Yellow-Billed Cuckoo Distribution, 

Abundance, and Habitat Use Along the 

Lower Colorado and Tributaries, 

2006 Annual Report

By Matthew J. Johnson, Jennifer A. Holmes, Christopher Calvo, Ivan 

Samuels, Stefani Krantz, and Mark K. Sogge1

Yellow-billed Cuckoo © Bob Steele

Open-File Report 2007-1097

2007

Funded by Bureau of Reclamation, Boulder City, Nev.

Interagency Agreement # 06AA300005

U.S. Department of the Interior

U.S. Geological Survey

1 Southwest Biological Science Center, Flagstaff, Ariz.
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia 2007

Revised and reprinted: 2007

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Suggested citation:

Johnson, M.J., Holmes, J.A., Calvo, Christopher, Samuels, Ivan, Krantz, Stefani, and

Sogge, M.K., 2007, Yellow-billed cuckoo distribution, abundance, and habitat use

along the lower Colorado and tributaries, 2006 annual report: U.S. Geological Survey

Open-File Report 2007-1097, 219 p. [http://pubs.usgs.gov/of/2007/1097/]

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ii 

Table of Contents 

List of Figures................................................................................................................................. iv 

List of Tables ................................................................................................................................... v 

List of Appendices .........................................................................................................................vii 

Executive Summary ......................................................................................................................viii 

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

 The Lower Colorado River Multi-Species Conservation Plan.................................................... 1 

 Breeding Biology, Habitat, Distribution, and Status .................................................................. 2 

 Project Objectives........................................................................................................................ 6 

 Document Organization............................................................................................................... 6 

Chapter 2: Yellow-Billed Cuckoo Breeding Surveys ........................................................................ 7 

 Survey Location and Selection of Study Sites ............................................................................ 7 

 Survey Methods........................................................................................................................... 10 

 Survey Results............................................................................................................................. 11 

 Littlefield Bridge, NV (Virgin River, Beaver Dam Wash)................................................... 13 

 Mesquite Bridge, NV (Virgin River) .................................................................................... 13 

 Pahranagat National Wildlife Refuge, NV (White River Drainage)..................................... 13 

 Overton Wildlife Management Area, NV (Muddy River).................................................... 14 

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

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

 Lake Mohave, AZ (Colorado River)..................................................................................... 18 

 Havasu National Wildlife Refuge, AZ (Colorado River) ..................................................... 18 

 Bill Williams River National Wildlife Refuge, AZ (Bill Williams River) ........................... 20 

 Cibola National Wildlife Refuge, AZ (Colorado River)....................................................... 23 

 Picacho State Recreation Area, CA (Colorado River).......................................................... 25 

 Imperial National Wildlife Refuge, AZ and CO (Colorado River) ...................................... 25 

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

 (Colorado River) ................................................................................................................ 26 

 Gila–Colorado River Confluence Area, AZ (Gila and Colorado Rivers)............................. 27 

 Yuma West Wetlands Park, AZ (Colorado River)................................................................ 28 

 Limitrophe Division, AZ (Colorado River) .......................................................................... 28 

 Gila River Highway 95, AZ (Gila River) ............................................................................. 29 

 Gila River/Ligurta, AZ (Gila River) ..................................................................................... 30 

 Gila River/Wellton, AZ (Gila River) .................................................................................... 31 

 Gila River/Quigley Pond Wildlife Management Area, AZ (Gila River) .............................. 31 

 Summary of Cuckoo Breeding Status Results............................................................................. 31 

 Discussion ................................................................................................................................... 34 

 Other Riparian Bird Detections................................................................................................... 34 

Chapter 3: Survey Methodology........................................................................................................ 35 

 Methods....................................................................................................................................... 36 

 Results ......................................................................................................................................... 36 

 Discussion ................................................................................................................................... 40 

 Survey Methodology Modifications for 2007 ............................................................................. 41 
iii 

Chapter 4. Habitat Vegetation Characteristics................................................................................... 42 

 Methods....................................................................................................................................... 42 

 Vegetation Sampling Design ................................................................................................ 43

 Vegetation Measures and Measurement Techniques............................................................ 44 

 Results ......................................................................................................................................... 46 

 Characteristics of the Canopy ............................................................................................... 46 

 Density of Woody Species.................................................................................................... 46 

 Discussion ................................................................................................................................... 53 

Chapter 5: Microclimate Analysis ..................................................................................................... 54 

 Methods....................................................................................................................................... 54 

 Temperature and Relative Humidity..................................................................................... 56 

 Soil Moisture and Canopy Cover.......................................................................................... 56 

 Occupied versus Unoccupied Sites....................................................................................... 56 

 Results ......................................................................................................................................... 57 

 Relative Humidity and Temperature..................................................................................... 57 

 Soil Moisture and Canopy Cover.......................................................................................... 58 

 Discussion ................................................................................................................................... 59 

 Microclimate Evaluation – 2006 and 2007 ................................................................................. 60 

Chapter 6. Riparian Habitat and the Status of Cuckoos in the Lower Colorado River Basin............ 61 

 Restoring Riparian Habitat for the Yellow-Billed Cuckoo: Additional Research Needs............ 63 

Acknowledgments.............................................................................................................................. 65 

Literature Cited .................................................................................................................................. 66 
iv 

List of Figures 

2.1. Yellow-billed cuckoo survey areas along the Virgin and Muddy Rivers, Nevada and 

 lower Colorado, Bill Williams and Gila Rivers in Arizona and California, 2006 ................... 9 

2.2. Yellow-billed cuckoo survey areas and number of cuckoo detections along the 

 Virgin and Muddy Rivers, Nevada and lower Colorado, Bill Williams and Gila 

 Rivers, Arizona and California, 2006....................................................................................... 12

3.1. Percentage of times that yellow-billed cuckoos first responded to survey vocalization 

 playbacks, based on sequential order of broadcast (180 total responses) ................................ 37 

3.2. Percentage of unsolicited responses by yellow-billed cuckoos at individual survey 

 areas (180 total responses). An unsolicited response is one in which the cuckoo 

 vocalized prior to the first tape playback recording................................................................. 37 

3.3. Percentage of times that yellow-billed cuckoos first responded to survey vocalization 

 playbacks at (A) Bill Williams River NWR, (B) Grand Canyon NP/Lake Mead NRA 

 and all site with <10 detections, based on sequential order of response and detection 

 types by season......................................................................................................................... 38

3.4. Number of yellow-billed cuckoo detections (solicited vs. unsolicited) by time period, 

 from 15 June to 15 August 2006.............................................................................................. 39 

3.5. Number of yellow-billed cuckoo aural, visual, or both aural and visual detections by 

 time period, from 15 June to 15 August 2006.......................................................................... 39 

4.1. Layout of vegetation subplots to characterize yellow-billed cuckoo habitat in occupied and 

 unoccupied sites ....................................................................................................................... 44 

4.2. Mean tree densities for occupied (green bars) and unoccupied (red bars) yellow-billed 

 cuckoo sites, within three geographic areas. ............................................................................ 46 

4.3. Mean tree densities in different size classes (< 8, 8–23, 23–38, and > 38 cm dbh), for 

 occupied (green bars) and unoccupied (red bars) yellow-billed cuckoo sites within 

 three areas................................................................................................................................. 47 

4.4. Mean shrub/sapling densities for occupied (green bars) and unoccupied (red bars) 

 yellow-billed cuckoo sites, within three areas. ........................................................................ 48 

4.5. The mean abundance of trees of differing size classes at three yellow-billed cuckoo 

 study areas, occupied and unoccupied sites combined, 2006................................................... 49 

4.6. Mean cottonwood abundance, by size class (cm dbh), of occupied (green bars) and 

 unoccupied (red bars) sites in three yellow-billed cuckoo study areas. ................................... 50 

4.7. Mean willow abundance, by size class (cm dbh), of occupied (green bars) and 

 unoccupied (red bars) sites in three yellow-billed cuckoo study areas. ................................... 51 

4.8. Mean tamarisk abundance, by size class (cm dbh), of occupied (green bars) and 

 unoccupied (red bars) sites in three yellow-billed cuckoo study areas. ................................... 52 
v 

List of Tables 

2.1. Yellow-billed cuckoo (YBCU) and Southwestern willow flycatcher (SWIFL) 2006 

 site 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 AZ and CA............. 7 

2.2. Number of visits and yellow-billed cuckoo detections per survey period in 2006 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 AZ and CA............. 10 

2.3. Dates (2006) for yellow-billed cuckoo surveys along the Virgin River at the Littlefield 

 Bridge site............................................................................................................................... 13 

2.4. Dates (2006) for yellow-billed cuckoo surveys along the Virgin River at the Mesquite 

 Bridge site............................................................................................................................... 13 

2.5. Dates (2006) for yellow-billed cuckoo surveys conducted at Pahranagat National 

 Wildlife Refuge sites .............................................................................................................. 14 

2.6. Dates (2006) for yellow-billed cuckoo surveys in the Overton Wildlife Management 

 Area ........................................................................................................................................ 15 

2.7. Yellow-billed cuckoo detections in 2006 in the Overton Wildlife Management Area .......... 15 

2.8. Dates (2006) for yellow-billed cuckoo surveys in Grand Canyon National Park and 

 Lake Mead National Recreation Area .................................................................................... 16 

2.9. Yellow-billed cuckoo detections in 2006 at Grand Canyon National Park and Lake Mead 

 National Recreation Area........................................................................................................ 17 

2.10. Yellow-billed cuckoo surveys in 2006 at sites adjacent to Lake Mojave along the 

 Colorado River ....................................................................................................................... 18 

2.11. Dates (2006) for yellow-billed cuckoo surveys at the Havasu National Wildlife 

 Refuge..................................................................................................................................... 19 

2.12. Dates (2006) for yellow-billed cuckoo surveys at the Bill Williams River National 

 Wildlife Refuge ...................................................................................................................... 20 

2.13. Yellow-billed cuckoo detections in 2006 at the Bill Williams River National 

 Wildlife Refuge ...................................................................................................................... 21 

2.14. Dates (2006) for yellow-billed cuckoo surveys at the Cibola National Wildlife 

 Refuge..................................................................................................................................... 23 

2.15. Yellow-billed cuckoo detections in 2006 at Cibola National Wildlife Refuge ...................... 23 

2.16. Dates (2006) for yellow-billed cuckoo surveys at the Picacho State 

 Recreation Area ...................................................................................................................... 25 

2.17. Dates (2006) for yellow-billed cuckoo surveys at Imperial National Wildlife Refuge.......... 25 

2.18. Yellow-billed cuckoo detections in 2006 at Imperial National Wildlife Refuge ................... 26 

2.19. Dates (2006) for yellow-billed cuckoo surveys at the Mittry Lake State Wildlife 

 Management Area................................................................................................................... 26 

2.20. Dates (2006) for yellow-billed cuckoo surveys at the area of the Gila River-Colorado 

 River confluence..................................................................................................................... 27 

2.21. Yellow-billed cuckoo detections in 2006 at the area of the Gila River- 

 Colorado River confluence..................................................................................................... 27 
vi 

2.22. Dates (2006) for yellow-billed cuckoo surveys in Yuma West Wetlands lower Colorado 

 River ....................................................................................................................................... 28 

2.23. Dates (2006) for yellow-billed cuckoo surveys in the Limitrophe Division area along the 

 lower Colorado River ............................................................................................................. 29 

2.24. Yellow-billed cuckoo detections in 2006 in the Limitrophe Division area along the lower Colorado 

River ....................................................................................................................................... 29 

2.25. Dates (2006) for yellow-billed cuckoo surveys at sites near the junction of the Gila River 

 and Highway 95...................................................................................................................... 30 

2.26. Dates (2006) for yellow-billed cuckoo surveys at the Gila River/Ligurta and Gila River/ 

 Wellton sites, and the Gila River/Quigley Pond Wildlife Management Area........................ 31 

2.27. Summary of breeding classifications for yellow-billed cuckoo detections in 2006 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...................................................... 32 

4.1. Vegetation and Microclimate study areas along the lower Colorado River and tributaries, 

 2006 ........................................................................................................................................ 43 

4.2. Mean percent canopy cover (and standard error) at all sites sampled .................................... 46 

4.3. Number of each tree species encountered, by dbh size classes, during vegetation .sampling 

 at all yellow-billed cuckoo study areas in 2006...................................................................... 48 

