in occupied and unoccupied (t205 = -0.6, p = 0.53; Fig. 4.6), 

and mean stem count of small tamarisk trees was over 20 times higher in occupied sites 

(t205 = 4.3, p<0.001; Fig. 4.6). Trees in the large and largest size class were mostly 

Goodding’s willow at both occupied and unoccupied sites, accounting for 57 percent and 

44 percent of total trees in these size classes, respectively. 

In summary, these finding suggest that occupied sites have a distinct vegetative 

composition. Specifically, occupied cuckoo sites include (1) a tall, dense overstory 

composed of native tree species, where native cottonwoods and willows dominate the 

larger size classes; (2) a sub-canopy composed of both native and exotic species; and (3) 

a dense understory dominated by tamarisk in the smaller classes.

67
Tree species

Cottonwood Willow Tamarisk

Mean Stem Count

0

2

4

6

8

10

20

40

60

80 Occupied 

Unoccupied 

Figure 4.5. Mean stem count of smallest trees (<8 cm DBH), in occupied versus 

unoccupied sites within the LCR MSCP boundary area, 2007. Note the break in the y-axis 

from 10–15. Trees in the smallest size class were counted within the 5 m plot. Error bars 

represent one standard error of the mean. 

Tree species

Cottonwood Willow Tamarisk

Mean Stem Count

0

1

2

3

4

5

Occupied 

Unoccupied 

Figure 4.6. Mean stem count of small trees (8–23 cm DBH) in occupied versus 

unoccupied sites within the LCR MSCP boundary area, 2007. Trees in the small size class 

were counted within the 5 m plot. Error bars represent one standard error of the mean. 

68
Yellow-billed Cuckoo Vegetation by Geographic Area 

To examine potential geographic variation in vegetation characteristics, we 

measured vegetation plots at five Geographic Study Areas; Grand Canyon NP/Lake 

Mead NRA (57 plots), Havasu NWR (20 plots), Bill Williams River NWR (62 plots), 

Cibola NWR (30 plots), and the Yuma Restoration Sites (38 plots). All of the plots at the 

Bill Williams River NWR were occupied, none of the plots at Grand Canyon NP/Lake 

Mead NRA were occupied, and the other Geographic Areas had plots in both occupied 

and unoccupied sites (Table 4.1). 

Characteristics of the Canopy 

We found some differences in cover and composition of the canopy but also 

considerable overlap in the canopy structure among the different Geographic Study 

Areas. Consistent with its occupied status, cover of the high canopy (>5m; 16.5 ft) was 

significantly greatest at Bill Williams River NWR compared to Grand Canyon NP/Lake 

Mead NRA, Cibola NWR, and the Yuma Restoration sites; however, the high canopy 

cover at Havasu NWR was not statistically different from the other Geographic Areas 

(F4,202 = 11.8, p<0.0001; Fig. 4.7). Because there were no differences in the cover of the 

canopy or sub-canopy layer between occupied or unoccupied sites, these variables might 

not be important in distinguishing suitable habitats for yellow-billed cuckoos; however, 

we found differences among the study areas in both of these parameters. The only 

differences in canopy cover among study areas were between the Cibola NWR and Grand 

Canyon NP/Lake Mead NRA (F4,202 = 2.6; p = 0.03; Fig. 4.7). The sub-canopy cover at the 

Grand Canyon NP –Lake Mead NRA and Bill Williams River NWR sites was 

significantly greater than at the Havasu and Cibola NWR sites (F4,202 = 9.8; p<0.001; Fig. 

4.7). Grand Canyon NP/Lake Mead NRA and Havasu NWR had the highest 

shrub/sapling cover (F4,202 = 8.1, p<0.0001; Fig. 4.7), but all other study areas were 

statistically indistinguishable in total shrub cover. 

Examining the different Geographic Study Areas from northernmost (Grand 

Canyon NP/Lake Mead NRA) to the southernmost (Yuma Restoration Sites), we did not 

detect any consistent pattern in the vegetation composition of the different canopy strata 

layers. The canopy layer was dominated by primarily by Goodding’s willow, Athel 

tamarisk, or Freemont cottonwood. We found tamarisk or Goodding’s willow as the 

dominant species in the sub-canopy layer although many plots did not have a developed 

sub-canopy layer. Overall shrub/sapling layers were not well developed across all study 

areas, but the dominance of tamarisk cover in the understory of Grand Canyon NP/Lake 

Mead NRA was an exception (Table 4.2). 

Mean total tree height varied by Geographic Area (F4,202 = 42.3, p<0.0001; Fig. 

4.8), with the tallest trees found at Bill Williams River NWR. Larger trees were usually 

Freemont cottonwoods or Goodding’s willows, probably due to their morphology. 

69
Density of Woody Species 

We found large differences among Geographic Study Areas in the density of 

woody species, primarily driven by the high stem counts at Grand Canyon NP/Lake 

Mead NRA. Grand Canyon NP/Lake Mead NRA had significantly greater total stem 

count (over 3.5 times greater) compared to all other areas, while all other areas were not 

statistically different from one another (F4,202 = 11.8; p<0.0001; Fig 4.9). Grand Canyon 

NP/Lake Mead NRA had twice the mean tree density as other study areas (F4,202 = 9.6, 

p<0.0001; Fig. 4.10) and nearly 3.5 times the shrub/sapling density (F4,202 = 8.4, p<0.001; 

Fig. 4.9). We found that the density of snags at Grand Canyon NP/Lake Mead NRA was 

over six times greater than Bill Williams River NWR and the Yuma Restoration Sites 

(F4,202 = 3.8, p = 0.005; Fig. 4.9). There were no significant differences in snag density 

among the other study areas. The greater number of snags at Grand Canyon NP/Lake 

Mead NRA is probably due to the high number of dead trees due to the lower water 

levels in 2007. 

Strata Layer

High Canopy Cover

Canopy Layer

Sub Canopy

Shrub / Sapling

Mean Cover (%)

0

1 0

2 0

3 0

4 0

5 0

6 0

Grand Canyon NP 

Lake Mead NRA

Havasu NWR

Bill W illiam s N W R

C ibola N W R

Yuma 

R estoration 

Sites

Figure 4.7. Canopy cover for high canopy >5 m, canopy layer, sub canopy, and 

shrub/sapling layer at each Geographic Area (Grand Canyon NP/Lake Mead NRA, Havasu 

NWR, Bill Williams River NWR, Cibola NWR and Yuma Restoration Sites), 2007. Error bars 

represent one standard error of the mean. 

70
Table 4.2. Dominant species by layer among geographic areas. Values indicate the 

percent of total plots within study areas that had indicated species as the dominant 

species. 

Site Canopy Sub-canopy Shrub/sapling 

Grand Canyon NP/Lake 

Mead NRA 

Goodding's willow 

(74%) Tamarisk (76%) Tamarisk (76%) 

Havasu NWR 

Freemont cottonwood 

(40%) Athel tamarisk 

(39%) 

Equally dominated by 

Athel tamarisk, 

Goodding's willow, 

Screwbean and honey 

mesquite 

Only 50% of plots had 

layer 

Bill Williams River 

NWR 

Goodding's willow 

(66%) 

Tamarisk (59%) 

Goodding's willow 

(28%) 

Only 5% of plots had 

layer 

Cibola NWR 

Freemont cottonwood 

and Goodding's willow 

(67%) 

Only 20% of plots had 

layer 

Only 23% of plots had 

layer 

Yuma Restoration Sites Freemont cottonwood 

(67%) 

Only 40% of plots had 

layer 

Only 13% of plots had 

layer 

Geographic Area

Grand Canyon NP - Lake Mead NRA

Havasu NWR

Bill Williams NWR

Cibola NWR

Yuma Restoration Sites

Mean Total Tree Height

0

5

10

15

20

25

Figure 4.8. Mean total tree height (in meters) by Geographic Area (Grand Canyon 

NP/Lake Mead NRA, Havasu NRA, Bill Williams River NWR, Cibola NWR and Yuma 

Restoration Sites), 2007. Error bars represent one standard error of the mean. 

71
Stem Class

Total stems Trees Shrubs / Saplings Snags

Mean Stem Count

0

100

200

300

400

500

600

Grand Canyon NP

Lake Mead NRA

Havasu NWR

Bill Williams NWR

Cibola NWR

Yuma 

Restoration

Sites

Figure 4.9. Mean stem count by total stems, trees, shrubs/saplings, and snags for all five 

Geographic Areas (Grand Canyon NP/Lake Mead NRA, Havasu NRA, Bill Williams River 

NWR, Cibola NWR and Yuma Restoration Sites), 2007. Trees with DBH <23 cm and shrubs 

and saplings were counted within the 5 m plot and trees >23 cm DBH and snags were 

counted within the 11.3 m plot. Error bars represent one standard error of the mean. 

Trees in the smallest and small size classes made up most of the tree density at all 

Geographic Areas (Fig 4.10). We examined the mean density of cottonwoods, willows, 

and tamarisk trees in these size classes. Recruitment of new trees into the different study 

areas can be best examined in the smallest and small size classes. The mean number of 

cottonwoods varied among Geographic Areas for the smallest (F4,202 = 3.2, p = 0.01; 

Fig. 4.11) and small (F4,202 = 19.9, p<0.001; Fig 4.12) size classes. For the smallest size 

class of cottonwoods, density at the Bill Williams River NWR and Yuma Restoration 

Sites was greater than at the Grand Canyon NP/Lake Mead NRA sites; but mean density 

of the smallest size class cottonwoods was not statistically different at other sites. The 

Cibola NWR had over 5-times the density of cottonwood trees in the small size class 

compared to other study areas. However, because cottonwoods were relatively rare on the 

landscape (especially compared to willow and tamarisk), cottonwood density was not 

well represented in the measurements of cover at any layer. 

The mean number of Goodding’s willow also varied by Geographic Area in the 

smallest (F4,202 = 4.5, p = 0.002; Fig. 4.11) and small (F4,202 = 4.6, p = 0.001; Fig. 4.12) tree 

size classes. The density of the smallest size class of willow trees was greater at Grand 

Canyon NP/Lake Mead NRA compared to Bill Williams River NWR, Cibola NWR, and 

Yuma Restoration Sites; but Havasu NWR was not statistically different from any 

Geographic Area. There were more willows in the small size class at Grand Canyon 

NP/Lake Mead NRA compared to Havasu and Cibola NWR, but there was no difference 

among the other Geographic Areas. Because willows are present at all sites in the 

smallest and small size classes, the potential exists that as these trees mature, the 

72
vegetation structure at any of these sites might become suitable for yellow-billed 

cuckoos, if in fact tall willow over-stories prove to be important for this species. 

Tamarisk in the smallest size class were almost four-times as dense at Grand 

Canyon NP/Lake Mead NRA compared to other Geographic Areas (F4,202 = 8.1, p<0.0001; 

Fig. 4.11) and tamarisk in the small size class were over five-times as dense at the Bill 

Williams River NWR compared to other Geographic Areas (F4,202 = 8.2, p<0.0001; Fig 

4.12). Although there we no cuckoos detected at any of the Grand Canyon NP/Lake 

Mead NRA sites in 2007, it is not clear that this was because of the high density of 

tamarisk in the smallest size class and associated dense cover of the shrub/sapling layer. 

It appears that cuckoos tolerate and maybe favor some tamarisk component based on the 

high density of small sized class tamarisk at the Bill Williams River NWR and the high 

degree of use of that study area by yellow-billed cuckoos. 

The dominant tree species in the large and largest size classes also varied among 

Geographic Area. At the Grand Canyon NP/Lake Mead NRA all trees in the large and 

largest size classes were Goodding’s willow. At Havasu NWR 70 percent of trees in the 

large and largest size classes were Athel tamarisk. At the Bill Williams River NWR 69 

percent of trees in the large and largest size classes were Goodding’s willow, and at both 

Cibola NWR and Yuma Restoration sites Fremont cottonwood were the dominant trees in 

the large and largest size classes making up 81 percent and 74 percent of trees in these 

sizes classes at these two areas, respectively. In general trees of the large and largest size 

classes corresponded to the dominant tree species and the high canopy and canopy layer 

of each study area indicating the role trees of these sizes play in determining vegetation 

structure. 

73
Tree size class

smallest small large largest

Mean Stem Count

0

10

20

60

90

120

150

180

210

Grand Canyon NP

Lake Mead NRA

Havasu NWR

Bill Williams NWR

Cibola NWR 

Yuma 

Restoration 

Sites

Figure 4.10. Total tree count by size class by Geographic Area (Grand Canyon NP/Lake 

Mead NRA, Havasu NRA, Bill Williams River NWR, Cibola NWR and Yuma Restoration 

Sites), 2007. Note the break in the y-axis between 25–35. Trees in the smallest and small 

size classes were counted within the 5 m plot and tress in the large and largest size 

classes were counted within the 11.3 m plot. Error bars represent one standard error of 

the mean. 

74
Tree species

Cottonwood Willow Tamarisk

Mean Stem Count

0

2

4

6

8

20

40

60

80

100

120

140

160

Grand Canyon NP

Lake Mead NRA

Havasu NWR

Bill Williams NWR

Cibola NWR

Yuma

Restoration 

Sites

Figure 4.11. Mean stem count of smallest trees by Geographic Area. (Grand Canyon 

NP/Lake Mead NRA, Havasu NRA, Bill Williams River NWR, Cibola NWR and Yuma 

Restoration Sites), 2007. Note the break in the y-axis at 10 and the different scales above 

and below the break. Trees in the smallest size class were counted within the 5 m plot. 

Error bars represent one standard error of the mean. 

Tree species

Cottonwood Willow Tamarisk

Mean Stem Count

0

2

4

6

8

10

12

14

16

Grand Canyon NP

Lake Mead NRA

Havasu NWR

Bill Williams NWR

Cibola NWR

Yuma 

Restoration

Sites

Figure 4.12. Mean stem count of small trees by Geographic Area. (Grand Canyon 

NP/Lake Mead NRA, Havasu NRA, Bill Williams River NWR, Cibola NWR and Yuma 

Restoration Sites), 2007. Trees in the small size class were counted within the 5 m plot. 

Error bars represent one standard error of the mean. 

75
Yellow-billed Cuckoo Vegetation at Bill Williams River NWR Sites 

At the Bill Williams River NWR we measured the vegetation characteristics of 

three sites— Mineral Wash (n = 20), Big Bend (n = 21), and Sandy Wash (n = 18)—in 

order to examine the variation within the Geographic Study Area that accounted for the 

majority of cuckoo detections. All of these sites were considered occupied at high density 

by yellow-billed cuckoos and together accounted for 44 percent of all survey detections 

at Bill Williams River NWR. 

Characteristics of the Canopy 

There was no difference among sites in mean canopy height (F2,56 = 0.4, p = 0.66; 

Fig 4.13), which ranged from 20.5 m–22.8 m. High canopy cover (>5 m high) varied 

among the three sites, with Mineral Wash and Sandy Wash both having significantly 

greater high canopy cover compared to Big Bend (F2,56 = 8.1, p = 0.008; Fig. 4.14). 

Canopy cover at Mineral Wash was significantly greater than Big Bend, but the canopy 

cover at Sandy Wash was not statistically different from either site (F2,56 = 5.9, p = 0.005; 

Fig. 4.14). Mean cover in the sub-canopy layer differed among the three sites (F2,56 = 5.8, 

p = 0.005; Fig. 4.14), with the sub-canopy cover of Sandy Wash over twice that of Big 

Bend, but Mineral Wash was not statistically different in sub-canopy cover from either 

site. There were no differences in the mean cover of the shrub layer among the different 

sites at the Bill Williams River NWR (F2,56 = 1.4, p = 0.25; Fig. 4.14). Because these three 

sites account for 57 percent of vegetation plots in occupied sites, the mean values of the 

canopy characteristics were similar to overall mean values of all occupied sites. 

Bill Williams NWR Sites

Mineral Wash Big Bend Sandy Wash

Mean Total Tree Height

0

5

10

15

20

25

30

Figure 4.13. Mean total tree height (in meters) at Bill Williams River NWR sites (Mineral 

Wash, Big Bend and Sandy Wash), 2007. Error bars represent one standard error of the 

mean. 

76
Canopy Strata

High Canopy Canopy Sub Canopy Shrub 

Mean Cover

0

10

20

30

40

50

60

Mineral Wash

Big Bend

Sandy Wash

Figure 4.14. Mean percent canopy cover of different layer of canopy strata at Bill 

Williams River NWR sites (Mineral Wash, Big Bend and Sandy Wash), 2007. Error bars 

represent one standard error of the mean. 

At all Bill Williams River NWR sites the canopy layer was dominated by 

Goodding’s willow, like most sites in the entire study area and accounted for the 

dominant species at 70 percent of plots at Mineral Wash, 57 percent of plots at Big Bend, 

and 72 percent of plots at Sandy Wash. The sub-canopy layer at Mineral Wash had 

tamarisk as the dominant species on 50 percent of plots. The sub-canopy at Big Bend was 

approximately equally dominated by tamarisk and Goodding’s willow on 43 percent and 

38 percent of plots, respectively. Almost all plots at Sandy Wash had tamarisk as the 

dominant sub-canopy species (94 percent). The shrub layer was absent on most plots 

within the Bill Williams River NWR (a distinct shrub layer was only present on 3 of the 

62 total plots; 5 percent). The presence of tamarisk in the sub-canopy at these sites that 

account for many of the cuckoo detections at the Bill Williams River NWR indicates that 

cuckoos are able to use habitats with some exotic component, although the dense overstories of tall Goodding’s willow and sparse under-stories might be important factors in 

yellow-billed cuckoo habitat selection. 

Density of Woody Species 

We detected differences in the total density of woody species, but it was primarily 

driven by the high number of snags at Sandy Wash. Total stem density at Sandy Wash 

was over three-times as great as Big Bend, but stem density at Mineral Wash was not 

statistically different from either site (F2,56 = 5.6, p = 0.006; Fig. 4.15). Density of trees 

and shrub/saplings were not significantly different among the three sites (trees: F2,56 = 1.0, 

p = 0.38; shrubs/saplings: F2,56 = 1.1, p = 0.32; Fig. 4.15). However, Sandy Wash had 

almost 10-times the snag density as Mineral Wash and Big Bend (F2,56 = 7.2, p = 0.002; 

Fig. 4.15). 

77
Stem Class

Total stems Trees Shrubs/Saplings Snags

Mean Stem Count

0

50

100

150

200

250

Mineral Wash

Big Bend

Sandy Wash

Figure 4.15. Mean stem count by stem class at Bill Williams River NWR sites (Mineral 

Wash, Big Bend and Sandy Wash), 2007. Trees with DBH <23 cm and shrubs and saplings 

were counted within the 5 m plot and trees >23 cm DBH and snags were counted within 

the 11.3 m plot. Error bars represent one standard error of the mean. 

The mean density of trees in the four different size classes did not vary among the 

sites (smallest trees: F2,56 = 0.9, p = 0.41; small trees: F2,56 = 0.1, p = 0.89; large trees: F2,56

= 0.1, p = 0.87; largest trees: F2,56 = 0.9, p = 0.42; Fig. 4.16). Much like the other study 

sites, most trees were in the smallest and small size classes’ at all three sites. At Mineral 

Wash 91 percent of trees were either in the smallest or small size classes, 89 percent of 

trees at Big Bend fell into the smallest and small size classes, and at Sandy Wash 93 

percent of trees were in the smallest and small size classes. Of trees that were in the large 

and largest size classes, most of these were Goodding’s willow at all sites: 82 percent at 

Mineral Wash, 72 percent at Big Bend, and 56 percent at Sandy Wash. 

We found no significant differences in the stem density of the most common tree 

species (cottonwood, Goodding’s willow, honey mesquite, and tamarisk) in the smallest 

size class among the three Bill Williams River NWR sites (cottonwood: F2,56 = 1.1, p = 

0.35; willow: F2,56 = 1.0, p = 0.37; mesquite: F2,56 = 0.3, p = 0.77; tamarisk: F2,56 = 1.6, p = 

0.21; Fig. 4.17, or in the small size class (cottonwood: F2,56 = 1.3, p = 0.28; willow: F2,56 = 

0.8, p = 0.45; mesquite: F2,56 = 0.7, p = 0.50; tamarisk: F2,56 = 1.7, p = 0.19; Fig. 4.18) The 

similarity in the density of trees in different size classes and different species might be in 

part due to the geographic proximity. 

78
Size Class

Smallest Small Large Largest

Mean Tree Stem Count

0

3

6

9

20

40

60

80

Mineral Wash

Big Bend

Sandy Wash

Figure 4.16. Total tree count by size class at Bill Williams River NWR sites (Mineral 

Wash, Big Bend and Sandy Wash), 2007. Note the break in the y-axis between 10–20. 

Trees in the smallest and small size classes were counted within the 5 m plot and tress in 

the large and largest size classes were counted within the 11.3 m plot. Error bars 

represent one standard error of the mean. 

79
Tree species

Cottonwood Willow Honey Mesquite Tamarisk

Mean stem count of smallest tree species

0

3

6

9

12

20

40

60

80

Mineral Wash

Big Bend

Sandy Wash

Figure 4.17. Mean stem count by of trees in the smallest size class at Bill Williams River 

NWR sites (Mineral Wash, Big Bend and Sandy Wash), 2007. Note the break in the y-axis 

between 12–20 and the different scales above and below the break. Trees in the smallest 

size class were counted within the 5 m plot. Error bars represent one standard error of the 

mean. 

Tree species

Cottonwood Willow Honey Mesquite Tamarisk

Mean stem count small trees

0

1

2

3

4

5

Mineral Wash

Big Bend

Sandy Wash

Figure 4.18. Mean stem count by major tree species in small size class at Bill Williams 

River NWR (Mineral Wash, Big Bend and Sandy Wash), 2007. Trees in the small size class 

were counted within the 5 m plot. Error bars represent one standard error of the mean. 

80
Discussion 

Our characterization of vegetation at yellow-billed cuckoo survey sites for 2007 

was a follow up to our preliminary analysis conducted in 2006. We were able to refine 

our methods in order to more accurately represent the vegetation characteristics of 

yellow-billed cuckoo habitat. In 2007, we compared habitat characteristics in: (1) yellowbilled cuckoo occupied areas versus unoccupied, (2) Geographic Areas (e.g. Cibola 

NWR) of the study area, and (3) more closely investigated the characteristics of sites 

within the heavily occupied Bill Williams River NWR. The dominant tree species at our 

cuckoo survey sites were cottonwood, willow, and tamarisk. Tamarisk was the most 

common tree due to the abundance of trees in the smallest size class. Trees in large and 

larger size classes were usually cottonwoods or willows. Mesquite was not regularly 

encountered at most sites we sampled. 

Vegetation by Cuckoo Occupancy Status 

We attempted to stratify vegetation sampling plots across the different 

Geographic Areas to include sites occupied by yellow-billed cuckoos and those that did 

not have cuckoos. We based this on occupancy patterns observed in 2006. Unfortunately, 

yellow-billed cuckoo detection patterns in 2007 were not consistent with previous years, 

resulting in most of our occupied sampling plot being within the Bill Williams River 

NWR and most of our unoccupied sampling plots within the Grand Canyon NP/Lake 

Mead NRA. While this might have skewed the vegetation characteristic statistics towards 

these two areas, we were able to observe some general patterns between occupied and 

unoccupied sites. 

Sites that were occupied by yellow-billed cuckoos in 2007 in general had higher 

canopies, denser cover in the upper layers of the canopy, and sparse shrub layers 

compared to unoccupied sites. This could indicate that cuckoos prefer areas with tall 

dense canopies for nesting with an open understory for foraging activities. Also areas 

with open under-stories may have fewer terrestrial predators. The upper layer of the 

canopy was consistently dominated by native riparian tree species (Fremont cottonwood 

and Goodding’s willow) at both occupied and unoccupied habitats. The sub-canopy of 

occupied sites was typically either tamarisk or Goodding’s willow. A distinct 

shrub/sapling layer was rare at occupied sites, but when present, this layer was dominated 

by native arrowweed or seep willow. At unoccupied sites the sub-canopy and shrub 

layers were consistently dominated by dense tamarisk. 

The density of woody species was consistently higher at unoccupied sites, except 

for stems in the snag class, which we found in equal numbers in occupied and unoccupied 

sites. For trees, the greater density in the unoccupied sites was driven by trees in the 

smallest size class, and trees in this class were the most abundant across the entire study 

area. Trees in the large and largest size classes were more numerous in occupied sites, 

and consistent with the dominant canopy layer across all occupancy classes, these trees 

were generally Goodding’s willow. However, in both occupied and unoccupied sites 

there was a mosaic of native and exotic tree species in the smallest and small size classes, 

indicating that cuckoos are able to use habitats that have exotic components. 

In 2006, occupied sites had greater canopy cover driven by denser low and midcanopies (Johnson et al. 2007). However, we found in 2007 that the differences between 

canopies in occupied and unoccupied sites were due to difference at higher canopy strata. 

Also in 2007, the canopies at both occupied and unoccupied sites were dominated by 

81
native species, while in 2006 only occupied sites were more consistently dominated by 

native species. Consistent between the two years was the greater tree density in 

unoccupied sites. Some of the difference we observed between years might be due to 

difference in the refined vegetation sampling methodology we used in 2007 and the 

different sites we measured due to changes in their occupancy status. Additional research 

examining characteristics of sites occupied by yellow-billed cuckoos and sites 

unoccupied is necessary to determine consistent annual patterns of vegetation 

characteristics in these riparian habitats. 

Vegetation by Geographic Area 

Among the different Geographic Study Areas, we found some differences in the 

cover at various canopy strata, but also instances of considerable overlap. The canopy 

layers among Geographic Areas were dominated by different tree species, likely driven 

by the histories of the study areas and also the degree of vegetation management that 

occurs at some sites (i.e., native plant restoration and tamarisk removal). The large 

differences in the density of woody species among the different study areas was largely 

due to the high number of stems counted on vegetation plots with the Grand Canon 

NP/Lake Mead NRA compared to other study areas. At all of the study sites the most 

numerous trees were those in the smallest and small size classes and there was high 

variation in the specific composition of the dominant riparian tree species among the 

different areas. In general, the species of the dominant trees in the large and largest size 

class corresponded to the dominant species in the upper canopy layer at each study area. 

The wide variety of canopy structures present within the LCR MSCP boundary area 

indicates that yellow-billed cuckoos have a wide range of habitats to select from when 

arriving on the breeding grounds. However in 2007, the majority of detections were 

within the Bill Williams River NWR, suggesting that within the LCR MSCP boundary, 

habitats with tall dense over-stories of Goodding’s willow and Freemont Cottonwood, 

sub-canopies with willow and tamarisk components, and sparse under-stories are most 

suitable for yellow-billed cuckoos. 

In 2006, we compared the vegetation characteristics among Grand Canyon 

NP/Lake Mead NRA, Bill Williams River NWR, and Cibola NWR. Generally speaking 

the characterization among these study areas was consistent between the two years of the 

study. Bill Williams River NWR had larger Goodding’s willow, Grand Canyon NP/Lake 

Mead NRA was dominated by willows and tamarisk in the smallest size class, and the 

row planting of native tree species at Cibola NWR distinguished it from other more 

“natural” riparian habitats. While the species and size class composition of trees at the 

Grand Canyon NP/Lake Mead NRA was consistent between the two years, in 2007 it 

contained no occupied sites after having three occupied sites in 2006 (Cuckoo Beach, 

Iceberg Ridge, and Chuckwalla Cove). One factor possibly contributing to this change in 

occupancy at Grand Canyon NP/Lake Mead NRA was the declining water levels of Lake 

Mead. This water stress on the plant communities in the deposited sediments along the 

river can be examined by the proportion of snags in total stem density. Snags accounted 

for 46 percent of all stem density in 2007 compared to only 14 percent in 2006, indicating 

that large tracts of riparian habitat that had been occupied by cuckoos in 2007 had died 

over the past survey season. It remains to be seen if this trend continues and what 

recruitment of young trees leads to habitat conditions appropriate for yellow-billed 

cuckoos at Grand Canyon NP/Lake Mead NRA. 

82
Vegetation among Occupied Sites at Bill Williams River NWR 

We studied the vegetation characteristics within three sites at the Bill Williams 

River NWR in order to examine the degree of variation among habitats in the area with 

the greatest number of cuckoo detections across the entire study. Since the three sites at 

the Bill Williams River NWR accounted for 62 vegetation sampling plots of the 104 

vegetation sampling plots in occupied patches across the LCR MSCP study area, it is not 

surprising that habitat characteristics of occupied habitats across the LCR MSCP and the 

Bill Williams River NWR are similar. Although Mineral Wash, Big Bend, and Sandy 

Wash were the sites with the greatest number of cuckoo detections, we were still able to 

detect substantial variation in the cover of the different strata. In general Big Bend had 

sparser cover at all layers. The sites within the Bill Williams River NWR all had 

Goodding’s willow as the dominant species of the canopy layer, but there was variation 

in the sub-canopy layer with tamarisk the dominant sub-canopy species at about half the 

plots in Mineral Wash and Big Bend (50 percent and 43 percent, respectively) and almost 

all the plots at Sandy Wash (94 percent). The composition of the canopy and sub-canopy 

layers could represent a range of “ideal” habitat conditions necessary for cuckoo 

occupancy, although there are certainly hydrologic conditions unique to the Bill Williams 

River NWR that might contribute to occupancy in these areas. All the Bill Williams 

River NWR had sparse shrub layers, which was also apparent in occupied sites in general 

and might indicate the importance of an open understory to cuckoos. The density of 

different riparian trees species did not differ among Mineral Wash, Big Bend, and Sandy 

Wash, although Sandy Wash did have a higher density of snags. It appears that there is 

some density threshold that provides the most suitable habitat structure to yellow-billed 

cuckoos. It is possible that the proximity of a diverse mosaic of habitat types present 

within the Bill Williams River NWR was a positive factor influencing cuckoos relatively 

high detection rates within some of these sites. Future sampling efforts should consider 

vegetation characteristics within a gradient of low to high cuckoo occupancy; however, 

based on two years of survey results, the habitat at the Bill Williams River NWR is the 

only location within the study area where this kind of effort would be possible. 

Because our data are derived from only two years of study, further research is key 

to determining the degree to which these are general patterns and to capture a potentially 

wider degree of natural variation than we have quantified to date. Ultimately a 

multivariate model would be a useful tool to use in order to determine the factors most 

important in yellow-billed cuckoo habitat selection. Identifying such characteristics is a 

key to effective restoration efforts for yellow-billed cuckoo habitat. 

83
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84
Chapter 5. Microclimate Characteristics 

Large-scale transformation of the riparian ecosystem along the lower Colorado 

River has produced extensive areas that are no longer suitable for breeding yellow-billed 

cuckoos. Because of this, previous surveys (e.g., Corman and Magill 2000, Johnson et al. 

2006b, Johnson et al. 2007) were conducted only in habitat that appeared suitable for 

cuckoos based on the “look see” method described in Chapter 2. Within suitable sites, 

however, occupation likely depends on both the presence of appropriate habitat structure 

and suitable microclimatic conditions. The Lower Colorado River Multi-Species 

Conservation Program calls for the creation of 1639 ha (4,050 acres) of yellow-billed 

cuckoo breeding habitat, including 546 ha (1,350 acres) created specifically for cuckoos 

(Lower Colorado River Multi-Species Conservation Program 2004). 

Characterization of vegetation within currently occupied sites will help guide 

cuckoo habitat restoration and creation. However, cuckoos might select breeding habitat 

or nest sites based on specific microclimatic conditions such as relative humidity 

(Hamilton and Hamilton 1965) or temperature, which along the lower Colorado River 

approach 50°C (122°F), subjecting birds and their nestlings to severe heat loading. There 

could be a range of suitable microclimate conditions that determine where nests will 

likely be constructed. Therefore, we designed a method to characterize the microclimate 

at occupied and unoccupied yellow-billed cuckoo survey sites in five areas that span 

much of the lower Colorado River. Additionally we characterized microclimate at three 

sites within the Bill Williams River NWR, the area with the greatest concentration of 

yellow-billed cuckoos. 

We used microclimate data collected in 2006 to guide our efforts in 2007 to 

further characterize aspects of yellow-billed cuckoo habitat microclimate at the habitat 

patch scale. In 2006 we found that occupied habitats were generally cooler and more 

humid than unoccupied habitats at Grand Canyon NP/Lake Mead NRA and Bill Williams 

River NWR, but at occupied sites in Cibola NWR only mean nocturnal temperate was 

lower than unoccupied sites (Johnson et al. 2007). Cuckoos have been observed using 

fairly large areas compared to typical songbird territories (Laymon 1999, Halterman 

2005, Johnson et al. 2006b, Johnson et al. 2007), so we selected point-based sampling 

measures that characterize riparian habitat at the survey site/patch level rather than at the 

nest or territory scale (i.e., multiple random samples within a site/patch are taken to 

describe the patch/site). We examined microclimate characteristics at the site/patch level 

rather than the nest site in order to provide information relevant to riparian patch 

restoration and not nest placement. We measured mean diurnal and nocturnal temperature 

and relative humidity, in addition to mean soil moisture at sampling locations across all 

study areas. Also, we took vegetation measurements (described in Chapter 4) at 

microclimate sampling locations in order to relate microclimate variables to vegetation 

structure and species composition. 

Methods 

We conducted microclimate analyses to investigate the correlation between 

cuckoo presence and microclimatic conditions and also to characterize the range of 

85
microclimate conditions across the entire study area. Due to logistical considerations, we 

stratified our LCR MSCP survey region from north to south and selected seven areas 

from the total list based on the presence of cuckoos and/or feasibility for the placement of 

microclimate data loggers (Table 5.1). We collected microclimate data at both occupied 

and unoccupied study sites. Sites were initially selected and classified based on 2006 

yellow-billed cuckoo surveys (Johnson et al. 2007). Sites were classified as occupied if 

cuckoos were detected during two or more survey periods in 2006 and unoccupied if one 

or fewer cuckoos were found. Sites with only a single detection were categorized as 

unoccupied because we believe that the cuckoos found at these sites were likely foraging 

away from their breeding sites, or were migrants or “wanderers” that did not breed within 

the detection area. Also, these single detections frequently occurred at sites where the 

habitat did not have the general characteristics considered important for breeding 

cuckoos. 

Loggers were placed in the field in early June and were removed in late 

September. Each logger was programmed to record an event (T/RH reading) every 15 

minutes for 80 days. Most data loggers were placed within the Grand Canyon NP/Lake 

Mead NRA and Bill Williams River NWR, with fewer at Havasu NWR, Cibola NWR, 

and the Yuma Restoration Sites (Table 5.1). At both occupied and unoccupied sites, data 

loggers (n = 95) were typically placed in mixed native-exotic habitat or exotic habitat 

within the riparian floodplain. Aerial photographs for each study site were used to 

identify habitat boundaries, and data logger locations were assigned to random UTM 

coordinates. These coordinates were located in the field with GPS, and a logger within a 

protective housing was then deployed within vegetation at 2-m high. In cases where 

random UTM locations were inaccessible or located in inappropriate habitat such as 

marsh, an alternate was selected by choosing a random compass bearing and a random 

distance to a new location. If the random distance could not be reached, the data logger 

was deployed at the first suitable patch of vegetation along that compass bearing. 

Temperature and Relative Humidity 

Temperature (T) and relative humidity (RH) were both recorded with HOBO Pro 

RH/Temp data loggers (Onset Computer Corporation, Pocasset, MA). HOBO loggers can 

be programmed to collect T (–30°C to 50°C; accurate to ± 0.2° C at 21° C; -22°F to 

122°F) and RH (0–100 percent, accurate to ± 3 percent) data at specified intervals. To 

protect each data logger from direct solar radiation, HOBOs were deployed in the field 

using a cost-effective method developed by McLeod et al. (2005). Each logger, operating 

under identical field conditions, was housed in a small, inverted plastic container with a 

sheet of shade cloth covering the top. The open bottom of the bowl was also covered with 

shade cloth to ensure that the HOBO was sampling free-flowing air, and thus could 

accurately measure T/RH. To ensure accuracy, we compared readings from HOBOs 

within our housings to those from the data loggers housed within Onset’s Solar Radiation 

Shields; we found almost no detectable difference between data loggers in these two 

housings. Therefore, all data loggers were deployed within our homemade housings. At 

each data logger we measured (1) mean diurnal and nocturnal temperatures: we used 

local sunrise and sunset times to delineate cutoff times between night and day and (2) 

mean diurnal and nocturnal relative humidity over 80 days from mid-June to early 

September. We used the canopy cover data collected at each data logger location to in an 

effort to investigate possible influence on microclimate conditions. 

86
Table 5.1. Microclimate study areas within the lower Colorado River, Multi-Species 

Conservation boundary area and adjacent locations, 2007. Sites with an asterisk (*) 

indicate sites that were analyzed as “Yuma Restoration Sites.” The table indicates the 

number of data loggers (HOBO) and soil moisture arrays that were placed within each 

study area in both occupied and unoccupied habitat. 

Study Areas Occupied sites 

HOBO / Soil Moisture 

Unoccupied sites: 

HOBO / Soil Moisture 

Pahranagat NWR 0 0 

Overton WMA 0 0 

Grand Canyon NP/Lake Mead NRA 0 24 / 25 

Havasu NWR 5 / 2 5 / 8 

Bill Williams River NWR 33 / 31 0 

CRIT Reservation 0 0 

Cibola NWR 5 / 5 10 / 10 

Picacho SRA 0 0 

Imperial NWR* 5 / 5 0 

Pratt Restoration* 0 5 / 5 

Yuma West Wetlands* 0 3 / 3 

Limitrophe 0 0 

Gila/Colorado Rivers Confluence 0 0 

Quigley Pond* 0 / 6 0 

Total 48 / 50 47 /51 

Soil Moisture 

We used an ML2x ThetaProbe with a type HH2 ThetaMeter type (Delta-T 

Devices Ltd., Cambridge, UK) to measure soil percent volumetric content to an accuracy 

of ± 1 percent once every survey period. Soil moisture sampling locations were centered 

at cuckoo nests and data logger locations (Table 5.1). At each sampling location we 

measured soil moisture directly under the data logger or nest and also took measurements 

at 1 m, 2 m, and 3 m (3.3 ft, 6.6 ft, and 9.9 ft) in the four cardinal directions from the 

center point. We calculated a mean value for each cluster of 13 measurements averaged 

across the four survey periods. In some cases we were not able to collect all 13 

measurements during each survey period due to dense vegetation or hard soil and based 

the mean value on fewer values. Soil type on the ThetaMeter was set to mineral soil, and 

measurements were taken at a depth of 60 mm (2.4 inches). McLeod et al. (2005) noted 

that for very high or very low voltage readings, the ThetaMeter reports volumetric soil 

moisture as above or below the table, respectively. To eliminate these qualitative 

readings, we recorded soil moisture in terms of voltage (mV), and later converted these 

values to percent soil moisture. 

87
Results 

During the 2007 breeding season we deployed 95 data loggers to sample the mean 

diurnal and nocturnal temperature and relative humidity across the entire study area. 

Microclimate was sampled from 19 June to 6 September, when data loggers were 

simultaneously collecting information for all deployed loggers. We compared the diurnal 

and nocturnal mean temperature and relative humidity by occupancy status (occupied 

versus unoccupied), among the Geographic Study Areas, and among three sites within the 

Bill Williams River NWR. 

Temperature and Relative Humidity by Yellow-billed Cuckoo Occupancy Status 

We collected information from 48 data loggers in occupied sites and 47 in 

unoccupied sites. We found that unoccupied sites were significantly warmer than 

occupied sites during the day (t93 = -4.0; p<0.0001; Fig. 5.1) but not at night (t93 = - 0.9; p 

= 0.37; Fig. 5.1). Diurnal temperatures in unoccupied sites averaged 2.5oC (4.5oF) higher 

than occupied sites. Relative humidity values in occupied sites during both diurnal (t93 = 

4.4; p<0.0001; Fig. 5.1) and nocturnal (t93 = 5.3; p<0.0001; Fig. 5.1) periods was 

approximately 10 percent higher than unoccupied sites. Consistent difference in relative 

humidity between occupied and unoccupied sites could indicate a more favorable 

microclimate regime in the occupied sites. Comparison of microclimate variables 

between occupied and unoccupied sites are confounded by geography because 67 percent 

of data loggers in occupied sites were from the Bill Williams River NWR and 50 percent 

of data loggers in unoccupied sites were from the Grand Canyon NP/Lake Mead NRA 

study area. 

Microclimate Variable

Diurnal Temp Nocturnal Temp Diurnal RH Nocturnal RH

Temperature (o C)

0

10

20

30

40

50

60

70

Relative Humidity (%)

0

10

20

30

40

50

60

70

Occupied 

Unoccupied 

Figure 5.1. Mean diurnal and nocturnal temperature and relative humidity of areas 

occupied by yellow-billed cuckoos and areas unoccupied within the LCR MSCP boundary 

area, 2007. Error bars represent one standard error of the mean. 

88
Temperature and Relative Humidity by Geographic Area 

We found differences in the microclimate characteristics among the different 

Geographic Study Areas. However, the distribution of data loggers across the different 

areas was not uniform (Table 5.1). The number of data loggers at each study area roughly 

corresponded to the size of the area. For example, Bill Williams River NWR is 

approximately 2,500 ha (6175 acres) and so we placed more data loggers there compared 

to Pratt Restoration Site (6 ha; 14.8 acres) within the Yuma Restoration Sites. We 

recorded the lowest daytime temperatures at the Bill Williams River NWR study area, 

and the mean of 32.9oC (91.2oF) was significantly lower than for the other study areas 

(range: 36.8–38.4oC; F4,90 = 22.1, p<0.0001; Fig. 5.2). Mean nighttime temperatures were 

greatest at Havasu NWR and the Yuma Restoration Sites (F4,90 = 14.9, p<0.0001; Fig. 

5.2), although the magnitude of the difference in nighttime temperatures among study 

areas was not as great as diurnal temperatures. We found that relative humidity was 

highest in the Bill Williams River NWR during both diurnal (F4,90 = 19.2, p<0.0001; Fig. 

5.2) and nocturnal (F4,90 = 23.2, p<0.0001; Fig. 5.2) periods. The diurnal relative humidity 

in the Bill Williams River NWR averaged 48.1 percent, significantly greater than the 

other study areas (which were not significantly different; range: 27.3–33.4 percent). The 

mean nocturnal relative humidity of the Bill Williams NWR (60.3 percent) was 

significantly greater than other study areas and was nearly 20 percent greater than Havasu 

NWR (41.1 percent), the site with the lowest nighttime relative humidity. The mean 

relative humidity at night in other study areas (Cibola NWR, Grand Canyon NP/Lake 

Mead NRA, and Yuma Restoration Areas) were not significantly different from one 

another (range: 48.7–53.8 percent), although they were lower than Bill Williams River 

NWR and greater than Havasu NWR. 

89
Microclimate Variables

Diurnal Temp Nocturnal Temp Diurnal RH Nocturnal RH

Temperature (o C)

0

10

20

30

40

50

60

70

Relative Humidity (%)

0

10

20

30

40

50

60

70

Grand Canyon NP - Lake Mead NRA

Havasu NWR

Bill Willimas NWR

Cibola NWR

Yuma Restoration Sites

Figure 5.2. Mean diurnal and nocturnal temperature and relative humidity among 

yellow-billed cuckoo Geographic Study Areas within the LCR MSCP boundary area, 2007. 

Error bars represent one standard error of the mean. 

Temperature and Relative Humidity at Bill Williams River NWR Study Sites 

We detected yellow-billed cuckoos most frequently at the Bill Williams River 

NWR; therefore to understand the range of microclimate variation suitable for cuckoos, 

we examined the microclimate characteristics within three of the most heavily occupied 

sites within the refuge: Mineral Wash, Big Bend, and Sandy Wash. We analyzed a total 

of 30 data loggers at these three sites; 10 at Mineral Wash, 11 at Big Bend, and 9 at 

Sandy Wash. We found that the diurnal mean temperature was significantly cooler at Big 

Bend (F2,27 = 15.7, p<0.0001; Fig. 5.3), while Mineral Wash was the hottest at nighttime 

(F2,27 = 9.0, p<0.001; Fig. 5.3). However, these within site differences in diurnal and 

nocturnal temperature were smaller than the variation we observed across the Geographic 

Study Areas. Consistent with being the coolest site, Big Bend had the highest diurnal 

relative humidity (F2,27 = 12.7, p<0.0001; Fig. 5.3). The nighttime relative humidity in Big 

Bend and Sandy Wash was greater than Mineral Wash (F2,27 = 7.2, p<0.003; Fig. 5.3). 

90
Microclimate Variables

Diurnal Temp Nocturnal Temp Diurnal RH Nocturnal RH

Temperature (o C)

0

10

20

30

40

50

60

70

Relative Humidity (%)

0

10

20

30

40

50

60

70

Mineral Wash

Big Bend

Sandy Wash

Figure 5.3. Mean diurnal and nocturnal temperature and relative humidity among sites 

within the Bill Williams River NWR, 2007. Error bars represent one standard error of the 

mean. 

Microclimate and Canopy Cover 

We suspected that mean diurnal temperature would be influenced by the amount 

of shading at a site, perhaps best represented by average canopy cover. However, we 

detected no relationship between the mean diurnal temperature and mean canopy cover at 

identical microclimate and vegetation sampling locations across the entire study area (n = 

92; F1,91 = 0.3, r2 = 0.004; p = 0.57; Fig 5.4). When we examined the relationship of 

temperature and canopy cover grouping points according to occupancy status, there was 

no correlation between these variables (occupied: n = 41; F1,45 = 0.2, r2

 = 0.005; p = 0.64; 

unoccupied: n = 45; F1,43 = 1.9, r2 = 0.04; p = 0.18). Among the different Geographic 

Study Areas, there appeared to be an inverse relationship between temperature and 

canopy cover at the Cibola NWR; however, this pattern was not consistent between 

occupied and unoccupied sites and might have been driven by the small number of data 

loggers used at the study area. Additionally there was not a relationship between mean 

soil moisture and mean canopy cover across the entire study area (n = 91; F1,89 = 3.3, r2

 = 

0.04; p = 0.07). It is likely that there are more complex factors involved in determining 

the microclimate regime of riparian habitats along the lower Colorado River. 

91
Mean Canopy Cover

0 20 40 60 80 100

Mean Diurnal Temperature

26

28

30

32

34

36

38

40

42

44

Figure 5.4. Mean diurnal temperature versus mean canopy cover and linear regression 

line for all yellow-billed cuckoo sampled areas within the LCR MSCP boundary area. 

Soil Moisture 

We collected soil moisture data from 101 locations across the entire study area. 

Mean soil moisture was 9 percent. We found no difference in mean soil moisture between 

occupied (n = 50) and unoccupied (n = 51) sites (t99 = -0.2, p = 0.80). While soil moisture 

measurements were not evenly distributed across the study area, we did detect difference 

in soil moisture among the different study areas (F4,96 = 2.5, p = 0.04; Fig. 5.5). For 

example, mean soil moisture at Cibola NWR more than 10-times greater then Havasu 

NWR; all other study areas were statistically equivalent. Within the Bill Williams River 

NWR, soil moisture at Big Bend was nearly 10-times greater than Sandy Wash (F2,26 = 

6.2, p = 0.006; Fig. 5.6), but Mineral Wash was not significantly different from either 

site. 

92
Geographic Study Area

Grand Canyon NP - Lake Mead NRA

Havasu NWR

Bill Williams River NWR

Cibola NWR

Yuma Restoration Sites

Soil Moisture (%)

0

2

4

6

8

10

12

14

16

18

Figure 5.5. Mean soil moisture among yellow-billed cuckoo Geographic Study Areas 

within the LCR MSCP boundary area, 2007. Error bars represent one standard error of the 

mean. 

93
Bill Williams River NWR Sites

Mineral Wash Big Bend Sandy Wash

Soil Moisture (%)

0

5

10

15

20

25

Figure 5.6. Mean soil moisture among sites within the Bill Williams River NWR, 2007. 

Error bars represent one standard error of the mean. 

Discussion 

We were able to detect some differences in microclimate conditions based on 

occupancy status, study area, and comparisons of sites within one study area. However, 

the mechanisms explaining the differences in microclimate regimes remain unclear. 

Factors such as nest predation and food limitation undoubtedly affect nest site selection 

(Martin 1995). The non-random distribution of nests in dense vegetation highlights the 

possible importance of microclimate, as nest placement will determine the extent of 

protection from wind and excess diurnal heat gain from solar radiation (Walsberg 1985, 

Gloutney and Clark 1997). Hamilton and Hamilton (1965) suggested that yellow-billed 

cuckoo nests in the Southwest are restricted to river bottoms because these areas are 

humid. Walsberg (1985) also noted that egg dehydration is sensitive to the microclimate 

to which the egg is exposed, and is primarily determined by nest humidity. Ultimately, 

factors such as predation, foraging sites, and favorable microclimate are not mutually 

exclusive and might interact in the selection of nest sites (Holway 1991). 

In 2007, occupied sites were consistently cooler during the day and more humid 

during all other times of the day and night compared to unoccupied sites across the entire 

study area. It appears that these findings are consistent with other studies indicating 

suitable cuckoo breeding habitat having a more benign microclimate regime compared to 

other habitats (Hamilton and Hamilton 1965, Walsberg 1985). However, the cooler and 

more humid conditions of occupied sites did not correspond with greater soil moisture; 

there was no difference in soil moisture between occupied and unoccupied habitats. 

Occupied sites in 2007 were primarily represented by the microclimate characteristics of 

the Bill Williams River NWR in terms of temperature and relative humidity because 67 

percent of data loggers were located there. 

The cooler and more humid microclimate conditions characteristic of occupied 

sites were also prevalent at the Bill Williams River NWR compared to other study areas. 

However, it is unclear whether these microclimate conditions at the Bill Williams River 

94
NWR were the driving force resulting in the majority of yellow-billed cuckoo detections 

occurring here. Even within the Bill Williams NWR, there were differences in the 

microclimate of the most densely occupied sites, but these differences were small 

compared to those observed across different study areas. Because the Bill Williams River 

NWR is so heavily populated with cuckoos, it is possible that the range of microclimate 

measured at sites in the Bill Williams NWR represent a range of suitable microclimate 

conditions for breeding activities. Diurnal temperatures at sites in Bill Williams River 

NWR averaged 31.6–33.6oC (88.9–92.5oF) and minimum relative humidity was 45 

percent and 56 percent for diurnal and nocturnal periods respectively. However, diurnal 

temperatures in occupied habitats at Havasu NWR, Cibola NWR, and the Yuma 

Restoration Sites ranged from 37–42oC (98.6–107.6oF), and minimum diurnal humidity 

in these sites ranges from 25–38 percent, suggesting that cuckoos are able to tolerate 

microclimate regimes less favorable than those found at the Bill Williams River NWR. 

While there was substantial variation in soil moisture of locations at both the site 

and study area scale, there was no apparent relationship of soil moisture with cuckoo 

occupancy. All sites within the Bill Williams River NWR had numerous cuckoo 

detections but soil moisture varied by almost 10-fold. Likewise, sites at both Cibola 

NWR and Havasu NWR were occupied but there was a 10-fold difference in the mean 

soil moisture between these areas. These preliminary results are based on just one year of 

data, and further research would be valuable in more fully characterizing the suitable 

microclimate conditions for yellow-billed cuckoos 

We also expected that microclimate conditions are in part driven by the vegetation 

composition and characteristics of the habitat patch. However, we did not find a 

relationship between mean canopy cover and mean diurnal temperature or mean soil 

moisture. There was also no relationship of these factors when comparing occupancy 

status, Geographic Study Area, or sites differences within the Bill Williams River NWR. 

It is likely that more complicated factors are involved in determining the microclimate 

regime of a patch including canopy height and complexity, dominant tree species, 

proximity to water, the nature of surrounding habitat, or many other variables. While 

yellow-billed cuckoos could respond to microclimate conditions in regards to nest 

placement, their decision to use one habitat and not another, or to focus their activities in 

one part of a habitat might be determined by coarser climatic conditions, broad vegetation 

characteristics, or the suitability of food resources. Any comparison of microclimate 

patterns between 2006 and 2007 will be limited based on the sparse data collected in 

2006; however, further investigation in all of these factors is warranted in order to 

understand yellow-billed cuckoo habitat requirements and thus could be important in 

managing for riparian restoration goals. 

95
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96
Chapter 6. Management and Research 

Considerations 

Yellow-billed Cuckoo Presence/Absence Surveys 

The Lower Colorado River Multi-Species Conservation Plan of 2004 calls for 

surveys to identify areas that cuckoos use and to collect information necessary to better 

define the species’ habitat requirements. This information will then be used to design and 

maintain riparian habitat suitable for yellow-billed cuckoos in the LCR MSCP planning 

area, which should help reduce the likelihood of future federal listing of this species. In 

order to have high confidence in the surveys and the resultant data, we recommend that 

four cuckoo surveys be conducted each year at all sites with suitable habitat within the 

MSCP boundary area. We also recommend evaluating habitat within the lower Colorado 

River watershed and expanding cuckoo surveys to areas where adequate cuckoo habitat 

may come available. The areas we recommend evaluating each year include sites along 

the Gila River in Arizona, and the Virgin and Muddy Rivers in Southern Nevada and 

southern Utah. 

Evaluation of Survey Protocol for Yellow-Billed Cuckoos 

One of the most important factors affecting the accuracy and precision of any 

survey method is detection probability (Pdetect; the probability that an observer will record 

a bird that is present during a survey; Pendleton 1995). To effectively determine an index 

of population size, detection probability should be both robust (high detection 

probability) and precise (low temporal variation in detection probability) (Johnson 1995). 

The tape broadcast survey technique has proven advantageous in eliciting 

responses from many bird species, especially those that are secretive or nocturnal. It often 

increases the total number of birds seen or heard for a given species in comparison to a 

conventional census (Johnson et al. 1981), especially for species with low song activity 

(Robbins 1978). Broadcast also has been helpful in estimating population size and 

investigating avian social behavior and territoriality. Broadcast surveys have been used 

primarily during the breeding season to study the presence and distribution of many 

species (Glahn 1974, Griese et al. 1980, Sogge et al. 1997), but also have been employed 

on wintering grounds (Koronkiewicz et al. 2006). 

The use of broadcast recordings in surveys of western yellow-billed cuckoos has 

increased the number of detections of this elusive and easily overlooked species 

(Hamilton and Hamilton 1965, Halterman et al. 2007). Studies, mostly of eastern yellowbilled cuckoos (Coccyzus americanus americanus), have found that calls are most 

frequent during pair formation and nest building; calls continue through nesting, and then 

become infrequent after the last young fledge (Hughes 1999). Unfortunately, little is 

known about whether cuckoos call more frequently when paired or unpaired, or if they 

call more frequently when solitary versus when they occur in higher densities. This lack 

of information complicates the interpretation of survey results. 

As with any field survey protocol, there is no way to be absolutely certain that an 

area with no detections is unoccupied. This might be especially true for yellow-billed 

97
cuckoos, which have a fairly low response rate; the standard survey method of using 

broadcast recordings might fail to detect all birds present in an area. In fact, it has been 

observed that some individuals known to be present in the area sometimes do not respond 

to broadcasted recordings (Halterman 2005, Johnson et al. 2006b, Johnson et al. 2007; 

and Holmes et al. in review). The extent to which call-broadcast surveys increase 

detection probability in comparison with passive surveys is currently not known for 

yellow-billed cuckoos. Likewise, whether broadcast surveys decrease temporal variation 

in detection probability is also not known. 

Therefore, in order to evaluate the effectiveness of the current yellow-billed 

cuckoo survey protocol, we recommend estimating detection probability and variance in 

detection probability associated with auditory and broadcast surveys, and using these 

estimates to evaluate the efficacy of broadcast surveys of yellow-billed cuckoos. 

Evaluating Survey Protocol 

In order to conduct this survey evaluation, we recommend surveying for cuckoos 

within the Bill Williams River NWR beginning in mid-June and continuing through lateAugust (the breeding season for most yellow-billed cuckoos; Halterman et al. 2007). We 

recommend conducting replicate surveys (1 every 3 weeks) along three survey routes in 

the Bill Williams River NWR. The design of this study has been used with other species, 

such as buff-breasted flycatchers (Empidonax fulvifrons; Conway and Kirkpatrick 2001), 

burrowing owls (Athene cunicularia; Conway and Simon 2003) and band-tailed pigeons 

(Patagioenas fasciata; Kirkpatrick et al. 2007). Therefore, we recommend adapting study 

designs for each of these studies to yellow-billed cuckoos. 

In order to evaluate the effectiveness of broadcast surveys relative to auditory 

(i.e., listening only) surveys, we recommend conducting a 5-minute auditory survey for 

each survey point followed immediately by a 5-minute call-broadcast survey (10 minutes 

total at each survey point). This paired survey design will increase the power of statistical 

tests and increase the ability to detect differences between the two survey methods. 

During the paired auditory and broadcast survey at each survey point, record each 

yellow-billed cuckoo detected on a separate line of a data sheet and record the type 

number of detection(s): visually flying, visual perched, kowlp call, coo-call, or kuk, kuk, 

kuk call during discrete time intervals within the 10-minute survey period. Divide the 5-

minute auditory survey into five 1-minute intervals and the 5-minute call-broadcast 

survey into five 1-minute intervals (a 15–20-sec broadcast interval followed by a 60-sec 

silent interval with this pattern repeated 5 times). Estimating the distance (m) to each 

cuckoo and record whether each cuckoo was a repeat detection (i.e., a cuckoo that was 

also detected earlier during the survey at a previous survey point) will eliminate repeat 

detections from the analyses. 

Estimating Detection Probability 

The probability of detecting birds auditorily during surveys (Pdetect) is the product 

of two components: (1) the probability that a bird within the survey area sings (Psings); and 

(2) the probability that a bird is heard given that it sings (Pheard). Estimating Psings and Pheard

for both auditory and call-broadcast surveys should use the following methods. For each 

cuckoo that is detected during surveys, create a detection history by recording when the 

cuckoo first vocalized during the discrete time intervals in the auditory survey period and 

98
in the call-broadcast survey period. Use these detection histories to estimate Psings

(Farnsworth et al. 2002). 

We also recommend conducting a 10 double-observer trials in which pairs of 

observers independently record cuckoos during auditory and call-broadcast surveys along 

survey routes. The data from these double-observer trials (using only those surveys where 

1 cuckoo was detected by at least one observer) can be used to estimate Pheard (Nichols 

et al. 2000, Conway and Simon 2003). 

Habitat Vegetation Characteristics 

Our study of vegetation characteristics within the LCR MSCP boundary in 2007 

indicated that occupied cuckoo habitat consists of riparian habitats with a tall, dense 

overstory dominated by native cottonwoods and willow, a subcanopy with both willow 

and tamarisk components, and a sparse understory. Although unoccupied habitats also 

were dominated by a cottonwood-willow overstory, the subcanopy and understory were 

consistently dominated by dense tamarisk. However, in some cases, cuckoos did use 

habitats with tamarisk-dominated subcanopies. While we detected general patterns of 

occupied cuckoo habitat, occupied and unoccupied habitats were not evenly distributed 

across the entire LCR MSCP study area and were overrepresented at the Bill Williams 

River NWR and Grand Canyon NP/Lake Mead NRA, respectively. Declining water 

levels in Lake Mead likely resulted in a greater than 3-fold increase in the proportions of 

snags at the Grand Canyon NP/Lake Mead NRA sites between 2006 and 2007. The lack 

of cuckoo detection at the Grand Canyon NP/Lake Mead NRA sites in 2007 might be due 

to the loss of suitable habitat. We are not aware of the long-term occupancy of cuckoos at 

sites within Grand Canyon NP/Lake Mead NRA, but additional monitoring of habitat 

conditions and studying of yellow-billed cuckoo colonization patterns could provide 

information on the suitability of these areas for breeding cuckoos. Because vegetation 

characteristics of occupied habitats was not entirely consistent between 2006 and 2007, 

further research is needed to determine the degree of temporal and spatial consistency 

[variation?] in the vegetation patterns we have observed. Ultimately, a multivariate model 

would be useful in determining the factors most important in yellow-billed cuckoo habitat 

selection. Identification of such factors is a key to effective restoration efforts for yellowbilled cuckoo habitat. 

Microclimate 

Across the entire LCR MSCP study area, soil moisture was not useful in 

predicting yellow-billed cuckoo habitat use. However, yellow-billed cuckoos did use 

habitats that were consistently cooler during the day and more humid at all times 

compared to unoccupied habitats. Although the sites at the Bill Williams River NWR 

generally corresponded to these favorable microclimate conditions, cuckoos used hotter 

and dryer habitats at Havasu NWR, Cibola NWR, and the Yuma Restoration Sites, 

suggesting that cuckoos are able to tolerate a wider range of microclimate regimes than 

would be evident based only on the Bill Williams River NWR. The mechanisms 

explaining the differences in microclimate regimes remain unclear; we did not find a 

relationship between vegetation characteristics and microclimate. While yellow-billed 

cuckoos might respond to microclimate conditions in regards to nest placement, their use 

of one habitat and not another or their focus of activities in one part of a habitat might be 

determined by coarser climatic conditions, broad vegetation characteristics, or the 

99
suitability of food resources. Comparison of microclimate patterns between 2006 and 

2007 were limited based on the sparse data collected in 2006; therefore, further 

investigation of all of these factors will be important in order to understand yellow-billed 

cuckoo habitat requirements and thus what end results might be important to manage for 

in terms of riparian restoration goals. 

Identifying Core Yellow-billed Cuckoo Breeding Habitat 

Within this landscape, the LCR MSCP calls for the Bureau of Reclamation to 

restore 5,940 acres of cottonwood (Populus spp.) - willow (Salix spp.) habitat, including 

4,050 acres specifically for the yellow-billed cuckoo. Consequently, there is a need to 

identify core breeding habitat areas and their characteristics for use as a basis for future 

habitat expansion through riparian habitat restoration efforts. To define core breeding 

habitat as those areas upon which yellow-billed cuckoos depend for breeding, we define 

core habitat as the highest quality yellow-billed cuckoo habitat available in the region. 

Radio telemetry has been used to determine core use areas of several passerines 

(e.g., Cardinal 2005; Vega Rivera et al. 1999, 2003; Bayne and Hobson 2001). Although 

yellow-billed cuckoo radio telemetry studies have been successful in determining the sex 

of individual birds, and can aid in locating nests and observing breeding behavior 

(Halterman 2005), capturing individual cuckoos is extremely time consuming and 

expensive, even in areas where they occur in relatively high densities (Johnson and 

Holmes pers. comm., Halterman pers. comm.). In addition, because cuckoos move large 

distances during the breeding season, tracking such wide-ranging birds can be extremely 

difficult (Laymon 1998, Hughes 1999, Halterman 2005). 

Given the challenges and relative expense of using radio telemetry to identify core 

breeding habitat, we recommend an alternative approach of using occupancy as a 

surrogate for habitat quality. Habitat quality has been considered to be the ability of the 

environment to provide conditions appropriate for individual and population persistence 

(Hall et al. 1997), and both territory occupancy and density have often been used as a 

measure of habitat quality. Sergio and Newton (2003), in a review of the use of 

occupancy as a measure of territory quality, report that the quality of a territory has been 

mainly measured as: (1) the quality and quantity of its resources (e.g., food or safe nest 

sites), based on knowledge of the species requirements; (2) the duration of its occupation, 

under the assumption or knowledge that territories occupied for longer are more 

profitable; (3) its capability to sustain high levels of survival or reproduction; (4) its date 

of occupation during the seasonal sequence of settlement, assuming that better territories 

are occupied earlier within any given year; and (5) the predictability of breeding success 

in that territory, which might be of value for a settling individual, and which is usually 

measured as the coefficient of variation of reproductive success (Ferrer and Donazar 

1996). 

Sergio and Newton (2003) also found, in their review of 22 studies of territory 

occupancy in 17 species, that occupancy was always correlated with productivity and/or 

with some other measure of territory or habitat quality. They suggest that occupancy 

might be a reliable method of habitat quality assessment, especially for populations in 

which not all territories are always occupied, and for species in which checking 

occupancy is easier than finding nests. Yellow-billed cuckoos are just such a species. 

100
Using Occupancy Patterns to Identify Core Yellow-billed Cuckoo Habitat 

Many species that are rare or difficult to detect are monitored by estimating trends 

in site occupancy as opposed to trends in numbers of animals detected (MacKenzie et al. 

2002). Therefore, site occupancy estimation may be a suitable and very effective 

approach for monitoring yellow-billed cuckoo core habitat use within the Lower 

Colorado River Multi-Species Conservation Program Area. 

Currently, survey sites are classified as either unoccupied (a site with no yellowbilled cuckoo detections), or occupied (a yellow-billed cuckoo had been detected at a site 

during at least two survey periods). These criteria were developed because individual 

cuckoos are known to wander, even within the breeding season, and there are numerous 

examples of cuckoos observed in obvious non-breeding habitat (Johnson et al. 2007). 

Consequently, a single detection of a cuckoo at a site does not indicate settling, pairing, 

or breeding at that location (i.e., occupied), so we classified sites as occupied if cuckoos 

were detected there during two or more survey periods. 

For the purpose of using occupancy to identify core cuckoo breeding habitat, we 

recommend refining the classification of occupied sites based on their duration of 

occupancy, i.e., the number of survey periods (out of four total survey periods) in which 

cuckoos are detected at the site. Using this approach, core breeding sites would be those 

with the longest duration of occupancy throughout the breeding season and over multiple 

years. We also recommend testing whether these sites would also be identified as core 

breeding habitat based on: (1) density of detections; (2) indication of breeding activity 

based on breeding confirmation, nest presence, and behavior; (3) habitat characteristics 

(see Chapter 4; Johnson et al. in prep.); and (4) follow-up survey results (described 

below). 

Methods for Yellow-billed Cuckoo Follow-up Visits 

Compared to the time and monetary expense of telemetry, we believe that a more 

cost-effective method to determine yellow-billed cuckoo habitat use is to conduct followup visits after cuckoos are detected during formal cuckoo surveys. The follow-up visits 

do not follow the formal survey guidelines, but involve thorough walk-through searches 

of the area where cuckoos were detected during the formal survey. During these followup visits, surveyors mainly observe cuckoo behavior and movements and use cuckoo 

song broadcasts sparingly (when cuckoos are not detected). During each of these followup surveys, we recommend estimating numbers of individual cuckoos detected, recording 

UTM coordinates of observed cuckoo locations, recording breeding activity and habitat 

use (i.e., tree species, height cuckoo is observed in the tree), and continually looking for 

nests. After each visit to known cuckoo locations, cuckoo detections should then be 

entered into a database and mapped on aerial photos. Copies of aerial photos should be 

taken into the field during each follow-up visit and updated with all new cuckoo 

detections. The addition of follow-up surveys will improve our ability to determine 

cuckoo habitat use, the number of individuals in the habitat patch, obtain breeding 

observations (e.g., interactions between individuals, copulation, food carry), and record 

additional cuckoo locations within the known patch.

101
Identifying Yellow-billed Cuckoo Habitat Model Variables 

Despite concern over its conservation future (USFWS 2002), few aspects of the 

yellow-billed cuckoo’s life history have been adequately studied, particularly in the 

Southwest, where its habitat selection patterns are largely unknown. Knowledge of 

habitat selection patterns and identification of potential breeding habitat is essential to 

guide conservation efforts (Laymon 1998, Hughes 1999). 

To meet this information need, concomitant with future cuckoo surveys, we 

recommend additional habitat characterization, including measures of plant species 

composition and vegetation structure within riparian patches, riparian patch size, and the 

surrounding landscape matrix, along the lower Colorado River and throughout the 

cuckoo’s western breeding range. These habitat data from multiple spatial scales could be 

used to construct a habitat model to determine associations between riparian habitat 

characteristics and Yellow-billed Cuckoo breeding-season occurrences. This information 

can then be used to construct a predictive model for yellow-billed cuckoo breeding 

season occurrences. This knowledge of habitat selection patterns and identification of 

potential breeding habitat can be used to guide conservation efforts, including 

prioritization of areas for conservation and restoration, identification of areas for future 

surveys, and areas for monitoring changes in habitat distribution and quality over time. 

Additionally, information regarding yellow-billed cuckoo habitat needs can help predict 

the effects of management options such as riparian restoration. 

Currently, two habitat models for yellow-billed cuckoos have been developed, 

both based on habitat measurements taken along the Kern and Sacramento Rivers in 

California. As the riparian vegetation structure and composition along these river 

drainages differ from the lower Colorado River and cuckoo habitat requirements might 

vary geographically, these models should be used with caution in other river drainages. 

The model by Gaines and Laymon (1984) showed that willow-cottonwood habitat of any 

age with high humidity and a habitat width of 325 ft (100 m) was necessary for suitable 

yellow-billed cuckoo habitat. Additional research based on occupancy rates allowed for 

refinement of the model; Laymon and Halterman (1989) and Laymon 1998 concluded 

that sites >80 ha (200 acres) in extent and wider than 600 m (1950 ft) were most optimal 

for yellow-billed cuckoos, sites 41–80 ha (101–200 acres) in extent and wider than 200 m 

(650 ft) were suitable, sites 20–40 ha (50–100 acres) in extent and 100–200 m (325–650 

ft) in width were marginal, and sites <15 ha (38 acres) in extent and <100 m (325 ft) in 

width were unsuitable. 

Additional work by Launer et al. (1990) also recommends that, in relation to 

protection of existing habitat, restoration efforts should be concentrated in areas adjacent 

to existing habitat patches, or in areas of sufficient extent to create comparatively large 

tracts of habitat (a minimum of 100 ha). Again, geographic considerations appear to be 

very important, and Launer et al. (1990) suggest that restoration efforts in the southern 

portion of the cuckoo nesting range should have first priority. 

In addition to affecting vegetation structure and composition, efforts to restore 

native riparian areas along the lower Colorado River also might influence another habitat 

component - avian food resources. Many bird species that breed in riparian habitats are 

insectivorous and the lush vegetation associated with riparian zones provides abundant 

arthropod food resources, especially when compared to surrounding upland habitats 

(Strong and Bock 1990). A particular food resource, the Apache cicada (Deceroprocta 

apache), has been suggested as a keystone species in the lower Colorado riverine 

102
ecosystem through their herbivory (Karban 1980, Anderson 1987, Anderson 1994) and 

their importance as a prey species for birds and mammals, especially during the breeding 

season (Rosenberg et al. 1982, Krohne et al. 1991). 

In the Southwest, yellow-billed cuckoo habitat use appears to be linked to cicadas. 

In cottonwood-willow habitat in the Colorado River Valley, Rosenberg et al. (1982) 

found cuckoos concentrated on cicadas, a superabundant, seasonally predictable resource 

(Strong and Bock 1990). The relatively late nesting period of the western population of 

cuckoo is thought to be an adaptation to the typical timing of cicada emergence 

(Rosenberg et al. 1982). In New Mexico, cuckoo nesting coincides with peak cicada 

(Tibicen dealbatus) emergence in unburned plots along the Rio Grande (Howe 1986). 

Emergence of cicadas prior to the cuckoo breeding season could be detrimental to the 

cuckoo’s nesting success (Andersen 1994). There is evidence in New Mexico (Smith et 

al. 2005) that cottonwood density and cottonwood canopy cover are important factors in 

cicada (T. dealbatus) emergence density and phenology; age and health of a cottonwood 

stand have a smaller effect on emergence density. Cottonwood canopy was correlated 

with lower soil temperatures, which are associated with later emergence dates (Smith et 

al. 2005). These findings suggest that the recovery and sustainability of yellow-billed 

cuckoo populations in the Southwest might depend on sustaining cicada populations. 

Riparian restoration that is designed to provide conditions that promote cicada emergence 

in densities and at times that provide the greatest benefits to cuckoos may prove to 

especially effective in managing for the cuckoo. Studies are needed to understand the 

relationships between vegetation associations and cicadas, the effects of vegetation 

structure and climate on cicada emergence density and phenology in riparian habitats 

along the lower Colorado River. 