5.1. Microclimate study areas along the lower Colorado River and adjacent locations, 2006. ..... 55 

5.2. Number of sites and number of microclimate data loggers (HOBOs) within the three survey 

 areas at Grand Canyon NP/Lake Mead NRA, Bill Williams River NWR, and Cibola NWR 

 yellow-billed cuckoo study areas, August–September, 2006 ................................................. 57 

5.3. Descriptive statistics (means and standard errors, in parentheses) for microclimate 

 data collected at Grand Canyon NP/Lake Mead NRA, Bill Williams River NWR, 

 and Cibola NWR yellow-billed cuckoo study areas, August–September 2006 ..................... 58 

5.4. Descriptive statistics (means and standard errors, in parentheses) for soil moisture 

 data collected at yellow-billed cuckoo study areas within Grand Canyon NP/Lake 

 Mead NRA, Bill Williams River NWR, and Cibola NWR .................................................... 59 

5.5. Descriptive statistics for percent canopy cover data from microclimate sampling 

 sites in Grand Canyon NP/Lake Mead NRA, Bill Williams River NWR, and Cibola 

 NWR yellow-billed cuckoo study areas in 2006 .................................................................... 59 
vii 

List of Appendices 

1. Survey sites and survey dates for yellow-billed cuckoo surveys in the lower Colorado River 

Watershed, along the along the Virgin and Muddy rivers, Nevada, lower Colorado, Bill 

 Williams and Gila rivers, Arizona and California, 2006 ........................................................ 74 

2. A narrative description of each yellow-billed cuckoo detection in the lower Colorado River 

Watershed, along the along the Virgin and Muddy rivers, Nevada, lower Colorado, Bill 

 Williams and Gila rivers, Arizona and California, 2006 ........................................................ 76 

3. Incidental yellow-billed cuckoo observations in the lower Colorado River Watershed, along 

 the Virgin and Muddy rivers, Nevada, lower Colorado, Bill William and Gila rivers, Arizona 

 and California, 2006 ............................................................................................................... 96 

4. Aerial photographs of yellow-billed cuckoo survey points, and detections according to 

 survey period at sites along the Virgin and Muddy rivers, Nevada, lower Colorado and Gila 

 rivers, Arizona and California, 2006 ...................................................................................... 98 

5. List of other bird species observed during yellow-billed cuckoo surveys, in the lower Colorado 

River Watershed along the Virgin and Muddy rivers, Nevada, lower Colorado, Bill William 

 and Gila rivers, Arizona and California, 2006........................................................................ 171 

6. Habitat photos of Yellow-billed Cuckoo survey areas and sites in the lower Colorado River 

Watershed along the Virgin and Muddy rivers, Nevada, lower Colorado, Bill Williams and 

 Gila rivers, Arizona and California, 2006. Listed with each photo is area name and site 

 name when applicable............................................................................................................. 191 
viii 

Executive Summary 

This 2006 annual report details the first 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 Plan boundary area. We conducted cuckoo surveys at 

55 sites within 17 areas, between 11 June and 13 September. 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 River National Wildlife Refuge AZ sites (n = 117 detections) and the Grand Canyon National 

Park–Lake Mead National Recreation Area AZ delta sites (n = 29 detections). There were also cuckoos at 

the Gila River–Colorado River Confluence, AZ (n = 9), Overton Wildlife Management, NV area (n = 7), 

and Limitrophe Division North, AZ (n = 6); however, at these sites the numbers were much lower and 

very few of these birds were considered to be paired or breeding. The greatest number of detections (n = 

79) occurred during the second survey period (3–23 July). In 2006, we confirmed five breeding events, 

including one nesting observation and sightings of four juveniles; all confirmed breeding was at the Bill 

Williams River NWR and Grand Canyon NP–Lake Mead NRA delta sites. The breeding status of most of 

our detections were unknown, however, we observed 17 adult cuckoos carrying nest material or food and 

40 cuckoo detections were detected while counter-calling occurred in same area during repeated surveys. 

We used playback recordings to survey for western 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 playback recordings may fail to detect all birds present in an area. In 2006, we found that the 

majority (72%) of cuckoo detections were solicited through playback 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 playback was 

initiated) remained fairly constant. The majority (64%) of cuckoo detections, solicited or unsolicited, 

were aural; 27 percent were both heard and seen and nine percent were visual detections only. Cuckoos in 

areas with the largest populations had the highest rate of vocalizations before playback 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 playback recordings. This type of baseline information will be used 

to help refine the survey protocol for 2007, and to create hypotheses that can serve as the foundation for a 

full-scale evaluation and optimization of this survey technique. 

Our preliminary analysis of vegetation data from occupied and unoccupied sites in 2006 focused on 

general patterns in the distribution and abundance of woody species. The density and composition of 

woody riparian vegetation varied considerably among the study areas. Much of the variation in tree 

density was due to the patterns of abundance of trees in the smallest size class (< 8 cm dbh). The 

dominant tree species at the cuckoo survey sites were cottonwood, willow, and tamarisk. Tamarisk was 

the most common tree, due to the abundance of small (< 8 cm dbh) individuals. When occupied and 

unoccupied sites were compared, 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. In addition, occupied sites in most areas had lower than average 

total tree density whereas unoccupied sites were denser than average. When densities of trees in different 

size classes were compared between occupied and unoccupied sites within areas, it appeared that cuckoos 

did not use areas with the highest density of small trees (< 8 cm dbh), mostly tamarisk. 
ix 

We also measured microclimate variables (temperature, relative humidity, soil moisture) at occupied and 

unoccupied sites. Microclimate sampling in 2006 was delayed due to equipment procurement difficulties, 

so our preliminary conclusions are based on late-year data only; conclusions and patterns may change as 

new data (especially from the early season) are collected in 2007. Microclimate measurements at Grand 

Canyon NP–Lake Mead NRA and Bill Williams River NWR showed that locations occupied by yellowbilled cuckoos were generally slightly cooler and more humid than unoccupied sites. This was not true at 

Cibola NWR, where only mean nocturnal temperature was lower at occupied sites. On average, soil 

moisture was slightly higher at occupied cuckoo locations. Although microclimate conditions may play a 

significant role in cuckoo habitat selection or breeding ecology, the factors underlying the microclimate 

conditions in riparian patches are not currently known. 
1 

Chapter 1. Introduction 

The Lower Colorado River Multi-Species Conservation Plan 

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, and (3) prevent the listing of additional species on 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 may 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 continental divide) represents a distinct population segment and warrants 

protection under the Endangered Species Act as “threatened,” but precluded. Thus, it became a Candidate 

Species under the Endangered Species Act (USFWS 2002a). The HCP requires 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. 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 habitat 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 MSCP conservation measures relative to yellow-billed cuckoos include the following: 

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

yellow-billed cuckoo’s 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 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 the types and frequency of management activities that may 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 geared specifically toward the 

cuckoo. 
2 

Breeding Biology, Habitat, Distribution, and Status 

Breeding Biology 

The yellow-billed cuckoo (Coccyzus americanus), a neotropical migrant, 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 may be triggered 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, ranging 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 be single-brooded (Hamilton and 

Hamilton 1965, Hughes 1999) but recent observations confirm that at least some individuals are doublebrooded (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) 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 also move broadly 

throughout riparian and adjacent habitats, especially early in the season and post-breeding. Such cuckoos 

may be foraging or evaluating potential breeding sites for the current or subsequent breeding seasons. 

Similarly, migrating cuckoos can be found in habitats that may not have the same vegetation types or 

characteristics as those in which they breed. As a result, cuckoos are sometimes detected in non-riparian 

habitats or within riparian habitats that are not suitable for breeding, so not every location at which a 

cuckoo is detected can necessarily be considered breeding habitat. The level of adult breeding site fidelity 

is not well known, but may it be relatively low, based on large yearly fluctuations in cuckoo detections at 

some sites. These natural history traits complicate the determination and characterization of breeding 

habitat. 

Habitat Requirements 

Western yellow-billed cuckoos require structurally complex riparian habitats with tall trees and a dense 

woody vegetative understory (Halterman 1991, Hughes 1999). They breed in large blocks of riparian 

habitat, particularly woodlands with cottonwoods and willows (Ehrlich et al. 1988, USFWS 2002a). 

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 foraging habitat (Laymon et al. 1997, USFWS 2002a). Nesting in the West occurs 

almost exclusively close to water and many researchers have hypothesized that the species may be 

restricted to nesting in moist river bottoms because of humidity requirements for successful breeding 

(Hamilton and Hamilton 1965, Rosenberg et al. 1991). 
3 

Much of what is known about yellow-billed cuckoo habitat use in Arizona is the result of surveys 

conducted by the Arizona Game and Fish Department (AGFD) and the U.S. Geological Survey’s 

Colorado Plateau Research Station (CPRS) in 1998 and 1999 (Corman and Magill 2000). The AGFDCPRS 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 (Tamarix spp.) cover. 

Historic Abundance and General Breeding Distribution 

Western yellow-billed cuckoos have historically bred in riparian zones 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). Comparisons of 

historic and current information suggest that the yellow-billed cuckoo’s range and population numbers 

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

2002a). Analysis of population trends is difficult because quantitative data, including historic population 

estimates, are generally lacking. However, rough extrapolations based on both observed densities of 

yellow-billed cuckoos and historic habitat distribution indicate that western populations were once 

substantial (USFWS 1985, USFWS 2002a). 

Cuckoo populations have suffered severe range contractions during the last 80 years, and have 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 irregular in Utah (J. Parrish 

pers. comm., Johnson and O’Brien 1998) and western Colorado (Kingery 1998). The yellow-billed 

cuckoos found in California, Arizona, and southern Nevada are western yellow-billed cuckoos; we use 

the two names interchangeably when discussing any yellow-billed cuckoo west of the continental divide. 

Current Conservation Status in the Western United States 

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 yellowbilled 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 precluded. 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 2002a). 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 2002a). 

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 may also have 
4 

contributed to the declines (Laymon and Halterman 1989). Populations may be further limited by food 

availability for the young; they may not nest if the food supply at the breeding grounds is inadequate 

(Veit and Petersen 1993) and food availability is likely affected by drought conditions (Newton 1980, 

Durst 2004, Scott et al. 2004). 

The early literature documents dozens of locations in California where the species was reported and/or 

collected historically, sometimes in apparent abundance, but where they have 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 was much reduced in 

population 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 mid-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 suitable habitat 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 5 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 the state were along the major drainages of the Agua Fria, San 

Pedro, and Verde Rivers, Cienega and Sonoita Creeks, and the Bill Williams River tributary along the 

lower Colorado River (Corman and Magill 2000). The Arizona Game and Fish Department has 

designated the yellow-billed cuckoo as Wildlife of Special Concern in Arizona, and the U.S. Forest 

Service Regional Forester designated it a Sensitive Species on National Forests within Arizona (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 (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 mated cuckoo 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 
5 

or two pairs in 2002 (Halterman 2003). The Nevada Natural Heritage Program ranks the western yellowbilled 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 Stephen’s (1903) observations of several cuckoos 

near Needles in 1902. Surveys in mid-June 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 may have been the last stronghold for the yellowbilled 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 speciesspecific 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, 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 and 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 are 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 in 1993, 1994, and 1997. Then starting in 

2001, results were reported as numbers of detections, which varied from 78 in 2001 to 34 in 2002 and 42 

in 2003. 

Prior to the 2006 field season, the most recent yellow-billed cuckoo surveys along the lower Colorado 

River were from 2005 (Johnson et al. 2006). The area of focus began at Cibola NWR and progressed 

south to San Luis, Arizona, at the United States–Mexico Southerly International Boundary. Additional 

surveys were conducted along the lower Gila River, at historical detection sites and locations that had 

appropriate yellow-billed cuckoo habitat. Across all sites and visits, there were 33 cuckoo detections 

during the 2005 breeding season, with most during July. The survey included behavioral observations and 

searching for nests in the sites with cuckoo detections; only one pair of cuckoos was confirmed. Breeding 

was not confirmed, and other detections were of unpaired cuckoos. 
6 

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 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. 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. 

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

through restoration efforts. 

4. 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 Multi-Species Conservation Plan. 