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104
Chapter 7. 2006-2007 LCR MSCP Yellow-billed 

Cuckoo Research Summary 

This chapter summarizes the two years of yellow-billed cuckoo research 

conducted by the U.S. Geological Survey for the Lower Colorado River Multi-Species 

Conservation Plan (LCR MSCP). The LCR MSCP of 2004 calls for the identification of 

areas used by yellow-billed cuckoos through surveys and the collection of information 

necessary to better define the species’ habitat requirements. This information will then be 

used to design and maintain riparian habitat suitable for yellow-billed cuckoos in the 

LCR MSCP planning area, which should help reduce the likelihood of future federal 

listing of this species. We conducted research on the distribution, abundance, and habitat 

use of yellow-billed cuckoos within the boundaries of the LCR MSCP in 2006 and 2007. 

The objectives of this project were to document the distribution, abundance, and 

habitat use of yellow-billed cuckoos in riparian areas of the lower Colorado River, and to 

provide information relevant to the Habitat Conservation Plan measures. Yellow-billed 

cuckoo surveys provide information on their status and distribution, and establish 

baseline data that can be used for continued monitoring of cuckoo populations and 

riparian vegetation under the MSCP. There are four specific project objectives. 

1. Conduct comprehensive, repeatable surveys in all potentially suitable habitat types 

within the MSCP project boundary. This work contributes to baseline information on 

yellow-billed cuckoo populations within these areas. All other avian species 

encountered within riparian habitats are also recorded. 

2. Evaluate the effectiveness of the current yellow-billed cuckoo breeding season survey 

protocol (Halterman et al. 2006) and refine it to use over the term of the MultiSpecies Conservation Plan. 

3. Determine breeding habitat selection and preferences in the areas of concern. This 

includes identifying the characteristics of habitats used during the breeding season, 

and comparing characteristics between occupied and unoccupied sites to identify 

factors that may influence habitat selection by cuckoos. 

4. Identify core yellow-billed cuckoo breeding habitat to use as a basis for future habitat 

expansion through restoration efforts. 

This chapter presents year-by-year summaries of our cuckoo breeding surveys, 

evaluation of the cuckoo survey methodology, habitat vegetation characteristics, 

microclimate analysis, and detection of other riparian bird species. Unless stated 

otherwise, all 2006 data are from Johnson et al. (2007). 

Yellow-Billed Cuckoo Presence/Absence Surveys 

Yellow-billed cuckoos have historically been considered a common breeding 

species within extensive riparian forests throughout the lower Colorado River Basin 

(Swarth 1905, Visher 1910, Phillips et al. 1964). In 1976, the estimated number of 

breeding cuckoo pairs along the lower Colorado River and its five tributaries was 846 

(Groschupf 1987). Later studies found a 93 percent decline along the lower Colorado 

105
River between 1976 and 1986 and an estimated 71 to 75 percent decline on the Bill 

Williams River delta during the same period (Rosenburg et al. 1991). 

We conducted our yellow-billed cuckoo presence/absence surveys in 2006 and 

2007 at most areas that were historically surveyed throughout the lower Colorado River 

Basin. The exact number of cuckoos present at our survey sites is not known since there 

was no way to tell whether detections on separate surveys represented the same or 

different individuals. Thus, the detections should not be interpreted as a count of the 

number of cuckoos present or as the number of birds breeding at a site. 

During formal cuckoo surveys, we documented 180 and 163 cuckoo detections in 

2006 and 2007, respectively. In 2006, we conducted 243 surveys that covered 521 hours 

at 55 sites. In 2007 we conducted only 169 surveys that covered 312 hours at 40 sites. 

The difference in survey effort between the two years was made up by supplemental 

(follow-up) surveys in 2007. During these supplemental surveys we focused on areas 

where cuckoos were detected during formal surveys and at sites with the highest 

likelihood for cuckoo presence and breeding activity. We conducted 93 follow-up 

surveys, mostly at the Bill Williams River NWR, that covered 204 hours and accounted 

for 253 additional yellow-billed cuckoo detections. Also likely due to the supplemental 

survey effort, we detected 27 breeding events at seven sites in 2007 compared to only 

five breeding events at three sites in 2006. While many of the 253 cuckoo detections on 

supplemental surveys were likely from the same individuals,we were able to obtain finer 

details of cuckoos behavior and habitat use from these observations (Appendix 2), 

therefore we consider these follow up visits invaluable in studying the biology of the 

yellow-billed cuckoo. 

The Bill Williams River NWR accounted for the majority of cuckoo detections 

during both years; 68 percent and 85 percent in 2006 and 2007, respectively. This area 

represents the largest stand and highest quality of suitable yellow-billed cuckoo habitat 

on the lower Colorado River (Figure 7.1). 

 Bill Williams River NWR, Honeycomb Bend Bill Williams River NWR, Mosquito Flats 

Figure 7.1. Lower Colorado River-Multi-Species Conservation Program, Yellow-billed 

cuckoo survey sites along the Bill Williams River NWR, AZ, 2007.

106
Because of differences in survey methods, specific areas surveyed, and probable 

differences in the criteria used to estimate the number of individuals, it is difficult to 

make direct comparisons between our results and estimates of cuckoo numbers from 

previous studies. However, we can compare the occupancy of yellow-billed cuckoos 

between our 2006 and 2007 surveys. In doing so it is important to keep in mind that some 

survey sites change as new habitat became suitable or old habitat unsuitable, and the 

boundaries of some survey sites were changed for logistical reasons. At Pahranagat 

National Wildlife Refuge, Overton Wildlife Management Area, Havasu National Wildlife 

Refuge, Cibola National Wildlife Refuge and among the Yuma, AZ sites (Colorado/Gila 

Confluence, Pratt Restoration Site, Yuma Wetlands, Limitrophe Division, and Quigley 

Pond Wildlife Management Area) we observed high variation between years (Table 7.1) 

in the number of cuckoos detected, sites occupied, and the number breeding 

confirmations. Grand Canyon NP/Lake Mead NRA showed the greatest differences 

between years. In 2006, we had 29 detections in three occupied sites (Chuckwalla Cove, 

Iceberg Ridge and Cuckoo Beach) and confirmed breeding at Chuckwalla Cove, in 2007, 

we had zero yellow-billed cuckoo detections presumably due to the drought conditions as 

detailed below. At Bill Williams River National Wildlife Refuge, we consistently 

detected cuckoo during both years. In 2006, we had eight occupied sites and confirmed 

breeding at two sites; in 2007, we had ten occupied sites with confirmed breeding at 

seven (Table 7.1). At Imperial National Wildlife Refuge we also consistently detected 

cuckoos at Imperial South restoration site, which was an occupied site in both 2006 and 

2007, yet breeding was not confirmed for either year. 

Table 7.1. Summary of yellow-billed cuckoo detections, number of occupied sites and 

number of breeding cuckoos in 2006 and 2007 at all areas and sites along the Muddy, 

Virgin and White Rivers in Nevada and the Colorado, Bill Williams, and Gila Rivers in 

Arizona and California. 

YBCU Detections # of YBCU 

Occupied Sites 

# YBCU Breeding 

Survey Area Detections 

2006 2007 2006 2007 2006 2007 

Pahranagat NWR 1 0 0 0 0 0 

Overton WMA 7 0 2 0 0 0 

Grand Canyon NP/Lake Mead NRA 29 0 3 0 1 0 

Havasu NWR 1 3 0 1 0 0 

Bill Williams River NWR 117 139 8 2 10 7 

Ahakhav Tribal Preserve - CRIT NA 2 NA 0 0 0 

Cibola NWR 3 7 1 1 0 0 

Picacho State Recreation Area 1 0 0 0 0 0 

Imperial NWR 3 3 1 1 0 0 

Pratt Restoration Area 0 0 0 0 0 0 

Gila–Colorado River Confluence 9 2 1 0 0 0 

Yuma West Wetlands 0 0 0 0 0 0 

Limitrophe Division 6 2 1 0 0 0 

Quigley Pond WMA 1 5 1 0 0 0 

107
So overall, with the exception of Bill Williams River NWR, there was a high 

degree of annual variation in site and yearly cuckoo detections, occupancy patterns and 

breeding conformations at all sites surveyed in 2006 and 2007. As habitat becomes more 

or less suitable, cuckoos likely respond by occupying those habitats that are most suitable 

for their breeding needs in any given year. Thus this annual variation in cuckoo 

distribution, abundance, and habitat use may be the norm for much of the lower Colorado 

River. 

Variation in Yellow-billed Cuckoo Detections, Occupied 

Sites and Habitat 

During the two years of this study we observed variation in the number of 

cuckoos detected, sites occupied and the quality of habitat they were detected and bred in. 

The changes in the number of cuckoo detections at the Grand Canyon NP/Lake Mead 

NRA area was the most striking difference between the two years. These differences as 

noted above are quite evident, which maybe due to the lake levels of Lake Mead, that 

were approximately 5 m (15 ft) lower in 2007 compared to 2006 

(http://www.usbr.gov/lc/region/g4000/hourly/mead-elv.html) due to long-term drought 

conditions in the Colorado River watershed. The greatest impact to the riparian habitat 

may be due to the declining lake levels ultimately affecting tree mortality (Figure 7.2), 

which was evident in the dramatic increase in the proportion of snags we detected in 

vegetation sampling plots between the two years. 

Iceberg Ridge, Lake Mead NRA, 2006 Iceberg Ridge, Lake Mead NRA, 2007

ey sites along the Colorado River at Lake Mead National Recreation Area, 

Ariz., 2007. 

t of the entire woody vegetation, but accounted 

for only 14 percent in 2006 (Figure 7.3). 

Figure 7.2. Lower Colorado River-Multi-Species Conservation Program, Yellow-billed 

cuckoo surv

In 2007, snags made up 46 percen

108
Year

2006 2007

Mean stem density

0

100

200

300

400

500

600

Shrub 

Tree 

Snag 

Figure 7.3. Lower Colorado River-Multi-Species Conservation Program, vegetation mean 

density for shrubs, trees and snags along the Colorado River, Lake Mead National 

Recreation Area, AZ, 2007.

These differences in habitat structure were also reflected when we examined 

microclimate characteristics at Grand Canyon NP/Lake Mead NRA between 2006 and 

2007. We found that mean diurnal temperatures were nearly 17 percent greater in 2007 

compared to 2006 (U6, 24 = - 2.4, p = 0.02) while diurnal relative humidity was 10 percent 

greater in 2006 than 2007 (U6, 24 = 1.9, p = 0.05; Figure 7.3). Likewise, nocturnal 

temperature was nearly 13 percent greater in 2007 compared to 2006 (U6, 24 = - 3.1, p = 

0.002), but there was not a significant difference in nocturnal relative humidity between 

the two years (U6, 24 = 0.7, p = 0.48). 

109
Microclimate Variables

Diurnal Temp Nocturnal Temp Diurnal RH Nocturnal RH

Temperature (o C)

0

10

20

30

40

50

60

Relative Humidity (%)

0

10

20

30

40

50

60

2006 

2007 

Figure 7.4. Lower Colorado River-Multi-Species Conservation Program, microclimate 

measurements (diurnal temperature, nocturnal temperature, diurnal relative humidity and 

nocturnal relative humidity) along the Colorado River, Lake Mead National Recreation 

Area, AZ.

However, this apparent drought induced stress on the vegetation was not 

evidenced in soil moisture readings. The soil moisture readings at Grand Canyon 

NP/Lake Mead NRA in 2007 (9 percent) where we had no presence of cuckoos was 

identical to values at the Bill Williams River NWR that was densely occupied by yellowbilled cuckoos. Thus, soil moisture may not be useful in predicting patterns of cuckoo 

occupancy. 

We are not aware of the long-term patterns of cuckoo occupancy at sites within 

Grand Canyon NP/Lake Mead NRA. Sites along the lower Colorado River have likely 

historically been exposed to periodic drought and disturbance, and further study of 

yellow-billed cuckoo colonization patterns would be a useful guide for habitat restoration 

efforts in terms of the larger landscape decisions such as selecting the most suitable 

location for long-term cuckoo occupancy. 

Yellow-billed Cuckoo Breeding Verification 

From our results it is obvious that it is challenging to confirm yellow-billed 

cuckoo breeding at a site. Cuckoos are very secretive, difficult to detect, and move over 

large areas (Laymon 1998, Hughes 1999, Halterman 2005, Johnson et al. 2007). 

Verifying that cuckoos are breeding in a particular patch thus requires finding young, a 

nest, or copulating adults; observing these behaviors can sometimes be difficult. This 

reality makes it safe to assume that we did not observe all breeding activities that 

occurred in 2006 or 2007. We know that more nests were present in our study sites than 

just the ones we were able to locate, because we found more fledglings than could be 

accounted for by nearby nests. Given this, the number of breeding activities recorded at a 

site should be interpreted as a minimum of breeding activity that occurred. However, all 

of our documented breeding activities were from the Bill Williams River NWR, 

110
indicating that this site has more and/or better breeding habitat than the other study sites 

on the lower Colorado River with the exception of Chuckwalla Cove in 2006. The 

difficulty of confirming cuckoo breeding highlights the importance of supplemental 

follow-up surveys. Total survey effort in both years was just over 500 hours, but when 

we used supplemental surveys in 2007 we detected 27 breeding events compared to only 

five breeding events in 2006 without the use of supplemental surveys.

Survey Methodology Evaluation 

In both years of this study we evaluated the playback survey methodology, 

refining many of the methodologies in the second year. Notable changes between the two 

years include the adoption of supplemental follow-up surveys in 2007. These 

supplemental surveys were focused in areas where cuckoo presence had been confirmed 

during formal surveys. They are designed to determine the continued presence of cuckoos 

detected during formal surveys, and provide opportunities to observe breeding behavior 

and search for nests. These surveys also better defined yellow-billed cuckoo use of the 

habitat and site. Because of the supplemental survey effort, we did not conduct as many 

protocol surveys in 2007 as we did in 2006; however, the number of sites where we 

detected cuckoos and total number of survey hours remained constant. Thus we were able 

to obtain more detailed information at each occupied cuckoo site and at the same time we 

abandoned survey effort at sites that had no probability of detecting cuckoos. 

The ways by which cuckoos were detected remained fairly constant across the 

two years, with 60 percent of detections made aurally, 10 percent visually, and 25 percent 

both aurally and visually. The number of broadcasts required to elicit a response from a 

yellow-billed cuckoo was variable. The abundance of cuckoos in a survey area may 

influence their response to playback, but response to playback was not consistent 

between the two years. At sites with the most detections, cuckoos were frequently 

detected unsolicited (prior to initial playback) or following the first playback in 2006. In 

2007, most detections at these dense sites occurred following the first or second 

playback, and unsolicited detections were no different than surveys in areas with few 

cuckoo detections. We also found that at sites with fewer than 10 cuckoo detections, 

detections occurred later in the playback sequence (third, forth, and fifth playback) in 

2006 (Johnson et al. 2007); in contrast in 2007 most detections in these areas occurred 

following the initial playback. The inconsistencies in cuckoos response warrants further 

investigation in order to develop the most effective survey protocol to detect yellowbilled cuckoos. Nevertheless since cuckoos continue to be detected after a fifth playback 

and also late in the breeding season, longer survey bouts over more survey periods appear 

to increase cuckoo’s detection probability. 

Habitat Vegetation Characteristics 

Another important change between years was the method used to identify plots to 

characterize vegetation and microclimate of occupied cuckoo habitat. In 2006 we based 

vegetation and microclimate sampling plots on the location of the 2005 and 2006 cuckoo 

detections. Rather than continue to describe the vegetation and microclimate of occupied 

habitats based on a cuckoo detection or a cuckoo nest, in 2007 we randomly placed 

vegetation and microclimate plots within occupied habitats to characterize the riparian 

habitat at the survey site-patch scale. The reason for the change in how vegetation plots 

were located was an issue of scale. Instead of looking the nest site or detection scale we 

111
wanted to examine it at a broader scale such as the patch scale. Any differences between 

the two years of this study should be interpreted in light of these methodological changes. 

In addition, vegetation sampling in 2006 was based on a center plot and three sub-plots, 

while in 2007 we only used a single plot. Differences in sampling methodology between 

the two years may confound some patterns in the characterization of yellow-billed 

cuckoo habitat. 

We found that the dominant riparian tree species across 2006 and 2007 at 

occupied yellow-billed cuckoo survey sites remained cottonwood, willow, and tamarisk. 

In 2006, occupied sites had greater canopy cover driven by denser low and mid-canopies. 

However, we found in 2007 that the differences between occupied and unoccupied 

canopies were due to difference at higher canopy strata. Also in 2007, the canopies at 

both occupied and unoccupied sites were dominated by native species while in 2006 only 

occupied sites were more consistently dominated by native species. In 2006 and 2007, we 

found trees in the large and largest size classes were more numerous in occupied sites, 

and consistent with the dominant canopy layer across all occupancy sites, these trees 

were generally Goodding’s willow. Consistent across both years was also the greater tree 

density in unoccupied sites. The density of woody species was consistently higher at 

unoccupied sites, except for stems in the snag class, which we found in equal numbers in 

the two occupancy statuses. For trees, the greater density in the unoccupied sites was 

driven by trees in the smallest size class, the most abundant size class across the entire 

study area. This could be a possible indication that cuckoos prefer areas with high dense 

canopies for nesting with an open understory for movement and foraging activities. 

Additional research can help determine consistent annual patterns of vegetation 

characteristics in these riparian habitats. 

Generally speaking, the characterization of vegetation patterns among these study 

areas was consistent between the two years of the study. Bill Williams River NWR had a 

greater number of large Goodding’s willow, Grand Canyon NP/Lake Mead NRA was 

dominated by willows and tamarisk in the smallest size class, and the row planting of 

native tree species at Imperial NWR, Cibola NWR, Pratt Restoration, Yuma West 

Wetlands and Quigley Pond WMA distinguished it from other more “natural” riparian 

habitats. 

Microclimate Characteristics 

We were able to measure the microclimate characteristics of riparian habitats 

during the entire yellow-billed cuckoo breeding season (covering 80 days) across a broad 

rage of habitats in 2007 compared to the late deployment (covering only 45 days), uneven 

distribution, and limited sampling size of microclimate analysis in 2006. However, in 

both years occupied habitats were more humid than unoccupied habitats. Although there 

were few temperature differences between occupied and unoccupied habitat in 2006, 

occupied habitats were cooler than unoccupied ones during the day in 2007. In 2006 

occupied habitats had greater soil moisture, but in 2007 the cooler and more humid 

conditions of occupied sites did not correspond with greater soil moisture. While most 

cuckoo detections were at the Bill Williams River NWR and, at least in 2007, cooler and 

more humid conditions were prevalent there. Yellow-billed cuckoos are able to use drier 

and hotter habitats than those at Bill Williams River NWR. Sample size by study area 

was not sufficient in 2006 to be able to draw inferences by study area across the two 

years of the study. Any differences between the two years may have been due to 

112
difference in the timing and placement of HOBO sensors and soil moisture probes in 

2006 and 2007. 

In 2007, we expected that microclimate conditions were in part driven by the 

vegetation composition and characteristics of the habitat patch. However, we did not find 

a relationship between mean canopy cover and mean soil moisture in either year. It is 

likely that more complicated factors are involved in determining the microclimate regime 

of a patch including canopy height and complexity, dominant tree species, proximity to 

water, the nature of surrounding habitat, or many other variables. While yellow-billed 

cuckoos may respond to microclimate conditions in regards to nest placement, their 

decision to use one habitat and not another, or to focus their activities in one part of a 

habitat may be determined by coarser climatic conditions, broad vegetation 

characteristics, or the suitability of food resources. The mechanisms explaining the 

differences in microclimate regimes remain unclear and further investigation in all of 

these factors is necessary in order to understand yellow-billed cuckoo habitat 

requirements and thus may be important in managing for in terms of riparian restoration 

goals. 

Other Riparian Bird Detections 

During the 2006 and 2007 yellow-billed cuckoo field seasons we documented 

other bird species at or near our survey sites. Most species were observed before, during, 

or after our yellow-billed cuckoo surveys. Because the focus of our efforts was on 

detecting cuckoos, we did not attempt to quantify abundance of these additional species, 

nor to track down and verify any species that were not readily identifiable or obvious to 

the surveyors. We documented 190 bird species in 2006 and 160 species in 2007. While a 

decline of 30 species detections may appear substantial, the focus of research over these 

two years was on the yellow-billed cuckoo and the detection of other bird species was 

likely not consistent between the two years because of the time spent detecting non-target 

species. Thus this decline should not be viewed as a real loss of avian diversity. 

Of the 190 total species detected in 2006 and 2007, nine were among the 

designated focal species under the Lower Colorado River Multi-Species Conservation 

Plan for both years. The composition of these nine species varied across our survey areas, 

but many were observed at Bill Williams River NWR. The willow flycatcher (Empidonax 

traillii), Bell’s vireo (Vireo bellii), and yellow warbler (Dendroica petechia) were the 

most widespread species. 

What Have We Learned? 

Over the past two years we have undertaken the complex task of studying yellowbilled cuckoos along the lower Colorado River within the Multi-Species Conservation 

Planning area. This project had many challenges and obstacles, yet we have learned a 

tremendous amount about yellow-billed cuckoo habitat use and behavior. Below we will 

summarize some of the main points of increased understanding. 

Because this study has only been conducted for the last two years, it is 

challenging to elucidate large-scale patterns. But there are some general conclusions we 

can draw from this research, particularly lessons from two important study areas; the Bill 

Williams River NWR and Grand Canyon NP/Lake Mead NRA. The Bill Williams River 

NWR appears to be the most important riparian habitat for yellow-billed cuckoos along 

the lower Colorado River. The majority of cuckoo detections and breeding activity 

113
occurred at this site during both years of the study. The riparian habitat at the Bill 

Williams River NWR appears to be ideal cuckoo habitat, with a tall dense overstory of 

native Goodding’s willow and Fremont cottonwood and a cool, moist microclimate. We 

found that trees in the larger size classes were also more numerous in occupied sites, and 

consistent with the dominant canopy layer across all occupancy sites, these trees were 

generally native. We also learned that greater tree density occurs in unoccupied sites, and 

is driven by trees in the smallest size class. This suggests that cuckoos prefer areas with 

high dense canopies for nesting with a less dense understory for foraging activities. 

The mechanisms explaining the differences in microclimate regimes remain 

unclear in yellow-billed cuckoo use of habitat and/or a site. The cuckoo’s decision to use 

one habitat and not another, or to focus their activities in one part of a habitat may be 

determined by coarser climatic conditions, broad vegetation characteristics, or the 

suitability of food resources. Therefore, further investigation of all of these factors is 

warranted in order to understand yellow-billed cuckoo habitat requirements, which will 

be important for accomplishing riparian restoration goals. Ultimately a multivariate 

model would be a useful tool to use in order to determine the factors most important in 

yellow-billed cuckoo habitat selection. Identifying such characteristics is a key to 

effective restoration efforts for cuckoo habitat. 

We also witnessed at the Grand Canyon NP/Lake Mead NRA site the effects of a 

long-term drought and associated tree mortality, which likely led to decreased live 

vegetation and an increase in the proportion of snags at this study area. We believe this 

led to the absence of cuckoo detections and breeding activity in 2007. This illustrates that 

rapid changes in habitat can have detrimental effect of local cuckoo populations, and 

other occupied sites could face the same fate if they are exposed to the same degree of 

environmental change. It remains to be seen if the riparian habitat at Grand Canyon 

NP/Lake Mead NRA will continue to be unsuitable for yellow-billed cuckoos in the nearterm. It is also unclear whether riparian restoration efforts along the lower Colorado 

River could result in an area rapidly becoming suitable for yellow-billed cuckoo breeding 

activity. Continued cuckoo surveys and monitoring of habitat conditions over the longterm would be essential to determine how natural and managed changes to riparian 

habitat influences yellow-billed cuckoo populations. 

We were also constantly reminded that this species is very secretive and elusive 

and the amount of information one can gather can be limited due to its behavior. 

However, we found that supplementing our formal surveys with supplemental (followup) surveys has helped obtain finer details of cuckoos behavior and habitat use, and 

consider these follow up visits invaluable in studying the biology of the yellow-billed 

cuckoo. 

And finally, we believe that continued monitoring of yellow-billed cuckoo 

population and habitat along the lower Colorado River is necessary to elucidate long-term 

patterns in their distribution, abundance, and habitat use in order best guide efforts to 

restore riparian habitat suitable for cuckoos along the lower Colorado River, and 

ultimately prevent the listing of yellow-billed cuckoos. 

Acknowledgments 

This project was made possible by the support and cooperation of many persons, 

agencies and private companies. Funding was provided by the Bureau of Reclamation in 

Boulder City, Nevada, under the Multi-Species Conservation Plan, and the USGS 

114
Southwest Biological Science Center in Flagstaff, Arizona. In particular, we thank Lorri 

Gray (Bureau of Reclamation) for her support of this project. The coordination and land 

access permission from the Bureau of Land Management and the Arizona Game and Fish 

Department was of particular importance. We also want to thank Greg Clune (Bureau of 

Reclamation) for administrative assistance and assisting the field crew. We would also 

like to thank Hira Walker and Carol Beardmore for their valuable peer review of this 

report. The success of the project is ultimately due to the efforts of the field personnel on 

the 2006 and 2007 USGS field crews: Chris Calvo, Ivan Samuels, Laura Riley, Geoffrey 

Bland, Brent Campos, Shawn Carroll, Julia Fromfeld, Mary Davis, Samantha Dorr, Sarah 

Brown and Ken Etzel. 

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Appendixes 1–6 

The following appendixes provide a summary of Yellow-billed Cuckoo detections, a description of each 

Yellow-billed Cuckoo detection, incidental detections, habitat photos, and a list of other bird species 

observed during surveys. 

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Appendix 1. Summary of Yellow-billed Cuckoo 

Detections by Survey Period, 2007 

Table 1–1. A summary of yellow-billed cuckoo detections by survey period in 2007 at all 

areas and sites along the Muddy and White rivers in Nevada and the Colorado, Bill 

Williams, and Gila Rivers in Arizona and California. Detections made on supplemental 

visits are displayed in parenthesis. 

Survey site name Survey 1 Survey 2 Survey 3 Survey 4 Survey 5 

Pahranagat NWR 

Pahranagat North 0 0 0 0 N/A 

Pahranagat South 0 0 0 0 N/A 

Total 0 0 0 0 

Overton WMA 

Honeybee Pond 0 0 0 0 N/A 

Overton Wildlife 0 0 0 0 N/A 

Total 0 0 0 0 

Grand Canyon NP/ Lake Mead NRA 

RM 274.5 0 0 0 0 N/A 

Cuckoo Beach 0 0 0 0 N/A 

Iceberg Ridge 0 0 0 0 N/A 

Chuckwalla Cove 0 0 0 0 N/A 

Big Horn Draw 0 0 0 0 N/A 

Total 0 0 0 0 

Havasu NWR 

Pintail Slough 0 1 0 0 N/A 

North Dike 0 1(2) 0 0 N/A 

Topock Marsh Restoration 1 0 0(7) 0 N/A 

Topock Tamarisk 0 0 0 0 N/A 

Total 1 2(2) 0(7) 0 

Bill Williams River NWR 

Teepee Trail 0 0 1 0 N/A 

Cottonwood Patch 3(4) 3(8) 2(1) 0 0 

Cave Wash 2(3) 3(33) 3(8) 3 0 

Honeycomb Bend 5(9) 3(6) 2(5) 1(4) 0 

Mineral Wash 13(11) 7 5(11) 2(1) 0 

Big Bend 4(7) 7(14) 2(5) 6(16) 1(1) 

Gibraltar Rock 4(11) 4(19) 0(2) 1 0 

Sandy Wash 0(1) 3(11) 6(18) 3(6) 2 

Fox Wash 0 1 1(1) 0 N/A 

Mosquito Flats 0 3 6(12) 4 2 

Saguaro Slot 0(1) 2(3) 4 2(8) 0 

North Burn 0 1 2 2 0 

127
Table 1–1. A summary of yellow-billed cuckoo detections by survey period in 2007 at all 

areas and sites along the Muddy and White rivers in Nevada and the Colorado, Bill 

Williams, and Gila Rivers in Arizona and California. Detections made on supplemental 

visits are displayed in parenthesis.—Continued 

Survey site name Survey 1 Survey 2 Survey 3 Survey 4 Survey 5 

Bill Williams River Marsh 1 0 4 3(3) 0 

Total 32(47) 37(94) 38(63) 27(38) 5(1) 

Ahakhav Tribal Preserve-CRIT Restoration 

Ahakhav Tribal PreserveCRIT Restoration 2 0 0 0 N/A 

Cibola NWR 

Cibola North Restoration 0 0 1 0 N/A 

Cibola Nature Trail 

Restoration 2 0 0 0 N/A 

Cibola Eucalyptus 

Restoration 1 1 0 0 N/A 

Cibola South Restoration 0 2 0 0 N/A 

Total 3 3 1 0 

Picacho SRA 

Picacho SRA 0 0 0 0 N/A 

Imperial NWR 

Imperial South Restoration 2 1 0 0 N/A 

Mittry Lake WMA/Pratt Restoration 

Mittry Lake WMA/Pratt 

Restoration 0 0 0 0 N/A 

Gila/Colorado River Confluence 

Colorado River 2 0 0 0 N/A 

Gila River 0 0 0 0 N/A 

Total 2 0 0 0 

Yuma West Wetlands 

Yuma West Wetlands 0 0 0 0 N/A 

Limitrophe Division 

Limitrophe Division North 0 0 0 0 N/A 

Limitrophe Division South 2 0 0 0 N/A 

Total 2 0 0 0 

Gila River/Quigley Pond WMA 

Gila River/Quigley Pond 

WMA 4 1 0 0 N/A 

Total All Areas 48(47) 44(96) 39(70) 27(38) 5(1) 

128
Appendix 2. Narrative Descriptions of Each Yellow-billed 

Cuckoo Detection in the Lower Colorado River 

Watershed, 2007 

The following are descriptions of each yellow-billed cuckoo detection of each 

yellow-billed cuckoo detection in the lower Colorado River watershed along the Muddy 

River, Nevada, lower Colorado, Bill Williams, and Gila rivers, Arizona and California, 

2007, made during the 2007 field season. Descriptions include how the bird was detected 

(solicited calls in response to playback recordings or unsolicited), the habitat the cuckoo 

was observed in, and behavioral observations such as vocalization type, courtship 

behavior, and breeding status. 

We assigned breeding status based on observations of cuckoo behavior conducted 

across all five surveys and supplemental visits. Breeding was considered “confirmed” if 

an attended nest was found, copulation was observed, and/or recently fledged young were 

observed at a site. Detections where these activities were not observed were classified as 

“unconfirmed” as the breeding status of individuals present was not known. 

Pahranagat National Wildlife Refuge (White River) 

Pahranagat North 

In 2007, no yellow-billed cuckoos were detected at this site. 

Pahranagat South 

In 2007, no yellow-billed cuckoos were detected at this site. 

Overton Wildlife Management Area (Muddy River) 

Honeybee Pond 

In 2007, no yellow-billed cuckoos were detected at this site. 

Overton Wildlife 

In 2007, no yellow-billed cuckoos were detected at this site. 

Grand Canyon National Park/Lake Mead National Recreation Area (Colorado 

River and Lake Mead) 

RM 274.5 

In 2007, no yellow-billed cuckoos were detected at this site. 

Cuckoo Beach 

In 2007, no yellow-billed cuckoos were detected at this site. 

129
Iceberg Ridge 

In 2007, no yellow-billed cuckoos were detected at this site. 

Chuckwalla Cove 

In 2007, no yellow-billed cuckoos were detected at this site. 

Big Horn Draw 

In 2007, no yellow-billed cuckoos were detected at this site. 

Havasu National Wildlife Refuge (Colorado River) 

Pintail Slough 

Pintail Slough Survey 2 – 07/03/2007, 0608, 726565 E, 3858609 N, 218°/75 m. Yellowbilled cuckoo gave knocker call after the 5th playback. The observer tracked the cuckoo to 

the North Dike survey site where it gave a kuk-kowlp call at 0620 from 726465 E, 

3858486 N, 200°/40 m. Aural detection only. Breeding classification: unconfirmed. 

North Dike 

North Dike Revisit 1 – 07/03/2007, 0628, 726127 E, 3858519 N, 0°/0 m. Cuckoo1 gave 

an unsolicited, soft knocker call to which Cuckoo2 responded with a knocker call and a 

ping-pong call. Cuckoo2 then flew to a tall stringer of Fremont cottonwood located at 

726147E, 3858754N in the Pintail Slough survey site while knocking. Cuckoo1 then flew 

across a field and joined Cuckoo2. After perching for several minutes, both cuckoos 

began to move east through the stringer, giving soft knocker calls. Aural and visual 

detection. Breeding classification: unconfirmed. 

North Dike Survey 2 – 07/10/2007, 0651, 726345 E, 3858317 N, Cuckoo1 @ 160°/30 m, 

Cuckoo2 @ 30°/50 m. Cuckoo1 seen flying through an open field into a patch of 

arrowweed near the road after the 4th playback. Cuckoo2 seen flying east behind us in 

open field into arrowweed patch. Ten minutes later, Cuckoo2 (?) gave a knocker-kowlp, 

then was seen flying through an open field and into the arrowweed. Aural and visual 

detection. Breeding classification: unconfirmed. 

Topock Marsh Restoration 

Topock Marsh Restoration Survey 1 – 06/12/2007, 0637, 723253 E, 3852176 N, 340°/15 

m. Yellow-billed cuckoo landed 6 m above the ground in a 10 m tall Fremont cottonwood 

after the 3rd playback. The cuckoo then flew east and landed in an 18 m tall Fremont 

cottonwood. After two minutes it flew southeast into a patch of tamarisk/arrowweed. 

Visual detection only. Breeding classification: unconfirmed. 

Topock Marsh Restoration Revisit 1– 07/26/2007, 0742, 723181 E, 3852289 N, 90°/75 

m. Yellow-billed cuckoo gave unsolicited series of coo calls from 8 m above the ground 

in a 10 m tall Fremont cottonwood. Observers followed this cuckoo as it moved around 

the northwest corner of the site, cooing, until 0842. Aural and visual detection. Breeding 

classification: unconfirmed. 

130
Topock Marsh Restoration Revisit 1 – 07/26/2007, 0925, 723671 E, 3852202 N, 35°/25 

m. Yellow-billed cuckoo gave an unsolicited kuk-kowlp call from 5 m above the ground 

in a 8 m tall Goodding’s willow. The bird then flew 75 m southwest and gave two coo

calls. Aural and visual detection. Breeding classification: unconfirmed. 

Topock Marsh Restoration Revisit 1 – 07/26/2007, 1133, 723219 E, 3852230 N, 

335°/125 m. Yellow-billed cuckoo gave three unsolicited coo calls. Aural detection only. 

Breeding classification: unconfirmed. 

Topock Marsh Restoration Revisit 2 – 07/27/2007, 0804, 723256 E, 3852296 N, 290°60 

m. Yellow-billed cuckoo gave an unsolicited kuk-kowlp call. Aural detection only. 

Breeding classification: unconfirmed. 

Bill Williams River National Wildlife Refuge (Bill Williams River) 

Teepee Trail 

Teepee Trail Survey 3 – 07/28/2007, 0637, 229027 E, 3794701 N, 290°/25 m. Yellowbilled cuckoo gave an unsolicited knocker-kowlp from a 4 m tall Fremont cottonwood. 

The cuckoo then flew 15 m southeast and called again. Aural and visual detection. 

Breeding classification: unconfirmed. 

Cottonwood Patch 

Cottonwood Patch Survey 1 – 06/26/2007, 0812, 227948 E, 3794132 N, Cuckoo1 and 

Cuckoo2 @ 340°/10 m. Cuckoo1 responded to the 1st playback with a kuk-kowlp call. At 

0818, Cuckoo1 and Cuckoo2 gave a series of kuk-kowlp counter-calls about 20 m apart 

from one another. At 0827, Cuckoo1 (?) gave several kuk calls. Aural detection only. 

Breeding classification: unconfirmed. 

Cottonwood Patch Survey 1 – 06/26/2007, 0835, 227636 E, 3794166 N, 22°/100 m. 

Yellow-billed cuckoo responded to the 1st playback with a kuk-kowlp call. Aural detection 

only. Breeding classification: unconfirmed. 

Cottonwood Patch Revisit 1 – 06/28/2007, 0732, 227751 E, 3794257 N, 270°/100 m. 

Yellow-billed cuckoo gave an unsolicited call. Aural detection only. Breeding 

classification: unconfirmed. 

Cottonwood Patch Revisit 1 – 06/28/2007, 0821, 227596 E, 3794187 N, 65°/15 m. 

Yellow-billed cuckoo gave an unsolicited coo call. Aural detection only. Breeding 

classification: unconfirmed. 

Cottonwood Patch Revisit 1 – 06/28/2007, 0835, 227578 E, 3794201 N, Cuckoo1 @ 

310°/100 m, Cuckoo2 (?) @ 260°/80 m. Cuckoo1 gave several unsolicited kuk-kowlp

calls. Then at 0840, Cuckoo2 (?) gave a kuk-kowlp call. Aural detection only. Breeding 

classification: unconfirmed. 

Cottonwood Patch Revisit 2 – 07/01/2007, 0643, 227989 E, 3794111 N, 346°/50 m. 

Yellow-billed cuckoo gave an unsolicited kuk-kowlp call. Aural detection only. Breeding 

classification: unconfirmed. 

131
Cottonwood Patch Survey 2 - 07/12/2007, 0717, 227911 E, 3794154 N, 302°/15 m. 

Yellow-billed cuckoo responded to the 1st playback with kuk-kowlp call. Aural detection 

only. Breeding classification: unconfirmed. 

Cottonwood Patch Survey 2 – 07/12/2007, 0740, 227737 E, 3794221 N, Cuckoo1 @ 

316°/25 m, Cuckoo2 @ 24°/15 m. Cuckoo1 gave an unsolicited kuk-kowlp call followed 

by kuks from Cuckoo2. At 0745, Cuckoo1 gave a series of very soft kuks. At 0753, an 

unspecified cuckoo flew into a 4 m high Goodding’s willow 20 m to the northeast of the 

survey point and gave a kuk-kowlp call before flying to the southeast. At 0757, an 

unspecified cuckoo was seen near this last location, this time 8 m above the ground in a 

Fremont cottonwood. This cuckoo gave a kuk-kowlp call and several soft kuks. Aural and 

visual detection. Breeding classification: unconfirmed. 

Cottonwood Patch Revisit 3 – 07/14/2007, 0635, 227691 E, 3794254 N, 86°/40 m. 

Yellow-billed cuckoo responded to the 1st playback with a kuk-kowlp call. This was soon 

followed by another kuk-kowlp call 30 m to the east. At 0639, soft knocker calls were 

heard from the second location. At 0647, a yellow-billed cuckoo was discovered sitting 

on a nest (CPNest1) 4 m above the ground in a 10 m tall Fremont cottonwood, right 

where the knocker calls had come from. Aural and visual detection. Breeding 

classification: confirmed. 

Cottonwood Patch Revisit 4 – 07/16/2007, 0659, 227747 E, 3794239 N, Cuckoo1 and 

Cuckoo2 @ 0°/0 m, Cuckoo3 @ 100°/30 m. Observer arrived at CPNest1 at 0659 to find 

no adults on the nest. When the nest was mirror-poled, a nestling (Cuckoo1) gaped at the 

mirror. The observer felt there may have been two nestlings but was not certain. The 

nestling looked very young. Its black down/feathers looked slightly slick but there were 

no signs of eggshells. At 0706, Cuckoo2 landed three inches from the nest with a large 

green item, possibly a katydid. Cuckoo2 looked at the observer, gave several knocker

calls, and then flew out of the nest area where it gave soft kuks and ping-pong calls from 

about 10 m away. The observer left but returned at 0730 to find a cuckoo sitting silently 

on the nest. At 0735, Cuckoo3 began to coo. The cuckoo on the nest responded with 

several soft, single kuks. Aural and visual detection. Breeding classification: confirmed. 

Cottonwood Patch Revisit 5 – 07/18/2007, 0845, 227747 E, 3794239 N, 0°/0 m. Yellowbilled cuckoo sitting on CPNest1, observer was able to see the head of one nestling. The 

next time the nest was checked on 07/25/2007, no nestlings, fledges, or adults were 

observed in the nest area. Visual detection only. Breeding classification: confirmed. 

Cottonwood Patch Survey 3 – 07/28/2007, 0728, 227972 E, 3794122 N, 325°/25 m. 

Yellow-billed cuckoo responded to the 1st playback with a knocker-kowlp call. Aural 

detection only. Breeding classification: unconfirmed. 

Cottonwood Patch Survey 3 – 07/28/2007, 0747, 227683 E, 3794199 N, 75°/75 m. 

Yellow-billed cuckoo responded to the 1st playback with a knocker-kowlp call. The 

cuckoo then flew northwest to an area near CPNest1 and gave another knocker-kowlp. 

Aural and visual detection. Breeding classification: unconfirmed. 

132
Cave Wash 

Cave Wash Survey 1 – 06/26/2007, 0634, 226683 E, 3794320 N, 27°/25 m. Yellow-billed 

cuckoo responded to the 5th playback with several kuk calls from a stand of young 

Fremont cottonwoods on river right. At 0642, several kuk calls were given from the same 

location. At 0659, the cuckoo responded to the 2nd playback being done at the next survey 

point 300 m away with a kuk-kowlp call. At 0703 and again at 0711, kuk-kowlp calls were 

heard from further back in the stand of Fremont cottonwood. Aural detection only. 

Breeding classification: unconfirmed. 

Cave Wash Revisit 1 – 06/26/2007, 0816, 226555 E, 3794499 N, Cuckoo1 @ 80°/30 m, 

Cuckoo2 @ 120°/70 m. Cuckoo1 gave an unsolicited kuk-kowlp call. At 0820 and at 

0826, Cuckoo1 (?) gave kuk-kowlp calls from approximately 20 m further northeast. At 

0827, Cuckoo2 responded, also with a kuk-kowlp call. Aural detection only. Breeding 

classification: unconfirmed. 

Cave Wash Revisit 1 – 06/26/2007, 0905, 226733 E, 3794395 N, 172°/9 m. Yellow-billed 

cuckoo gave an unsolicited knocker call. One minute later it flew west from the top of an 

8 m tall Fremont cottonwood. Aural and visual detection. Breeding classification: 

unconfirmed. 

Cave Wash Revisit 2 – 07/01/2007, 0538, 226789 E, 3794398 N, Cuckoo1 @ 172°/10 m, 

Cuckoo2 @ 340°/40 m, Cuckoo3 (?) @ 240°/15 m, Cuckoo4 (?) @ 156°/15 m. Cuckoo1 

gave an unsolicited kuk-kowlp call, then moved west through a stand of Fremont 

cottonwood. At 0543, Cuckoo1 gave another kuk-kowlp call and flew off to the west. 

Cuckoo2 gave kuk-kowlp call at 0547. At 06:00, Cuckoo3 (?) gave a kuk-kowlp call and 

at 0601 and 0614, Cuckoo4 (?) gave rolling kowlp calls. The observer believed there 

were at least three birds in this area. Aural and visual detection. Breeding classification: 

unconfirmed. 

Cave Wash Revisit 2 – 07/01/2007, 0632, 226800 E, 3794347 N, 54°/15 m. Yellow-billed 

cuckoo gave an unsolicited rolling kowlp. Aural detection only. Breeding classification: 

unconfirmed. 

Cave Wash Revisit 2 – 07/01/2007, 0639, 226831 E, 3794370 N, 90°/7 m. Yellow-billed 

cuckoo observed unsolicited 7 m above the ground in a 9 m tall Fremont cottonwood. 

The cuckoo foraged within a 5 m radius for two minutes, then flew 20 m to the southwest 

and gave several kuks. Aural and visual detection. Breeding classification: unconfirmed. 

Cave Wash Revisit 2 – 07/01/2007, 0710, 226780 E, 3794339 N, 45°/30 m. Yellow-billed 

cuckoo gave unsolicited kuk-kowlp calls at 0710 and 0726. Aural detection only. 

Breeding classification: unconfirmed. 

Cave Wash Revisit 2 – 07/01/2007, 0800, 226766 E, 3794402 N, 143°/15 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call. At 0810, a cuckoo gave a knocker call 

20 m to the southeast of this location from 8m above the ground in an 11m tall Fremont 

cottonwood. The cuckoo was observed perching until 0816 when it flew west 10 m, 

disappeared into the vegetation, and gave a kuk-kowlp call. Aural and visual detection. 

Breeding classification: unconfirmed. 

133
Cave Wash Revisit 2 – 07/01/2007, 0830, 226782 E, 3794380 N, Cuckoo1 @ 305°/10 m, 

Cuckoo2 @ 75°/30 m, Cuckoo3 (?) @ 340°/75 m, Cuckoo4 (?) @ 2°/50 m. Cuckoo1 

flew unsolicited into a Goodding’s willow and gave a kuk call. Cuckoo2 responded 

immediately with a kuk call. At 0856, Cuckoo3 (?) gave a kuk-kowlp call and at 09:00, 

Cuckoo4 (?) gave a kuk-kowlp call. The observer felt there were at least three cuckoos at 

this location. Aural and visual detection. Breeding classification: unconfirmed. 

Cave Wash Revisit 2 – 07/01/2007, 0845, 226600 E, 3794495 N, 290°/80 m. Yellowbilled cuckoo gave an unsolicited coo call. Aural detection only. Breeding classification: 

unconfirmed. 

Cave Wash Survey 2 – 07/12/2007, 0553, 226678 E, 3794323 N, 40°/100 m. Yellowbilled cuckoo responded to the 2nd playback with a kuk-kowlp call. At 0557 and 0632, 

kuk-kowlp calls were given from the same location. Kuk-kowlp calls were given 

approximately every ten minutes until 0712, after which time no additional calls were 

heard. Aural detection only. Breeding classification: unconfirmed. 

Cave Wash Survey 2 – 07/12/2007, 0626, 227166 E, 3794407 N, 280°/35 m. Yellowbilled cuckoo responded to the 5th playback with a kuk-kowlp call from within a dense 

Fremont cottonwood/Goodding’s willow thicket. Aural detection only. Breeding 

classification: unconfirmed. 

Cave Wash Survey 2 – 07/12/2007, 0727, 227597 E, 3794576 N, 5°/3 m. Yellow-billed 

cuckoo landed 5 m above the ground in an 8 m tall Fremont cottonwood after the 4th

playback. One minute later, the cuckoo flew 13 m east and landed 5 m above the ground 

in another Fremont cottonwood where it was observed eating a cicada. At 0738, the 

cuckoo flew 100 m to the south before it disappeared from view. The observer suspected 

the cuckoo was headed to Cottonwood Patch which is located about 400 m south of this 

survey point. Visual detection only. Breeding classification: unconfirmed. 

Cave Wash Revisit 3 – 07/12/2007, 0813, 226821 E, 3794518 N, Cuckoo1 @ 100°/50 m, 

Cuckoo2 @ 350°/75 m, Cuckoo3 (?) @ 210°/60 m. Cuckoo1 gave an unsolicited kukkowlp call. One minute later, Cuckoo2 responded with a knocker call. Ten seconds later, 

Cuckoo3 (?) gave a kuk-kowlp call. The observer suspected these calls were given by 

three different individuals. Aural detection only. Breeding classification: unconfirmed. 

Cave Wash Revisit 4 – 07/14/2007, 0820, 226799 E, 3794378 N, 115°/100 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call. Aural detection only. Breeding 

classification: unconfirmed. 

Cave Wash Revisit 4 – 07/14/2007, 0825, 226837 E, 3794353 N, 260°/10 m. Yellowbilled cuckoo gave an unsolicited knocker call three times from a Fremont cottonwood, 

then flew 50 m west and gave several kowlp calls. Aural and visual detection. Breeding 

classification: unconfirmed. 

Cave Wash Revisit 4 – 07/14/2007, 0849, 226729 E, 3794343 N, 90°/40 m. Yellow-billed 

cuckoo foraging unsolicited in a Fremont cottonwood. The cuckoo then flew into the 

vegetation and out of sight. Visual detection only. Breeding classification: unconfirmed. 

134
Cave Wash Revisit 4 – 07/14/2007, 0912, 226822 E, 3794345 N, 360°/15 m. Yellowbilled cuckoo gave two kuk-kowlp calls from a Fremont cottonwood. Aural and visual 

detection. Breeding classification: unconfirmed. 

Cave Wash Revisit 4 – 07/14/2007, 0940, 226831 E, 3794351 N, Cuckoo1 @ 0°/0 m, 

Cuckoo2 @ 0°/0 m. Cuckoo1 gave an unsolicited knocker call 6m above the ground in an 

8 m tall Fremont cottonwood. Cuckoo2, a fledgling, was observed perched 3.5 m above 

the ground in the lower branches of the same tree. The fledgling had a very short tail, no 

yellow on its bill, and no eye-ring. It was smaller than an adult but fully feathered. 

Cuckoo1 flew around giving knocker calls in an attempt to lead the observers away from 

the fledgling. Cuckoo1 was also observed carrying food about 10 m northeast of this 

location. Observers later located a nest (CWNest1) about 10 m to the north that they 

suspected was associated with this fledgling, however, they did not observe the adult or 

fledgling at the nest. Aural and visual detection. Breeding classification: confirmed. 

Cave Wash Revisit 5 – 07/16/2007, 0811, 226827 E, 3794344 N, 340°/30 m. Yellowbilled cuckoo gave an unsolicited knocker call. Aural detection only. Breeding 

classification: unconfirmed. 

Cave Wash Revisit 5 – 07/16/2007, 0817, 226834 E, 3794368 N, 20°/20 m. Yellow-billed 

cuckoo gave an unsolicited kuk-kowlp call. Aural detection only. Breeding classification: 

unconfirmed. 

Cave Wash Revisit 5 – 07/16/2007, 0833, 226835 E, 3794358 N, 8°/4 m. Fledgling 

yellow-billed cuckoo perched 4 m above the ground in an 8 m tall Fremont cottonwood, 

1⁄4 m away from CWNest1. Fledgling did not move the entire time, no calls were heard 

after it was spotted. Visual detection only. Breeding classification: confirmed. 

Cave Wash Revisit 6 – 07/18/2007, 0955, 226880 E, 3794385 N, Cuckoo1 and Cuckoo2 

@ 260°/80 m. Cuckoo1 gave an unsolicited knocker call from an 8 m tall Fremont 

cottonwood. Cuckoo2 responded immediately with another knocker call. Visual and aural 

detection. Breeding classification: unconfirmed. 

Cave Wash Survey 3 – 07/25/2007, 0612, 226504 E, 3794332 N, 34°/100 m. Yellowbilled cuckoo responded to the 1st playback with a full kuk-kowlp call. Aural detection 

only. Breeding classification: unconfirmed. 

Cave Wash Survey 3 – 07/25/2007, 0637, 226929 E, 3794341 N, 320°/20 m. Yellowbilled cuckoo responded to the 2nd playback with two knocker-kowlp calls. Ten minutes 

later, kowlp calls were heard from 25 m back in the vegetation. Aural detection only. 

Breeding classification: unconfirmed. 

Cave Wash Survey 3 – 07/25/2007, 0655, 227223 E, 3794448 N, 276°/40 m. Yellowbilled cuckoo responded to the 3rd playback. Aural detection only. Breeding classification: 

unconfirmed. 

Cave Wash Revisit 7 – 07/25/2007, 0942, 226841 E, 3794361 N, 300°/10 m. Yellowbilled cuckoo gave several unsolicited knocker calls when observer approached 

CWNest1. Aural detection only. Breeding classification: unconfirmed. 

135
Cave Wash Revisit 8 – 08/07/2007, 0758, 226827 E, 3794358 N, 270°/10 m. Yellowbilled cuckoo gave an unsolicited knocker call. Aural detection only. Breeding 

classification: unconfirmed. 

Cave Wash Revisit 8 – 08/07/2007, 0806, 226820 E, 3794380 N, 300°/10 m. Yellowbilled cuckoo gave several unsolicited knocker call from the top of a 13 m tall Fremont 

cottonwood. The cuckoo flew east 20 m and gave another knocker call. Aural and visual 

detection. Breeding classification: unconfirmed. 

Cave Wash Revisit 8 – 08/07/2007, 0831, 226871 E, 3794336 N, Cuckoo1 @ 350°/15 m, 

Cuckoo2 @ 40°/30 m. Cuckoo1 observed moving around unsolicited in a Fremont 

cottonwood. Cuckoo1 then flew 5 m west and gave a kuk-kowlp call at 0906. Cuckoo2 

responded immediately. Aural and visual detection. Breeding classification: unconfirmed. 

Cave Wash Revisit 8 – 08/07/2007, 1003, 226820 E, 3794380 N, 60°/30 m. Yellow-billed 

cuckoo gave an unsolicited knocker call. Aural detection only. Breeding classification: 

unconfirmed. 

Cave Wash Revisit 8 - 08/07/2007, 1011, 226856 E, 3794381 N, 150°/10 m. Yellowbilled cuckoo gave several unsolicited knocker calls from 8 m above the ground in a 10 m 

tall Fremont cottonwood. Aural and visual detection. Breeding classification: 

unconfirmed. 

Cave Wash Survey 4 – 08/14/2007, 0648, 226462 E, 3794397 N, 308°/100 m. Yellowbilled cuckoo responded to the 1st playback with a kowlp call. Aural detection only. 

Breeding classification: unconfirmed. 

Cave Wash Survey 4 – 08/14/2007, 0705, 226757 E, 3794332 N, 320°/17 m. Yellowbilled cuckoo was observed 6 m above the ground in a 10 m tall Fremont cottonwood at 

the edge of a thick Fremont cottonwood patch after the 5th playback. The cuckoo stayed in 

view for one minute, the flew back into the patch towards CWNest1. Visual detection 

only. Breeding classification: unconfirmed. 

Cave Wash Survey 4 – 08/14/2007, 0754, 227404 E, 3794595 N, 213°/150 m. Yellowbilled cuckoo responded to the 1st playback with a kuk-kowlp call. Aural detection only. 

Breeding classification: unconfirmed. 

Honeycomb Bend 

Honeycomb Bend Survey 1 – 06/19/2007, 0652, 225859 E, 3794653 N, 278°/20 m. 

Yellow-billed cuckoo responded to the 2nd playback with four rolling kowlps from a 

Goodding’s willow. At 0726, a kuk-kowlp call was given by an unspecified cuckoo, 60 m 

downstream from a Goodding’s willow. At 0730, this cuckoo flew upriver and gave a 

kuk-kowlp call within 20 m of the point. The cuckoo continued to move upstream and 

giving kuk-kowlp calls through 0742. Aural and visual detection. Breeding classification: 

unconfirmed. 

Honeycomb Bend Survey 1 – 06/19/2007, 0712, 225552 E, 3794690 N, 286°/5 m. 

Yellow-billed cuckoo flew into a dead tree after the 1st playback and gave a kuk-kowlp

136
call. At 0820, kuk-kowlp calls were heard near this location, then two cuckoos flew 100 m 

upstream together. Aural and visual detection. Breeding classification: unconfirmed. 

Honeycomb Bend Survey 1- 06/19/2007, 0800, 225119 E, 3794413 N, Cuckoo1 @ 

102°/20 m, Cuckoo2 @ 226°/10 m. Two cuckoos began to call five minutes after the 5th

playback. Cuckoo1 gave a series of soft kuks, Cuckoo2 gave a long kuk-kowlp call. At 

0815, both cuckoos flew into a 12 m tall Fremont cottonwood, both gave several kukkowlp calls, then flew to the north side of the river and landed 20 m apart where they 

continued to call to one another. Starting at 0830, one cuckoo began to move downstream 

giving occasional kuk-kowlp calls. Aural and visual detection. Breeding classification: 

unconfirmed. 

Honeycomb Bend Revisit 1 – 06/20/2007, 0625, 226474 E, 3794216 N, 320°/25 m. 

Yellow-billed cuckoo gave an unsolicited rolling kowlps then a kuk-kowlp call. Aural 

detection only. Breeding classification: unconfirmed. 

Honeycomb Bend Revisit 1 – 06/20/2007, 0715, 225873 E, 3794617 N, Cuckoo1, 2, and 3 

@ 342°/20 m, Cuckoo4 and 5 (?) @0°/50 m. Cuckoo1, 2, and 3 flew unsolicited from a 

Goodding’s willow on the north bank to a Goodding’s willow on the south bank. At the 

same time, Cuckoo4 gave coo calls from the vegetation on the north bank. For the next 

seventy-five minutes, four cuckoos were observed flying back and forth across the river, 

sometimes in a group, sometimes singly. Rolling kowlps and kuk-kowlp calls were given 

frequently from both banks. At 0830, two pairs of cuckoos crossed the river near the 

survey point, then about one minute later, Cuckoo5 (?) gave a coo call. Aural and visual 

detection. Breeding classification: unconfirmed. 

Honeycomb Bend Revisit 1 – 06/20/2007, 225199 E, 3794453 N, 200°/15 m. Yellowbilled cuckoo located unsolicited in a Fremont cottonwood. At 0935, a kuk-kowlp call 

was heard and at 0952 an unspecified cuckoo was seen 15 m upstream from the point. 

Aural and visual detection. Breeding classification: unconfirmed. 

Honeycomb Bend Revisit 2 – 06/29/2007, 0605, 225873E, 3794617N, 130°/100m. 

Yellow-billed cuckoo gave an unsolicited soft coo call. Aural detection only. Breeding 

classification: unconfirmed. 

Honeycomb Bend Revisit 2 – 06/29/2007, 0737, 225143 E, 3794423 N, 352°/10 m. 

Yellow-billed cuckoo gave an unsolicited ping-pong call. Twelve minutes later, a cuckoo 

gave two kuks followed by another ping-pong call. At 0800, observers saw a cuckoo 

about 75 m south of this location, 8 m above the ground in a Goodding’s willow, picking 

off leaves and placing them in the tree. A second cuckoo joined the first, and gave a kukkowlp call; it too had leaves in its bill. After several minutes, Cuckoo2 flew to a nearby 

tree and vanished. The first cuckoo began to preen, then flew northeast at 0813. At 0900, 

two cuckoos were spotted across the river in the same tree together, 100 m from the last 

sighting. Aural and visual detection. Breeding classification: unconfirmed. 

Honeycomb Bend Survey 2 – 07/09/2007, 0715, 225586 E, 3794686 N, 62°/25 m. 

Yellow-billed cuckoo flew from river right to river left after 5th playback. Visual 

detection only. Breeding classification: unconfirmed. 

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Honeycomb Bend Survey 2 – 07/09/2007, 0739, 225308E, 225308 E, 3794567 N, 230°/30 

m. Yellow-billed cuckoo responded to the 2nd playback with kuk call. Aural detection 

only. Breeding classification: unconfirmed. 

Honeycomb Bend Survey 2 – 07/09/2007, 0755, 225269 E, 3794526 N, Cuckoo1 @ 

280°/10 m, Cuckoo2 @ 100°/12 m. Cuckoo1 observed 2 m above the ground in a 

Goodding’s willow, carrying an unidentified food item. At the same time, Cuckoo2 flew 

into a Goodding’s willow. Both cuckoos gave short calls to one another. After an hour of 

monitoring, a nest (HCNest1) was located in a Goodding’s willow about 40 m west of the 

survey point. When the nest was mirror poled the next day the nestlings had fledged. No 

adults or juveniles were located on that day. Aural and visual detection. Breeding 

classification: confirmed. 

Honeycomb Bend Revisit 6 – 07/12/2007, 0941, 225289 E, 3794497 N, 40°/10 m. 

Yellow-billed cuckoo observed unsolicited holding a cicada about 40 m south of 

HCNest1. The cuckoo gave a knocker call, looked directly at the observer, and then flew 

into the vegetation with the cicada still in its mouth. No juveniles were located and the 

adult was not detected again. Aural and visual detection. Breeding classification: 

unconfirmed. 

Honeycomb Bend Revisit 7 – 07/14/2007, 0655, 225239 E, 3794527 N, 78°/20 m. 

Yellow-billed cuckoo gave an unsolicited knocker call followed by a kuk-kowlp call near 

HCNest1. Another knocker call was heard at 0708. Aural detection only. Breeding 

classification: unconfirmed. 

Honeycomb Bend Revisit 7 – 07/14/2007, 0742, 225273 E, 3794513 N, Cuckoo1 and 

Cuckoo2 @155°/15 m. Cuckoo1 flew unsolicited across the river and landed 8m above 

the ground in a 10m tall Goodding’s willow. Cuckoo2 flew through this area at 0747, 

after which both birds disappeared. Visual detection only. Breeding classification: 

unconfirmed. 

Honeycomb Bend Survey 3 – 08/07/2007, 0640, 226380 E, 3794325 N, 80°/30 m. 

Yellow-billed cuckoo responded to the 3rd playback with a kuk-kowlp call. At 0723, a 

cuckoo gave a kuk-kowlp call from the same location. Aural detection only. Breeding 

classification: unconfirmed. 

Honeycomb Bend Survey 3 – 08/07/2007, 0816, 225315 E, 3794581 N, 4°/25 m. Yellowbilled cuckoo located in a large Goodding’s willow after the 5th playback. The cuckoo 

was observed foraging in the tree then it began to slowly move upstream, foraging. 

Cuckoo was last seen about 150 m upstream. Visual detection only. Breeding 

classification: unconfirmed. 

Honeycomb Bend Revisit 9 – 08/07/2007, 0725, 226433 E, 3794328 N, 8°/15 m. Yellowbilled cuckoo gave an unsolicited kuk call from a Fremont cottonwood/Goodding’s 

willow patch, then again at 0750. Aural detection only. Breeding classification: 

unconfirmed. 

Honey Bend Revisit 9 – 08/07/2007, 1010, 225226 E, 3794522 N, 0°/0 m. Two fledgling 

yellow-billed cuckoos gave unsolicited, soft, hoarse versions of the adult kuk-kowlp call, 

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both from within 15 m of HCNest1.A visual was obtained on one of the fledglings. It had 

a very short tail, a mostly black bill, and was small compared to an adult. This fledgling 

was actively calling and clumsily flying/hopping 4 m above the ground among the 

branches of a 9 m tall Goodding’s willow. Aural and visual detection. Breeding 

classification: confirmed. 

Honeycomb Bend Revisit 10 – 08/10/2007, 1045, 225256 E, 3794513 N, Cuckoo1 and 

Cuckoo2 @ 320°/10 m. Cuckoo1, a fledgling, gave several unsolicited soft, hoarse kukkowlps near HCNest1. Cuckoo2, an adult, then gave a knocker call from the same 

location. At 1055, Cuckoo2 was seen flying back further into the vegetation. Aural and 

visual detection. Breeding classification: confirmed. 

Honeycomb Bend Revisit 11 – 08/14/2007, 1037, 225265 E, 3794559 N, 340°/10 m. 

Yellow-billed cuckoo gave unsolicited knocker calls from 13m above the ground in 17m 

tall Fremont cottonwood. Aural and visual detection. Breeding classification: 

unconfirmed. 

Honeycomb Bend Survey 3 – 08/23/2007, 0735, 225483 E, 3794678 N, 106°/35 m. 

Yellow-billed cuckoo responded to 1st playback with a kowlp call from a stand of 8m tall 

Goodding’s willow/Fremont cottonwood. Aural detection only. Breeding classification: 

unconfirmed. 

Honeycomb Bend Revisit 12 – 08/23/2007, 0952, 225230 E, 3794516 N, 78°/50 m. 

Yellow-billed cuckoo gave an unsolicited kuk-kowlp call across the river from HCNest1. 

Aural detection only. Breeding classification: unconfirmed. 

Honeycomb Bend Revisit 12 – 08/23/2007, 0958, 225259 E, 3794521 N, 198°/15 m. 

Yellow-billed cuckoo responded immediately to the 1st playback with kuk-kowlp calls and 

cooing from a 20m tall Fremont cottonwood. The cuckoo then flew downstream and out 

of sight where it gave one more kuk-kowlp call. Aural and visual detection. Breeding 

classification: unconfirmed. 

Honeycomb Bend Revisit 13 – 08/27/2007, 0725, 225242 E, 3794529 N, 9°/45 m. 

Yellow-billed cuckoo gave unsolicited kuk-kowlp calls over a ten minute period while 

observers were measuring vegetation at HCNest1. Aural detection only. Breeding 

classification: unconfirmed. 

Mineral Wash 

Mineral Wash Survey 1 – 06/18/2007, 0550, 775347 E, 3794446 N, Cuckoo1 @ 60°/40 

m, Cuckoo2 and Cuckoo3 (?) @ ~90°/45 m, Cuckoo4 (?) @ ~90°/150 m. Cuckoo1 gave 

unsolicited kuk calls. Later, Cuckoo2 and Cuckoo3 (?) were observed 45 m upstream, 

flying together across the river to the north bank. Cuckoo4 (?) was seen another 100 m 

upstream flying from the north to the south bank. Kuk-kowlp calls were heard from this 

area as well. Aural and visual detection. Breeding classification: unconfirmed. 

Mineral Wash Survey 1 – 06/18/2007, 0615, 775787 E, 3794347 N, Cuckoo1 @ 128°/50 

m, Cuckoo2 (?) @ NA/5 m, Cuckoo3 (?) @ ~90°/50 m, Cuckoo4 (?) @ ~275°/60 m. 

Cuckoo1 responded to the 4th playback with soft kuks. Cuckoo2 (?) gave a kuk-kowlp call 

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a few minutes later from a large Goodding’s willow. Cuckoo3 (?) then gave a kuk-kowlp

from upriver, after which, Cuckoo4 (?) gave a kuk-kowlp call from downriver. All calls 

except that of Cuckoo1 were within two minutes of one another. The observer believed 

there were at least two, likely three, birds here. The cuckoos continued to call from both 

upstream and downstream until the observer left the area at 0715. Aural detection only. 

Breeding classification: unconfirmed. 

Mineral Wash Survey 1 – 06/18/2007, 0641, 776092 E, 3794370 N, 332°/15 m. Yellowbilled cuckoo flew across river to the south bank where it perched in a Goodding’s 

willow after the 1st playback. The cuckoo then gave two kuk-kowlp calls before flying 10 

m upriver to a clump of Goodding’s willow at 0647. Aural and visual detection. Breeding 

classification: unconfirmed. 

Mineral Wash Survey 1 – 06/18/2007, 0714, 223872 E, 3794425 N, 255°/20 m. Yellowbilled cuckoo flew upriver into a Goodding’s willow and gave a kuk-kowlp call after the 

5th playback. After a couple minutes, it flew 10 m upriver and landed in a Goodding’s 

willow. At 0727, it flew upriver and out of view. At 0739, a kuk-kowlp” call was given 

from a clump of Fremont cottonwoods 10 m further upriver. Aural and visual detection. 

Breeding classification: unconfirmed. 

Mineral Wash Survey 1 – 06/18/2007, 0754, 224174 E, 3794464 N, Cuckoo1 @ 280°/40 

m, Cuckoo2 @ 280°/20 m, Cuckoo3 (?) @ ~280°/70 m. Cuckoo1 gave an unsolicited 

kuk-kowlp call from behind a stand of large Fremont cottonwoods. At 0801, Cuckoo2 

flew in from downriver and landed about 20 m from the survey point. Cuckoo1 

immediately gave a kuk-kowlp call which it repeated at 0809. At 0808, Cuckoo3 (?) was 

observed downriver from the survey point. Aural and visual detection. Breeding 

classification: unconfirmed. 

Mineral Wash Survey 1 – 06/18/2007, 0826, 224458 E, 3794341 N, Cuckoo1 @ 350°/10 

m, Cuckoo2 @ 290°/65 m, Cuckoo3 @ 80°/80 m. Cuckoo1 flew in from upriver after the 

2nd playback and gave a kuk-kowlp call. At 0832, it flew 30 m upriver. At 0835, Cuckoo2 

gave two kuk-kowlp calls. Cuckoo1 and Cuckoo2 counter-called several times, then, at 

0855, two cuckoos were seen sunning themselves in a Fremont cottonwood 20 m 

upstream from the survey point. At this time, Cuckoo3 flew in about 50 m upriver of the 

sunning cuckoos. Aural and visual detection. Breeding classification: unconfirmed. 

Mineral Wash Survey 1 – 06/18/2007, 0912, 224708 E, 3794385 N, 44°/40 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call. Aural detection only. Breeding 

classification: unconfirmed. 

Mineral Wash Survey 1 – 06/18/2007, 0939, 224947 E, 3794350 N, 40°/30 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call from back in the vegetation near a sandy 

wash. Aural detection only. Breeding classification: unconfirmed. 

Mineral Wash Revisit 1 – 06/18/2007, 0631, 775464 E, 3794446 N, Cuckoo1 @ 140°/14 

m, Cuckoo2 @ 130°/12 m, Cuckoo3 (?) 180°/9 m. Cuckoo1 gave an unsolicited kukkowlp call from 7 m above the ground in a 10 m tall willow. Cuckoo2 responded with a 

kuk call. Cuckoo1 then flew toward Cuckoo2 and disappeared. At 0646, a cuckoo flew 

out of a Goodding’s willow within 1 m of where Cuckoo2 called from, into the 

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Goodding’s willow Cuckoo1 had called from. Thirty seconds later, Cuckoo3 (?) flew 

from a tamarisk around the Goodding’s willow where the other cuckoo was perched. 

Aural and visual detection. Breeding classification: unconfirmed. 

Mineral Wash Revisit 1 - 06/18/2007, 0715, 775565 E, 3794439 N, 130°/30 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call. Aural detection only. Breeding 

classification: unconfirmed. 

Mineral Wash Revisit 2 – 06/19/2007, 0536, 775470 E, 3794455 N, 240°/11 m. Yellowbilled cuckoo flew unsolicited into a Goodding’s willow and gave kuk-kowlp call. The 

cuckoo then moved to the back of the tree and out of sight. At 0541, it gave a kuk-kowlp

call. Aural and visual detection. Breeding classification: unconfirmed. 

Mineral Wash Revisit 2 – 06/19/2007, 0558, 775438 E, 3794384 N, Cuckoo1 and 

Cuckoo2 @ 325°/20 m, Cuckoo3 @ 325°/50 m. Cuckoo1 and Cuckoo2 seen unsolicited 

together in a Goodding’s willow. Cuckoo3 then gave a kuk-kowlp call from the other side 

of the river. Aural and visual detection. Breeding classification: unconfirmed. 

Mineral Wash Revisit 3 – 06/29/2007, 0522, 775482 E, 3794477 N, 150°/30 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call. Aural detection only. Breeding 

classification: unconfirmed. 

Mineral Wash Revisit 3 – 06/29/2007, 0744, 775787 E, 3794354 N, Cuckoo1 @ 315°/75 

m, Cuckoo2 @ 65°/20 m. Cuckoo1 gave an unsolicited kuk-kowlp call. Cuckoo2 

responded with its own kuk-kowlp call from 8 m above the ground in a 13 m tall 

Goodding’s willow. After calling, Cuckoo2 flew south into the vegetation. Aural and 

visual detection. Breeding classification: unconfirmed. 

Mineral Wash Revisit 3 – 06/29/2007, 0759, 775886 E, 3794339 N, Cuckoo1 @ 60°/60 

m, Cuckoo2 @ 320°/10 m. Cuckoo1 was seen unsolicited 5 m above the ground in a 7 m 

tall Goodding’s willow. Cuckoo1 alternately preened and perched until Cuckoo2 gave a 

kuk-kowlp call at 0808. Cuckoo1 flew toward Cuckoo2 and as it passed, Cuckoo2 joined 

it in flight. The two birds then flew off together at a 310° bearing. Aural and visual 

detection. Breeding classification: unconfirmed. 

Mineral Wash Revisit 3 – 06/29/2007, 0830, 775669 E, 3794312 N, Cuckoo1 and 

Cuckoo2 @ 0°/0 m. Cuckoo1 gave an unsolicited knocker calls from 6 m above the 

ground in an 18 m tall Fremont cottonwood. After about twenty minutes, Cuckoo1 and 

Cuckoo2 flew out of the cottonwood and into some mesquite where they were observed 

foraging. Aural and visual detection. Breeding classification: unconfirmed. 

Mineral Wash Survey 2 – 07/02/2007, 0620, 775774 E, 3794354 N, Cuckoo1 and 

Cuckoo2 @ 110°/35 m. Cuckoo1 seen five minutes after the 5th playback 8 m above the 

ground in a dead tree. At 0630, Cuckoo1 flew into a Goodding’s willow 2 m away and 

gave a soft kuk call. At 0632, Cuckoo2 gave a kowlp call from a 10 m tall Goodding’s 

willow 10 m from Cuckoo1. Aural and visual detection. Breeding classification: 

unconfirmed. 