Document Organization 

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

describes the survey design, survey effort, and results of the yellow-billed cuckoo surveys conducted 

during the 2006 breeding season. Chapter 3 (Survey Methodology) provides descriptive information 

about how cuckoos responded to our survey methodology. It also poses hypotheses and questions that 

may prove useful in further optimizing the cuckoo survey protocol. Chapter 4 (Yellow-billed Cuckoo 

Habitat Vegetation) describes the riparian vegetation sampling design, provides preliminary 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 (Riparian Habitat and Yellow-billed 

Cuckoo Distribution and Status in the Lower Colorado River Basin) describes the history of change in 

riparian habitat, how this may have contributed to changes in the yellow-billed cuckoo’s status and 

distribution within the region, and the potential effects on the cuckoo of riparian conservation and 

restoration under the LCR MSCP. 
7 

Chapter 2: Yellow-Billed Cuckoo Breeding 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. This project was initiated in the spring of 2006, and cuckoo surveys were 

conducted, using standardized methodologies, throughout the breeding season. 

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). To 

examine historic yellow-billed cuckoo breeding range and to determine the current range throughout the 

lower Colorado River basin, we expanded surveys in 2006 to include sites along the Gila River near 

Yuma, Arizona, the Virgin and Muddy Rivers 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 selected prior to the initial survey season, using the “look 

see” method. This method, which was employed during previous AGFD-CPRS surveys (see Bibby et al. 

1992), calls for identification of suitable habitats before conducting surveys. 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, 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. Many of the yellow-billed cuckoo survey sites selected in 2006 

overlap with Southwestern willow flycatcher surveys sites, which have their own site names (Table 2.1). 

Some of these site names we adopted for the 2006 cuckoo survey, however a number of our sites 

encompass a much larger area than the flycatcher sites or do not overlap at all, and therefore many names 

that were established during cuckoo surveys in 2005 (Johnson et al. 2006) remained the same. 

Table 2.1. Yellow-billed cuckoo (YBCU) and Southwestern willow flycatcher (SWIFL) 2006 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 2006 Site Name SWIFL 2006 Site Name

Littlefield Bridge Littlefield North 

Mesquite Bridge Mesquite East 

Pahranagat NWR-Pahranagat North Pahranagat North 

Pahranagat NWR-Pahranagat East Pahranagat Maps to the southwest 

Pahranagat NWR-Pahranagat South Pahranagat South 

Pahranagat NWR-Pahranagat West Pahranagat Maps & Pahranagat West 

Overton WMA-Honeybee Pond Overton WMA to the south 

Overton WMA-Overton North None 

Overton WMA-Overton Tamarisk Overton WMA 

Overton WMA-Overton Wildlife Overton WMA 

Grand Canyon NP/Lake Mead NRA-Spencer Canyon None 

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

Grand Canyon NP/Lake Mead NRA-River Delta/RM 285.3N RM 285.3N 

Grand Canyon NP/Lake Mead NRA-Cuckoo Beach Kowlp Corner, RM 286N, Twin Coves 
8 

Table 2.1 (continued) 

YBCU 2006 Site Name SWIFL 2006 Site Name

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

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

Lake Mohave-Waterwheel Cove None 

Lake Mohave-Mohave Patch None 

Havasu NWR-Pintail Slough None 

Havasu NWR-North Dike None 

Havasu NWR-Topock Marsh Restoration None 

Havasu NWR-Sacramento Wash None 

Havasu NWR-Havasu Tamarisk None 

Havasu NWR-Topock Tamarisk None 

Bill Williams River NWR-Cave Wash 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, Site 5 near 

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

Cibola NWR-Cibola North Restoration None 

Cibola NWR-Cibola Nature Trail Restoration Cibola Nature Trail 

Cibola NWR-Cibola Eucalyptus Restoration None 

Cibola NWR-Cibola South Restoration None 

Cibola NWR-Cibola Cross River Cibola Site 2 

Cibola NWR-Cibola East Side Cibola Site 1 

Picacho SRA Picacho NW 

Imperial NWR-Imperial Paradise Paradise 

Imperial NWR-Imperial South Restoration Imperial Nursery, Nursery NW 

Mittry Lake WMA/Pratt Restoration Mittry South 

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

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

Yuma West Wetlands None 

Limitrophe Division-Limitrophe Division North Morelos Dam 

Limitrophe Division-Limitrophe Division South Gadsden, Hunters Hole 

Gila River Highway 95-Gila 95 Bridge None 

Gila River Highway 95-Gila 95 Canal None 

Gila River Highway 95-Gila 95 Tall Tamarisk None 

Gila River/Ligurta None 

Gila River/Wellton None 

Gila River/Quigley Pond WMA None 
9 

Figure 2.1. Yellow-billed cuckoo survey areas along the Virgin and Muddy Rivers, Nevada and lower Colorado, 

Bill Williams and Gila Rivers in Arizona and California, 2006.
10 

Survey Methods 

Surveys for presence/absence of cuckoos were conducted following established methodologies (Laymon 

1998a, 1998b, Halterman et al. 2006, Johnson et al. 2006) that involve a minimum of four surveys 

distributed throughout the four survey periods between 10 June and 15 September (Table 2.2). Surveys at 

each site are conducted 10–14 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 they may still be breeding at that site, an additional (fifth) survey is then 

recommended to be conducted during that fourth period. Previous surveys on the Bill Williams River 

NWR, conducted in mid August, detected several new pairs (Halterman 2002). 

Table 2.2. Number of visits and yellow-billed cuckoo detections per survey period in 2006 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. 

 No. of Visits Detections 

Survey Period Survey Dates (n = 243) (n = 180) 

 1 6/11–7/02 65 46 

 2 7/03–7/23 67 79 

 3 7/24–8/10 67 36 

 4 8/11–9/13 44 19 

We used a taped recording of the yellow-billed cuckoo’s kowlp call (Hughes 1999) during survey. 

Playback 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 made through the habitat for every 200 m (656 ft) of 

habitat width. Two hectares is considered an absolute minimum size for cuckoo occupancy, as no cuckoos 

have been detected attempting to nest in patches that size or smaller in Arizona or California (Corman and 

Magill 2000, Halterman et al. 2006). Because the playback vocalizations are broadcast loudly enough to 

cover a large area, surveys do not need always to be conducted within the habitat; however, surveyors 

should be no more than 15 m (49 ft) from the habitat edge. Choosing a survey point that is not surrounded 

by dense vegetation provides a better view of a larger swath of the riparian habitat, making it easier to 

detect cuckoos that respond by flying closer but do not vocalize. Broadcasting the kowlp recording from 

the edge of the habitat enables the call to be broadcast to a larger area. Being on the edge also allows the 

surveyor to see cuckoos coming in silently to the observer. Areas with small narrow stringers of habitat, 

steep banks, and backwater sloughs can be surveyed by 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 

(i.e., the unsuitable habitat is at least 300 m in extent). 

The surveyor initially stopped at a survey point and remained quiet for 1 minute to acclimate to the 

ambient noise and to listen for spontaneously calling cuckoos. If no cuckoos were heard in this 1-minute 

period, the surveyor then played the kowlp call once, followed by 1 minute of silence to listen for a 

response. If no detections occurred, this playback-listen sequence was repeated an additional four times. 

The surveyor then moved 100 m (328 ft) along the transect (by foot or by boat) and repeated the 

playback-listen protocol. If a cuckoo was detected at the survey point, the surveyor moved 300 m (984 ft) 

before resuming survey playbacks to reduce the probability of re-detecting or attracting the same bird. 

At all survey points we recorded UTM coordinates (using GPS), estimated number of individual cuckoos 

detected, and estimated distance and direction (i.e., the compass bearing) from the surveyor to the 

detected cuckoo. 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. 
11 

If a cuckoo was detected, the surveyor attempted to also observe the estimated number of individuals in 

the habitat patch, the appearance of a nesting pair, the stage of nesting, the cuckoo’s use of the habitat 

patch, possible interactions between individuals, any apparent breeding behavior (e.g., food carry), and 

types of vocalization The interpretation of these behaviors was later used to help determine breeding 

status. 

Survey Site Classifications 

Based on survey results across all four visits, sites were classified as either unoccupied (a site with no 

yellow-billed cuckoo detections), detected (a yellow-billed cuckoo had been detected at a site during one 

visit, occupied (a yellow-billed cuckoo had been detected at a site during at least two survey periods). The 

presence of a cuckoo at a site does not necessarily equate to pairing and breeding at that location. So at 

sites with one or more cuckoo detections, breeding was considered “confirmed” only if an attended 

cuckoo nest was found, copulation was observed, and/or recently fledged young were seen. The detection 

of multiple cuckoos during a single survey or throughout the season, or of cuckoos carrying food or 

nesting material, is suggestive of pairing and breeding, but was not considered confirmation.

Nest Searching and Monitoring 

Nest searching was conducted either when we detected a cuckoo during a survey or after surveys were 

completed. To get a vantage point of the possible nesting area, surveyors would move about 100 m (328 

ft) back and search every tree for nests (Martin and Geupel 1993). Alternatively, two to three people 

would work together, triangulating on vocalizations of nesting cuckoos. When a nest was located, we 

took a GPS reading approximately 10 m (33 ft) from the nest to avoid disturbance; a more accurate 

reading was taken later when the nest was inactive. Nests were monitored every 5–8 days, and were 

checked from a distance of 20 m (66 ft) to avoid disturbing the birds. Nest contents were only checked if 

the adult was not on the nest, at which time we documented the number of eggs and young and estimated 

nestling age. Determining whether or not a nest actually fledged young can be difficult. In the absence of 

other cues, we assumed that chicks had fledged successfully if the median date between the last nest 

check during which the nest was active and the final nest check when the nest was empty was within 2 

days of the predicted fledging date (Martin and Geupel 1993). 

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 playback survey was conducted) and 

cuckoo detections (the coordinate point at which the surveyor estimated the cuckoo to be located). 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.). 

Survey Results 

During the 2006 field season, we surveyed 55 sites between 10 June and 15 September, for a total of 521 

survey hours (Appendix 1). The number of surveys varied per site due to the restructuring of survey sites. 

The 243 visits across all sites resulted in 180 yellow-billed cuckoo detections. The greatest number of 

detections occurred during the second survey period (3–23 July). At all sites, detections fell off sharply 

during the fourth breeding-season surveys in late August and early September (Appendices 2 and 3). 

Cuckoos were detected in 27 of 55 sites (49%), with the highest number at the Bill Williams River NWR 

area and Lake Mead NRA–Grand Canyon NP area (Figure 2.2; Appendix 2). 
12 

Survey sites and results 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 4. 

Figure 2.2. Yellow-billed cuckoo survey areas and number of cuckoo detections along the Virgin and Muddy 

Rivers, Nevada and lower Colorado, Bill Williams and Gila Rivers, Arizona and California, 2006.
13 

Littlefield Bridge, NV (Virgin River, Beaver Dam Wash) 

Littlefield Bridge lies along the Virgin River paralleling U.S Highway 91 within the town of Littlefield, 

approximately 15 km (9.3 miles) northeast of Mesquite, Nevada (Figure 2.1; Appendix 4). The Littlefield 

Bridge is the only site in this area. It consists of one large patch along the Beaver Dam Wash tributary, 

and another smaller patch that starts at the bridge and extends 500 m (1,640 ft) downstream along the 

Virgin River. The habitat consists of Fremont cottonwood (Populus fremontii) and Goodding’s willow 

(Salix gooddingii), with large tamarisk patches intermixed. Stands of cattail (Typha spp.) and arrowweed 

(Pluchea sericea) are also present. Canopy height is 10–14 m (32–46 ft). In 2006, standing water was not 

present within the site, which is surrounded by urban development and desert upland scrub. Site elevation 

is 500 m (1,804 ft). Although two cuckoos were detected at this site in 2000 (McKernan and Braden 

2001), no cuckoos were detected during the five surveys conducted in 2006 (Table 2.3). 

Table 2.3. Dates (2006) for yellow-billed cuckoo surveys along the Virgin River at the Littlefield Bridge site. 