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Mineral Wash Survey 2 – 07/02/2007, 0648, 776081 E, 3794377 N, 8°/100 m. Yellowbilled cuckoo gave coo calls for ten minutes following the 4th playback from an area near 

a very large Fremont cottonwood surrounded by tamarisk and mesquite. Aural detection 

only. Breeding classification: unconfirmed. 

Mineral Wash Survey 2 – 07/02/2007, 0712, 223857 E, 3794427 N, Cuckoo1 @ 40°/40 

m, Cuckoo2 (?) @ 22°/20 m. Cuckoo1 responded to the 3rd playback with a kuk-kowlp

call. At 0733, Cuckoo2 (?) gave a kuk-kowlp call from a medium Goodding’s willow. At 

0742, Cuckoo2 (?) flew 20 m downstream where it gave two kuk-kowlp calls before 

flying back into the vegetation on the north bank. Several more calls were heard over the 

next 45 minutes, progressively further downstream. At 0851, a cuckoo was observed 

~100 m downstream from the survey point as it flew from a sandy wash on the south 

bank into the vegetation on the north bank. The cuckoo may have been carrying a food 

item, but the observer was not certain. Aural and visual detection. Breeding 

classification: unconfirmed. 

Mineral Wash Survey 2 – 07/02/2007, 0755, 224264 E, 3794484 N, Cuckoo1 @ 56°/20 

m, Cuckoo2 @ ~90°/50 m, Cuckoo3 (?) @ 146°/20 m. Cuckoo1 responded to the 1st

playback with a kuk-kowlp call. Later, Cuckoo2 was seen perched in a dead tree. 

Cuckoo3 (?) was then seen as it flew across the river to the south bank. Aural and visual 

detection. Breeding classification: unconfirmed. 

Mineral Wash Survey 2 – 07/02/2007, 0850, 224852 E, 3794416 N, 128°/15 m. Yellowbilled cuckoo responded to the 5th playback with soft kowlp call from a Goodding’s 

willow overhanging the river. Aural and visual detection. Breeding classification: 

unconfirmed. 

Mineral Wash Revisit 6 – 07/24/2007, 0821, 775565 E, 3794470 N, Cuckoo1 @ 320°/45 

m, Cuckoo2 (?) @ 320°/90 m. Cuckoo1 gave an unsolicited rapid knocker call followed 

by several rolling kowlps. At 0830, a knocker call was given from the same location. 

Three minutes later, a Cuckoo2 (?) gave a knocker call. Aural detection only. Breeding 

classification: unconfirmed. 

Mineral Wash Survey 3 – 07/30/2007, 0606, 775343 E, 3794453 N, 130°/30 m. Yellowbilled cuckoo responded to the 1st playback with a kuk-kowlp call. Aural detection only. 

Breeding classification: unconfirmed. 

Mineral Wash Survey 3 – 07/30/2007, 0618, 775642 E, 3794387 N, Cuckoo1 @ 250°/20 

m, Cuckoo2 @ 100°/10 m, Cuckoo3 (?) @ 50°/10 m. Cuckoo1 responded to the 3rd

playback with a kuk-kowlp call from a large Goodding’s willow. Cuckoo2 responded 

from the other side of the river with a knocker-kowlp call. At 0623, Cuckoo1 (?) gave a 

knocker-kowlp call to which Cuckoo3 (?) responded with a kuk-kowlp call from a 

medium Goodding’s willow. At 0630, Cuckoo1 gave a knocker call. Two minutes later, 

Cuckoo2 was seen flying from its initial location to a Goodding’s willow about 10 m 

west. Aural and visual detection. Breeding classification: unconfirmed. 

Mineral Wash Survey 3 – 07/30/2007, 0756, 224168E, 3794463 N, 100°/50 m. Yellowbilled cuckoo responded to the 4th playback with a kuk-kowlp call. At 0809, a knocker142
kowlp was heard from the same tree. Aural detection only. Breeding classification: 

unconfirmed. 

Mineral Wash Survey 3 – 07/30/2007, 0823, 224553 E, 3794353 N, 286°/100 m. Yellowbilled responded to the 1st playback with a kuk-kowlp call near the previous survey point. 

Aural detection only. Breeding classification: unconfirmed. 

Mineral Wash Revisit 7 – 07/30/2007, 0637, 775659 E, 3794393 N, Cuckoo1 @ 300°/30 

m, Cuckoo2 (?) @ 20°/40 m. Cuckoo1 gave an unsolicited knocker-kowlp call. Cuckoo2 

(?) gave a knocker-kowlp call at 0652. Aural detection only. Breeding classification: 

unconfirmed. 

Mineral Wash Revisit 7 – 07/30/2007, 0640, 775482 E, 3794449 N, 136°/15 m. Observer 

was monitoring the 0606 survey detection and had not heard anything additional until this 

time. One playback was done to which a yellow-billed cuckoo responded with a kukkowlp call from a stand of medium Fremont cottonwood. Aural detection only. Breeding 

classification: unconfirmed. 

Mineral Wash Revisit 7 – 07/30/2007, 0655, 775672 E, 3794385 N, Cuckoo1 @ 110°/30 

m, Cuckoo2 (?) @ 300°/25 m. Cuckoo1 gave an unsolicited kuk-kowlp call. Three 

minutes later, Cuckoo2 (?) gave kuk-kowlp call. Aural detection only. Breeding 

classification: unconfirmed. 

Mineral Wash Revisit 7 – 07/30/2007, 0659, 775596 E, 3794490 N, 242°/10 m. Yellowbilled cuckoo gave an unsolicited knocker-kowlp from a large Goodding’s willow. Aural 

detection only. Breeding classification: unconfirmed. 

Mineral Wash Revisit 7 – 07/30/2007, 0832, 224477 E, 3794381 N, 50°/15 m. Observer 

was monitoring the 0823 survey detection when a yellow-billed cuckoo gave an 

unsolicited kuk-kowlp call from a medium Fremont cottonwood in a wash north of the 

river. At 0836 and 0839, a cuckoo gave kuk-kowlp calls from the 0823 detection location. 

Aural detection only. Breeding classification: unconfirmed. 

Mineral Wash Survey 4 – 08/13/2007, 0819, 224403 E, 3794380 N, Cuckoo1 @ 75°/9 m, 

Cuckoo2 @ 138°/85 m. Cuckoo1 landed 6m above the ground in an 8 m tall Goodding’s 

willow after the 5th playback and gave six kuk calls. Cuckoo2 responded with a kuk call. 

At 0827, Cuckoo1 gave another kuk call and Cuckoo2 responded again with a kuk call. 

Cuckoo1 then flew over a clump of tamarisk toward Cuckoo2 and disappeared. At 0850, 

a cuckoo was sighted in a tamarisk tree, 9 m east of Cuckoo1’s initial location where it 

perched for four minutes before flying away to the east. Aural and visual detection. 

Breeding classification: unconfirmed. 

Big Bend 

Big Bend Survey 1- 06/12/2007, 0545, 775342 E, 3794448 N, 320°/50 m. Yellow-billed 

cuckoo responded to the 2nd playback with a kuk-kowlp call from 8 m above the ground in 

a dead section of a 12 m tall Goodding’s willow. The cuckoo then flew east 20 m, 

disappearing over a bank of tamarisk. At 0630, a yellow-billed cuckoo gave a kuk-kowlp

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call within 15 m of this last location. Aural and visual detection. Breeding classification: 

unconfirmed. 

Big Bend Survey 1- 06/12/2007, 0623, 774911 E, 3794742 N, 140°/15 m. Yellow-billed 

cuckoo responded to the 1st playback with a kuk-kowlp call. Called again from across the 

river and was observed perched 5 m above ground in a tamarisk tree. Cuckoo called three 

times total, moving further upstream with each successive call. Aural and visual 

detection. Breeding classification: unconfirmed. 

Big Bend Survey 1 – 06/12/2007, 0803, 774317E, 3795688 N, 152°/25 m. Yellow-billed 

cuckoo responded to the 5th playback with a series of very quiet kuks from a Goodding’s 

willow. Aural detection only. Breeding classification: unconfirmed. 

Big Bend Survey 1 – 06/12/2007, 1000, 773570 E, 3795166 N, Cuckoo1 @106°/5 m, 

Cuckoo2 (?) @ 250°/50 m. Cuckoo1 silently flew upstream after the 1st playback and 

landed 7 m above the ground in a 10 m tall Goodding’s willow. Cuckoo1 then flew into a 

second Goodding’s willow one meter away where it preened for fifteen minutes. At 1018, 

Cuckoo1 flew east into a 10 m tall Goodding’s willow and disappeared. At 1030, 

Cuckoo2 (?) gave a kuk-kowlp call then at 1035 Cuckoo2 (?) flew across the river and 

disappeared into the same willow thicket as Cuckoo1. Aural and visual detection. 

Breeding classification: unconfirmed. 

Big Bend Revisit 1 – 06/15/2007, 0545, 775258 E, 3794542 N, 100°/35 m. Yellow-billed 

cuckoo gave an unsolicited kuk-kowlp call. Aural detection only. Breeding classification: 

unconfirmed. 

Big Bend Revisit 1 – 06/15/2007, 0735, 775258 E, 3794502 N, 52°/18 m. Yellow-billed 

cuckoo flew unsolicited from an 8 m tall Goodding’s willow northwest 40 m to an 18 m 

tall Fremont cottonwood. The cuckoo was observed foraging within the top five meters of 

this tree. At 0739, the cuckoo flew northwest and out of sight. Visual detection only. 

Breeding classification: unconfirmed. 

Big Bend Revisit 1 – 06/15/2007, 0819, 775028 E, 3794639 N, 325°/40 m. Yellow-billed 

cuckoo flew unsolicited from 10 m above the ground in a 16 m tall Fremont cottonwood, 

downstream and out of sight. Visual detection only. Breeding classification: 

unconfirmed. 

Big Bend Revisit 1 – 06/15/2007, 1125, 775104 E, 3794574 N, 155°/50 m. Yellow-billed 

cuckoo flew unsolicited downstream to the northwest about 40 m and disappeared around 

a bend in the river. Visual detection only. Breeding classification: unconfirmed. 

Big Bend Re-visit 2 - 06/20/2007, 0953, 775249 E, 3794563 N, Cuckoo1 @ 0°/0 m, 

Cuckoo2 @ 270°/20 m, Cuckoo3 @ 180°/5 m. Cuckoo1 gave unsolicited knocker calls. 

Cuckoo2 was seen and Cuckoo3 called while observer was monitoring Cuckoo1. Aural 

and visual detections. Breeding classification: unconfirmed. 

Big Bend Survey 2 – 07/02/2007, 0552, 775199 E, 3794502 N, 332°/150 m. Yellowbilled cuckoo responded to the 2nd playback with a quiet knocker call from river right. 

Aural detection only. Breeding classification: unconfirmed. 

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Big Bend Survey 2 – 07/02/2007, 0625, 774755 E, 3794908 N, 95°/27 m. Yellow-billed 

cuckoo responded to the 2nd playback with a kuk-kowlp call. Fifteen seconds later it gave 

a single coo call followed by several coo calls ten seconds later. Aural detection only. 

Breeding classification: unconfirmed. 

Big Bend Survey 2 – 07/02/2007, 0700, 774386 E, 3795360 N, 81°/31 m. Yellow-billed 

cuckoo seen flying across the river after the 1st playback. The cuckoo landed 8 m above 

the ground in a 10 m tall Fremont cottonwood, then moved south along the river through 

a stand of Fremont cottonwood/Goodding’s willow where it gave a loud knocker call. 

Aural and visual detection. Breeding classification: unconfirmed. 

Big Bend Survey 2 – 07/02/2007, 0738, 774225 E, 3795831 N, 18°/19 m. Yellow-billed 

cuckoo gave an unsolicited coo call from river right. Aural detection only. Breeding 

classification: unconfirmed. 

Big Bend Survey 2 – 07/02/2007, 0817, 773803 E, 3795626 N, Cuckoo1 @ 145°/40 m, 

Cuckoo2 (?) @ 188°/90 m, Cuckoo3 (?) @ ~350° /50 m. Cuckoo1 responded to the 1st

playback with a loud knocker call from a patch of Honey Mesquite. At 8:20, Cuckoo2 (?) 

gave a kuk-kowlp call downstream of Cuckoo1. At 0829, Cuckoo3 (?) gave a coo call 

from a large Fremont cottonwood 50 m north of the survey point. This bird then flew 45 

m upstream and gave several coo calls. It then flew further upstream and gave coo calls 

232 m from its initial location. Aural and visual detection. Breeding classification: 

unconfirmed. 

Big Bend Survey 2 – 07/02/2007, 0830, 773731 E, 3795336 N, 15°/40 m. Yellow-billed 

cuckoo responded to the 2nd playback with a loud kuk-kowlp call. Aural detection only. 

Breeding classification: unconfirmed. 

Big Bend Survey 2 – 07/02/2007, 0848, 773531 E, 3795101 N, 212°/35 m. Yellow-billed 

cuckoo flew towards survey point from these coordinates after the 2nd playback. The 

cuckoo landed 9 m above the ground in a 14 m tall Goodding’s willow. At 0850, it gave a 

kuk-kowlp call, then at 0853, flew across the river and perched 12 m above ground in a 

16m tall Fremont cottonwood. The cuckoo preened for three minutes then gave a kukkowlp call. Aural and visual detection. Breeding classification: unconfirmed. 

Big Bend Revisit 4 - 07/17/2007, 0602, 773735 E, 3795409 N, 330°/25 m. Yellow-billed 

cuckoo gave unsolicited knocker-kowlp calls. Aural detection only. Breeding 

classification: unconfirmed. 

Big Bend Revisit 4 – 07/17/2007, 0618, 773764 E, 3795395 N, Cuckoo 1@ 30°/90 m, 

Cuckoo2 @ 295°/10 m, Cuckoo3 (?) @ NA. Cuckoo1 gave an unsolicited kuk-kowlp. 

One minute later, Cuckoo2 responded. Cuckoo2 then flew toward the waypoint, where it 

landed 7 m above the ground in an 8 m tall Goodding’s willow. It raised its tail 

methodically seven or eight times before Cuckoo3 (?), unseen before this time, hopped 

onto Cuckoo2’s back from 0.5 m above with a cicada in its mouth. Both cuckoos held the 

cicada with their bills while copulating for twenty seconds. Cuckoo3 (?) then flew toward 

where Cuckoo1 was detected. Cuckoo2 stayed in the willow for ten minutes more, during 

which time it swallowed the cicada, before flying upstream 100 m and out of sight. Aural 

and visual detection. Breeding classification: confirmed. 

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Big Bend Revisit 4 – 07/17/2007, 0635, 773776 E, 3795448 N, 20°/40 m. Yellow-billed 

cuckoo gave an unsolicited knocker-kowlp call. Aural detection only. Breeding 

classification: unconfirmed. 

Big Bend Revisit 4– 07/17/2007, 0639, 773781 E, 3795474 N, 230°/50 m. Unsolicited 

yellow-billed cuckoo seen carrying food. Visual detection only. Breeding classification: 

unconfirmed. 

Big Bend Revisit 4 – 07/17/2007, 0646, 773765 E, 3795468 N, Cuckoo1 @90°/75 m, 

Cuckoo2 @ 340°/ 5 m. Cuckoo1 gave an unsolicited knocker-kowlp call. Cuckoo2 

immediately responded, and then flew northeast. Aural and visual detection. Breeding 

classification: unconfirmed. 

Big Bend Revisit 4 - 07/17/2007, 0748, 773740 E, 3795426 N, Cuckoo1, 2, and 3 (?) @ 

0°/0 m. Cuckoo1 flew in unsolicited from the north with food, landing 10 m above 

ground in a 12 m high Goodding’s willow. Gave a knocker-kowlp call, then flew down 

into the vegetation. At 0903, a cuckoo gave unsolicited, rapid, and prolonged knocker

calls from the same willow. A potential but unconfirmed nest was later found in this tree. 

At 0910, a juvenile (Cuckoo2) was spotted 8 m above ground on a curving, horizontal 

branch in a 10 m tall Goodding’s willow, attended by Cuckoo3 (?). Aural and visual 

detection. Breeding classification: confirmed. 

Big Bend Survey 3 – 07/25/2007, 0942, 773826 E, 3795660 N, 250°/15 m. Yellow-billed 

cuckoo gave an unsolicited coo call, then flew across the river. Aural and visual 

detection. Breeding classification: unconfirmed. 

Big Bend Survey 3 – 07/15/2007, 0956, 773744 E, 3795367 N, 170°/10 m. Yellow-billed 

cuckoo responded to the 1st playback with a kuk call, then flew west across the river. At 

1010 and 1015 more kuk calls were heard in this area. Aural and visual detection. 

Breeding classification: unconfirmed. 

Big Bend Revist 5 – 07/29/2007, 0648, 773778 E, 3795383 N, Cuckoo1 @ 132°/30 m, 

Cuckoo2 (?) @ 20°/20 m. Cuckoo1 responded to 1st playback with a kuk-kowlp call. At 

0653 and again at 0705 an unsolicited knocker-kowlp call was given by Cuckoo2 (?). 

Aural detection only. Breeding classification: unconfirmed. 

Big Bend Revisit 6 – 08/07/2007, 0900, 774286 E, 3795801 N, 0°/0 m. Yellow-billed 

cuckoo gave an unsolicited, soft knocker call. On a subsequent visit a potential but 

unconfirmed nest was located within 3 m of this location. Aural detection only. Breeding 

classification: unconfirmed. 

Big Bend Revisit 7 – 08/09/2007, 0920, 773801 E, 3795597 N, 70°/10 m. Yellow-billed 

cuckoo flew in unsolicited and landed 10 m above the ground in a Goodding’s willow. 

The cuckoo foraged for a couple minutes, and then gave a very quiet kowlp call ten times. 

The cuckoo then moved down two branches, spread both wings and raised its tail, 

remaining in this position for ten minutes, after which time, the cuckoo flew about 50 m 

northeast into the vegetation and knocked softly three separate times. Aural and visual 

detection. Breeding classification: unconfirmed. 

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Big Bend Revisit 7 – 08/09/2007, 0919, 773613 E, 3795188 N, 0°/20 m. Yellow-billed 

cuckoo flew unsolicited from river left to river right and landed in a young Fremont 

cottonwood. It then flew to a mature Fremont cottonwood, stayed still for two minutes 

and flew off. Visual detection only. Breeding classification: unconfirmed. 

Big Bend Survey 4 – 08/13/2007, 0640, 774865 E, 3794777 N, Cuckoo1 @ 20°/15 m, 

Cuckoo2 @ 104°/20 m. Cuckoo1, a fledgling, responded to the 4th playback with very 

hoarse, off-sounding coo calls. Cuckoo2, an adult, responded with knocker calls from a 

medium Goodding’s willow. At 0645, Cuckoo1 gave hoarse kowlp calls which Cuckoo2 

responded to with a kuk-kowlp call. At 0705 kuk-kowlp calls were heard approximately 

30 m downstream. Aural and visual detection. Breeding classification: confirmed. 

Big Bend Survey 4 – 08/13/2007, 0743, 774370 E, 3795432 N, 2°/40 m. Yellow-billed 

cuckoo responded to the 3rd playback with knocker calls then flew to a medium 

Goodding’s willow 15 m upstream on river left. At 0830, a nest (BBNest1) was located 

on river left right across from where the cuckoo was first detected. The nest was 4.5m 

above ground in a tamarisk tree and had “something” inside it. A yellow-billed cuckoo 

gave a knocker call when the nest was approached. The observer left the area at 0835 but 

returned at 1100 to find an adult yellow-billed cuckoo sitting on the nest. A second adult 

gave knocker calls nearby. Aural and visual detection. Breeding classification: confirmed. 

Big Bend Survey 4 – 08/13/2007, 0904, 773791 E, 3795584 N, 126°/10 m. Yellow-billed 

cuckoo responded to the 4th playback with a knocker call. The cuckoo then flew from a 

medium Goodding’s willow to a medium Fremont cottonwood on river left and knocked

again before flying back across the river and knocking again from its original location. 

More knocker calls were heard from this Goodding’s willow at 0923. Aural and visual 

detection. Breeding classification: unconfirmed. 

Big Bend Survey 4 – 08/13/2007, 0923, 773714 E, 3795302 N, 10°/40 m. Yellow-billed 

cuckoo responded to the 1st playback with a kuk-kowlp call. Aural detection only. 

Breeding classification: unconfirmed. 

Big Bend Survey 4 – 08/13/2007, 0949, 773518 E, 3795075 N, 250°/10 m. Yellow-billed 

cuckoo flew in from the north after the 1st playback. It landed 8 m above ground in a 10 m 

tall Goodding’s willow and gave a kowlp call. The cuckoo then disappeared into the 

vegetation. Aural and visual detection. Breeding classification: unconfirmed. 

Big Bend Revisit 8 – 08/13/2007, 0751, 774358 E, 3795465 N, Cuckoo1 @ 15°/15 m, 

Cuckoo2 @ 100°/10 m. Cuckoo1 gave an unsolicited, high pitched kuk-kowlp call from a 

large Fremont cottonwood on river left, followed by a knocker-kowlp given by Cuckoo2 

from a 10 m tall Goodding’s willow on river left. Cuckoo2 then flew across the river and 

gave a kuk-kowlp call. Aural and visual detection. Breeding classification: unconfirmed. 

Big Bend Revisit 8 – 08/13/2007, 0815, 774350 E, 3795428 N, 210°/10 m. Yellow-billed 

cuckoo seen unsolicited, 6 m above the ground in a 12 m tall Goodding’s willow on river 

right holding a cicada. It sat still, knocked at the observer, then ate the cicada and cleaned 

its bill. The cuckoo then flew south across the river and landed 8 m above the ground in 

a Goodding’s willow. Here it gave a knocker call before flying back across the river and 

knocking again. The 0751 and 0815 Revisit1 detections were both made in the area of the 

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0743 survey detection and should not be considered independent events. Aural and visual 

detection. Breeding classification: unconfirmed. 

Big Bend Revisit 9 – 08/14/2007, 1100, 774359 E, 3795439 N, 0°/0 m. Observers mirrorpoled BBNest1 and discovered a nestling yellow-billed cuckoo sitting on the rim. The 

nestling’s feathers had burst and it had a short tail. Streaks of skin could still be seen 

around its bill. Its back was very dark and had no dandruff. Upon seeing the mirror pole, 

the nestling began to gape. It then jumped to a nearby branch, flapping its wings. It 

struggled to grasp the branch but held on. Observers estimated the nestling’s age to be 

approximately seven or eight days based on feather development. While observers were 

mirror-poling the nest, an adult yellow-billed cuckoo gave several knocker calls. Aural 

and visual detection. Breeding classification: confirmed. 

Big Bend Revisit 10 - 8/22/2007, 0652, 774355 E, 3795432 N, Cuckoo1 @ 70°/50 m, 

Cuckoo2 (?) @ 15 m/350°, Cuckoo3 @ 37°/75 m. Cuckoo1 gave an unsolicited kukkowlp call while observer checking BBNest1. At 0754, Cuckoo2 (?) gave a kuk-kowlp

call, then flew across the river from a Gooding’s willow carrying a large (potentially 

orthopteran) prey item. Upon landing, Cuckoo2 (?) gave a “kuk-kowlp call. At 0757, it 

flew back towards the nest, disappearing 8 m above ground in a Goodding’s willow 6 m 

north of the nest. At 0816, Cuckoo2 (?) gave a kuk call. Cuckoo3 responded with a kukkowlp call. Cuckoo2 (?) responded immediately to Cuckoo3 with a kuk-kowlp call, then 

flew into view with no prey in its bill. At 0818, Cuckoo2 (?) looked directly at the 

observer and gave five knocker calls within the next two minutes. Cuckoo3 responded 

one time with a kowlp call. Cuckoo2(?) was observed moving about the Goodding’s 

willows near the nest for the next five minutes, after which it flew off to the southeast. 

No eggs, nestlings, or fledges were located, however, based on adult behavior, 

fledgling(s) suspected to be near the nest. No cuckoos detected here at the next nest check 

on 08/25/2007. Aural and visual detection. Breeding classification: confirmed. 

Big Bend Survey 5 – 09/06/2007, 0914, 773926 E, 3795881 N, 346°/10 m. Yellow-billed 

cuckoo flew northeast across the river after the 2nd playback from a Fremont cottonwood 

into a Goodding’s willow/Fremont cottonwood stringer on river right. The cuckoo moved 

northeast, foraging along the stringer for ten minutes, after which time it disappeared into 

the vegetation. Visual detection only. Breeding classification: unconfirmed. 

Big Bend Revisit 12 – 09/06/2007, 1012, 7738224 E, 3795454 N, 196°/30 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call. No detections were made at this 

location when the survey came through just thirty minutes earlier. Aural detection only. 

Breeding classification: unconfirmed. 

Gibraltar Rock 

Gibraltar Rock Survey 1 – 06/13/2007, 0625, 772082 E, 3795855 N, 3°/200 m. Yellowbilled cuckoo responded to the 3rd playback with a kuk-kowlp call and coo calls from the 

location of the cuckoo detected in Sandy Wash at 0602. Aural detection only. Breeding 

classification: unconfirmed. 

Gibraltar Rock Survey 1 – 06/13/2007, 0715, 772647 E, 3795585 N, 284°/200 m. 

Yellow-billed cuckoo responded to the 1st playback with a series of “coo” calls. At 0724, 

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the cuckoo was seen at this location 6m above the ground in a 9 m tall Goodding’s 

willow giving coo and kuk-kowlp calls. The cuckoo flew upstream from clump to clump 

of Goodding’s willows, cooing as it went, until it landed behind some tamarisk about 20 

m from the survey point. The cuckoo continued to give coo calls and was last heard at 

0748, 200 m upstream from the survey point. Observer believed this to be the same 

individual detected at 0625. Aural and visual detection. Breeding classification: 

unconfirmed. 

Gibraltar Rock Survey 1 – 06/13/2007, 0844, 773184 E, 3794899 N, Cuckoo1 @ 352°/10 

m, Cuckoo2 @ 252°/20 m. Two yellow-billed cuckoos flew in silently after the 2nd

playback. Cuckoo1 landed in a patch of tamarisk, Cuckoo2 in a clump of 8 m tall 

Goodding’s willow. Cuckoo1 immediately flew over to Cuckoo2’s location. They 

remained here until 0849, when they both flew downriver and behind a wall of tamarisk. 

Visual detection only. Breeding classification: unconfirmed. 

Gibraltar Rock Revisit 2 – 06/25/2007, 0638, 773180 E, 3794925 N, 108°/50 m. Yellowbilled cuckoo gave two unsolicited kuk-kowlp calls fifteen seconds apart. Aural detection 

only. Breeding classification: unconfirmed. 

Gibraltar Rock Revisit 2 – 06/25/2007, 0711, 773183 E, 3794895 N, 98°/70 m. Yellowbilled cuckoo gave an unsolicited kowlp call followed by a kuk call. Aural detection only. 

Breeding classification: unconfirmed. 

Gibraltar Rock Revisit 2 – 06/25/2007, 0740, 773294 E, 3794856 N, 270°/50 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call. Aural detection only. Breeding 

classification: unconfirmed. 

Gibraltar Rock Revisit 3 – 06/30/2007, 0535, 773212 E, 3794921 N, 80°/150 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call. Aural detection only. Breeding 

classification: unconfirmed. 

Gibraltar Rock Revisit 3 – 06/30/2007, 0550, 773276 E, 3794914 N, 39°/74 m. Yellowbilled cuckoo gave an unsolicited knocker call. Aural detection only. Breeding 

classification: unconfirmed. 

Gibraltar Rock Revisit 3 – 06/30/2007, 0611, 773317 E, 3794928 N, Cuckoo1 @ 53°/30 

m, Cuckoo2 (?) @ 178°/15 m. Cuckoo1 gave a single, unsolicited, soft, rolling kuk from 

a thin stringer of Goodding’s willow. Five minutes later, Cuckoo2 (?) gave a knocker

call. Aural detection only. Breeding classification: unconfirmed. 

Gibraltar Rock Revisit 3 – 06/30/2007, 0618, 773422 E, 3794974 N, 270°/100 m. 

Yellow-billed cuckoo gave an unsolicited kuk-kowlp call. Aural detection only. Breeding 

classification: unconfirmed. 

Gibraltar Rock Revisit 3 – 06/30/2007, 0621, 773345 E, 3794839 N, Cuckoo1 @ 253°/7 

m, Cuckoo2 @ 279°/10 m. Cuckoo1 and Cuckoo2 gave a series of unsolicited contact 

calls from a clump of Fremont cottonwoods. Cuckoo1 remained stationary and gave 

rolling kowlps while Cuckoo2 moved around the cottonwoods and responded with kukkowlp calls. Aural detection only. Breeding classification: unconfirmed. 

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Gibraltar Rock Survey 2 – 07/03/2007, 0711, 772784 E, 3795523 N, 100°/40 m. Yellowbilled cuckoo responded to the 2nd playback with a kuk-kowlp call from a 15 m tall, 

yellowing Fremont cottonwood. Aural detection only. Breeding classification: 

unconfirmed. 

Gibraltar Rock Survey 2 – 07/03/2007, 0731, 772827 E, 3795216 N, Cuckoo1 @ 36°/40 

m, Cuckoo2 @ 90°/30 m. Cuckoo1 responded to the 2nd playback with a kuk-kowlp call. 

At 0740, Cuckoo1 gave another kuk-kowlp call to which Cuckoo2 responded. At 0742, 

Cuckoo1 gave one more kuk-kowlp call. Aural detection only. Breeding classification: 

unconfirmed. 

Gibraltar Rock Survey 2 – 07/03/2007, 0817, 773107 E, 3794926 N, 226°/20 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call from a stringer of 8 m tall Goodding’s 

willows. Two more kuk-kowlp calls were heard between 0820 and 0927. Aural detection 

only. Breeding classification: unconfirmed. 

Gibraltar Rock Revisit 4- 07/13/2007, 0600, 773006 E, 3794884 N, 0°/0 m. Yellowbilled cuckoo gave unsolicited coo calls from 11 m above the ground in a Fremont 

cottonwood, then flew off. Aural and visual detection. Breeding classification: 

unconfirmed. 

Gibraltar Rock Revisit 4 – 07/13/2007, 0607, 773183 E, 3794879 N, Cuckoo1 @ 45°/5 

m, Cuckoo2 @ 270°/30 m. Cuckoo1 landed unsolicited 2 m above the ground in a 3 m 

tall Fremont cottonwood and gave a kuk-kowlp call. Cuckoo2 immediately responded 

with a kuk-kowlp from the direction of the cuckoo detected at 0600. Cuckoo1 then flew 

30 m southeast and gave a kuk-kowlp call. Aural and visual detection. Breeding 

classification: unconfirmed. 

Gibraltar Rock Revisit 4 – 07/13/2007, 0627, 773141 E, 3794831 N, 277°/50 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call. Aural detection only. Breeding 

classification: unconfirmed. 

Gibraltar Rock Revisit 4 – 07/13/2007, 0630, 773006 E, 3794884 N, Cuckoo1 and 

Cuckoo2 @ 0°/0 m. Cuckoo1 flew unsolicited to the Fremont cottonwood the cuckoo 

was detected in at 0600 and landed 11m above the ground. Cuckoo2 was perched 1 m 

below and behind Cuckoo1. Cuckoo1 flew to a branch 1 m below Cuckoo2 and gave five 

tail pumps. Cuckoo2 landed on Cuckoo1 and copulation occurred for two seconds. 

Cuckoo2 then flew away. Cuckoo1 remained for five minutes then flew off. Visual 

detection only. Breeding classification: confirmed. 

Gibraltar Rock Revisit 4 – 07/13/2007, 0635, 773044 E, 3794855 N, Cuckoo1 @ 170°/45 

m, Cuckoo2 @ 85°/100 m. Cuckoo1 gave an unsolicited kuk-kowlp call to which 

Cuckoo2 responded with six series of coo calls. Aural detection only. Breeding 

classification: unconfirmed. 

Gibraltar Rock Revisit 4 – 07/13/2007, 0657, 773251 E, 3794864 N, 65°/70 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call. Aural detection only. Breeding 

classification: unconfirmed. 

150
Gibraltar Rock Revisit 4 – 07/13/2007, 0721, 773293 E, 3794853 N, 70°/60 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call. Aural detection only. Breeding 

classification: unconfirmed. 

Gibraltar Rock Revisit 4- 07/13/2007, 0745, 772926 E, 3794849 N, Cuckoo1 and 

Cuckoo2 @ 0°/0 m. Two yellow-billed cuckoos were seen unsolicited in the top canopy 

giving soft knocker and coo calls. Cuckoo1 flew north to a large Fremont cottonwood 

where it caught and ate an unidentified food item. Cuckoo1 then flew to the west along 

the river. Cuckoo2 remained where it was first located and called until 0800. Aural and 

visual detection. Breeding classification: unconfirmed. 

Gibraltar Rock Revisit 5 – 07/16/2007, 0552, 772953 E, 3794896 N, Cuckoo1 @ 350°/20 

m, Cuckoo2 and Cuckoo3 @ 230°/15 m. Cuckoo1 gave unsolicited soft kowlps to which 

Cuckoo2 immediately responded with a kuk-kowlp call. Cuckoo3 immediately responded 

to Cuckoo2 with a knocker call. The observer later located three cuckoos foraging in the 

14 m tall Fremont cottonwood Cuckoo2 and Cuckoo3 had called from. At 0657, a 

yellow-billed cuckoo gave a kuk-kowlp call, and at 0747 a ping-pong call came from this 

same Fremont cottonwood. Aural and visual detection. Breeding classification: 

unconfirmed. 

Gibraltar Rock Revisit 5 – 07/16/2007, 0828, 772910 E, 3794876 N, 0°/0 m. Unsolicited 

yellow-billed cuckoo seen flying with food from near the river to an area 20 m west of 

the Fremont cottonwood cuckoos were detected in at 0552. Upon landing, the cuckoo 

gave a harsh kuk-kowlp call followed by several knocks. Aural and visual detection. 

Breeding classification: unconfirmed. 

Gibraltar Rock Revisit 6 – 07/29/2007, 0818, 772919 E, 3794873 N, 320°/5 m. Yellowbilled cuckoo gave an unsolicited knocker-kowlp. At 0827, a knocker-kowlp was given 20 

m further west. Aural detection only. Breeding classification: unconfirmed. 

Gibraltar Rock Revisit 7 – 08/09/2007, 0654, 772927 E, 3794857 N, 210°/50 m. Yellowbilled cuckoo gave an unsolicited kowlp call. Aural detection only. Breeding 

classification: unconfirmed. 

Gibraltar Rock Survey 4 – 08/15/2007, 0847, 773027 E, 3794918 N, 210°/8 m. Yellowbilled cuckoo fledgling responded to the 3rd playback with an immature call; a 

combination of a kuk and a coo. The fledgling was fully feathered including its tail and 

had yellow on its bill but it appeared to lack an eye ring. Aural and visual detection. 

Breeding classification: confirmed. 

Sandy Wash 

Sandy Wash Revisit 1 – 06/13/2007, 0602, 771859 E, 3796073 N, 20°/30 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call followed by coo calls for the next two 

minutes. Kuk-kowlp calls and rolling kowlps were given after that. Aural detection only. 

Breeding classification: unconfirmed. 

151
Sandy Wash Survey 2 – 07/11/2007, 0555, 771266 E, 3796325 N, 40°/70 m. Yellowbilled cuckoo gave unsolicited coo calls from an 18 m tall Fremont cottonwood. Aural 

detection only. Breeding classification: unconfirmed. 

Sandy Wash Survey 2 – 07/11/2007, 0726, 771748 E, 3796616 N, Cuckoo1 @ 4°/20 m, 

Cuckoo2 (?) @ 352°/100 m. Cuckoo1 responded to the 1st playback with soft kuks. At 

0737, Cuckoo2 (?) began to coo. Aural detection only. Breeding classification: 

unconfirmed. 