 Survey Survey Survey Survey 

Geographic Area Site Name Period 1 Period 2 Period 3 Period 4 

Littlefield Bridge Littlefield Bridge 6/20 7/03, 7/15 7/28 9/09 

Mesquite Bridge, NV (Virgin River) 

The Mesquite Bridge site lies along the Virgin River where Highway 170 crosses the river about 1.3 km 

(0.8 miles) south of Mesquite, Nevada (Figure 2.1; Appendix 4). The Mesquite Bridge is the only site in 

this area. The habitat consists of a dense stringer of Fremont cottonwood, Goodding’s willow, and 

tamarisk, mainly along the south side of the Virgin River. Canopy height is 12–14 m (39–46 ft) and site 

elevation is 465 m (1,526 ft). Standing water was not present within this site in 2006. It is surrounded by 

agricultural and urban development on both sides of the river. Disturbance due to construction (home 

sites) has eliminated habitat on the north side of the river. 

Cuckoos were detected at this site in 2000 and 2003 (McKernan and Braden 2001, Braden et al. 2005a). 

We conducted five surveys in 2006 (Table 2.4), and detected a cuckoo at the Mesquite Bridge site during 

the second survey period. This cuckoo responded immediately and aggressively to the tape playback and 

it was seen and heard by two observers (Appendix 2). Breeding of this individual cuckoo was not 

confirmed, and no cuckoos were detected during later surveys. 

Table 2.4. Dates (2006) for yellow-billed cuckoo surveys along the Virgin River at the Mesquite Bridge site. 

 Survey Survey Survey Survey 

Geographic Area Site Name Period 1 Period 2 Period 3 Period 4 

City of Mesquite Mesquite Bridge 6/20 7/03, 7/15 7/28 9/09 

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 15 km (9.3 miles) northwest of Las Vegas (Figure 2.1; Appendix 4). All surveys were 

conducted at 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 and desert scrub. We divided this area into four survey 

sites (see below), covering the lake perimeter where cuckoo habitat exists. 
14 

Yellow-billed cuckoos were detected in 2000 at Pahranagat NWR (Halterman 2001). We conducted 17 

surveys in 2006 (Table 2.5), and detected a single cuckoo at the Pahranagat North site during the third 

survey period; no other cuckoos were detected in this area. Breeding of this individual cuckoo was not 

confirmed, and no cuckoos were detected during later surveys. This bird responded immediately after the 

first playback with cooing and kowlping that lasted about an hour (Appendix 2). 

Table 2.5. Dates (2006) for yellow-billed cuckoo surveys conducted at Pahranagat National Wildlife Refuge sites. 

 Survey Survey Survey Survey 

Geographic Area Site Name Period 1 Period 2 Period 3 Period 4 

Pahranagat NWR Pahranagat North 6/27 7/14 7/27 8/12, 8/25 

 Pahranagat East 6/27 7/14 7/27 8/12 

 Pahranagat South 6/27 7/14 7/27 8/12 

 Pahranagat West 6/27 7/14 7/27 8/11 

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

The north end of the lake is the best quality cuckoo habitat at the upper Pahranagat Lake. It consists of 

Fremont cottonwood and Goodding’s willow. Canopy height is 15–18 m (49–59 ft). In 2006, standing 

water was not present within this site; however, refuge personnel reported that standing water was present 

in May. This site is surrounded by marsh along the lake’s edge, which consists mainly of lizard tail 

(Yerba manza). 

Pahranagat East (Elevation 1,015 m; 3,330 ft) 

Pahranagat East consists of a thin stringer of Fremont cottonwoods and Goodding’s willow along the 

shore of the lake, with intermittent marsh understory. Canopy height is 13–15 m (43–49 ft). Standing 

water was not present within this site in 2006. The upland habitat adjacent to this site consists of creosote 

and desert scrub. A dirt road with a number of individual campsites surrounds the patch. 

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. The site is bordered by open marsh on the lake side. Tamarisk and Russian olive 

(Elaeagnus angustifolia) form a sparse understory. Canopy height is 16–18 m (52–59 ft). Standing water 

was not present within this site in 2006. The upland habitat adjacent to this site is creosote and desert 

scrub. There are extensive trails and campsites in and around this site, with attendant impacts to the 

riparian vegetation. 

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

Pahranagat West consists of thin stringers of Fremont cottonwoods that are pocketed between marsh 

areas, mainly along the lake shore. Canopy height is 14–16 m (46–52 ft). Standing water was not present 

within this site in 2006. The adjacent upland habitat is creosote and desert scrub. A dirt road intersects the 

site. 

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 habitat comprises 

seasonally flooded marshes, dense tamarisk, willow patches, scattered mesquite thickets, and isolated 

stringers of Fremont cottonwood. There are agricultural fields and ponds throughout the WMA, which are 

managed for waterfowl. Numerous roads intersect the refuge, for easy access to all sites. Four survey sites 
15 

were established (see below) within Overton WMA. Cuckoos were detected at Overton WMA at the 

Honey Bee Pond site in 2000 and 2002 (McKernan and Braden 2001, Rathbun and Braden 2003). 

We conducted 16 surveys at four sites within the management area (Table 2.6). Two sites, Honeybee 

Pond and Overton Wildlife, were considered adequate yellow-billed cuckoo habitat and were surveyed 

throughout the breeding season. Sites with lower quality habitat, Overton North and Overton Tamarisk, 

were surveyed fewer times due to time constraints. 

We detected four cuckoos at the Honeybee Pond site, and three at the Overton Wildlife site during the 

second and third survey periods (Table 2.7). No cuckoos were detected at either the Overton North site or 

Overton Tamarisk site. We did not confirm breeding at Honeybee Pond or the Overton Wildlife site 

(Appendix 2). However, the two cuckoos detected at the Overton Wildlife site during the second survey 

period were observed counter-calling within the site. 

Table 2.6. Dates (2006) for yellow-billed cuckoo surveys in the Overton Wildlife Management Area. 

Site Name Survey Period 1 Survey Period 2 Survey Period 3 Survey Period 4 

 Honeybee Pond 6/21 7/03, 7/15 7/28, 8/10 8/27 

Overton North 6/21 no survey 7/28, 8/10 no survey 

Overton Tamarisk no survey no survey 8/10 no survey 

Overton Wildlife 6/21 7/03, 7/15 7/28, 8/10 8/27 

Table 2.7. Yellow-billed cuckoo detections in 2006 in the Overton Wildlife Management Area. 

 Survey Survey Survey Survey Total 

Site Name Period 1 Period 2 Period 3 Period 4 Detections 

Honeybee Pond 0 3 1 0 4 

Overton North 0 no survey 0 no survey 0 

Overton Tamarisk no survey no survey 0 no survey 0 

Overton Wildlife 1 2 0 0 3 

Total Detections 1 5 1 0 7 

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

This is the largest pond in the management area. The site has tamarisk, young coyote willow, and a few 

scattered California fan palms (Washingtonia filifera). Canopy height is 4–8 m (13–26 ft). In 2006, 

standing water was present within this site. A dense stand of tamarisk surrounds the pond area. 

Overton North (Elevation 373 m; 1,223 ft) 

This site consists of a stringer of large Fremont cottonwoods that have been planted in rows. It lacks 

understory because the site is mowed. Canopy height is 12–14 m (39–46 ft). In 2006, standing water was 

not present within the site. A canal runs along its east side, with many housing structures within the site. 

Overton Tamarisk (Elevation 368 m; 1,207 ft) 

This is a small patch of older tamarisk within a dense patch of younger tamarisk. Canopy height is 4–10 

m (13–33 ft). Standing water was not present within the site in 2006. The site is surrounded by a large 

area of younger tamarisk. 

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

This is a small isolated site with multi-structured vegetation including coyote willow and tamarisk, as 

well as a re-vegetation site that consists of dense even-aged coyote willow. Canopy height is 4–8 m (13–
16 

26 ft). In 2006, standing water was not present within this site except for the canal, which has water all 

year. The canal separates the two main parts of this patch. Most of the site is surrounded by an 

impenetrably dense thicket of tamarisk. 

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

Mead) 

Where the Colorado River emerges from the Grand Canyon and flows into the northern end of Lake 

Mead, deposited sediments have been exposed by a 27 m (89 ft) drop in lake levels since 2000. Large 

tracts of riparian habitat have developed on these formerly inundated areas, with patches of willow, 

cottonwood, tamarisk, and arrowweed. The habitat extends from the river’s edge to the edges of the 

floodplain at the inflow. We surveyed much of the new riparian habitat, and divided the area into six 

survey sites (Figure 2.1; Appendix 4). 

We made 19 visits to the Grand Canyon/Lake Mead sites (Table 2.8). Low lake levels that resulted in 

shallow sandbars and other obstructions in the lower reaches of the river prevented us from accessing the 

Spencer Canyon site early in the season, so it was surveyed only during periods three and four. During the 

first visit to the River Delta/RM 285.3N site (see below) we determined it to be unsuitable cuckoo habitat 

and conducted no further surveys there. 

We detected 29 yellow-billed cuckoos, most during the first survey period (Table 2.9). Most detections 

were at Chuckwalla Cove and Cuckoo Beach; no cuckoos were found at Spencer Canyon or River Delta. 

We confirmed yellow-billed cuckoo breeding during the first survey period at Chuckwalla Cove. After 

surveys were completed, a juvenile cuckoo was seen in the presence of three adult cuckoos. The habitat at 

this sighting was a multi-layered canopy structure consisting mainly of coyote willow intermixed with 

young tamarisk. Canopy height within the patch was 6–8 m (20–26 ft) with the taller trees (10 m; 33 ft) 

toward the back of the patch. We also detected cuckoos at Cuckoo Beach during visits later in the season. 

Breeding was not confirmed at Cuckoo Beach, but counter-calling between two cuckoos was heard 

(Appendix 2). Cuckoos were also detected at Iceberg Ridge, also during later surveys, but breeding was 

not confirmed. One individual cuckoo was detected at RM 274.5 in late July. Breeding of this individual 

cuckoo was not confirmed, and no cuckoos were detected there during later surveys (Appendix 2). 

Table 2.8. Dates (2006) for yellow-billed cuckoo surveys in Grand Canyon National Park and Lake Mead National 

Recreation Area. 

Site Name Survey Period 1 Survey Period 2 Survey Period 3 Survey Period 4 

Spencer Canyon no survey no survey no survey 8/11, 8/27 

RM 274.5 6/29 7/13 8/10 8/26 

River Delta/RM285.3N 6/29 no survey no survey no survey 

Cuckoo Beach 6/29–6/30 7/12 8/10 8/25 

Iceberg Ridge 6/29 7/12 8/10 8/25 

Chuckwalla Cove 6/29–6/30 7/12 8/09 8/25 
17 

Table 2.9. Yellow-billed cuckoo detections in 2006 at Grand Canyon National Park/Lake Mead National Recreation 

Area. 

 Survey Survey Survey Survey Total 

Site Name Period 1 Period 2 Period 3 Period 4 Detections 

Spencer Canyon no survey no survey 0 0 0 

RM 274.5 0 0 1 0 1 

River Delta/RM285.3N 0 no survey no survey no survey 0 

Cuckoo Beach 6 3 0 1 10 

Iceberg Ridge 2 1 0 0 3 

Chuckwalla Cove 13 2 0 0 15 

Total Detections 21 6 1 1 29 

Spencer Canyon (Elevation 359 m; 1,179 ft) 

Spencer Canyon is a narrow canyon with steep walls and a perennial creek, approximately 47 km (29 

miles) upstream from the Canyon Mile 274 site (Appendix 4). At the mouth of the canyon where the 

creek intersects the Colorado River, the habitat consists mainly of dense tamarisk approximately 4 m (13 

ft) tall. About 70 m (230 ft) up the canyon, there are stringers of willow with tamarisk understory. 

Canopy height within the site is 8–10 m (26–33 ft). Except for the creek running through the canyon, 

standing water was not present within this site in 2006. The adjacent habitat is desert upland and canyon 

walls. 

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 (Appendix 4). It 

comprises mainly dense coyote willow and tamarisk, with many seeps and small creeks; one larger creek 

divides the patch in half. Canopy height within the site is 8–10 m (26–33 ft). Standing water was present 

during all surveys in 2006. The site is bordered by desert upland and canyon walls. 

River Delta/RM 285.3N (Elevation 367 m; 1,204 ft) 

River Delta/RM 285/3N is 4 km (2.5 miles) upstream of Cuckoo Beach. This site is a canyon delta 

dominated by tamarisk, with one narrow stringer of willow surrounded by tamarisk. Canopy height within 

the site is 3–5 m (10–16 ft). Except for the creek running through the canyon, standing water was not 

present during surveys in 2006. The adjacent habitat is desert upland. This site was surveyed once and 

rated as poor yellow-billed cuckoo habitat, and was not surveyed later. 

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

Cuckoo Beach lies approximately 1.5 km (0.9 miles) upstream from the Iceberg Ridge site, and extends 

on both sides of the river (Appendix 4). It consists of stringers of coyote willow lining the river’s edge 

and extending inland approximately 100 m (328 ft). Limited tamarisk is present toward the back of the 

site. Canopy height is 8–10 m (26–33 ft), with the taller trees toward the back of the site. In 2006, 

standing water was not present within this site. The adjacent habitat is desert upland. 

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 (Appendix 4). This site consists of large patches of willow and tamarisk. 

The upstream portion is more sparsely vegetated, with open spaces between the willows and tamarisk. 

The middle section consists of dense coyote willow of various ages and size. The downstream end has 

dense coyote willow approximately 4–5 m (13–16 ft) tall. Canopy height is 8–10 m (26–33 ft). Most of 
18 

this site is underlain with standing water that supports reeds (Phragmites spp.) and cattails (Typhus spp.). 

The site is bordered by desert upland habitat. 

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

Chuckwalla Cove is the first delta site on the river upstream from Lake Mead proper, located on river 

right approximately 14.5 km (9 miles) from the South Cove boat ramp (Appendix 4). Low water levels in 

the past 6 years have allowed the development of suitable yellow-billed cuckoo habitat, consisting of 

large patches of willow and tamarisk. The habitat exists throughout the entire floodplain, approximately 

250 m (820 ft) from the river’s edge. Canopy height is 8–10 m (26–33 ft). In 2006, standing water was 

not present within this site. The adjacent habitat is desert upland. 

Lake Mohave, AZ (Colorado River) 

Lake Mohave is a 107 km (66 miles) long reservoir created by Davis Dam, at the southern end of Lake 

Mead National Recreation Area (Figure 2.1; Appendix 4). The Lake Mohave surveys were conducted at 

two sites: Mohave Patch and Waterwheel Cove. Each site was surveyed three times, and no cuckoos were 

detected (Table 2.10). 

Table 2.10. Yellow-billed cuckoo surveys in 2006 at sites adjacent to Lake Mojave along the Colorado River. 

Site Name Survey Period 1 Survey Period 2 Survey Period 3 Survey Period 4 

Waterwheel Cove 7/02 no survey 7/25, 8/10 no survey 

Mohave Patch 7/02 no survey 7/26, 8/10 no survey 

Waterwheel Cove (Elevation 192 m; 630 ft) 

The Waterwheel Cove site is a series of coves along the lake’s edge approximately 29 km (18 miles) 

upstream of Davis Dam (Appendix 4). The habitat consists of large tamarisk interspersed among young 

tamarisk, with some scattered willows that appear stressed from being partially submerged in the 

reservoir. Canopy height is 4–6 m (13–20 ft). Most of the site was partially submerged in 2006. 

Waterwheel cove is bordered by desert upland habitat. 

Mohave Patch(Elevation 198 m; 650 ft) 

The Mohave Patch site lies along the edge of the lake approximately 1 km (0.6 miles) downstream of 

Waterwheel Cove, 28 km (17 miles) upstream of Davis Dam (Appendix 4). Most of the site consists of 

young tamarisk interspersed with larger tamarisk, with some scattered willows that are stressed from 

being partially submerged. There are also a number tamarisk snags throughout this site. Canopy height is 

13–20 ft (4–6 m). In 2006, standing water was present in sections of the site. There is desert upland 

habitat adjacent to the site. 

Havasu National Wildlife Refuge, AZ (Colorado River) 

The Havasu National Wildlife Refuge, which is 15,181 ha (37,515 acres), includes 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, which covers approximately 1619 ha (4000 acres) of the refuge, and contains 

most of the riparian habitat in the refuge. It is maintained through a dike system that was created upon the 

implementation of the refuge. Topock Marsh presently comprises 40 percent of all backwater habitat on 

the entire Colorado River system. We divided the Havasu National Wildlife Refuge area into six (see 

below) yellow-billed cuckoo survey sites (Appendix 4). 
19 

We conducted 29 survey visits to the Havasu National Wildlife Refuge sites (Table 2.11). A single 

cuckoo was detected at the Pintail Slough site during the first survey period. Breeding of this individual 

cuckoo was not confirmed, and no cuckoos were detected during later surveys (Appendix 2). No cuckoos 

were detected at the five other survey sites within the refuge. 

Table 2.11. Dates (2006) for yellow-billed cuckoo surveys at the Havasu National Wildlife Refuge. 

Site Name Survey Period 1 Survey Period 2 Survey Period 3 Survey Period 4 

Pintail Slough 6/15, 6/29 7/11 7/26, 8/09 9/06 

North Dike 6/15, 6/29 7/11 7/26, 8/09 no survey 

Topock Marsh Restoration 6/15, 6/28 7/10 7/25, 8/10 9/05 

Sacramento Wash 6/18, 6/30 7/12 7/29 no survey 

Havasu Tamarisk 6/18, 6/30 7/12 7/29 no survey 

Topock Tamarisk 6/14, 6/28 7/10 7/24 no survey 

Pintail Slough (Elevation 135 m; 443 ft) 

Pintail Slough is a re-vegetation site that consists of young Fremont cottonwood, with a small area of 

large cottonwoods just north of the re-vegetation plot (Appendix 4). This site was planted only 3 years 

ago and therefore lacks an understory or multi-structure canopy. Current canopy height is 4–6 m (13–20 

ft). In 2006, standing water was not present within this site. It is surrounded by large swaths of tamarisk. 

North Dike (Elevation 137 m; 449 ft) 

North Dike is a re-vegetation site about 300 m (984 ft) east of Pintail Slough, with large Fremont 

cottonwoods along the edge and some mesquite along the border (Appendix 4). Canopy height is 8–10 m 

(26–33 ft). There was no standing water within this site in 2006, except for the surrounding canals. There 

is also a large patch of monotypic tamarisk and arrowweed surrounding the site. 

Topock Marsh Restoration (Elevation 136 m; 446 ft) 

The restoration site in Topock Marsh, adjacent to the Colorado River, consists of 5-year-old Fremont 

cottonwoods intermixed with 2-year-old cottonwoods and willow, with an adjacent mesquite revegetation plot (Appendix 4). Canopy height is 5–7 m (16–23 ft). There was no standing water within this 

site in 2006. A large patch of monotypic tamarisk and arrowweed surrounds the site. 

Sacramento Wash (Elevation 142 m; 466 ft) 

Sacramento Wash is mostly an Athel tamarisk (Tamarix aphylla) forest that is completely devoid of 

young recruitment (Appendix 4). The understory consists of a thick duff layer with many downed trees. 

Canopy height is 8–10 m (26–33 ft). In 2006, standing water was not present within this site. Mesquite, 

acacia (Acacia spp.), and creosote (Larrea spp.) surround the site. 

Havasu Tamarisk (Elevation 150 m; 492 ft) 

This site is an Athel tamarisk forest mostly devoid of young recruitment and surrounded by mesquite, 

acacia and creosote. The understory consists of a thick duff layer with many downed trees. Canopy height 

is 8–10 m (26–33 ft). In 2006, standing water was not present at the site. 

Topock Tamarisk (Elevation 143 m; 469 ft) 

This is an Athel tamarisk forest that borders the Topock Platform site (Appendix 4). A thick understory of 

young tamarisk occurs in some portions, while others have no understory at all, only a thick duff layer 

mixed with many downed trees. A small stringer of tall cottonwoods runs along a section of road that 
20 

borders the site. Canopy height is 8–10 m (26–33 ft). In 2006, standing water was not present at this site. 

It is bordered by a large patch of young monotypic tamarisk and arrowweed. 

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 and Bill Williams Rivers (Figure 2.1; Appendix 4). Alamo Lake, which is 

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

Wildlife Refuge (NWR) 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). 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 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 nine cuckoo survey sites (Appendix 4). The sites (see 

below) were picked from historic survey routes where cuckoos had been detected in 1994, 1995, 1998, 

and 2001–2003 (Halterman and Laymon 1994, Halterman and Laymon 1995, Halterman 1998, 2001, 

2002, 2003). Routes were also added that connected each site within the refuge riparian system. 

In 2006, we conducted 39 surveys (Table 2.12). Most of the 117 cuckoo detections came during the 

second survey period (Table 2.13). Cave Wash and Big Bend had the greatest number of detections, but 

each site had at least one detection during the 2006 field season. 

We confirmed breeding at the Big Bend and Saguaro Slot sites (Appendix 2). At Big Bend, a juvenile was 

observed at a territory that had been consistently occupied during all visits. Three adults were confirmed 

visually in this territory and a food carry was seen (Appendix 2). On a subsequent visit, adults were 

observed feeding a juvenile. The nest search was unsuccessful, but adults were repeatedly seen in this 

area where the initial food carry was taken. 

The one nest located this summer was found in the Saguaro Slot site. It contained two eggs and one 

hatchling about 5–6 days old. The nest was located 3.4 m (11.2 ft) above the ground in an extremely 

dense patch of tamarisk with a 6–12 m (20–39 ft) tall overstory of Goodding’s willow. The average 

canopy cover was 83 percent. The nest was not monitored on a continuous basis so the fate of the nestling 

and eggs is unknown, but it is likely that two of the eggs never hatched (Appendix 2). 

Table 2.12. Dates (2006) for yellow-billed cuckoo surveys at the Bill Williams River National Wildlife Refuge. 

Site Name Survey Period 1 Survey Period 2 Survey Period 3 Survey Period 4 

Cave Wash no survey 7/05, 7/19 8/02 8/15 

Mineral Wash no survey 7/05, 7/19 8/01 8/15 

Big Bend no survey 7/05, 7/19 8/02 8/15 

Gibraltar Rock 6/17 7/04, 7/18 8/01 8/14 

Sandy Wash no survey 7/04, 7/18 7/31 8/13 

Fox Wash 6/17 7/04, 7/18 8/01 8/13 

Mosquito Flats 6/17 7/04, 7/18 7/30 8/13 

Saguaro Slot 6/17 7/18 7/30 8/13 

Bill Williams River Marsh no survey 7/05, 7/19 7/31 8/14 
21 

Table 2.13. Yellow-billed cuckoo detections in 2006 at the Bill Williams River National Wildlife Refuge. 

 Survey Survey Survey Survey Total Site Name Period 1 Period 2 Period 3 Period 4 Detections 

Cave Wash no survey 12 5 4 21 

Mineral Wash no survey 8 6 1 15 

Big Bend no survey 12 4 3 19 

Gibraltar Rock 1 2 1 4 8 

Sandy Wash no survey 9 5 0 14 

Fox Wash 1 0 0 0 1 

Mosquito Flats 3 9 5 0 17 

Saguaro Slot 2 3 5 0 10 

Bill Williams River Marsh no survey 6 4 2 12 

Total Detections 7 61 35 14 117 

At Cave Wash and Sandy Wash we saw cuckoos carrying food in areas where birds had been detected 

consistently over at least two surveys (Appendix 2). In Bill Williams River Marsh, two cuckoos were 

detected in the same area three times and they were counter-calling during each detection. At Mineral 

Wash two individual cuckoos were exhibiting agitated behavior in response to playback, and cuckoos 

were detected during repeated visits in the same area. At Gibraltar Rock, all individuals detected at this 

site were not consistently detected in the same areas and the presence of more than one individual per 

survey point was never confirmed. Only one cuckoo was detected in Fox Wash, and no other cuckoos 

were detected during later surveys. 

Cave Wash (Elevation 175 m; 574 ft) 

Cave Wash is located at the most eastern edge of the refuge (Appendix 4). This site is a wide floodplain 

consisting of young willows and cottonwoods along the river’s edge. The cottonwood 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). Similar to Mineral Wash, the river is very braided here, 

supporting thicker riparian patches, with some standing water away from the main river channel. This site 

is surrounded by Sonoran Desert upland. 