Sandy Wash Survey 2 – 07/11/2007, 0857, 771466 E, 3796612 N, Cuckoo1 @ 324°/15 

m, Cuckoo2 (?) @ 58°/40 m. Cuckoo1 gave unsolicited kuks from a 17 m tall Fremont 

cottonwood, then again at 0904. Two minutes later, Cuckoo2 (?) gave a series of kuks

from another large Fremont cottonwood. Aural detection only. Breeding classification: 

unconfirmed. 

Sandy Wash Revisit 3 – 07/11/2007, 0800, 771761 E, 3796743 N, 236°/20 m. Yellowbilled cuckoo gave unsolicited kuks from a clump of small Goodding’s willows. Then at 

0826, a kuk-kowlp call was given. Aural detection only. Breeding classification: 

unconfirmed. 

Sandy Wash Revisit 3 – 07/11/2007, 0806, 771739 E, 3796757 N, 290°/30 m. Yellowbilled cuckoo gave unsolicited coo calls from two 17m tall Fremont cottonwoods for four 

minutes, and then gave kuks at 0813. Aural detection only. Breeding classification: 

unconfirmed. 

Sandy Wash Revisit 3 – 07/11/2007, 0821, 771703 E, 3796779 N, 290°/25 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call from a clump of medium Goodding’s 

willows. At 0834 and 0835, kuks were given from this location. Aural detection only. 

Breeding classification: unconfirmed. 

Sandy Wash Revisit 3 – 07/11/2007, 0832, 771659 E, 3796732 N, 226°/30 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call from a clump of large Fremont 

cottonwoods. At 0840, a kowlp call was given here. The survey detection at 0726 and the 

revisit detections for this date were all close to one another and should not be viewed as 

independent events. Aural detection only. Breeding classification: unconfirmed. 

Sandy Wash Revisit 4 – 07/15/2007, 0628, 771894 E, 3796283 N, 200°/40 m. Yellowbilled cuckoo flew in and gave an unsolicited kuk-kowlp call. Aural and visual detection. 

Breeding classification: unconfirmed. 

Sandy Wash Revisit 4 – 07/15/2007, 0920, 771644 E, 3796738 N, 333°/50 m. Yellowbilled cuckoo gave several unsolicited coo calls before flying across a wash into a large 

Fremont cottonwood. Here it gave rolling kowlps then two knocker calls. Aural and 

visual detection. Breeding classification: unconfirmed. 

Sandy Wash Revisit 5 – 07/17/2007, 0602, 771892 E, 3796216 N, 150°/50 m. Yellowbilled cuckoo gave an unsolicited knocker-kowlp. Aural detection only. Breeding 

classification: unconfirmed. 

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Sandy Wash Revisit 5 – 07/17/2007, 0636, 771956E, 3796250N, 150°/20m. Yellowbilled cuckoo gave an unsolicited “knocker-kowlp” call. Aural detection only. Breeding 

classification: unconfirmed. 

Sandy Wash Revisit 5 – 07/17/2007, 0751, 771637 E, 3796830 N, Cuckoo1 and Cuckoo2 

@ 170°/50 m. Cuckoo1, a juvenile, gave an unsolicited grr-brr call, which Cuckoo2, an 

adult, followed with a knocker-kowlp call. After the adult called, the juvenile gave 

another grr-brr call. Aural detection only. Breeding classification: confirmed. 

Sandy Wash Survey 3 – 07/26/2007, 0643, 771705 E, 3796102 N, 205°/10 m. Yellowbilled cuckoo seen unsolicited in a medium Goodding’s willow after the 2nd playback. 

The cuckoo took flight, caught an unidentified insect, and brought it back to a large 

Fremont cottonwood 20 m northeast of its original location. Visual detection only. 

Breeding classification: unconfirmed. 

Sandy Wash Survey 3 – 07/26/2007, 0710, 771890 E, 3796336 N, Cuckoo1 @ 5°/75 m, 

Cuckoo2 @ 25°/45 m, Cuckoo3 (?) @ 5°/40 m. Cuckoo1 responded to the 2nd playback 

with a knocker-kowlp call. Cuckoo2 immediately responded to Cuckoo1 with a knockerkowlp call. Cuckoo1 responded to this with another knocker-kowlp call. Cuckoo1 called 

several more times and was last heard at 0735. Cuckoo3 (?) called at 0739. Aural 

detection only. Breeding classification: unconfirmed. 

Sandy Wash Survey 3 – 07/26/2007, 0826, 771692 E, 3796682 N, 100°/75 m. Yellowbilled cuckoo responded to the 2nd playback with a knocker-kowlp call. Over the next 45 

minutes, Cuckoo1 called a total of three more times from the same location, one of which 

was followed shortly afterwards by a call from the cuckoo detected at 0830 on Revisit 6. 

After Cuckoo1’s last call, a cuckoo flew east from this location. A food carry was later 

observed as a cuckoo flew west across the wash toward Cuckoo1’s original location. 

Activity primarily centered on an area of several emergent Fremont cottonwoods with an 

understory of dense tamarisk. Aural and visual detection. Breeding classification: 

unconfirmed. 

Sandy Wash Survey 3 – 07/26/2007, 1005, 771403 E, 3796578 N, 90°/40 m. Yellowbilled cuckoo responded to the 2nd playback with three minutes of coo calls. Nineteen 

minutes later, more coo calls were heard approximately 60 m to the north. Aural 

detection only. Breeding classification: unconfirmed. 

Sandy Wash Revisit 6 – 07/26/2007, 0804, 771878 E, 3796437 N, 30°/50 m. Yellowbilled cuckoo gave unsolicited kowlps. Aural detection only. Breeding classification: 

unconfirmed. 

Sandy Wash Revisit 6 – 07/26/2007, 0830, 771796 E, 3796543 N, 180°/50 m. Yellowbilled cuckoo gave a response to calls given by the cuckoo detected on the survey at 

0826. Aural detection only. Breeding classification: unconfirmed. 

Sandy Wash Revisit 6 – 07/26/2007, 0838, 771735 E, 3796604 N, 152°/30 m. Yellowbilled cuckoo gave unsolicited kuks. Aural detection only. Breeding classification: 

unconfirmed. 

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Sandy Wash Revisit 6 – 07/26/2007, 0845, 771653 E, 3796750 N, 30°/30 m. Yellowbilled cuckoo gave unsolicited kuks. At 0855, a kuk-kowlp call was heard 15m to the 

north. Then at 0909 and 0923, kuk-kowlp calls were given 20 m west of the initial 

detection. Aural detection only. Breeding classification: unconfirmed. 

Sandy Wash Revisit 7 – 07/29/2007, 0555, 771770 E, 3796576 N, Cuckoo1 @ 25°/30 m, 

Cuckoo2 (?) @ 20°/50 m, Cuckoo3 (?) @ 175°/8 m. Cuckoo1 gave two series of 

unsolicited kuks followed by a knocker-kowlp call at 0606. At 0615, Cuckoo2 (?) gave a 

knocker-kowlp. Cuckoo 3 (?) gave a knocker-kowlp five minutes later. Aural detection 

only. Breeding classification: unconfirmed. 

Sandy Wash Revisit 7 – 07/29/2007, 0642, 771735 E, 3796632 N, 40°/50 m. Yellowbilled cuckoo responded to the 1st playback with a knocker-kowlp call. Aural detection 

only. Breeding classification: unconfirmed. 

Sandy Wash Revisit 7 – 07/29/2007, 0710, 771637 E, 3796882 N, 100°/25 m. Yellowbilled cuckoo responded to the 1st playback with a knocker-kowlp call from the north side 

of a small pond. Aural detection only. Breeding classification: unconfirmed. 

Sandy Wash Revisit 7 – 07/29/2007, 0720, 771633 E, 3796891 N, 170°/25 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call from a large Fremont cottonwood. Aural 

detection only. Breeding classification: unconfirmed. 

Sandy Wash Revisit 7 – 07/29/2007, 0726, 771628 E, 3796855 N, 270°/40 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call. At 0737, it gave the same call again. 

Aural detection only. Breeding classification: unconfirmed. 

Sandy Wash Revisit 7 – 07/29/2007, 0834, 771762 E, 3796586 N, 350°/15 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call from a small Goodding’s willow. The 

cuckoo then flew approximately 40 m southwest to a patch of large Fremont cottonwoods 

where it gave a kuk-kowlp call at 0847. Aural and visual detection. Breeding 

classification: unconfirmed. 

Sandy Wash Revisit 7 – 07/29/2007, 0928, 771740 E, 3796531 N, Cuckoo1 @ 270°/35 

m, Cuckoo2 @ 310°/25 m. Yellow-billed cuckoo responded to the 3rd playback with two 

knocker-kowlps from a large Fremont cottonwood, followed by a knocker-kowlp from 

Cuckoo2. Aural detection only. Breeding classification: unconfirmed. 

Sandy Wash Revisit 8 – 08/08/2007, 0904, 771754 E, 3796627 N, 10°/50 m. Yellowbilled cuckoo gave unsolicited kuks from a clump of 4 m tall Goodding’s willow. At 

0923, a kuk-kowlp call was given from the same location. Aural detection only. Breeding 

classification: unconfirmed. 

Sandy Wash Revisit 8 – 08/08/2007, 0952, 771778 E, 3796648 N, 40°/30 m. Yellowbilled cuckoo responded to the 1st playback with a kuk-kowlp call. Aural detection only. 

Breeding classification: unconfirmed. 

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Sandy Wash Revisit 8 – 08/08/2007, 1003, 771779 E, 3796663 N, 260°/50 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call. Aural detection only. Breeding 

classification: unconfirmed. 

Sandy Wash Revisit 8 - 08/08/2007, 1031, 771273 E, 3796322 N, 125°/15 m. Yellowbilled cuckoo gave an unsolicited knocker call from 12 m above the ground in a 15 m tall 

Fremont cottonwood. The cuckoo was observed for thirty seconds before flying to the 

north. Aural and visual detection. Breeding classification: unconfirmed. 

Sandy Wash Revisit 8 – 08/08/2007, 1043, 771817 E, 3796657 N, 335°/15 m. Yellowbilled cuckoo responded to the 2nd playback with a kuk-kowlp call. When observers 

approached its location, it began to knock. It was later spotted by observers as it flew out 

of sight. Aural and visual detection. Breeding classification: unconfirmed. 

Sandy Wash Survey 4 – 08/15/2007, 0631, 771375 E, 3796249 N, 84°/8 m. Yellow-billed 

cuckoo responded to the 1st playback with kuks from 10 m above the ground in a Fremont 

cottonwood. It then flew to the southwest. Aural and visual detection. Breeding 

classification: unconfirmed. 

Sandy Wash Survey 4 – 08/15/2007, 0720, 771834 E, 3796429 N, 50°/100 m. Yellowbilled cuckoo responded to the 4th playback with a kuk-kowlp call. Aural detection only. 

Breeding classification: unconfirmed. 

Sandy Wash Survey 4 – 08/15/2007, 0744, 771642 E, 3796778 N, 264°/100 m. Yellowbilled cuckoo responded to the 5th playback with coo calls. Aural detection only. Breeding 

classification: unconfirmed. 

Sandy Wash Revisit 10 – 08/26/2007, 0805, 771707 E, 3796689 N, 106°/20 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call from a stand of Goodding’s willow. 

Aural detection only. Breeding classification: unconfirmed. 

Sandy Wash Revisit 11 – 08/27/2007, 0625, 771821 E, 3796123 N, 0°/0 m. A fledgling 

yellow-billed cuckoo was seen, unsolicited, on the edge of a wash, 3 m above the ground 

in a 6 m tall Goodding’s willow. The bird had no yellow on its bill, a tail of full length, 

and was almost completely feathered. Pin feathers were apparent between the nape, 

cheek, and supra loral region. The cuckoo pumped its tail a few times, hopped around the 

willow’s branches, and after 20 seconds flew north into the vegetation. It was very agile 

and maneuverable. The fledgling moved through the willow like an adult bird would. 

Visual detection only. Breeding classification: confirmed. 

Sandy Wash Revisit 12 – 08/28/2007, 0736, 771870 E, 3796399 N, 316°/60 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call. Aural detection only. Breeding 

classification: unconfirmed. 

Sandy Wash Revisit 12 – 08/28/2007, 0803, 771788 E, 3796424 N, 40°/80 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call, then kuks at 0808. Aural detection only. 

Breeding classification: unconfirmed. 

155
Sandy Wash Revisit 12 – 08/28/2007, 0835, 771876 E, 3796461 N, 258°/70 m. Yellowbilled cuckoo gave several unsolicited kuk-kowlp calls and knocker calls. Aural detection 

only. Breeding classification: unconfirmed. 

Sandy Wash Revisit 13 – 08/29/2007, 0700, 771722 E, 3796743 N, 150°/35 m. Yellowbilled cuckoo gave unsolicited knocker calls while flying successively closer to where 

observers were measuring vegetation. At 0712, the cuckoo was spotted 5 m above the 

ground in a 10 m tall Goodding’s willow about 15 m away from the observers. The 

cuckoo fell silent at 0720 and was not heard from again. Aural detection only. Breeding 

classification: unconfirmed. 

Sandy Wash Survey 5 – 09/07/2007, 0759, 771666 E, 3796708 N, 254°/50 m. Yellowbilled cuckoo responded to the 4th playback with kuk-kowlp and coo calls from a patch of 

Fremont cottonwoods. Aural detection only. Breeding classification: unconfirmed. 

Fox Wash 

Fox Wash Survey 2 – 07/03/2007, 0824, 770846 E, 3797861 N, 208°/90 m. Yellow-billed 

cuckoo gave an unsolicited kuk-kowlp call. Observer stayed in area until 0900 and did not 

detect the cuckoo again. Aural detection only. Breeding classification: unconfirmed. 

Fox Wash Survey 3 – 08/11/2007, 0730, 770980 E, 3797401 N, 285°/250 m. Yellowbilled cuckoo responded to the 2nd playback with a series of coo calls. At 0711, the 

cuckoo moved into a stand of 14 m tall Fremont cottonwoods 20 m south of the survey 

point and continued to coo. Aural detection only. Breeding classification: unconfirmed. 

Mosquito Flats 

Mosquito Flats Survey 2 – 07/11/2007, 0735, 770624 E, 3797065 N, 52°/100 m. Yellowbilled cuckoo responded to the 2nd playback with three series of coo calls. Aural 

detection only. Breeding classification: unconfirmed. 

Mosquito Flats Survey 2 – 07/11/2007, 0753, 770866 E, 3796866 N, 340°/120 m. 

Yellow-billed cuckoo responded to the 5th playback with a series of coo calls. Observer 

suspected this was the same bird detected at 0735. Aural detection only. Breeding 

classification: unconfirmed. 

Mosquito Flats Survey 2 – 07/11/2007, 0832, 771178 E, 3796647 N, 335°/120 m. 

Yellow-billed cuckoo responded to the 4th playback with a kuk-kowlp call. Aural 

detection only. Breeding classification: unconfirmed. 

Mosquito Flats Survey 3 – 08/08/2007, 0614, 769838 E, 3797115 N, 30°/100 m. Yellowbilled cuckoo responded to the 3rd playback with a knocker call. Aural detection only. 

Breeding classification: unconfirmed. 

Mosquito Flats Survey 3 – 08/08/2007, 0650, 770142 E, 3797051 N, 60°/50 m. Yellowbilled cuckoo responded to the 2nd playback. Aural detection only. Breeding 

classification: unconfirmed. 

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Mosquito Flats Survey 3 – 08/08/2007, 0705, 770386 E, 3796995 N, 340°/30 m. Yellowbilled cuckoo gave an unsolicited knocker call. Aural detection only. Breeding 

classification: unconfirmed. 

Mosquito Flats Survey 3 – 08/08/2007, 0720, 770447 E, 3796936 N, 10°/70 m. Yellowbilled cuckoo gave an unsolicited coo call. Aural detection only. Breeding classification: 

unconfirmed. 

Mosquito Flats Survey 3 – 08/08/2007, 0808, 770866 E, 3795880 N, 290°/250 m. 

Yellow-billed cuckoo responded to the 3rd playback with four series of coo calls. Aural 

detection only. Breeding classification: unconfirmed. 

Mosquito Flats Survey 3 – 08/08/2007, 0827, 771091 E, 3796678 N, 55°/25 m. Yellowbilled cuckoo responded to the 2nd playback with a kuk-kowlp call. Aural detection only. 

Breeding classification: unconfirmed. 

Mosquito Flats Revisit 2 – 08/08/2007, 0640, 769927 E, 3797163 N, 120°/40 m. Yellowbilled cuckoo gave an unsolicited soft knocker call. Aural detection only. Breeding 

classification: unconfirmed. 

Mosquito Flats Revisit 2 – 08/08/2007, 0655, 769927 E, 3797163 N, 47°/75 m. Yellowbilled cuckoo gave unsolicited soft knocker calls and a kowlp call from the same area as 

the bird detected at 0640. Aural detection only. Breeding classification: unconfirmed. 

Mosquito Flats Revisit 2 – 08/08/2007, 0730, 769969 E, 3797221 N, Cuckoo1 @ 346°/35 

m, Cuckoo2 @ 40°/30 m, Cuckoo3 (?) @ 75°/100 m. Cuckoo1 gave an unsolicited soft 

kowlp call. Cuckoo2 responded with a soft knocker call. Cuckoo3 (?) gave a coo call at 

0805. Aural detection only. Breeding classification: unconfirmed. 

Mosquito Flats Revisit 3 – 08/11/2007, 0600, 769918 E, 3797290 N, Cuckoo1 @ 45°/30 

m, Cuckoo2 @ 260°/50 m, Cuckoo3 (?) @130°/100 m. Cuckoo1 gave an unsolicited kukkowlp call to which Cuckoo2 responded with its own kuk-kowlp call. At 0610, Cuckoo3 

(?) gave a coo call. Aural detection only. Breeding classification: unconfirmed. 

Mosquito Flats Revisit 3 – 08/11/2007, 0710, 769921 E, 3797333 N, Cuckoo1 @ 200°/15 

m, Cuckoo2 (?) @ 156°/20 m. Cuckoo1 gave unsolicited knocker calls. At 0817, 

Cuckoo2 (?) gave a knocker call. Aural detection only. Breeding classification: 

unconfirmed. 

Mosquito Flats Revisit 3 – 08/11/2007, 0832, 769918E, 3797293N, Cuckoo1 

@137°/20m, 127°/10m. Cuckoo1 gave an unsolicited “kuk-kowlp” call. At 0837, a “kukkowlp” call was heard from Cuckoo2(?). Aural detection only. Breeding classification: 

unconfirmed. 

Mosquito Flats Revisit 3 – 08/11/2007, 0947, 769983 E, 3797356 N, Cuckoo1 @ 170°/20 

m, Cuckoo2 @ 20°/20 m. Cuckoo1 gave an unsolicited knocker call, to which Cuckoo2 

responded with a kuk-kowlp call. Cuckoo1 then gave another knocker call. Aural 

detection only. Breeding classification: unconfirmed. 

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Mosquito Flats Survey 4 – 08/21/2007, 0623, 769867 E, 3797162 N, 49°/50 m. Yellowbilled cuckoo responded to the 3rd playback with a knocker call, then rolling kowlps. 

Aural detection only. Breeding classification: unconfirmed. 

Mosquito Flats Survey 4 –08/21/2007, 0648, 770235 E, 3797014 N, 43°/70 m. Yellowbilled cuckoo responded to the 3rd playback with ten kowlps. This was repeated two 

minutes later. Aural detection only. Breeding classification: unconfirmed. 

Mosquito Flats Survey 4 – 08/21/2007, 0702, 770532 E, 3796943 N, Cuckoo1 330°/30 

m, Cuckoo2 @ 15°/50 m. Cuckoo1 responded to the 3rd playback with a knocker-kowlp

call to which Cuckoo2 responded with its own knocker-kowlp. Cuckoo1 gave two more 

of the same call over the next six minutes. Aural detection only. Breeding classification: 

unconfirmed. 

Mosquito Flats Survey 5 – 09/07/2007, 0658, 770237 E, 3797039 N, Cuckoo1 @ 38°/45 

m, Cuckoo2 @ 320°/100 m. Cuckoo1 responded to the 2nd playback with a rapid kukkowlp call. Cuckoo2 responded with a coo call. Aural detection only. Breeding 

classification: unconfirmed. 

Saguaro Slot 

Saguaro Slot Revisit 1 – 06/27/2007, 0840, 769567 E, 3797523 N, 90°/50 m. Yellowbilled cuckoo gave two unsolicited kuk-kowlp calls within five minutes of one another. 

Aural detection only. Breeding classification: unconfirmed. 

Saguaro Slot Survey 2 – 07/11/2007, 0544, 769509 E, 3797585 N, Cuckoo1 @ 332°/50 

m, Cuckoo2 (?) @ 320°/15 m. Cuckoo1 responded to the 5th playback with kuk-kowlp 

call. At 0807, Cuckoo2 (?) gave a kuk-kowlp call, then another at 0817. Aural detection 

only. Breeding classification: unconfirmed. 

Saguaro Slot Survey 2 – 07/11/2007, 0610, 769348 E, 3797766 N, 44°/55 m. Yellowbilled cuckoo responded to the 5th playback with a kuk-kowlp call. Aural detection only. 

Breeding classification: unconfirmed. 

Saguaro Slot Revisit 2 – 07/15/2007, 0701, 769504 E, 3797593 N, 120°/100 m. Yellowbilled cuckoo gave a series of unsolicited coo calls, followed by a kuk-kowlp call at 0706, 

and a kuk call at 0712. Aural detection only. Breeding classification: unconfirmed. 

Saguaro Slot Revisit 2 – 07/15/2007, 0748, 769615 E, 3797444 N, 100°/75 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call. Aural detection only. Breeding 

classification: unconfirmed. 

Saguaro Slot Revisit 2 – 07/15/2007, 0810, 769596E, 3797375N, 35°/100m. Yellowbilled cuckoo gave an unsolicited “kuk-kowlp” call. Aural detection only. Breeding 

classification: unconfirmed. 

Saguaro Slot Survey 3 – 08/01/2007, 0545, 769502 E, 3797591 N, Cuckoo1 @ 110°/25 

m, Cuckoo2 @ 100°/150 m. Cuckoo1 responded to the 3rd playback with a knocker-kowlp

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call. Cuckoo2 responded a giving several coo calls. Aural detection only. Breeding 

classification: unconfirmed. 

Saguaro Slot Survey 3 – 08/01/2007, 0603, 769350 E, 3797770 N, 45°/25 m. Yellowbilled cuckoo responded to the 2nd playback with two knocker calls. Aural detection only. 

Breeding classification: unconfirmed. 

Saguaro Slot Survey 3 – 08/01/2007, 0703, 769790 E, 3797356 N, 358°/50 m. Yellowbilled cuckoo responded to the 1st playback with a kuk-kowlp call. Aural detection only. 

Breeding classification: unconfirmed. 

Saguaro Slot Survey 4 – 08/21/2007, 0630, 769513 E, 3797628 N, 40°/65 m. Yellowbilled cuckoo responded to the 5th playback with two kuk calls from a clump of tall 

Goodding’s willow. At 0646, 0707, and 0708, kuk-kowlp calls were given from this same 

location. Aural detection only. Breeding classification: unconfirmed. 

Saguaro Slot Survey 4 – 08/21/2007, 0801, 769619 E, 3797336 N, 90°/100 m. Yellowbilled cuckoo responded to the 1st playback with kuk calls from a clump of large 

Goodding’s willow. Aural detection only. Breeding classification: unconfirmed. 

Saguaro Slot Revisit 3 – 08/21/2007, 0638, 769503 E, 3797588 N, 90°/80 m. Yellowbilled cuckoo gave an unsolicited kuk-kowlp call. Aural detection only. Breeding 

classification: unconfirmed. 

Saguaro Slot Revisit 3 – 08/21/2007, 0822, 769747 E, 3797322 N, Cuckoo1 @ 196°/20 

m, Cuckoo2 (?) @ 330°/80 m. Cuckoo1 gave an unsolicited kuk call from 13 m above the 

ground in a 17 m tall, stressed Goodding’s willow. The cuckoo was working on getting 

the wings off a Microcentrum katydid, and then it hopped behind a clump of leaves and 

out of sight. At 0851, the observer did one playback to which Cuckoo2 (?) responded 

with rolling kowlps. At 0857, a fast, high-pitched kuk-kowlp was heard from the same 

location. Aural detection only. Breeding classification: unconfirmed. 

Saguaro Slot Revisit 4 – 08/27/2007, 0709, 769522 E, 3797572 N, 2°/30 m. Yellowbilled cuckoo did not respond to five plays of survey tape but did respond to one play of 

recorded coo call with a kuk-kowlp call from a clump of large Goodding’s willow. The 

cuckoo gave knocker calls at 0727 and 0730 from the same location. At 0750, knocker

calls came from some low, bushy Goodding’s willows in the same area. At 0823, another 

coo call was played and a cuckoo responded with knocks from a medium Goodding’s 

willow. At 0841, a cuckoo flew 50 m west to some large Goodding’s willows and gave 

three knocker calls in the next minute. Aural detection only. Breeding classification: 

unconfirmed. 

Saguaro Slot Revisit 4 – 08/27/2007, 0947, 769718 E, 3797312 N, Cuckoo1 @ 40°/120 

m, Cuckoo2 @ NA/50 m. Cuckoo1 responded to coo calls with a series of coo calls that 

lasted until 0952. It then gave two knocker-kowlps and several rolling knocker-kowlps. 

After this, Cuckoo2 began to coo 50 m west of Cuckoo1. At 1008, Cuckoo1 flew south 

through the high canopy. Aural and visual detection. Breeding classification: 

unconfirmed. 

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North Burn 

North Burn Survey 2 – 07/17/2007, 0919, 770276 E, 3798127 N, 203°/30 m. Yellowbilled cuckoo responded to the 2nd playback with hard kuks from a stand of dense, 

medium-sized Goodding’s willow. Aural detection only. Breeding classification: 

unconfirmed. 

North Burn Survey 3 – 08/08/2007, 0843, 770033 E, 3798393 N, 156°/80 m. Yellowbilled cuckoo gave unsolicited coo calls from a stand of large Fremont cottonwoods. 

Over the next fifteen minutes, the cuckoo continued to coo while moving south and west 

through the patch. Aural detection only. Breeding classification: unconfirmed. 

North Burn Survey 3 – 08/08/2007, 0905, 770253 E, 3798163 N, 256°/90 m. Yellowbilled cuckoo gave unsolicited coo calls from some large Fremont cottonwoods. The 

cuckoo was still cooing when the observers left the area at 0920. Aural detection only. 

Breeding classification: unconfirmed. 

North Burn Survey 4 – 08/26/2007, 0900, 770187 E, 3798244 N, 160°/75 m. Yellowbilled cuckoo responded to the 1st playback with a kuk-kowlp call from a stand of 10-15 m 

tall Fremont cottonwoods. Aural detection only. Breeding classification: unconfirmed. 

North Burn Survey 4 – 08/26/2007, 0915, 770423 E, 3798050 N, 200°/130 m. Yellowbilled cuckoo responded to the 2nd playback with a kuk-kowlp call from a stand of 10-15 

m tall Fremont cottonwoods. Aural detection only. Breeding classification: unconfirmed. 

Bill Williams Marsh 

Bill Williams Marsh Survey 1 – 06/14/2007, 0710, 769178 E, 3798091 N, 108°/60 m. 

Yellow-billed cuckoo responded to the 5th playback with a kuk-kowlp call. Aural 

detection only. Breeding classification: unconfirmed. 

Bill Williams Marsh Survey 3 – 08/01/2007, 0650, 769087 E, 3798176 N, Cuckoo1 @ 

15°/40 m, Cuckoo2 @ 42°/30 m, Cuckoo3 (?) @ 280°/100 m. Cuckoo1 gave an 

unsolicited kuk-kowlp call from river right followed by coo calls for the next seven 

minutes. Cuckoo2 responded with several coo calls at 0654. At 0658 Cuckoo3 (?) called 

from an 11m tall Goodding’s willow on river left. Aural detection only. Breeding 

classification: unconfirmed. 

Bill Williams Marsh Survey 3 – 08/01/2007, 0708, 769311 E, 3797975 N, 125°/120 m. 

Yellow-billed cuckoo gave an unsolicited kuk-kowlp call once at 0708 and again at 0711. 

Aural detection only. Breeding classification: unconfirmed. 

Bill Williams Marsh Survey 4 – 08/24/2007, 0710, 768990 E, 3798191 N, Cuckoo1 @ 

185°/30 m, Cuckoo2 @ 130°/20 m. Cuckoo1 gave a quick kuk-kowlp call after the 2nd

playback. At 0734, Cuckoo1 (?) flew from river right to a tamarisk on river left with prey 

in its bill. An observer entered the vegetation near Cuckoo1 (?) to nest/juvenile search 

and the cuckoo knocked upon her approach. By the time the observer obtained a visual on 

the cuckoo at 0735, it no longer was carrying prey. At 0736, the cuckoo flew back across 

the river and into the vegetation on river right. At 0759, Cuckoo1 (?) again flew back 

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across to river left, this time with an enormous moth in its bill. Upon landing, it began to 

knock at the observer who was still inside the habitat. The cuckoo flew further into the 

vegetation, towards a mesquite patch on the outer edge of the riparian zone giving 

knocker calls. Cuckoo1 (?) then jumped back into the vegetation, out of view with the 

moth still in its bill. At 0815 and again at 0829, Cuckoo1 (?) gave kuk-kowlp calls from 

river right. In addition to these observations, at 0734 and again 0750, a Cuckoo2 gave a 

kuk-kowlp call from near the Saguaro Slot survey route. Aural and visual detection. 

Breeding classification: unconfirmed. 

Bill Williams Marsh Survey 4 – 08/24/2007, 0911, 769536 E, 3797753 N, Cuckoo1 @ 

142°/80 m, Cuckoo2 (?) @ NA/40m. Cuckoo1 responded to the 1st playback with a kukkowlp call from river right. At 0915, Cuckoo2 (?) gave a kuk-kowlp call from river left 

from about 40 m back in the vegetation. At 0917, an unspecified cuckoo gave a kukkowlp from river right about 70 m upstream of the survey point. Additional kuk-kowlp

and knocker calls were heard from this area over the next half hour. Aural detection only. 

Breeding classification: unconfirmed. 

Ahakhav Tribal Preserve (Colorado River) 

Ahakhav Tribal Preserve 

Ahakhav Tribal Preserve Survey 1 – 06/16/2007, 0600, 745877 E, 3779802 N, 212°/70 

m. Yellow-billed cuckoo responded to the 4th playback with five kuks from 12 m above 

the ground in a Fremont cottonwood. Aural detection only. Breeding classification: 

unconfirmed. 

Ahakhav Tribal Preserve Survey 1 – 06/16/2007, 0620, 745918 E, 3779499 N, 24°/140 

m. Yellow-billed cuckoo responded to the 2nd playback with five kuks from a patch of 

young Goodding’s willows. Observer felt this may have been the same bird detected at 

0600. Aural detection only. Breeding classification: unconfirmed. 

Cibola National Wildlife Refuge (Colorado River) 

North Restoration 

North Restoration Survey 3 – 07/27/2007, 0618, 715867 E, 3695242 N, 170°/75 m. 

Yellow-billed cuckoo gave a quiet knocker-kowlp call after the 1st playback. Aural 

detection only. Breeding classification unconfirmed. 

Nature Trail Restoration 

Nature Trail Restoration Survey 1 - 06/16/2007, 0607, 716124 E, 3694449 N, 190°/20 m. 

Yellow-billed cuckoo flew in after the 2nd playback from the northwest and landed in the 

top of a 20 m tall Fremont cottonwood. The cuckoo flew southeast and out of sight, then 

gave a knocker-kowlp call 30 m away. Aural and visual detection. Breeding 

classification: unconfirmed. 

Nature Trail Restoration Survey 1 – 06/16/2007, 0625, 715898 E, 3694379 N, 150°/50 

m. Yellow-billed cuckoo gave a knocker-kowlp after the 2nd playback. The call came from 

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an area of mostly mesquite and arrowweed. Aural detection only. Breeding classification: 

unconfirmed. 

Nature Trail Restoration Revisit 1 – 07/02/2007, 716117 E, 3694428 N. Yellow-billed 

cuckoo flew unsolicited into a 15 m high tree and out of view. Visual detection only. 

Breeding classification: unconfirmed. 

Eucalyptus Restoration 

Eucalyptus Restoration Survey 2 – 07/02/2007, 0733, 713781 E, 3693750 N, 298°/10 m. 

Yellow-billed cuckoo flew in from previous survey point and perched 10 m above the 

ground in a eucalyptus. The cuckoo perched here for a couple minutes, and then flew 

south into another eucalyptus. Visual detection only. Breeding classification: 

unconfirmed. 

South Restoration 

South Restoration Survey 1 – 06/16/2007, 0858, 715917 E, 3684645 N, 290°/50 m. 

Yellow-billed cuckoo responded to the 5th playback with a knocker-kowlp call. This area 

of the patch contains the largest Fremont cottonwoods. Aural detection only. Breeding 

classification: unconfirmed. 

South Restoration Survey 2 – 07/02/07, 0734, 716008 E, 3684633 N, 180°/75 m.Yellowbilled cuckoo responded to the 1st playback with a knocker-kowlp call. Aural detection 

only. Breeding classification: unconfirmed. 

Picacho State Recreation Area (Colorado River) 

In 2007, no yellow-billed cuckoos were detected at this site. 

Imperial National Wildlife Refuge (Colorado River) 

Imperial South Restoration 

Imperial South Restoration Survey 1 – 06/27/2007, 0530, 734354 E, 3653848 N, 240°/50 

m. Yellow-billed cuckoo responded to the 1st playback with two knocker-kowlp calls. 

Several minutes later, another knocker-kowlp call was heard. Aural detection only. 

Breeding classification unconfirmed. 

Imperial South Restoration Survey 1 – 06/27/2007, 0601, 734370 E, 3653848 N, 75°/50 

m. Yellow-billed cuckoo gave an unsolicited knocker-kowlp after the survey was 

complete. Aural and visual detection. Breeding classification: unconfirmed. 

Imperial South Restoration Survey 2 – 07/18/2007, 0603, 734245 E, 3653885 N, 230°/50 

m. Yellow-billed cuckoo responded to the 1st playback with a knocker-kowlp call, then 

flew into a Fremont cottonwood. The cuckoo gave another knocker-kowlp call, flew out 

of sight, and gave one more knocker-kowlp. Aural and visual detection. Breeding 

classification: unconfirmed. 

162
Mittry Lake Wildlife Management Area/Pratt Restoration (Colorado River) 

In 2007, no yellow-billed cuckoos were detected at this site. 

Gila/Colorado River Confluence (Gila and Colorado Rivers) 

Colorado Confluence 

Colorado Confluence Survey 1 – 06/26/2007, 0817, 729869 E, 3623200 N, 300°/50 m. 

Yellow-billed cuckoo responded to the 1st playback with a kuk call. It then gave a 

knocker-kowlp call followed by several minutes of coo calls. All calls came from the 

California side of the river. Aural detection only. Breeding classification: unconfirmed. 

Colorado Confluence Survey 1 – 06/26/2007, 0840, 729495 E, 3623057 N, 40°/20 m. 

Yellow-billed cuckoo gave unsolicited knocker calls from the California side of the river. 

Aural detection only. Breeding classification: unconfirmed. 

Gila Confluence 

In 2007, no yellow-billed cuckoos were detected at this site. 

Yuma West Wetlands (Colorado River) 

In 2007, no yellow-billed cuckoos were detected at this site. 

Limitrophe Division (Colorado River) 

Limitrophe Division North 

In 2007, no yellow-billed cuckoos were detected at this site. 

Limitrophe Division South 

Limitrophe Division South Survey 1 – 06/13/2007, 0535, 707416 E, 3604314 N, 320°/50 

m. Yellow-billed cuckoo responded to 3rd playback with soft knocker-kowlp calls. Aural 

detection only. Breeding classification: unconfirmed. 

Limitrophe Division South Survey 1 – 06/13/2007, 0558, 707299 E, 3603923 N, 300°/100 

m. Yellow-billed cuckoo flew unsolicited toward survey point, landed out of view, and 

gave a knocker-kowlp call. The observer believed this cuckoo to be the same individual 

detected at 0535. Five minutes later, a cuckoo was seen 10 m above the ground in a 

Goodding’s willow. After two minutes, the cuckoo flew west and out of sight. Aural and 

visual detection. Breeding classification: unconfirmed. 