Mineral Wash (Elevation 160 m; 525 ft) 

Mineral Wash has dense, mature riparian vegetation lining both banks (Appendix 4). The vegetation is 

mixed native and exotic, with native species predominating. There are many patches with multi-tiered 

layers of uneven-aged cottonwood and Gooding’s willow stands with a dense understory of willow, 

cattail, tamarisk, 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 bend in the Bill Williams River that winds through Bill Williams River Canyon (Appendix 

4). The canyon widens and narrows throughout the site and dense riparian vegetation lines the riverbanks 

throughout. The vegetation is mixed native and exotic, with native species predominating. There are 

many patches with multi-tiered layers of uneven-aged cottonwood and Gooding’s willow stands with a 

dense understory of willow, cattail, and tamarisk. Canopy height is 12–14 m (39–46 ft). The river washes 

were dry during all surveys in 2006. This site is surrounded by sandy deltas with mesquite where the 

canyon floodplain exists; however, there are strips of young willow and cottonwood in areas where the 

sandy uplands have flooded. 
22 

Gibraltar Rock (Elevation 145 m; 476 ft) 

Gibraltar Rock consists of a large sandy floodplain with much cobble. This washed-out section of the 

river is straddled at either end by two healthy riparian patches consisting of mature and young cottonwoods, and young willows (Appendix 4). Throughout the wash portion there are many tamarisk 

stringers, and thicker tamarisk patches running into the upland desert habitat. Canopy height is 10–12 m 

(33–39 ft). The river washes were dry during all surveys in 2006. The site is bordered by Sonoran Desert 

upland habitat. 

Sandy Wash (Elevation 146 m; 473 ft) 

Researchers Trail Site has lush riparian habitat on either side of sandy braids of river washes. In this site, 

the river runs up against a cliff face on the northern side of the patch, well away from the main part of the 

riparian habitat (Appendix 4). The patches consist of large cottonwoods and willows, with a thick 

understory dominated by tamarisk with some younger cottonwood and willows evident. Canopy height is 

12–14 m (39–46 ft). The river washes were dry during all surveys in 2006. The site is surrounded by 

patches of mesquite, paloverde (Parkinsonia microphylla), and arrowweed. 

Fox Wash (Elevation 145 m; 476 ft) 

Fox Wash is the most northern survey site on the refuge (Appendix 4). It is extremely diverse, consisting 

of desert washes lined with tamarisk stringers, old growth tamarisk patches with some mixed native old 

growth components, and a very unique section of mainly large cottonwood and willow with very little 

understory except for large patches of young tamarisk dispersed throughout this site. Canopy height is 

12–14 m (39–46 ft). There were pools of standing water within this site during all 2006 surveys. The site 

is surrounded by patches of mesquite, paloverde, and arrowweed. 

Mosquito Flats (Elevation 140 m; 459 ft) 

Mosquito Flats is the broadest riparian area on the refuge; it is approximately 500 m (1640 ft) wide 

(Appendix 4). Our survey focus was on the southern edge of the site, where trails provide easy access. 

However, sections of this patch were too remote to survey without a large amount of trail clearing, which 

we did not do. The patch consisted of native and non-native vegetation in multiple stages of growth. 

Large cottonwoods and willows are predominant throughout the site. Canopy height is 12–14 m (39–46 

ft). There was standing water within this site during all 2006 surveys. The site is bordered by large 

patches of mesquite, paloverde, and arrowweed. 

Saguaro Slot (Elevation 135 m; 443 ft) 

Saguaro Slot is an extremely thick and virtually impenetrable native and exotic mixed site that is roughly 

100 m (328 ft) away from the river at its farthest edge (Appendix 4). The overstory includes many large 

willows and some cottonwoods, with an understory of many thick clumps of small-diameter tamarisk. 

There are numerous downed logs in this portion of the site and a thick decomposing layer of duff on the 

floor. Canopy height within the site is 12–14 m (39–46 ft). There were pools of standing water during all 

2006 surveys. The site is surrounded by an impenetrable thicket of dense mesquite. 

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

Bill William River Marsh was accessible by boat by paddling across Lake Havasu to the confluence of 

the Bill Williams River. Surveyors continued upriver approximately 1.6 km (0.9 miles), to the beginning 

of the site (Appendix 4). Habitat consisted mainly of Fremont cottonwood and willow along the river’s 

edge and throughout the floodplain, with large patches of tamarisk and willow making up most of the 

understory. The habitat was extremely dense in some areas due to the thick tamarisk understory. 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. 
23 

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 channelized 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 to produce forage for migratory waterfowl, and 318 (785 acres) consists of desert. Most of the 

alluvial river bottom is dominated by tamarisk, mesquite, and arrowweed. Most cuckoo survey sites were 

located at riparian restoration sites 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. The second fire burned 

part of the Cross River site described below. We established six cuckoo survey sites at Cibola National 

Wildlife Refuge (see below). 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. 2006) 

We conducted 32 survey visits (Table 2.14), resulting in cuckoo detections at the Cibola Nature Trail 

Restoration and Cibola South Restoration sites (Table 2.15); these sites were revisited during the fourth 

survey period because cuckoos were detected in these plots earlier in the season. 

The individual yellow-billed cuckoo detected at the Cibola South Restoration site was only detected 

during one survey, it did not respond to playback, and no other individuals were seen or heard in this area 

during later surveys (Appendix 2). At the Cibola Nature Trail Restoration site, at least one cuckoo was 

detected in the same area during two consecutive survey periods (aural detection during the first survey 

period, visual detection during the second); no breeding behavior was observed and only one cuckoo was 

confirmed per detection. 

Table 2.14. Dates (2006) for yellow-billed cuckoo surveys at the Cibola National Wildlife Refuge. 

Site Name Survey Period 1 Survey Period 2 Survey Period 3 Survey Period 4 

Cibola North Restoration 6/20 7/03, 7/17 7/31 8/12 

Cibola Nature Trail Restoration 6/20 7/03, 7/17 7/31 8/12, 9/10 

Cibola Eucalyptus Restoration 6/20 7/03, 7/17 7/31 8/12 

Cibola South Restoration 6/20 7/03, 7/17 7/31 8/12, 9/08 

Cibola Cross River 6/20 7/03, 7/17 7/31 8/12 

Cibola East Side 6/20 7/03, 7/17 7/31 8/12 

Table 2.15. Yellow-billed cuckoo detections in 2006 at Cibola National Wildlife Refuge. 

 Survey Survey Survey Survey Total 

Site Name Period 1 Period 2 Period 3 Period 4 Detections 

Cibola North Restoration 0 0 0 0 0 

Cibola Nature Trail Restoration 1 1 0 0 2 

Cibola South Restoration 0 1 0 0 1 

Cibola Eucalyptus Restoration 0 0 0 0 0 

Cibola Cross River 0 0 0 0 0 

Cibola East Side 0 0 0 0 0 

Total Detections 1 2 0 NA 3 
24 

Cibola North Restoration (Elevation 68 m; 223 ft) 

The Cibola North Restoration site lies approximately 500 m (1640 ft) north of Cibola Nature Trail 

(Appendix 4). It is a younger restoration site composed almost entirely of young (2–3 years old) 

cottonwoods. This restoration site is square in shape, since it was planted within the area of one 

abandoned agricultural field. Canopy height is 4–6 m (13–20 ft). In 2006, 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 (Appendix 4). Within the ring of cottonwoods, the north part is dominated by a 

lower canopy of willows and the south part is dominated by mesquite with a tall grass understory. 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, and the restoration site is periodically irrigated by refuge staff, 

however in 2006 standing water was not present. The site is surrounded on all sides by agriculture. 

Cibola Eucalyptus Restoration (Elevation 71 m; 233 ft) 

The Cibola Eucalyptus Restoration site was managed as a eucalyptus restoration site, but also contains 

numerous cottonwoods (Appendix 4). Other tree species include tamarisk, mesquite, and paloverde. A 

refuge levee road bisects the site, which extends for 1 km (3.3 ft) in a north-south orientation. Canopy 

height is 10–12 m (33–39 ft). The Colorado River lies 328 ft (100 m) to the east, and in 2006 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 is dominated by rows of planted cottonwoods interspersed with 

willows (Appendix 4). The understory of the restoration site is mostly open. This site lies about 300 m 

(984 ft) west of the Colorado River, and is irrigated by refuge staff (Appendix 4). A fuel break was 

bulldozed along the southeast edge of the site to successfully protect it from the 10 August 2006 fire. 

Canopy height is 10–15 m (33–49 ft). In 2006, standing water was not present within this site. It is 

bordered by monotypic tamarisk and dense stands of mesquite with arrowweed in the understory. 

Cibola Cross River (Elevation 65 m; 268 ft) 

The Cibola Cross River site is near the East Side survey site in the southern section of the refuge 

(Appendix 4). Half of the site is located on the east side of the river, and the other half lies on the west 

side. The vegetation is very similar to the East Side survey site, with several large cottonwoods and 

willows spread amongst a thick understory of tamarisk, mesquite, and arrowweed. Canopy height is 10–

12 m (33–39 ft). In 2006, there was no evidence of standing water within this site. On 10 August 2006 a 

lightning-ignited wildfire burned the entire western portion of this site, killing all native riparian trees. 

Cibola East Side (Elevation 66 m; 271 ft) 

The Cibola East Side site is located in the southern section of the refuge, and is dominated by several 

large cottonwoods and willows (Appendix 4). The understory is primarily tamarisk, mesquite, and 

arrowweed with a small patch of died-off marsh vegetation. Canopy height is 10–12 m (33–39 ft). A 

levee road borders the west side of the site, which is approximately 25 m (82 ft) from the Colorado River. 

In 2006, there was no evidence of standing water within this site. It is surrounded by a low-canopy 

monotypic stand of tamarisk. 
25 

Picacho State Recreation Area, CA (Colorado River) 

This 46 ha (120 acre) recreation area is located on the California side of the Colorado River, within the 

Imperial National Wildlife Refuge (Figure 2.1; Appendix 4). Most of the park is dominated by desert 

scrub and washes, but it includes a riparian restoration area adjacent to the park headquarters and the 

river. Large cottonwoods dominate the canopy, but a small number of willows contribute to the high 

canopy. Willow, mesquite, and arrowweed make up the understory. The riparian area surrounding the 

restoration site consists almost entirely of non-native vegetation dominated by tamarisk. Canopy height is 

12–14 m (39–46 ft). In 2006, there was no evidence of standing water within this site. The elevation of 

the park is 52 m (171 ft). This entire site is surrounded by desert upland habitat. Historically no yellowbilled cuckoos have been detected at this site. 

We established only one survey site, which was reached by boat from Imperial NWR. This area was 

surveyed five times (Table 2.16), and a single yellow-billed cuckoo was detected during survey period 

three. This cuckoo was seen and heard by the observer. It was only detected once, and responded eagerly 

to playback (Appendix 2). One cuckoo was heard vocalizing on 5 July by a SWCA Willow Flycatcher 

Project employee near where our individual was detected (Appendix 3). 

Table 2.16. Dates (2006) for yellow-billed cuckoo surveys at the Picacho State Recreation Area. 

Site Name Survey Period 1 Survey Period 2 Survey Period 3 Survey Period 4 

Picacho State Park 6/21 7/03, 7/17 8/02 8/11 

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 miles) stretch of the original Colorado River (Figure 2.1; Appendix 4). The 

refuge borders Cibola NWR to the south. It is dominated by desert ridges, and by riparian vegetation 

along the Colorado River. Native riparian vegetation is rare, and most of the habitat is dominated by 

exotic tamarisk and reeds (Phragmites spp.). We searched for yellow-billed cuckoos at two sites within 

the refuge. In 2005, a single cuckoo was detected during two visits at the Imperial South Restoration site 

(Johnson et al. 2006). 

We conducted 10 survey visits (Table 2.17), and made two cuckoo detections at the Imperial South 

Restoration site (Table 2.18). No cuckoos were found at the Imperial North Site. The cuckoo detected at 

Imperial South Restoration on 15 July was heard outside of a formal survey, and was observed carrying 

food (Appendix 2). Later in the season, two cuckoos were confirmed at the South Restoration site because 

vocalizations were heard simultaneously in two different areas of the refuge. The nest search was 

unsuccessful but a vocalization was solicited from a cuckoo in the area where the food was carried to—a 

tall stand of tamarisk in the middle of the marsh. The area is a matrix of marsh vegetation, roads, and 

stringers of cottonwoods, ponds and waterways. The cuckoos were detected in a small even-aged 

cottonwood restoration stand with sparse understory vegetation. This area borders extensive upland desert 

with mesquite, and one cuckoo was seen in a mesquite tree approximately 900 m (2953 ft) from the 

cottonwood restoration stand near the refuge residential buildings (Appendices 2 and 3). 

Table 2.17. Dates (2006) for yellow-billed cuckoo surveys at Imperial National Wildlife Refuge. 

Site Name Survey Period 1 Survey Period 2 Survey Period 3 Survey Period 4 

Imperial Paradise 6/21 7/03 8/02 8/11 

Imperial South Restoration 6/19, 7/02 7/15 7/30 8/12, 9/13 
26 

Table 2.18. Yellow-billed cuckoo detections in 2006 at Imperial National Wildlife Refuge. 

 Survey Survey Survey Survey Total 

Site Name Period 1 Period 2 Period 3 Period 4 Detections 

Imperial Paradise 0 0 0 0 0 

Imperial South Restoration 2 1 0 0 3 

Total Detections 2 1 0 0 3 

Imperial Paradise (Elevation 60 m; 197 ft) 

This remote site on the California side of the river is approximately 25 km (15.5 miles) northwest of the 

Imperial NWR headquarters (Appendix 4), and is accessible only by boat. It is dominated by mature 

cottonwoods and smaller patches of coyote willow, with dense thickets of tamarisk. The understory is 

composed of ravennagrass (Saccharum ravennae), phragmites, cattails, tamarisk, and arrowweed. 

Suitable cuckoo habitat runs in a north-south orientation, with trail access. Canopy height within the site 

is 12–14 m (39–46 ft). During heavy rains, portions of the site had standing water. West of the site is 

desert scrub and east is the Colorado River. 

Imperial South Restoration (Elevation 56 m; 184 ft) 

The Imperial South Restoration site consists of a restoration plot that was planted in 1993 (Appendix 4). 

The canopy is dominated by cottonwoods, with small but dense stands of willows in 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 restoration 

site is periodically flooded by refuge staff. However, in 2006, there was no evidence of standing water 

within this site. Marsh habitat occurs to the north and east of the restoration site. To the south and west, 

the Bureau of Reclamation is currently funding additional restoration of both riparian and fish habitats. 

Mittry Lake State Wildlife Management Area/Pratt Restoration Area, AZ (Colorado River) 

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; 

Appendix 4). The Pratt Restoration Site is dominated by a tall canopy of cottonwoods (12–14 m; 39–46 

ft), with small numbers of willows in the understory. Most of the restoration site has an open understory 

covered only by leaf litter. However, the southern part of the restoration site is now dominated by a dense 

growth of baccharis (Baccharis spp.) with scattered young cottonwoods. The habitat at Betty’s Kitchen is 

mostly exotic, dominated by 8–10 m (26–33 ft) tall Athel tamarisk, but large mesquite trees are also 

present. The rest of the survey area is open water or marsh. In 2006, there was no evidence of standing 

water within the Pratt Restoration site. The elevation is 52 m (171 ft). This entire site is surrounded by 

agriculture fields and desert upland habitat. 

In 2005, one yellow-billed cuckoo was detected at the Pratt Restoration area (Johnson et al. 2006). We 

conducted five survey visits in 2006 (Table 2.19), but no yellow-billed cuckoos were detected. 

Table 2.19. Dates (2006) for yellow-billed cuckoo surveys at the Mittry Lake State Wildlife Management Area. 

Site Name Survey Period 1 Survey Period 2 Survey Period 3 Survey Period 4 

Mittry Lake/Pratt Restoration 6/14, 6/26 7/11 7/25, 8/07 no survey 
27 

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

This confluence area, located 10 km (6.2 miles) east of Yuma, is primarily managed by the Bureau of 

Land Management (Figure 2.1; Appendix 4). Most riparian habitat in this area is dominated by exotic 

vegetation and bordered by agriculture. Only the habitat upriver from the confluence on both rivers was 

surveyed for cuckoos. This area was divided into two survey sites based on the dominant drainage 

(Appendix 4). In 2005, two cuckoo detections occurred at the Colorado River confluence site and five at 

the Gila River site (Johnson et al. 2006). 

We conducted 10 survey visits at the Gila River–Colorado River confluence sites (Table 2.20). There 

were nine cuckoo detections (Table 2.21), mainly in extensive habitat patches along the Colorado River, 

and two detections in small patches along the Gila River. 

In 2006, two cuckoo detections occurred at the confluence over two visits in July (Appendix 2). During 

the first visit, two birds were confirmed in the same patch as they were counter-calling. At another patch, 

upstream of the confluence, two birds were also confirmed in the same area. All other cuckoos found 

along the Colorado River confluence, and those on the Gila River, were detected only during the first 

survey period and were not detected during later survey periods (Appendix 2). 

Table 2.20. Dates (2006) for yellow-billed cuckoo surveys at the area of the Gila River–Colorado River confluence. 

Site Name Survey Period 1 Survey Period 2 Survey Period 3 Survey Period 4 

Colorado River 6/16, 7/01 7/14 7/27, 8/08 no survey 

Gila River 6/16, 7/01 7/14 7/27, 8/08 no survey 

Table 2.21. Yellow-billed cuckoo detections in 2006 at the area of the Gila River–Colorado River confluence. 

 Survey Survey Survey Survey Total 

Site Name Period 1 Period 2 Period 3 Period 4 Detections 

Colorado River 5 2 0 no survey 7 

Gila River 2 0 0 no survey 2 

Total Detections 7 2 0 0 9 

Colorado River (Elevation 39 m; 128 ft) 

Most of the suitable riparian habitat at this site is on the north side of the river (Appendix 4), which we 

surveyed entirely by kayak. Thin patches of cottonwood and willow occur sporadically, close to the river; 

habitat north of the river’s edge is not suitable for cuckoos. As the Gila–Colorado confluence is 

approached, the riparian habitat on the north side abruptly transitions into a citrus orchard. On the south 

side of the river, only a thin belt of riparian vegetation exists between the river and agricultural fields. It is 

almost entirely composed of exotic tamarisk, with very little native riparian vegetation. Canopy height is 

8–10 m (26–33 ft). In 2006 there was no evidence of standing water within this site. This entire site is 

surrounded by agriculture fields. 

Gila River (Elevation 39 m; 128 ft) 

The Gila River site is dominated by exotic tamarisk with very few native riparian trees. The few small 

patches of native cottonwood and coyote willow are interspersed with large stretches of unsuitable 

habitat. Canopy height within the site is 8–10 m (26–33 ft). Initially we used kayaks to cover all habitat 

along the river. However, this approach was abandoned after we determined that suitable habitat for 

cuckoos along the river itself was very limited. There is some riparian vegetation close to the river, but 

much of what remains is distant with broad expanses of tamarisk and arrowweed in between. Canopy 
28 

height is 8–10 m (26–33 ft). In 2006, there was no evidence of standing water within this site. 

Agricultural fields border the Gila River on both the north and south sides. In late August, one of the best 

remaining patches of native cottonwoods was disturbed by heavy machinery at the edge of a farm field. 

Yuma West Wetlands, AZ (Colorado River) 

This park is surrounded by urban housing tracts on the edge of Yuma (Figure 2.1; Appendix 4), and is 

managed by the city of Yuma. Most of the park is a riparian restoration area that borders the Colorado 

River on one side and a levee on the other. The vegetative composition here is almost all native, with 

cottonwood, willow, and mesquite stands that are approximately 8–10 years old. Canopy height is 8–10 m 

(26–33 ft). The entire site is regularly irrigated and invasive exotic species are controlled. 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. The elevation is 36 m (118 ft). 

Historically, yellow-billed cuckoo had not been surveyed at this site. We conducted six surveys (Table 

2.22), but no yellow-billed cuckoos were detected. 

Table 2.22. Dates (2006) for yellow-billed cuckoo surveys in Yuma West Wetlands along the lower Colorado 

River. 

Site Name Survey Period 1 Survey Period 2 Survey Period 3 Survey Period 4 

Yuma West Wetlands 6/21, 6/01 7/16 7/29, 8/09 no survey 

Limitrophe Division, AZ (Colorado River) 

The Limitrophe survey area is the last stretch of the Colorado River before the river passes into Mexico 

(Figure 2.1; Appendix 4). It starts at the Northerly International Border by Morales Dam and ends at San 

Luis, Arizona, at the Southerly International Border with Mexico. Only the riparian habitat on the east 

side of the river was surveyed, since the western riverbank is in Mexico. The habitat, which is enclosed 

by a series of tightly controlled gates, was actively patrolled by border security personnel. Permission to 

enter was requested from the Border Patrol prior to each survey due to border security issues. Agricultural 

fields border the riparian habitat on both sides. The habitat was divided into north and south survey 

sections, above and below the Cocopah Indian Reservation. In 2005, six cuckoo detections occurred at 

Limitrophe Division North, and one detection occurred at Limitrophe Division South (Johnson et al. 

2006). 

We made nine survey visits to the Limitrophe Division sites (Table 2.23). The survey conducted in late 

July was partitioned over 2 days due to high heat, and a scheduled survey at Limitrophe Division South 

during the second period was cancelled due to high winds (constant winds over 15 mph with gusts to 35 

mph). No surveys were conducted during survey period four because the last surveys on 10 August did 

not result in a cuckoo detection (Table 2.24). 

In 2006, six yellow-billed cuckoos were detected in the area, all at Limitrophe Division North (Table 

2.23). Two individuals were confirmed in areas along the river within a large patch of old-growth cottonwoods surrounded by strips of multi-tiered riparian vegetation. The birds were never detected in this 

patch during later surveys. Further north, near the Morelos Dam, cuckoos were detected during three 

surveys. The first detections were unsolicited birds that were heard giving knocking calls, the next was a 

visual detection of a silent bird, and the third was auditory only. The cuckoos detected at Morelos Dam 

were detected in the same patch until 28 July. This patch at Morelos Dam was also occupied by a single 

cuckoo in 2005 (Johnson et al. 2006). Some portions of the habitat were not searched due to border 

security issues (see Appendix 2). The SWCA Willow Flycatcher Project crew detected a yellow-billed 

cuckoo vocalizing at the northern edge of the Limitrophe Division South site, near the border with the 
29 

Cocopah Reservation (see Appendix 3). At least one individual cuckoo was heard vocalizing on 20 June, 

and two individuals were heard counter-calling and one cuckoo was seen on 1 July. 

Table 2.23. Dates (2006) for yellow-billed cuckoo surveys in the Limitrophe Division area along the lower 

Colorado River. 

Site Name Survey Period 1 Survey Period 2 Survey Period 3 Survey Period 4 

Limitrophe Division North 6/18, 6/28 7/16 7/28, 7/29, 8/10 no survey 

Limitrophe Division South 6/17, 6/27 no survey 7/28, 8/10 no survey 

Table 2.24. Yellow-billed cuckoo detections in 2006 in the Limitrophe Division area along the lower Colorado 

River. 

 Survey Survey Survey Survey Total 

Site Name Period 1 Period 2 Period 3 Period 4 Detections 

Limitrophe Division North 4 1 1 no survey 6 

Limitrophe Division South 0 no survey 0 no survey 0 

Total Detections 4 1 1 NA 6 

Limitrophe Division North (Elevation 36 m; 118 ft) 

This site starts at the Northerly International Border by Morales Dam and extends to the northern border 

of the Cocopah Indian Reservation (Figure 2.1; Appendix 4). The riparian habitat here transitions 

frequently from mostly native vegetation with a canopy of cottonwood and willow to mostly exotic 

dominated by tamarisk. In some places, riparian vegetation becomes very sparse and is dominated by a 

low-stature monotypic arrowweed scrub. Canopy height within the site is 4–10 m (13–33 ft). In 2006, 

there was no evidence of standing water within this site. 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 Reservation and continues south to San Luis, 

Arizona, the Southerly International Border with Mexico (Figure 2.1; Appendix 4). As with the 

Limitrophe Division North site, the habitat here also transitions frequently between dense riparian 

vegetation and sparse scrub. However, 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 southernmost of these patches is primarily a mix of native riparian trees and marsh, 

whereas the northern patch lacks the marsh component. Canopy height within the site is 4–10 m (13–33 

ft). In 2006, there was no evidence of standing water within this site. There are agricultural fields adjacent 

to the site. 