Quigley Pond Wildlife Management Area (Gila River) 

Quigley Pond Wildlife Management Area 

Quigley Pond WMA Survey 1 - 06/12/2007, 0537, 222632 E, 3625566 N, 210°/100 m. 

Yellow-billed cuckoo responded immediately to the 1st playback with a knocker-kowlp

call. It then flew 50 m northeast, landing in a top of a 20 m tall Fremont cottonwood. The 

163
cuckoo vocalized, and then flew southeast to the opposite side of the patch where it 

continued to call. Aural and visual detection. Breeding classification: unconfirmed. 

Quigley Pond WMA Survey 1 - 06/12/2007, 0631, 222392 E, 3625494 N, 300°/200 m. 

Yellow-billed cuckoo responded to 3rd playback with a slow knocks from an area of 

Goodding’s willow/tamarisk with scattered Fremont cottonwoods. Aural detection only. 

Breeding classification: unconfirmed. 

Quigley Pond WMA Survey 1 – 06/12/2007, 0730, 222204 E, 3625813 N, 110°/20 m. 

Yellow-billed cuckoo observed as it perched in a 10 m tall Goodding’s willow after the 

survey was complete. The bird flew off towards the middle of the patch. A couple 

minutes later, a soft knocker call was heard outside the patch. Aural and visual detection. 

Breeding classification: unconfirmed. 

Quigley Pond WMA Survey 2 – 07/09/2007, 0644, 222619 E, 3625363 N, 315°/50 m. 

Yellow-billed cuckoo responded to the 4th playback with a knocker-kowlp call from the 

top of a Goodding’s willow. It then flew off to the southwest. Aural and visual detection. 

Breeding classification: unconfirmed. 

164
Appendix 3. Incidental Yellow-billed Cuckoo 

Observations in the Lower Colorado River Watershed, 

2007 

Throughout the 2007 field season yellow-billed cuckoos were occasionally 

detected independent of USGS surveys in the lower Colorado River watershed along the 

Virgin River, Nevada, lower Colorado, Bill Williams and Gila Rivers, Arizona, 2007. 

These incidental sightings were made by staff of SWCA consulting firm while 

conducting field research on southwestern willow flycatchers, a species that has extensive 

habitat overlap with yellow-billed cuckoos. With the exception of Mormon Mesa, NV, 

and Imperial NWR/Great Blue Heron, AZ all of the locations where incidental sightings 

occurred were also surveyed by USGS employees this year, and many of these same 

birds were likely detected on our surveys. Please refer to Table 2.1 for site name overlap. 

Date Time Observer Number Location UTM* Comments 

7/16/2007 NA SWCA 1 Mormon Mesa, NV NA Individual heard 

calling. 

7/27/2007 NA BOR 1 Havasu NWR NA At Beal Lake calling. 

7/28/2007 NA BOR 1 Havasu NWR NA At Beal Lake calling in 

mesquite. 

6/26/2007 NA SWCA NA Bill Williams River 

NWR/Site 5 NA Calls heard. 

7/2/2007 NA SWCA 1 Bill Williams River 

NWR/Site 3 NA Individual heard calling. 

7/13/2007 NA SWCA 1 Bill Williams River 

NWR/Mineral Wash NA 

Individual heard 

calling. Individual 

observed to the North. 

7/25/2007 NA SWCA 1 

Bill Williams River 

NWR/Beaver Pond/Site 

8 

NA 

Individual heard 

calling, between beaver 

pond site and Site 8. 

7/3/2007 NA SWCA 1 Imperial NWR/Imperial 

Nursery NA Individual heard calling. 

7/24/2007 NA SWCA 2 Imperial NWR/Great 

Blue Heron NA 2 individuals heard counter calling. 

7/11/2007 NA SWCA 1 Gila Confluence North NA Individual heard 

calling. 

7/19/2007 NA SWCA 1 Gadsen NA Individual captured in 

mist net. 

165
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166
Appendix 4. Aerial Photographs of Yellow-billed Cuckoo 

Survey Points and Detections According to Survey 

Period, 2007 

Figures 4–1 through 4–13 are aerial photographs of yellow-billed cuckoo survey 

points and detections according to survey period, as well as supplemental visit detections 

on separate maps at sites along the White and Muddy Rivers, Nevada, lower Colorado 

and Gila Rivers, Arizona and California, 2007. 

Figure 4–1A. Orthorectified aerial photo display Pahranagat National Wildlife Refuge, 

NV, yellow-billed cuckoo survey area, 2007. 

167
Figure 4–1B. Orthorectified aerial photo display yellow-billed cuckoo survey points at 

Pahranagat National Wildlife Refuge, NV, Pahranagat North, 2007. No cuckoos were 

detected at this site in 2007. Red boundary line represents yellow-billed cuckoo survey 

habitat patch. 

168
Figure 4–1C. Orthorectified aerial photo display yellow-billed cuckoo survey points at 

Pahranagat National Wildlife Refuge, NV, Pahranagat South, 2007. No cuckoos were 

detected at this site in 2007. Red boundary line represents yellow-billed cuckoo survey 

habitat patch. 

169
Figure 4–2A. Orthorectified aerial photo display Overton Wildlife Management Area, NV, 

yellow-billed cuckoo survey area, 2007. 

170
Figure 4–2B. Orthorectified aerial photo display yellow-billed cuckoo survey points at 

Overton Wildlife Management Area, NV, Honeybee Pond, 2007. No cuckoos were 

detected at this site in 2007. Red boundary line represents yellow-billed cuckoo survey 

habitat patch. 

171
Figure 4–2C. Orthorectified aerial photo display yellow-billed cuckoo survey points at 

Overton Wildlife Management Area, NV, Overton Wildlife, 2007. No cuckoos were 

detected at this site in 2007. Red boundary line represents yellow-billed cuckoo survey 

habitat patch. 

172
Figure 4–3A. Orthorectified aerial photo display Grand Canyon National Park/ Lake 

Mead National Recreation Area, AZ, yellow-billed cuckoo survey area, 2007.

173
Figure 4–3B. Orthorectified aerial photo display yellow-billed cuckoo survey points at 

Grand Canyon National Park/Lake Mead National Recreation Area, AZ, RM 274.5, 2007. No 

cuckoos were detected at this site in 2007. Red boundary line represents yellow-billed 

cuckoo survey habitat patch. 

174
Figure 4–3C. Orthorectified aerial photo display yellow-billed cuckoo survey points at 

Grand Canyon National Park/Lake Mead National Recreation Area, AZ, Cuckoo Beach, 

2007. No cuckoos were detected at this site in 2007. Red boundary line represents yellowbilled cuckoo survey habitat patch. 

175
Figure 4–3D. Orthorectified aerial photo display yellow-billed cuckoo survey points at 

Grand Canyon National Park/Lake Mead National Recreation Area, AZ, Iceberg Ridge, 

2007. No cuckoos were detected at this site in 2007. Red boundary line represents yellowbilled cuckoo survey habitat patch.

176
Figure 4–3E. Orthorectified aerial photo display yellow-billed cuckoo survey points at 

Grand Canyon National Park/Lake Mead National Recreation Area, AZ, Chuckwalla Cove, 

2007. No cuckoos were detected at this site in 2007. Red boundary line represents yellowbilled cuckoo survey habitat patch. 

177
Figure 4–3F. O rthorectified aerial photo display yellow-billed cuckoo survey points at 

Grand Canyon National Park/Lake Mead National Recreation Area, AZ, Big Horn Draw, 

2007. No cuckoos were detected at this site in 2007. Red boundary line represents yellowbilled cuckoo survey habitat patch. 

178
Figure 4–4A. Orthorectified aerial photo display Havasu National Wildlife Refuge, AZ, 

yellow-billed cuckoo survey area, 2007. 

179
Figure 4–4B. O rthorectified aerial photo display yellow-billed cuckoo survey points and 

detection locations at Havasu National Wildlife Refuge area, AZ, Pintail Slough, 2007. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 

180
Figure 4–4C. Orthorectified aerial photo display yellow-billed cuckoo survey points and 

detection locations at Havasu National Wildlife Refuge area, AZ, North Dike, 2007. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 

181
Figure 4–4D. Orthorectified aerial photo display the yellow-billed cuckoo follow-up 

survey detection location at Havasu National Wildlife Refuge area, AZ, North Dike, 2007. 

182
Figure 4–4E. Orthorectified aerial photo display yellow-billed cuckoo survey points and 

detection locations at Havasu National Wildlife Refuge area, AZ, Topock Marsh 

Restoration, 2007. Red boundary line represents yellow-billed cuckoo survey habitat 

patch. 

183
Figure 4–4F. Orthorectified aerial photo display yellow-billed cuckoo follow-up survey 

detection locations at Havasu National Wildlife Refuge area, AZ, Topock Marsh 

Restoration, 2007. 

184
Figure 4–4G. Orthorectified aerial photo display yellow-billed cuckoo survey points at 

Havasu National Wildlife Refuge area, AZ, Topock Tamarisk, 2007. No cuckoos were 

detected at this site in 2007. Red boundary line represents yellow-billed cuckoo survey 

habitat patch. 

185
Figure 4–5A. Orthorectified aerial photo display Bill Williams National Wildlife Refuge, 

AZ, survey, 2007. 

186
Figure 4–5B. Orthorectified aerial photo display yellow-billed cuckoo survey points and 

detection locations at Bill Williams National Wildlife Refuge, AZ, Teepee Trail, 2007. 

187
Figure 4–5C. Orthorectified aerial photo display yellow-billed cuckoo survey points and 

detection locations at Bill Williams National Wildlife Refuge, AZ, Cottonwood Patch, 2007. 

188
Figure 4–5D. Orthorectified aerial photo display yellow-billed cuckoo follow-up survey 

detection locations at Bill Williams National Wildlife Refuge, AZ, Cottonwood Patch, 2007. 

189
Figure 4–5E. Orthorectified aerial photo display yellow-billed cuckoo survey points and 

detection locations at Bill Williams National Wildlife Refuge, AZ, Cave Wash, 2007. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 

190
Figure 4–5F. Orthorectified aerial photo display yellow-billed cuckoo follow-up survey 

detection locations at Bill Williams National Wildlife Refuge, AZ, Cave Wash, 2007. 

191
Figure 4–5G. Orthorectified aerial photo display yellow-billed cuckoo survey points and 

detection locations at Bill Williams National Wildlife Refuge, AZ, Honeycomb Bend, 2007. 

192
Figure 4–5H. Orthorectified aerial photo display yellow-billed cuckoo follow-up survey 

detection locations at Bill Williams National Wildlife Refuge, AZ, Honeycomb Bend, 2007. 

193
Figure 4–5I. Orthorectified aerial photo display yellow-billed cuckoo survey points and 

detection locations at Bill Williams National Wildlife Refuge, AZ, Mineral Wash, 2007. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 

194
Figure 4–5J. Orthorectified aerial photo display yellow-billed cuckoo follow-up survey 

detection locations at Bill Williams National Wildlife Refuge, AZ, Mineral Wash, 2007. 

195
Figure 4–5K. Orthorectified aerial photo display yellow-billed cuckoo survey points and 

detection locations at Bill Williams National Wildlife Refuge, AZ, Big Bend, 2007. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 

196
Figure 4–5L. Orthorectified aerial photo display yellow-billed cuckoo follow-up survey 

detection locations at Bill Williams National Wildlife Refuge, AZ, Big Bend, 2007. 

197
Figure 4–5M. Orthorectified aerial photo display yellow-billed cuckoo survey points and 

detection locations at Bill Williams National Wildlife Refuge, AZ, Gibraltar Rock, 2007. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 

198
Figure 4–5N. Orthorectified aerial photo display yellow-billed cuckoo follow-up survey 

detection locations at Bill Williams National Wildlife Refuge, AZ, Gibraltar Rock, 2007. 

199
Figure 4–5O. Orthorectified aerial photo display yellow-billed cuckoo survey points and 

detection locations at Bill Williams National Wildlife Refuge, AZ, Sandy Wash, 2007. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 

200
Figure 4–5P. Orthorectified aerial photo display yellow-billed cuckoo follow-up survey 

detection locations at Bill Williams National Wildlife Refuge, AZ, Sandy Wash, 2007. 

201
Figure 4–5Q. Orthorectified aerial photo display yellow-billed cuckoo survey points and 

detection locations at Bill Williams National Wildlife Refuge, AZ, Fox Wash, 2007. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 

202
Figure 4–5R. Orthorectified aerial photo display yellow-billed cuckoo follow-up survey 

detection locations at Bill Williams National Wildlife Refuge, AZ, Fox Wash, 2007. 

203
Figure 4–5S. Orthorectified aerial photo display yellow-billed cuckoo survey points and 

detection locations at Bill Williams National Wildlife Refuge, AZ, Mosquito Flats, 2007. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 

204
Figure 4–5T. Orthorectified aerial photo display yellow-billed cuckoo follow-up survey 

detection locations at Bill Williams National Wildlife Refuge, AZ, Mosquito Flats, 2007. 

205
Figure 4–5U. Orthorectified aerial photo display yellow-billed cuckoo survey points and 

detection locations at Bill Williams National Wildlife Refuge, AZ, Saguaro Slot, 2007. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 

206
Figure 4–5V. Orthorectified aerial photo display yellow-billed cuckoo follow-up survey 

detection locations at Bill Williams National Wildlife Refuge, AZ, Saguaro Slot, 2007. 

207
Figure 4–5W. Orthorectified aerial photo display yellow-billed cuckoo survey points and 

detection locations at Bill Williams National Wildlife Refuge, AZ, North Burn, 2007. 

208
Figure 4–5X. Orthorectified aerial photo display yellow-billed cuckoo survey points and 

detection locations at Bill Williams National Wildlife Refuge, AZ, Bill Williams River 

Marsh, 2007. Red boundary line represents yellow-billed cuckoo survey habitat patch. 

209
Figure 4–5Y. Orthorectified aerial photo display yellow-billed cuckoo follow-up survey 

detection locations at Bill Williams National Wildlife Refuge, AZ, Bill Williams River 

Marsh, 2007. 

210
Figure 4–6A. Orthorectified aerial photo display Ahakhav Tribal Preserve area, AZ 

yellow-billed cuckoo survey, 2007. 

211
Figure 4–6B. Orthorectified aerial photo display yellow-billed cuckoo survey points at 

Ahakhav Tribal Preserve, AZ, 2007. 

212
Figure 4–7A. Orhorectified aerial photo display Cibola National Wildlife Refuge area, AZ, 

yellow-billed cuckoo survey, 2006. 

213
Figure 4–7B. Orthorectified aerial photo display yellow-billed cuckoo survey points and 

detection locations at Cibola National Wildlife Refuge area, AZ, Cibola North Restoration, 

2007. Red boundary line represents yellow-billed cuckoo survey habitat patch. 

214
Figure 4–7C. Orthorectified aerial photo display yellow-billed cuckoo survey points and 

detection locations at Cibola National Wildlife Refuge area, AZ, Cibola Nature Trail 

Restoration, 2007. Red boundary line represents yellow-billed cuckoo survey habitat 

patch. 

215
Figure 4–7D. Orthorectified aerial photo display yellow-billed cuckoo survey points and 

detection locations at Cibola National Wildlife Refuge area, AZ, Cibola Eucalyptus 

Restoration, 2007. Red boundary line represents yellow-billed cuckoo survey habitat 

patch. 

216
Figure 4–7E. Orthorectified aerial photo display yellow-billed cuckoo survey points and 

detection location at Cibola National Wildlife Refuge area, AZ, Cibola South Restoration, 

2007. Red boundary line represents yellow-billed cuckoo survey habitat patch. 

217
Figure 4–8A. Orthorectified aerial photo display Picacho SRA, CA, yellow-billed cuckoo 

survey, 2007. 

218
Figure 4–8B. Orthorectified aerial photo display yellow-billed cuckoo survey points at 

Picacho SRA, CA along the lower Colorado River, CA, 2007. No cuckoos were detected at 

this site in 2007. Red boundary line represents yellow-billed cuckoo survey habitat patch. 

219
Figure 4–9A. Orthorectified aerial photo display Imperial National Wildlife Refuge, AZ 

yellow-billed cuckoo survey area, 2007. 

220
Figure 4–9B. Orthorectified aerial photo display yellow-billed cuckoo survey points and 

detection locations at Imperial National Wildlife Refuge, AZ, Imperial South Restoration, 

2007. Red boundary line represents yellow-billed cuckoo survey habitat patch. 

221
Figure 4–10A. Orthorectified aerial photo display Mittry Lake WMA/Pratt Restoration, AZ 

yellow-billed cuckoo survey area, 2007. 

222
Figure 4–10B. Orthorectified aerial photo display yellow-billed cuckoo survey points at 

Mittry Lake WMA/Pratt Restoration, AZ, 2006. No cuckoos were detected at this site in 

2007. Red boundary line represents yellow-billed cuckoo survey habitat patch. 

223
Figure 4–11A. Orthorectified aerial photo display Gila/Colorado River Confluence, AZ 

yellow-billed cuckoo survey area, 2007. 

224
Figure 4–11B. Orthorectified aerial photo display yellow-billed cuckoo survey points and 

detection locations at Gila/Colorado River Confluence, AZ, Colorado River, 2007. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 

225
Figure 4–11C. Orthorectified aerial photo display yellow-billed cuckoo survey points at 

Gila/Colorado River Confluence, AZ, Gila River, 2007. No cuckoos were detected at this 

site in 2007. Red boundary line represents yellow-billed cuckoo survey habitat patch. 

226
Figure 4–12A. Orthorectified aerial photo display Yuma West Wetlands, AZ, yellow-billed 

cuckoo survey area, 2006. 

227
Figure 4–12B. Orthorectified aerial photo display yellow-billed cuckoo survey points at 

Yuma West Wetlands, AZ, 2007. No cuckoos were detected at this site in 2007. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 

228
Figure 4–13A. Orthorectified aerial photos display Limitrophe Division, AZ yellow-billed 

cuckoo survey area, 2007. 

229
Figure 4–13B. Orthorectified aerial photos display yellow-billed cuckoo survey points at 

Limitrophe Division, AZ, Limitrophe Division North, 2007. No cuckoos were detected at this 

site in 2007. Red boundary line represents yellow-billed cuckoo survey habitat patch. 

230
Figure 4–13C. Orthorectified aerial photos display yellow-billed cuckoo survey points 

and detection locations at Limitrophe Division, AZ, Limitrophe Division South, 2007. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 

231
Figure 4–14A. Orthorectified aerial photo display Gila River/Quigley Pond WMA, AZ 

yellow-billed cuckoo survey area along the Gila River, 2007. 

232
Figure 4–14B. Orthorectified aerial photo display yellow-billed cuckoo survey points and 

cuckoo detection location at Gila River/Quigley Pond WMA, AZ, along the Gila River, 2007. 

Red boundary line represents yellow-billed cuckoo survey habitat patch. 

233
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234
Appendix 5. Habitat photos of yellow-billed cuckoo 

survey areas and sites in the lower Colorado River 

Watershed, 2007

Habitat photos of yellow-billed cuckoo survey areas and sites in the lower 

Colorado River watershed along the Muddy River, Nevada, lower Colorado, Bill 

Williams and Gila Rivers, Arizona and California, 2007. Listed with each photo are area 

name and site name when applicable. 

Pahranagat National Wildlife Refuge, NV 

 

 Pahranagat NWR, Pahranagat North Pahranagat NWR, Pahranagat North 

Pahranagat NWR, Pahranagat South Pahranagat NWR, Pahranagat South 

235
Overton Wildlife Management Area, NV 

 

Overton WMA, Honey Bee Pond. 

Photo taken from helicopter. 

Overton WMA, Honey Bee Pond

Overton WMA, Honey Bee Pond Overton WMA, Overton Wildlife. 

Photo taken from helicopter. 

Overton WMA, Overton Wildlife Overton WMA, Overton Wildlife 

236
Grand Canyon National Park/Lake Mead National Recreation Area, AZ 

 

 

Grand Canyon NP, River Mile 274. 

Photo taken from helicopter. 

Grand Canyon NP, River Mile 274 

Grand Canyon NP, River Mile 274 Lake Mead NRA, Cuckoo Beach. 

Photo taken from helicopter. 

Lake Mead NRA, Cuckoo Beach Lake Mead NRA, Cuckoo Beach 

237
Grand Canyon National Park/Lake Mead National Recreation Area, AZ (continued) 

 

Lake Mead NRA, Iceberg Ridge. 

Photo taken from helicopter. Lake Mead NRA, Iceberg Ridge 

Lake Mead NRA, Iceberg Ridge Lake Mead NRA, Chuckwalla Cove. 

Photo taken from helicopter. 

Lake Mead NRA, Chuckwalla Cove Lake Mead NRA, Chuckwalla Cove 

238
Grand Canyon National Park/Lake Mead National Recreation Area, AZ (continued) 

Havasu National Wildlife Refuge, AZ 

Lake Mead NRA, Big Horn Draw Lake Mead NRA, Big Horn Draw 

Havasu NWR, Pintail Slough Havasu NWR, North Dike 

Havasu NWR, North Dike Havasu NWR, Pintail Slough 

239
Havasu National Wildlife Refuge, AZ (continued) 

 

Havasu NWR, Topock Marsh Restoration Havasu NWR, Topock Marsh Restoration 

Havasu NWR, Topock Marsh Restoration. Havasu NWR, Topock Tamarisk 

Area of 2007 tree maintenance. 

Havasu NWR, Topock Tamarisk Havasu NWR, Topock Tamarisk. 

After monsoon flooding. 

240
Bill Williams River National Wildlife Refuge, AZ 

 Bill Williams River NWR, Teepee Trail Bill Williams River NWR, Teepee Trail 

 Bill Williams River NWR, Cottonwood Patch Bill Williams River NWR, Cottonwood Patch 

Bill Williams River NWR, Cave Wash Bill Williams River NWR, Cave Wash 

241
Bill Williams River National Wildlife Refuge, AZ (continued) 

 Bill Williams River NWR, Honeycomb Bend Bill Williams River NWR, Honeycomb Bend 

 Bill Williams River NWR, Mineral Wash Bill Williams River NWR, Mineral Wash 

 Bill Williams River NWR, Big Bend Bill Williams River NWR, Big Bend 

242
Bill Williams River National Wildlife Refuge, AZ (continued) 

 Bill Williams River NWR, Big Bend. 

 Photo taken from helicopter. 

Bill Williams River NWR, Gibraltar Rock 

 Bill Williams River NWR, Gibraltar Rock Bill Williams River NWR, Gibraltar Rock 

 Bill Williams River NWR, Sandy Wash Bill Williams River NWR, Sandy Wash 

243
Bill Williams River National Wildlife Refuge, AZ (continued) 

 Bill Williams River NWR, Fox Wash Bill Williams River NWR, Fox Wash 

 Bill Williams River NWR, Fox Wash Clockwise from top middle, North Burn, 

 Photo taken from helicopter. Mosquito Flats, Saguaro Slot, Bill 

 Williams Marsh. 

 Photo taken from helicopter 

 Bill Williams River NWR, Mosquito Flats Bill Williams River NWR, Mosquito Flats 

244
Bill Williams River National Wildlife Refuge, AZ (continued) 

Bill Williams River NWR, Saguaro Slot Bill Williams River NWR, Saguaro Slot 

 Bill Williams River NWR, North Burn Bill Williams River NWR, North Burn 

 Bill Williams River NWR, North Burn Bill Williams River NWR, 

 Bill Williams Marsh 

 Photo taken from helicopter. 

245
Ahakhav Tribal Preserve, AZ 

 

 

 

 Colorado River Indian Tribes Restoration Colorado River Indian Tribes Restoration 

Cibola National Wildlife Refuge, AZ 

 

Cibola NWR, North Restoration Cibola NWR, North Restoration 

Cibola NWR, Nature Trail Restoration Cibola NWR, Nature Trail Restoration 

246
Cibola National Wildlife Refuge, AZ (continued) 

Picacho State Recreation Area, CA 

Cibola NWR, Eucalyptus Restoration Cibola NWR, Eucalyptus Restoration 

Cibola NWR, South Restoration 

Picacho SRA 

Cibola NWR, South Restoration 

Picacho SRA 

247
Imperial National Wildlife Refuge, AZ 

Mittry Lake Wildlife Management Area 

 

 

Imperial NWR, Imperial South Restoration Imperial NWR, Imperial South Restoration

 

 Pratt Restoration Pratt Restoration 

Gila/Colorado River Confluence, AZ and CA 

Gila/Colorado River Confluence, 

Colorado River 

 Gila/Colorado River Confluence, Colorado 

River 

248
Gila/Colorado River Confluence, AZ and CA (continued) 

Yuma West Wetlands, AZ 

 

 Gila/Colorado River Confluence, Gila River 

 Gila/Colorado River Confluence, Gila River

 

Limitrophe Division, AZ 

 Yuma West Wetlands Yuma West Wetlands 

 Limitrophe Division North Limitrophe Division North 

249
Limitrophe Division, AZ (continued) 

 

 Limitrophe Division North Limitrophe Division North burn

Limitrophe Division South Limitrophe Division South 

250
125BGila River/Quigley Pond Wildlife Management Area, AZ 

 

126BGila River/Quigley Pond Wildlife Management Area, AZ 

 

Gila River/Quigley Pond WMA Gila River/Quigley Pond WMA 

Gila River/Quigley Pond WMA Gila River/Quigley Pond WMA 

251
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252
43BAppendix 6. List of Other Bird Species Observed During 

Yellow-billed Cuckoo Surveys in the Lower Colorado 

River Watershed 

TTable 6–1.T List of other bird species observed during 2007 yellow-billed cuckoo surveys, 

in the lower Colorado River watershed along the White and Muddy Rivers, Nevada, lower 

Colorado, Bill Williams and Gila Rivers, Arizona and California. 

Common name Scientific name Survey 

1 

Survey 

2 

Survey 

3 

Survey 

4 

Survey 

5 

Pahranagat National Wildlife Refuge (White River)

Clarks's Grebe Aechmophorus clarkii - - X X 

American White Pelican Pelecanus erythrorhynchos - - X - 

Great Blue Heron Ardea herodias X X X - 

Great Egret Ardea alba - - X - 

Turkey Vulture Cathartes aura X - - X 

Canada Goose Branta canadensis X X X - 

Osprey Pandion haliaetus - - X - 

American Kestrel Falco Sparverius - - X - 

Virginia Rail Rallus limicola - - X - 

American Coot Fulica americana X - X X 

Spotted Sandpiper Actitus macularia - - X - 

Belted Kingfisher Ceryle alcyon - - - X 

Nuttall's Woodpecker Picoides nuttallii - - X - 

Willow Flycatcher Empidonax traillii X - X - 

Brown-crested Flycatcher Myiarchus tyrannulus X X X - 

Warbling Vireo Vireo gilvus - - X - 

Common Raven Corvus corax - - X - 

Violet-green Swallow Tachycineta thalassina - - X - 

Cliff Swallow Petrochelidon pyrrhonota - - X - 

Bewick's Wren Thryomanes bewickii - - X - 

Marsh Wren Cistothorus palustris - - X - 

Lucy's Warbler Vermivora luciae - - X - 

Townsend's Warbler Dendroica townsendi - - X - 

Yellow Warbler Dendroica petechia X X X - 

Common Yellowthroat Geothlypis trichas - - X - 

Yellow-breasted Chat Icteria virens X - X - 

Western Tanager Piranga ludoviciana - - X - 

Song Sparrow Melospiza melodia - - X - 

253
TTable 6–1.T List of other bird species observed during 2007 yellow-billed cuckoo surveys, 

in the lower Colorado River watershed along the White and Muddy Rivers, Nevada, lower 

Colorado, Bill Williams and Gila Rivers, Arizona and California.—Continued 

Common name Scientific name Survey 

1 

Survey 

2 

Survey 

3 

Survey 

4 

Survey 

5 

Lazuli Bunting Passerina amoena - - X - 

Red-winged Blackbird Agelaius phoeniceus - - X - 

Great-tailed Grackle Quiscalus mexicanus - - X - 

Brown-headed Cowbird Molothrus ater X - - - 

Bullock's Oriole Icterus bullockii - - X - 

House Finch Carpodacus mexicanus - - X - 

Lesser Goldfinch Carduelis psaltria - - X - 

Overton Wildlife Management Area (Muddy River)

Clarks's Grebe Aechmophorus clarkii - X X - 

Double-crested Cormorant Phalacrocorax auritus - X - - 

American Bittern Botaurus lentiginosus - X - - 

Great Blue Heron Ardea herodias X X X - 

Cattle Egret Bubulcus ibis - X - - 

Black-crowned Night Heron Nycticorax nycticorax - - X - 

Canada Goose Branta canadensis - X X X 

Mallard Anas platyrhynchos - - X - 

Cooper's Hawk Accipiter cooperii - - X - 

American Kestrel Falco Sparverius - X - - 

Wild Turkey Meleagris gallopavo X X - - 

Gambel's Quail Callipepla gambellii - X X - 

Virginia Rail Rallus limicola - - - X 

American Coot Fulica americana - - X - 

Spotted Sandpiper Actitus macularia - - X - 

White-winged Dove Zenaida asiatica - X - - 

Mourning Dove Zenaida macroura X X X - 

Greater Roadrunner Geococcyx californianus - X X X 

Great Horned Owl Bubo virginianus - - - X 

Willow Flycatcher Empidonax traillii X X - - 

Common Raven Corvus corax - - X - 

Northern Rough-winged 

Swallow Stelgidopteryx serripennis X - - - 

Yellow Warbler Dendroica petechia X X X X 

254
TTable 6–1.T List of other bird species observed during 2007 yellow-billed cuckoo surveys, 

in the lower Colorado River watershed along the White and Muddy Rivers, Nevada, lower 

Colorado, Bill Williams and Gila Rivers, Arizona and California.—Continued 

Common name Scientific name Survey 

1 

Survey 

2 

Survey 

3 

Survey 

4 

Survey 

5 

Common Yellowthroat Geothlypis trichas X X X - 

Yellow-breasted Chat Icteria virens X X X - 

Song Sparrow Melospiza melodia X - X - 

Red-winged Blackbird Agelaius phoeniceus X - X X 

Great-tailed Grackle Quiscalus mexicanus - - X - 

Brown-headed Cowbird Molothrus ater X X - - 

Grand Canyon National Park/Lake Mead National Recreation Area (Colorado River)

Brown Pelican Pelecanus occidentalis - - X - 

Great Blue Heron Ardea herodias X X - X 

Snowy Egret Egretta thula - X - - 

Black-crowned Night-heron Nycticorax nycticorax - - X - 

White-Faced Ibis Plegadis chihi X - X - 

Turkey Vulture Cathartes aura X X - X 

Sharp-shinned Hawk Accipiter striatus - X - - 

Red-tailed Hawk Buteo jamaicensis - X X - 

Perigrine Falcon Falco peregrinus - - X - 

Gambel's Quail Callipepla gambellii - - X - 

Spotted Sandpiper Actitus macularia X - - X 

Ring-billed Gull Larus delewarensis - - X - 

Mourning Dove Zenaida macroura - - X - 

White-throated Swift Aeronautes saxatalis - X X X 

Greater Roadrunner Geococcyx californianus - X - - 

Western Wood-Pewee Contopus sordidulus X - - - 

Willow Flycatcher Empidonax traillii X - - - 

Black Phoebe Sayornis nigricans X - - X 

Ash-throated Flycatcher Myiarchus cinerascens X X - - 

Bell's Vireo Vireo bellii X X X X 

Plumbeous Vireo Vireo plumbeus X - - - 

Common Raven Corvus corax X X X - 

Violet-Green Swallow Tachycineta thalassina X - - - 

Northern Rough-winged 

Swallow Stelgidopteryx serripennis X - - - 

255
TTable 6–1.T List of other bird species observed during 2007 yellow-billed cuckoo surveys, 

in the lower Colorado River watershed along the White and Muddy Rivers, Nevada, lower 

Colorado, Bill Williams and Gila Rivers, Arizona and California.—Continued 

Common name Scientific name Survey 

1 

Survey 

2 

Survey 

3 

Survey 

4 

Survey 

5 

Bushtit Psaltriparus minimus X - - - 

Rock Wren Salpinctes obsoletus - - X - 

Canyon Wren Catherpes mexicanus X X X X 

Bewick's Wren Thryomanes bewickii X - X - 

Blue-gray Gnatcatcher Polioptila caerulea X - - - 

Yellow Warbler Dendroica petechia X X X X 

Yellow-rumped Warbler Dendroica coronata - - X - 

Common Yellowthroat Geothlypis trichas - X X X 

Yellow-breasted Chat Icteria virens X X X X 

Summer Tanager Piranga rubra - - X - 

Western Tanager Piranga ludoviciana X - X - 

Black-throated Sparrow Amphispiza bilineata - X - - 

Song Sparrow Melospiza melodia X X X X 

Blue Grosbeak Guiraca caerulea - - X - 

Lazuli Bunting Passerina amoena X X X - 

Red-winged Blackbird Agelaius phoeniceus X X X - 

Brown-headed Cowbird Molothrus ater X X X - 

Bullock's Oriole Icterus bullockii - X - - 

House Finch Carpodacus mexicanus - - X - 

Havasu National Wildlife Refuge (Colorado River)

Eared Grebe Podiceps nigricollis X - - - 

Western Grebe Aechmophorus occidentalis X - - - 

Clarks's Grebe Aechmophorus clarkii - X - - 

Double-crested Cormorant Phalacrocorax auritus - - X - 

Great Blue Heron Ardea herodias - X - - 

Great Egret Ardea alba - X - X 

Green Heron Butorides virescens - - X X 

Black-crowned Night Heron Nycticorax nycticorax - X - - 

White-faced Ibis Plegadis chihi - X - X 

Turkey Vulture Cathartes aura X X X X 

Canada Goose Branta canadensis - - - X 

Cinnamon Teal Anas cyanoptera - - - X 

256
TTable 6–1.T List of other bird species observed during 2007 yellow-billed cuckoo surveys, 

in the lower Colorado River watershed along the White and Muddy Rivers, Nevada, lower 

Colorado, Bill Williams and Gila Rivers, Arizona and California.—Continued 

Common name Scientific name Survey 

1 

Survey 

2 

Survey 

3 

Survey 

4 

Survey 

5 

Cooper's Hawk Accipeter cooperii X - - - 

Common Black Hawk Buteogallus anthracinus - - X - 

Red-tailed Hawk Buteo jamaicensis X - - - 

American Kestrel Falco Sparverius - - X X 

Gambel's Quail Callipepla gambellii X X X X 

Virginia Rail Rallus limicola - - X - 

American Coot Fulica americana X X X - 

Killdeer Charadrius vociferus - - X - 

Greater Yellowlegs Tringa melanoleuca - - - X 

Spotted Sandpiper Actitus macularia - - X - 

Western Sandpiper Calidris mauri - - - X 

White-winged Dove Zenaida asiatica X X X X 

Mourning Dove Zenaida macroura X X X X 

Yellow-billed Cuckoo Coccyzus americanus X X X - 

Greater Roadrunner Geococcyx californianus X X - X 

Great Horned Owl Tyto alba - X - - 

Lesser Nighthawk Chordeiles acutipennis X X - - 

Black-chinned Hummingbird Archilochus alexandri X X - - 

Broad-tailed Hummingbird Selasphorus platycercus X - - - 

Gila Woodpecker Melanerpes uropygialis - X X X 

Ladder-backed Woodpecker Picoides scalaris - X X - 

Pacific-slope Flycatcher Empidonax difficilis - - X - 

Black Phoebe Sayornis nigricans - X X X 

Say's Phoebe Sayornis saya X - - - 

Ash-throated Flycatcher Myiarchus cinerascens X X X X 

Brown-crested Flycatcher Myiarchus tyrannulus - - X - 

Cassin's Kingbird Tyrannus vociferans X - - - 

Western Kingbird Tyrannus verticalis X X X X 

Bell's Vireo Vireo bellii X X X - 

Warbling Vireo Vireo gilvus - X X - 

Common Raven Corvus corax - - X X 

257
TTable 6–1.T List of other bird species observed during 2007 yellow-billed cuckoo surveys, 

in the lower Colorado River watershed along the White and Muddy Rivers, Nevada, lower 

Colorado, Bill Williams and Gila Rivers, Arizona and California.—Continued 

Common name Scientific name Survey 

1 

Survey 

2 

Survey 

3 

Survey 

4 

Survey 

5 

Northern Rough-winged 

Swallow Stelgidopteryx serripennis - - X - 

Cliff Swallow Petrochelidon pyrrhonota - X X - 

Verdin Auriparus flaviceps - - X X 

Marsh Wren Cistothorus palustris - X - - 

Blue-gray Gnatcatcher Polioptila caerulea X - - - 

Black-tailed Gnatcatcher Polioptila melanura - - X - 

Northern Mockingbird Mimus polyglottos X - X - 

Crissal Thrasher Toxostoma crissale - - - X 

Nashville Warbler Vermivora ruficapilla - - X - 

Lucy's Warbler Vermivora luciae X - X - 

Yellow Warbler Dendroica petechia - - - X 

Common Yellowthroat Geothlypis trichas X - - X 

Yellow-breasted Chat Icteria virens X X X - 

Western Tanager Piranga ludoviciana - - X - 

Abert's Towhee Pipilo aberti X X X X 

Song Sparrow Melospiza melodia X - X - 

Black-headed Grosbeak Pheucticus melanocephalus - X X - 

Blue Grosbeak Guiraca caerulea X X X X 

Red-winged Blackbird Agelaius phoeniceus X X X X 

Yellow-headed Blackbird Xanthocephalus xanthocephalus - X - - 

Great-tailed Grackle Quiscalus mexicanus X X X X 

Brown-headed Cowbird Molothrus ater X X X - 

Hooded Oriole Icterus cucullatus - - X - 

Bullock's Oriole Icterus bullockii X X X - 

House Finch Carpodacus mexicanus X - X X 

Bill Williams River National Wildlife Refuge (Bill Williams River)

Pied-billed Grebe Podilymbus podiceps - - X X X 

Eared Grebe Podiceps nigricollis - - - X - 

Western Grebe Aechmophorus occidentalis X X X X X 

Clark's Grebe Aechmophorus clarkii X X X X X 

Double-crested Cormorant Phalacrocorax auritus - X X - X 

258
TTable 6–1.T List of other bird species observed during 2007 yellow-billed cuckoo surveys, 

in the lower Colorado River watershed along the White and Muddy Rivers, Nevada, lower 

Colorado, Bill Williams and Gila Rivers, Arizona and California.—Continued 

Common name Scientific name Survey 

1 

Survey 

2 

Survey 

3 

Survey 

4 

Survey 

5 

Magnificent Frigatebird Fregata magnificens - - - - X 

Least Bittern Ixobrychus exilis - X X X X 

Great Blue Heron Ardea herodias X X X X X 

Great Egret Ardea alba - X X X X 

Snowy Egret Egretta thula X X - X X 

Green Heron Butorides virescens X X X X X 

Black-crowned Night Heron Nycticorax nycticorax - X - X X 

White-faced Ibis Plegadis chihi X X X X X 

Turkey Vulture Cathartes aura X X X X X 

Greater White-fronted Goose Anser albifrons - - - - X 

Gadwall Anas strepera - - - - X 

Mallard Anas platyrhynchos X X X X X 

Cinnamon Teal Anas cyanoptera - - - X X 

Northern Shoveler Anas clypeta - - - - X 

Green-winged Teal Anas creeca - - X - - 

Sharp-shinned Hawk Accipiter striatus - - - - X 

Cooper's Hawk Accipiter cooperii X - - X X 

Red-tailed Hawk Buteo Jamaicensis X X X X - 

American Kestrel Falco sparverius - X - X - 

Peregrine Falcon Falco peregrinus - X X X - 

Gambel's Quail Callipepla gambelli X X X X X 

Black Rail Laterallus jamaicensis X X X - - 

Clapper Rail Rallus longirostris X - X - - 

Virginia Rail Rallus limicola X X X X X 

Sora Porzana carolina - - X X - 

Common Moorhen Gallinula chloropus - - X X X 

American Coot Fulica americana X - X X X 

Long-billed Curlew Numenius americanus X X - - - 

Killdeer Charadrius vociferus X X X X - 

American Avocet Recurvirostra americana - - - X X 

Black-necked Stilt Himantopus mexicanus - - - - X 

Spotted Sandpiper Actitus macularia - X X - - 

259
TTable 6–1.T List of other bird species observed during 2007 yellow-billed cuckoo surveys, 

in the lower Colorado River watershed along the White and Muddy Rivers, Nevada, lower 

Colorado, Bill Williams and Gila Rivers, Arizona and California.—Continued 

Common name Scientific name Survey 

1 

Survey 

2 

Survey 

3 

Survey 

4 

Survey 

5 

Least Sandpiper Tachycineta bicolor - X - X - 

Ring-billed Gull Larus delewarensis - - X X X 

Caspian Tern Sterna caspia - - - - X 

Forster's Tern Sterna forsteri - - - X X 

Rock Dove Columba livia - - - X - 

Mourning Dove Zenaida macraura X X X X X 

White-winged Dove Zenaida asiatica X X X X - 

Common Ground-Dove Columbina passerina - X - X - 

Greater Roadrunner Geococcyx californianus X X X X X 

Great Horned Owl Bubo virginianus X X - X X 

Lesser Nighthawk Chordeiles acutipennis X X X X X 

Common Nighthawk Chordeiles acutipennis X - - - - 

White-throated Swift Aeronautes saxatalis X X - X - 

Black-chinned Hummingbird Archilochus alexandri X X - X - 

Anna's Hummingbird Calypte anna - X X - X 

Costa's Hummingbird Calypte costae X - - - - 

Belted Kingfisher Ceryle alcyon - - - X X 

Gila Woodpecker Melanerpes uropygialis X X X X X 

Ladder-backed Woodpecker Picoides scalaris X X X X X 

Hairy Woodpecker Dendrocopos villosus - X - - - 

Gilded Flicker Colaptes chrysoides - - - - X 

Northern Flicker Colaptes auratus - - X X - 

Western Wood-Pewee Contopus sordidulus X - - X X 

Willow Flycatcher Empidonax traillii X X - X X 

Western Flycatcher Empidonax difficilis - X - X - 

Pacific-slope Flycatcher Empidonax difficilis - X X X X 

Black Phoebe Sayornis nigricans X X X X X 

Say's Phoebe Sayornis saya X X X - - 

Vermillion Flycatcher Pyrocephalus rubinus X X - X - 

Ash-throated Flycatcher Myiarchus cinerascens X X X X X 

Brown-crested Flycatcher Myiarchus tyrannulus X X X X X 

Cassin's Kingbird Tyrannus vociferans - - X - - 

260
TTable 6–1.T List of other bird species observed during 2007 yellow-billed cuckoo surveys, 

in the lower Colorado River watershed along the White and Muddy Rivers, Nevada, lower 

Colorado, Bill Williams and Gila Rivers, Arizona and California.—Continued 

Common name Scientific name Survey 

1 

Survey 

2 

Survey 

3 

Survey 

4 

Survey 

5 

Western Kingbird Tyrannus verticalis X X X X X 

Loggerhead Shrike Lanius ludovicianus - - - X X 

Bell's Vireo Vireo bellii X X X X X 

Cassin's Vireo Vireo cassinii - - - X - 

Warbling Vireo Vireo gilvus - - - X X 

Common Raven Corvus corax X X - - X 

Tree Swallow Tachycineta bicolor - X X X X 

Violet-green Swallow Tachycineta thalassina X X - X - 

Northern Rough-winged 

Swallow Stelgidopteryx serripennis X X X X X 

Cliff Swallow Petrochelidon pyrrhonota X X X X X 

Barn Swallow Hirundo rustica - - - X X 

Verdin Auriparus flaviceps X X X X X 

Bushtit Psaltriparus minimus - X - - - 

White-breasted Nuthatch Sitta carolinensis - - - - X 

Cactus Wren Campylorhynchus brunneicapillus - X - - X 

Rock Wren Salpinctes obsoletus - X - - - 

Canyon Wren Catherpes mexicanus X X X X X 

Bewick's Wren Thryomanes bewickii X X - X X 

House Wren Troglodytes aedon - - - X X 

Marsh Wren Cistothorus palustris - X X X X 

Blue-gray Gnatcatcher Polioptila caerulea - - - X X 

Black-tailed Gnatcatcher Polioptila nigriceps X X X X X 

Northern Mockingbird Mimus polyglottos - - X - X 

Crissal Thrasher Toxostoma crissale X X X X X 

Phainopepla Phainopepla nitens X - X X X 

Orange-crowned Warbler Vermivora celata X - - X X 

Nashville Warbler Vermivora ruficapilla - - - X X 

Lucy's Warbler Vermivora luciae X X X X - 

Yellow Warbler Dendroica petechia X X X X X 

Magnolia Warbler Dendroica magnolia - - - X - 

Yellow-rumped Warbler Dendroica coronata - - - - X 

261
TTable 6–1.T List of other bird species observed during 2007 yellow-billed cuckoo surveys, 

in the lower Colorado River watershed along the White and Muddy Rivers, Nevada, lower 

Colorado, Bill Williams and Gila Rivers, Arizona and California.—Continued 

Common name Scientific name Survey 

1 

Survey 

2 

Survey 

3 

Survey 

4 

Survey 

5 

Black-throated Gray Warbler Dendroica nigrescens - - - X X 

Townsend's Warbler Dendroica townsendi - - - - X 

Common Yellowthroat Geothlypis trichas X X X X X 

Wilson's Warbler Wilsonia pusilla - - X X - 

Yellow-breasted Chat Icteria virens X X X X X 

Summer Tanager Piranga rubra X X X X X 

Western Tanager Piranga ludoviciana X X X X X 

Canyon Towhee Pipilo fuscus - X - X - 

Abert's Towhee Pipilo aberti X X X X X 

Cassin's Sparrow Aimophila cassinii - X - - - 

Chipping Sparrow Spizella passerina - X - X X 

Black-throated Sparrow Amphispiza bilineata - X X X - 

Song Sparrow Melospiza melodia X X X X X 

Black-headed Grosbeak Pheucticus melanocephalus X X X X X 

Blue Grosbeak Guiraca caerulia X X X X X 

Lazuli Bunting Passerina amoena - - X X X 

Indigo Bunting Passerina cyanea - X - - - 

Red-winged Blackbird Agelaius phoenieus X X X X X 

Yellow-headed Blackbird Xanthocephalus Xanthocephalus X X - X X 

Great-tailed Grackle Quiscalus mexicanus X X X X X 

Brown-headed Cowbird Molothrus ater X X X X - 

Bullock's Oriole Icterus bullockii X X X X X 

House Finch Carpodacus mexicanus X X X X X 

Lesser Goldfinch Carduelis psaltria X X X X X 

Ahakhav Tribal Preserve (Colorado River)

Double-crested Cormorant Phalacrocorax auritus - X - - 

Black-crowned Night Heron Nycticorax nycticorax - - - X 

Cooper's Hawk Accipiter cooperii - - - X 

Peregrine Falcon Falco peregrinus - - - X 

Gambel's Quail Callipepla gambellii - X X X 

White-winged Dove Zenaida asiatica - X X X 

Mourning Dove Zenaida Macraura - X X X 

262
TTable 6–1.T List of other bird species observed during 2007 yellow-billed cuckoo surveys, 

in the lower Colorado River watershed along the White and Muddy Rivers, Nevada, lower 

Colorado, Bill Williams and Gila Rivers, Arizona and California.—Continued 

Common name Scientific name Survey 

1 

Survey 

2 

Survey 

3 

Survey 

4 

Survey 

5 

Barn Owl Tyto alba - X - - 

Great Horned Owl Bubo virginianus - X X - 

Lesser Nighthawk Chordeiles acutipennis - X - - 

Black-chinned Hummingbird Archilochus alexandri - X - - 

Anna's Hummingbird Calypte anna - X - X 

Rufous Hummingbird Selasphorus rufus - - X X 

Ladder-backed Woodpecker Picoides scalaris - - X X 

Pacific-slope Flycatcher Empidonax difficilis - - - X 

Willow Flycatcher Empidonax traillii - - - X 

Black Phoebe Sayornis nigricans - - - X 

Vermillion Flycatcher Pyrocephalus rubinus - X - - 

Brown-crested Flycatcher Myairchus tyrannulus - - X X 

Ash-throated Flycatcher Myiarchus cinerascens - X - X 

Western Kingbird Tyrranus verticalis - X - X 

Common Raven Corvus corax - - - X 

Tree Swallow Tachycineta bicolor - X - - 

Cliff Swallow Petrochelidon pyrrhonota - X - - 

Verdin Auriparus flaviceps - X X X 

Bewick's Wren Thryomanes bewickii - - X - 

House Wren Troglodytes aedon - - - X 

Ruby-crowned Kinglet Regulus calendula - - - X 

Blue-gray Gnatcatcher Polioptila caerulea - - - X 

Northern Mockingbird Mimus polyglottos - X - - 

Phainopepla Phainopepla nitens - - - X 

Orange-crowned Warbler Vermivora celata - - - X 

Nashville Warbler Vermivora ruficapilla - - - X 

Lucy's Warbler Vermivora luciae - - - X 

Yellow Warbler Dendroica petechia X - - X 

Black-throated Gray Warbler Dendroica nigrescens - - - X 

Common Yellowthroat Geothlypis trichas - - - X 

Wilson's Warbler Wilsonia pusilla - - X X 

Yellow-breased Chat Icteria virens X - - - 

263
TTable 6–1.T List of other bird species observed during 2007 yellow-billed cuckoo surveys, 

in the lower Colorado River watershed along the White and Muddy Rivers, Nevada, lower 

Colorado, Bill Williams and Gila Rivers, Arizona and California.—Continued 

Common name Scientific name Survey 

1 

Survey 

2 

Survey 

3 

Survey 

4 

Survey 

5 

Western Tanager Piranga ludoviciana - - - X 

Spotted Towhee Pipilo maculates - - - X 

Abert's Towhee Pipilo aberti - X X X 

Song Sparrow Melospiza melodia X - - X 

Black-headed Grosbeak Pheuticus melanocephalus - X X 

Blue Grosbeak Guiraca caerulea X X - X 

Lazuli Bunting Passerina ciris - - X X 

Red-winged Blackbird Agelaius phoeniceus - X X - 

Western Meadowlark Sternella neglecta - - X X 

Yellow-headed Blackbird Xanthocephalus xanthocephalus - X - - 

Great-tailed Grackle Quiscalus mexicanus - X X X 

Brown-headed Cowbird Molothrus ater - X X - 

Bullock's Oriole Icterus bullockii - X - X 

House Finch Carpodacus mexicanus - X X X 

Lesser Goldfinch Carduelis psaltria - X X X 

Cibola National Wildlife Refuge (Colorado River)

Snowy Egret Egretta thula - - - X 

White-faced Ibis Plegadis chihi - - - X 

Turkey Vulture Cathartes aura - X - - 

Northern Harrier Circus cyaneus - - - X 

American Kestrel Falco sparverius - - X X 

Prairie Falcon Falco mexicanus - - - X 

Gambel's Quail Callipepla gambellii - - X - 

Killdeer Charadrius vociferus - - X - 

American Coot Fulica americana - - X - 

Eurasian Collared Dove Streptopelia decaocto - - X - 

White-winged Dove Zenaida asiatica X X X X 

Mourning Dove Zenaida macraura X X X - 

Common Ground-dove Columbina passerine - - - X 

Great Horned Owl Bubo virginianus X - X - 

Lesser Nighthawk Chordeiles acutipennis - X - - 

Black-chinned Hummingbird Archilochus alexandri - - X - 

264
TTable 6–1.T List of other bird species observed during 2007 yellow-billed cuckoo surveys, 

in the lower Colorado River watershed along the White and Muddy Rivers, Nevada, lower 

Colorado, Bill Williams and Gila Rivers, Arizona and California.—Continued 

Common name Scientific name Survey 

1 

Survey 

2 

Survey 

3 

Survey 

4 

Survey 

5 

Anna's Hummingbird Calypte anna - - - X 

Ladder-backed Woodpecker Picoides scalaris X X - - 

Willow Flycatcher Empidonax traillii - - - X 

Pacific-slope Flycatcher Empidonax difficilis - - - X 

Black Phoebe Sayornis nigricans - - - X 

Ash-throated Flycatcher Myiarchus cinerascens X X X X 

Western Kingbird Tyrannus verticalis X X X X 

Bell's Vireo Vireo bellii - X - X 

Common Raven Corvus corax - - X - 

Cliff Swallow Petrochelidon pyrrhonota X - - - 

Verdin Auriparus flaviceps - X - - 

Bewick's Wren Thyromanes bewickii - - - X 

Northern Mockingbird Mimus polyglottos - X X X 

Crissal Thrasher Toxostoma crissale - - X - 

Black-tailed Gnatcatcher Polioptila melanura - - X X 

Yellow Warbler Dendroica petechia - X - X 

American Redstart Setophaga ruticilla - - - X 

Common Yellowthroat Geothlypis trichas - - X - 

Wilson's Warbler Wilsonia pusilla - - - X 

Yellow-breasted Chat Icteria virens X X X - 

Western Tanager Piranga ludoviciana - - X - 

Abert's Towhee pipilo aberti X X X X 

Black-headed Grosbeak Pheuticus melanocephalus - - X - 

Blue Grosbeak Guiraca caerulea - X - X 

Yellow-headed Blackbird Xanthocephalus xanthocephalus X X - - 

Red-winged Blackbird Agelaius phoeniceus - X X - 

Great-tailed Grackle Quiscalus mexicanus X X X - 

Brown-headed Cowbird Molothrus Ater X - X X 

Bullock's Oriole Icterus bullockii - - X - 

House Finch Carpdacus mexicanus - - - X 

Picacho State Recreation Area (Colorado River)

Green Heron Butorides virescens X - - - 

265
TTable 6–1.T List of other bird species observed during 2007 yellow-billed cuckoo surveys, 

in the lower Colorado River watershed along the White and Muddy Rivers, Nevada, lower 

Colorado, Bill Williams and Gila Rivers, Arizona and California.—Continued 

Common name Scientific name Survey 

1 

Survey 

2 

Survey 

3 

Survey 

4 

Survey 

5 

White-faced Ibis Plegadis chihi - - - X 

Turkey Vulture Cathartes aura X X X X 

Gambel's Quail Callipepla gambellii - X X X 

White-winged Dove Zenaida asiatica X X X - 

Great Horned Owl Bubo virginianus X - - - 

Gila Woodpecker Melanerpes uropygialis X X X - 

Ladder-backed Woodpecker Picoides scalaris X X - - 

Ash-throated Flycatcher Myiarchus cinerascens X X X - 

Western Kingbird Tyrannus verticalis X X - - 

Loggerhead Shrike Lanius ludovicianus - X X X 

Bell's Vireo Vireo bellii - X X X 

Verdin Auriparus flaviceps X X X X 

Black-tailed Gnatcatcher Polioptila melanura - - - X 

Wilson's Warbler Wilsonia pusilla - - - X 

Common Yellowthroat Geothlypis trichas X X - - 

Yellow-breasted Chat Icteria virens X X - - 

Western Tanager Piranga ludoviciana - X X - 

Abert's Towhee pipilo aberti X - - X 

Black-headed Grosbeak Pheuticus melanocephalus - - X - 

Great-tailed Grackle Quiscalus mexicanus X - - X 

Brown-headed Cowbird Molothrus Ater - X - - 

Bullock's Oriole Icterus bullockii - - - X 

House Finch Carpdacus mexicanus X - X - 

Imperial National Wildlife Refuge (Colorado River)

Pied-billed Grebe Podilymbus podiceps X - - - 

Least Bittern Ixobrychus exilis X - - - 

White-faced Ibis Plegadis chihi X - - - 

American Coot Fulica americana X - - - 

White-winged Dove Zenaida asiatica X - - - 

Lesser Nighthawk Chordeiles acutipennis X - - - 

Ladder-backed Woodpecker Picoides scalaris X - - - 

Ash-throated Flycatcher Myiarchus cinerascens X - - - 

266
TTable 6–1.T List of other bird species observed during 2007 yellow-billed cuckoo surveys, 

in the lower Colorado River watershed along the White and Muddy Rivers, Nevada, lower 

Colorado, Bill Williams and Gila Rivers, Arizona and California.—Continued 

Common name Scientific name Survey 

1 

Survey 

2 

Survey 

3 

Survey 

4 

Survey 

5 

Loggerhead Shrike Lanius ludovicianus X - - - 

Bell's Vireo Vireo bellii X - - - 

Verdin Auriparus flaviceps X - - - 

Summer Tanager Piranga rubra X - - - 

Blue Grosbeak Guiraca caerulea X - - - 

Red-winged Blackbird Agelaius phoeniceus X - - - 

Great-tailed Grackle Quiscalus mexicanus X - - - 

Bullock's Oriole Icterus bullockii X - - - 

Mittry Lake Wildlife Magangement Area (Colorado River)

Great Egret Ardea alba X - X - 

White-faced Ibis Plegadis chihi X - - X 

Turkey Vulture Cathartes aura - - - X 

Cooper's Hawk Accipeter cooperi - - - X 

Zone-tailed Hawk Buteo albonotatus - - - X 

Ring-necked Pheasant Phasianus colcichus - - - X 

Gambel's Quail Callipepla gambellii X X - - 

American Coot Fulica americana X X X X 

Killdeer Charadrius vociferus - - - X 

White-winged Dove Zenaida asiatica X X X X 

Mourning Dove Zenaida macroura X X X - 

Common Ground-Dove Columbina passerine - - - X 

Great Horned Owl Bubo virginianus - - X - 

Lesser Nighthawk Chordeiles acutipennis X X - - 

Anna's Hummingbird Calypte anna - X - - 

Gila Woodpecker Melanerpes uropygialis X - - - 

Ladder-backed Woodpecker Picoides scalaris X X X X 

Ash-throated Flycatcher Myiarchus cinerascens X - - - 

Western Kingbird Tyrannus verticalis X - - - 

Bell's Vireo Vireo bellii X - - - 

Cliff Swallow Petrochelidon pyrrhonota X X - - 

Verdin Auriparus flaviceps X X - - 

Common Yellowthroat Geothlypis trichas X - - - 

267
TTable 6–1.T List of other bird species observed during 2007 yellow-billed cuckoo surveys, 

in the lower Colorado River watershed along the White and Muddy Rivers, Nevada, lower 

Colorado, Bill Williams and Gila Rivers, Arizona and California.—Continued 

Common name Scientific name Survey 

1 

Survey 

2 

Survey 

3 

Survey 

4 

Survey 

5 

Western Tanager Piranga ludoviciana - - X - 

Abert's Towhee Pipilo aberti X X X X 

Song Sparrow Melospiza melodia X X X - 

Red-winged Blackbird Agelaius phoeniceus X X X X 

Black-headed Grosbeak Pheucticus melanocephalus - X - - 

Great-tailed Grackle Quiscalus mexicanus - X - - 

Brown-headed Cowbird Molothrus Ater X X - - 

House Finch Carpdacus mexicanus X - - - 

Gila/Colorado Rivers Confluence (Gila and Colorado Rivers)

Great Egret Ardea alba - - X - 

Snowy Egret Egretta thula - X - - 

Green Heron Butorides virescens X - - - 

White-faced Ibis Plegadis chihi X - - - 

Northern Harrier Circus cyaneus - X - - 

Red-tailed Hawk Buteo jamaicensis X - - - 

American Kestrel Falco sparverius X X X - 

Black-necked Stilt Himantopus mexicanus X X - - 

Gambel's Quail Callipepla gambellii X X X - 

Common Moorhen Gallinula chloropus - X - - 

American Coot Fulica americana - X X - 

Killdeer Charadrius vociferus - X - - 

Black Tern Chlidonias niger - X - - 

White-winged Dove Zenaida asiatica X X X - 

Mourning Dove Zenaida macroura X X X - 

Common Ground-Dove Columbina passerine X - - - 

Great Horned Owl Bubo virginianus - X - - 

Anna's Hummingbird Calypte anna - - X - 

Black-chinned Hummingbird Archilochus alexandri - X - - 

Gila Woodpecker Melanerpes uropygialis - - X - 

Ladder-backed Woodpecker Picoides scalaris X - X - 

Willow Flycatcher Empidonax traillii - - - X 

Ash-throated Flycatcher Myiarchus cinerascens - X - - 

268
TTable 6–1.T List of other bird species observed during 2007 yellow-billed cuckoo surveys, 

in the lower Colorado River watershed along the White and Muddy Rivers, Nevada, lower 

Colorado, Bill Williams and Gila Rivers, Arizona and California.—Continued 

Common name Scientific name Survey 

1 

Survey 

2 

Survey 

3 

Survey 

4 

Survey 

5 

Black Phoebe Sayornis nigricans - - X - 

Western Kingbird Tyrannus verticalis X X X - 

Northern Rough-winged 

Swallow Stelgidopteryx serripennis - X - - 

Verdin Auriparus flaviceps X - X - 

Cactus Wren Campylorhynchus brunneicapillus - X - - 

Marsh Wren Cistothorus palustris - X - - 

Black-tailed Gnatcatcher Polioptila melanura X - - - 

Northern Mockingbird Mimus polyglottos X - - - 

Yellow Warbler Dendroica petechia - - - X 

Common Yellowthroat Geothlypis trichas - X X - 

Abert's Towhee pipilo aberti X X X - 

Song Sparrow Melospiza melodia - - X - 

Red-winged Blackbird Agelaius phoeniceus X X - - 

Yellow-headed Blackbird Xanthocephalus xanthocephalus - - X - 

Blue Grosbeak Guiraca caerulea X - X - 

Great-tailed Grackle Quiscalus mexicanus X X - - 

Brown-headed Cowbird Molothrus Ater X - - - 

House Finch Carpdacus mexicanus - - X - 

Lesser Goldfinch Carduelis psaltria - X - - 

Yuma West Wetlands (Colorado River)

Great Egret Ardea alba - X - X 

Snowy Egret Egretta thula - X - - 

Green Heron Butorides virescens X X X - 

Black-crowned Night Heron Nycticorax nycticorax - X - - 

White-faced Ibis Plegadis chihi - X X - 

American Kestrel Falco sparverius - - X - 

Gambel's Quail Callipepla gambellii - X - - 

Common Moorhen Gallinula chloropus X - - - 

Rock Dove Columba livia X - - - 

White-winged Dove Zenaida asiatica X X X X 

Mourning Dove Zenaida macraura X X - X 

269
TTable 6–1.T List of other bird species observed during 2007 yellow-billed cuckoo surveys, 

in the lower Colorado River watershed along the White and Muddy Rivers, Nevada, lower 

Colorado, Bill Williams and Gila Rivers, Arizona and California.—Continued 

Common name Scientific name Survey 

1 

Survey 

2 

Survey 

3 

Survey 

4 

Survey 

5 

Common Ground-Dove Columbina passerine X X X X 

Greater Roadrunner Geococcyx californianus - X - - 

Burrowing Owl Athene cunicularia X - - - 

Black-chinned Hummingbird Archilochus alexandri - - X - 

Anna's Hummingbird Calypte anna X X X X 

Gila Woodpecer Melanerpes uropygialis - X X X 

Ladder-backed Woodpecker Picoides scalaris - X - - 

Black Phoebe Sayornis nigricans - - X - 

Ash-throated Flycatcher Myiarchus cinerascens - X X - 

Western Kingbird Tyrannus verticalis X X X - 

Loggerhead Shrike Lanius ludovicianus - X - - 

Bell's Vireo Vireo bellii - X X X 

Cliff Swallow Petrochelidon pyrrhonota - - - X 

Verdin Auriparus flaviceps X X - X 

Cactus Wren Campylorhynchus brunneicapillus X X X X 

Northern Mockingbird Mimus polyglottos X X X X 

Nashville Warbler Vermivora ruficapilla - - - X 

Yellow Warbler Dendroica petechia - - - X 

Common Yellowthroat Geothlypis trichas X X - X 

Wilson's Warbler Wilsonia pusilla - - - X 

Abert's Towhee pipilo aberti X X X X 

Red-winged Blackbird Agelaius phoeniceus - X - X 

Black-headed Grosbeak Pheuticus melanocephalus - X - X 

Blue Grosbeak Guiraca caerulea - - X X 

Great-tailed Grackle Quiscalus mexicanus X - X X 

House Finch Carpdacus mexicanus - - X - 

Lesser Goldfinch Carduelis psaltria - X - - 

Limitrophe Division (Colorado River)

Great Blue Heron Ardea herodias - X X - 

Great Egret Ardea alba X X X - 

Snowy Egret Egretta thula X - - - 

Green Heron Butorides virescens - - X X 

270
TTable 6–1.T List of other bird species observed during 2007 yellow-billed cuckoo surveys, 

in the lower Colorado River watershed along the White and Muddy Rivers, Nevada, lower 

Colorado, Bill Williams and Gila Rivers, Arizona and California.—Continued 

Common name Scientific name Survey 

1 

Survey 

2 

Survey 

3 

Survey 

4 

Survey 

5 

Black-crowned Night Heron Nycticorax nycticorax X - - - 

Cattle Egret Bubulcus ibis X - - - 

White-faced Ibis Plegadis chihi X - - X 

Turkey Vulture Cathartes aura X X X - 

Osprey Pandion haliaetus X - - - 

Northern Harrier Circus cyaneus - - - X 

American Kestrel Falco sparverius - - X - 

Ring-necked Pheasant Phasianus colcichus X X - - 

Gambel's Quail Callipepla gambellii X X X X 

Common Moorhen Gallinula chloropus - X - X 

American Coot Fulica Americana X - - - 

Killdeer Charadrius vociferus - - X X 

Western Sandpiper Calidris mauri - - - X 

Rock Dove Columba livia - X - - 

White-winged Dove Zenaida asiatica X X X X 

Mourning Dove Zenaida macraura X X X X 

Common Ground-Dove Columbina passerine - X - X 

Greater Roadrunner Geococcyx californianus X - - X 

Burrowing Owl Athene cunicularia X X - - 

Lesser Nighthawk Chordeiles acutipennis X - X - 

Black-chinned Hummingbird Archilochus alexandri X - - - 

Anna's Hummingbird Calypte anna X X X X 

Belted Kingfisher Ceryle alcyon - - - X 

Ladder-backed Woodpecker Picoides scalaris X X X X 

Willow Flycatcher Empidonax traillii - - - X 

Black Phoebe Sayornis nigricans X - X X 

Vermillion Flycatcher Pyrocephalus rubinus - - - X 

Ash-throated Flycatcher Myiarchus cinerascens X - - - 

Brown-crested Flycatcher Myiarchus tyrannulus - - - X 

Western Kingbird Tyrannus verticalis X X X X 

Warbling Vireo Vireo gilvus - - X - 

Northern Rough-winged 

Swallow Stelgidopteryx serripennis - X - - 

271
TTable 6–1T.T List of other bird species observed during 2007 yellow-billed cuckoo surveys, 

in the lower Colorado River watershed along the White and Muddy Rivers, Nevada, lower 

Colorado, Bill Williams and Gila Rivers, Arizona and California.—Continued 

Common name Scientific name Survey 

1 

Survey 

2 

Survey 

3 

Survey 

4 

Survey 

5 

Cliff Swallow Petrochelidon pyrrhonota X - X X 

Verdin Auriparus flaviceps X X - X 

Cactus Wren Campylorhynchus brunneicapillus X X X X 

Bewick's Wren Thryomanes bewickii - - - X 

Black-tailed Gnatcatcher Polioptila melanura X X - - 

Hermit Thrush Catharus guttatus - - - X 

Northern Mockingbird Mimus polyglottos X X X X 

Crissal Thrasher Toxostoma crissale - - - X 

European Starling Sturnus vulgaris X X - - 

Nashville Warbler Vermivora ruficapilla - - - X 

Lucy's Warbler Vermivora luciae - X - - 

Yellow Warbler Dendroica petechia - - X X 

Common Yellowthroat Geothlypis trichas X X X - 

Wilson's Warbler Wilsonia pusilla - - - X 

Yellow-breasted Chat Icteria virens X - - - 

Western Tanager Piranga ludoviciana X - - X 

Song Sparrow Melospiza melodia X - - - 

Abert's Towhee pipilo aberti X X X X 

Red-winged Blackbird Agelaius phoeniceus X X X X 

Yellow-headed Blackbird Xanthocephalus xanthocephalus X - - - 

Black-headed Grosbeak Pheuticus melanocephalus - - X - 

Blue Grosbeak Guiraca caerulea X X X X 

Great-tailed Grackle Quiscalus mexicanus X X X X 

Brown-headed Cowbird Molothrus Ater X X X - 

House Finch Carpdacus mexicanus X X X X 

Lesser Goldfinch Carduelis psaltria - X - - 

Gila River/Quigley Pond Wildlife Management Area (Gila River)

Great Blue Heron Ardea herodias X - X - 

Great Egret Ardea alba - X - - 

Cattle Egret Bubulcus ibis - X - - 

Green Heron Butorides virescens - - X X 

Turkey Vulture Cathartes aura - X - X 

272
TTable 6–1.T List of other bird species observed during 2007 yellow-billed cuckoo surveys, 

in the lower Colorado River watershed along the White and Muddy Rivers, Nevada, lower 

Colorado, Bill Williams and Gila Rivers, Arizona and California.—Continued 

Common name Scientific name Survey 

1 

Survey 

2 

Survey 

3 

Survey 

4 

Survey 

5 

Zone-tailed Hawk Buteo albonotatus X - - - 

Red-tailed Hawk Buteo jamaicensis - X - - 

Gambel's Quail Callipepla gambellii X X - X 

White-winged Dove Zenaida asiatica X X X - 

Mourning Dove Zenaida macroura X X X X 

Common Ground-Dove Columbina passerine - X X X 

Greater Roadrunner Geococcyx californianus X X X - 

Lesser Nighthawk Chordeiles acutipennis - X - - 

Black-chinned Hummingbird Archilochus alexandri X - X - 

Ladder-backed Woodpecker Picoides scalaris - X X - 

Willow Flycatcher Empidonax traillii X - - - 

Black Phoebe Sayornis nigricans - X X X 

Vermillion Flycatcher Pyrocephalus rubinus X - - - 

Western Kingbird Tyrannus verticalis X X - X 

Bell's Vireo Vireo bellii - - X - 

Warbling Vireo Vireo gilvus - - - X 

Northern Rough-winged 

Swallow Stelgidopteryx serripennis - - X X 

Verdin Auriparus flaviceps - - X X 

House Wren Troglodytes aedon - - X - 

Black-tailed Gnatcatcher Polioptila melanura - X - - 

Yellow Warbler Dendroica petechia X X X X 

Wilson's Warbler Wilsonia pusilla - - - X 

Yellow-breasted Chat Icteria virens X - X - 

Western Tanager Piranga ludoviciana - - X X 

Abert's Towhee pipilo aberti X X - X 

Lark Sparrow Chondestes grammacus - X - - 

Song Sparrow Melospiza melodia - X - - 

Black-headed Grosbeak Peucticus melanocephalus - - X X 

Blue Grosbeak Guiraca caerulea X X X - 

Lazuli Bunting Passerina amoena - - X X 

Red-winged Blackbird Agelaius phoeniceus X X X X 

Western Meadowlark Sternella neglecta - - - X 

273
TTable 6–1.T List of other bird species observed during 2007 yellow-billed cuckoo surveys, 

in the lower Colorado River watershed along the White and Muddy Rivers, Nevada, lower 

Colorado, Bill Williams and Gila Rivers, Arizona and California.—Continued 

Common name Scientific name Survey 

1 

Survey 

2 

Survey 

3 

Survey 

4 

Survey 

5 

Great-tailed Grackle Quiscalus mexicanus X X - X 

Brown-headed Cowbird Molothrus Ater X X X X 

Bullock's Oriole Icterus bullockii - X X - 

House Finch Carpdacus mexicanus X X - - 

Lesser Goldfinch Carduelis psaltria - - X X 

Lawrence's Goldfinch Carduelis lawrencei - X - - 

274
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Johnson and others—Yellow-billed Cuckoo Distribution, Abundance, and Habitat Use Along the Lower Colorado River and its Tributaries, 2007 Annual 

Report—Open-File Report 2008–1177