Gila River Highway 95, AZ (Gila River) 

This area is located where Highway 95 crosses the Gila River (Figure 2.1; Appendix 4). In addition to 

riparian vegetation along the river itself, survey sites also included habitat adjacent to irrigation canals 

and agricultural fields. Most of the habitat occurs as thin strips of trees in an otherwise human-modified 

landscape. We divided this area into three cuckoo survey sites (Appendix 4). 

In 2005, one cuckoo detection occurred in this area of the Gila River Highway 95 Bridge site (Johnson et 

al. 2006). We made 15 survey trips to the Gila River Highway 95 sites in 2006 (Table 2.25); no yellowbilled cuckoos were detected. 
30 

Table 2.25. Dates (2006) for yellow-billed cuckoo surveys at sites near the junction of the Gila River Highway 95 

Area. 

Site Name Survey Period 1 Survey Period 2 Survey Period 3 Survey Period 4 

Gila 95 Bridge 6/13, 6/27 7/13 7/24, 8/07 no survey 

Gila 95 Canal 6/13, 6/27 7/13 7/24, 8/07 no survey 

Gila 95 Tall Tamarisk 6/13, 6/27 7/13 7/24, 8/07 no survey 

Gila 95 Bridge (Elevation 44 m; 144 ft) 

The Gila-95 Bridge site also borders the Gila River itself but it is on the west side of Highway 95 

(Appendix 4). We surveyed the area from a dirt road with an agricultural field on one side and riparian 

habitat on the other. A large abandoned steel bridge crosses the river midway through the site. Habitat 

here is mostly tamarisk, but scattered cottonwoods and coyote willows form the top of the canopy. 

Canopy height is 10–12 m (33–39 ft). In 2006, there was no evidence of standing water within this site. 

This entire site is surrounded by desert upland habitat. 

Gila 95 Canal (Elevation 54 m, 177 ft) 

The Gila 95 Canal site is on the east side of Highway 95 and borders the Gila River on one side and a 

large citrus orchard on the other (Appendix 4). Parts of the site also lie adjacent to an intricate network of 

irrigation canals, although much of this habitat is monotypic tamarisk. Native riparian vegetation is fairly 

sparse, with mostly young cottonwoods and coyote willows. Canopy height is 8–12 m (26–39 ft). In 

2006, there was no evidence of standing water within this site. It is entirely surrounded by desert upland 

habitat. 

Gila 95 Tall Tamarisk (Elevation 45 m; 148 ft) 

The Gila 95 Tall Tamarisk site runs parallel to Highway 95 and is approximately 300 m (984 ft) east 

(Appendix 4). It is composed entirely of tall tamarisk growing in a long narrow strip 8–12 m (26–39 ft) 

wide. The site is bisected by 3rd Street, which provides access to Dome Valley. Canopy height is 8–10 m 

(26–33 ft). In 2006, there was no evidence of standing water within this site. It is bordered by an 

irrigation canal on one side and sparse desert scrub on the other. 

Gila River/Ligurta, AZ (Gila River) 

The Gila River/Ligurta site is a very small patch of native riparian trees located approximately 35 km (22 

miles) west of the Gila River/Quigley Pond Wildlife Management Area (WMA) and about 2 km (1.2 

miles) north of the town of Ligurta (Figure 2.1; Appendix 4). It contains a small number of large cottonwood trees and a few large Goodding’s willows with a dense understory of arrowweed. Canopy height is 

8–10 m (26–33 ft). In 2006, there was no evidence of standing water within this site. It is surrounded on 

all sides by agricultural fields. Site elevation is 197 ft (60 m). 

There have been no previous surveys of yellow-billed cuckoos at this site. We conducted four survey 

visits to the site in 2006 (Table 2.26); no yellow-billed cuckoos were detected. 
31 

Table 2.26. Dates (2006) for yellow-billed cuckoo surveys at the Gila River/Ligurta, Gila River/Wellton and Gila 

River/Quigley Pond Wildlife Management Area. 

Site Name Survey Period 1 Survey Period 2 Survey Period 3 Survey Period 4 

Gila River/Ligurta 6/26 7/11 7/30 8/11 

Gila River/Wellton 6/26 7/11 7/30, 8/11 8/11 

Gila River/Quigley Pond WMA 6/14, 6/26 7/11 7/30, 8/11 no survey 

Gila River/Wellton, AZ (Gila River) 

The Gila River/Wellton site is a small patch of native riparian trees located approximately 25 km (16 

miles) west of the Gila River/Quigley Pond WMA, about 5 km (3 miles) northwest of the town of 

Wellton (Figure 2.1; Appendix 4). The canopy is dominated by large mature cottonwoods and 

Goodding’s willows, with a dense understory of tamarisk and arrowweed. Canopy height is 8–10 m (26–

33 ft). In 2006, there was no evidence of standing water. The site is surrounded on all sides by 

agricultural fields. The elevation of this site is 64 m (210 ft). 

There have been no previous surveys of yellow-billed cuckoos at this site. We conducted four survey 

visits to the site (Table 2.26), and detected a single cuckoo during the first survey period (Appendix 2). 

No cuckoos were detected during later surveys. 

Gila River/Quigley Pond Wildlife Management Area, AZ (Gila River) 

The Gila River/Quigley Wildlife Management Area, located in the Gila River floodplain approximately 6 

km (4 miles) south of the U.S. Highway 8 Tacna exit (Figure 2.1; Appendix 4), is managed by the 

Arizona Game & Fish Department as wildlife habitat. The site includes a riparian restoration plot 

dominated by cottonwoods with a small number of willows in the understory. Adjacent to this is a larger 

section of mixed native-exotic habitat with a canopy of mostly young cottonwoods and willows, and a 

dense understory of arrowweed. Approximately 500 m (1640 ft) to the north is the Gila River itself, 

which is mostly dominated by tamarisk, with very few native trees. Canopy height is 8–14 m (26–46 ft). 

The Arizona Game & Fish Department routinely floods the restoration site; however, in 2006 there was 

no evidence of standing water within this site. The surrounding landscape consists of an intensively 

managed mosaic of agricultural fields. The elevation of this site is 67 m (220 ft). 

In 2005, eight yellow-billed cuckoo detections occurred at this site. A pair was detected during one 

survey, with one cuckoo carrying nest material, but breeding was not confirmed (Johnson et al. 2006). We 

conducted six survey visits to the site in 2006 (Table 2.26), and detected a single cuckoo during the first 

survey period. This cuckoo was seen foraging in a cotton field on the edge of the restoration area 

(Appendix 2). Subsequent surveys yielded no further detections. 

Summary of Cuckoo Breeding Status Results 

Of our 180 yellow-billed cuckoo detections, we confirmed five breeding events by locating an active nest 

or observing juveniles (Table 2.27). The juveniles we found could not be easily linked to any particular 

adult parental birds. Yellow-billed cuckoos show evidence of cooperative breeding, so the mere presence 

of adults nearby does not confirm that these are the parents of a given juvenile. At the Cave Wash site in 

Bill Williams River NWR, a juvenile cuckoo was detected but no adults were found nearby; therefore, we 

cannot rule out the possibility that this juvenile hatched and fledged from a different site. 

As noted in Chapter 1, cuckoos are secretive, difficult to detect, move over large areas, and can 

sometimes be found in areas outside of breeding habitats. Verifying that cuckoos are breeding in a 

particular patch thus requires finding young or a nest; most of our detections could not confirm breeding 
32 

status. Cuckoos we detected were frequently only heard, and it was unclear on subsequent surveys if the 

same birds were being detected. In some cases cuckoos were detected in the same spot on subsequent 

surveys, but even then the two detections may represent different birds (especially at sites with larger or 

denser populations). It is likely that at least some individual birds were detected on multiple surveys. 

Given all of these confounding realities, the detections summarized in Table 2.26 should not be 

interpreted as a count of the number of birds present or the number of birds breeding at a site. 

Table 2.27. Summary of breeding classifications for yellow-billed cuckoo detections in 2006 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. 

Survey Area/Site Breeder Juvenile Unknown Total 

Littlefield Bridge 0 0 0 0 

Mesquite Bridge 0 0 0 1 

Pahranagat NWR 

 Pahranagat North 0 0 1 1 

 Pahranagat East 0 0 0 0 

 Pahranagat South 0 0 0 0 

 Pahranagat West 0 0 0 0 

 Total 0 0 1 0 

Overton WMA 

 Honeybee Pond 0 0 4 4 

 Overton North 0 0 0 0 

 Overton Tamarisk 0 0 0 0 

 Overton Wildlife 0 0 3 3 

 Total 0 0 7 7 

Grand Canyon NP– 

Lake Mead National Recreation Area 

 Spencer Canyon 0 0 0 0 

 RM 274.5 0 0 1 1 

 River Delta/RM 285.3 0 0 0 0 

 Cuckoo Beach 0 0 10 10 

 Iceberg Ridge 0 0 3 3 

 Chuckwalla Cove 2 1 12 15 

 Total 2 1 26 29 

Lake Mohave Sites 0 0 0 0 

Havasu NWR 

 Pintail Slough 0 0 1 1 

 North Dike 0 0 0 0 

 Topock Marsh Restoration 0 0 0 0 

 Sacramento Wash 0 0 0 0 

 Havasu Tamarisk 0 0 0 0 

 Topock Tamarisk 0 0 0 0 

 Total 0 0 1 1 
33 

Table 2.27 (continued) 

Survey Area/Site Breeder Juvenile Unknown Total 

Bill Williams River NWR 

 Cave Wash 0 1 26 27 

 Mineral Wash 0 0 15 15 

 Big Bend 2 1 16 19 

 Gibraltar Rock 0 0 8 8 

 Sandy Wash 0 0 14 14 

 Fox Wash 0 0 1 1 

 Mosquito Flats 0 0 17 17 

 Saguaro Slot 1 1* 8 10 

 Bill Williams River Marsh 0 0 12 12 

 Total 3 3 117 123 

Cibola NWR 

 Cibola North Restoration 0 0 0 0 

 Cibola Nature Trail Restoration 0 0 2 2 

 Cibola Eucalyptus Restoration 0 0 0 0 

 Cibola South Restoration 0 0 1 1 

 Cibola Cross River 0 0 0 0 

 Cibola East Side 0 0 0 0 

 Total 0 0 3 3 

Picacho SRA 0 0 1 1 

Imperial NWR 

 Imperial Paradise 0 0 0 0 

 Imperial South Restoration 0 0 3 3 

 Total 0 0 3 3 

Mittry Lake WMA/Pratt Restoration 0 0 0 0 

Gila/Colorado River Confluence 

 Colorado River 0 0 7 7 

 Gila River 0 0 2 2 

 Total 0 0 9 9 

Yuma West Wetlands 0 0 0 0 

Limitrophe Division 

 Limitrophe Division North 0 0 6 6 

 Limitrophe Division South 0 0 0 0 

 Total 0 0 6 6 

Gila River/Hwy 95 0 0 0 0 

Gila River/Ligurta 

Gila River/Wellton 0 0 1 1 

Gila River/Quigley Pond WMA 0 0 1 1 

Total All Areas 5 4 171 180 
34 

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). 

Our yellow-billed cuckoo surveys in 2006 included most areas that were surveyed historically throughout 

the lower Colorado River basin; we recorded only 180 cuckoo detections. The vast majority of detections 

were from the Bill Williams River NWR and Grand Canyon NP/Lake Mead NRA; these two areas 

accounted for 100 percent of the confirmed breeders in 2006 (Table 2.26). The exact number of 

individuals in these areas is unknown, but these two areas clearly had the most yellow-billed cuckoos and, 

presumably, more and/or better breeding habitat. Both sites consist of extensive native riparian 

vegetation, although the Grand Canyon NP/Lake Mead NRA area habitat is much younger. The available 

habitat at the Cibola NWR, Imperial NWR, Mittry Lake WMA/Pratt Restoration, Gila River, and 

Limitrophe Division Area, where cuckoos were absent, few, or solitary, lacked multi-structure canopy, 

was dominated by exotic vegetation, had no standing water, or was noticeably fragmented or influenced 

by adjacent land practices (e.g., agriculture, urbanization). 

Because of differences in survey methods, specific areas surveyed, and probable differences in the criteria 

used to estimate the number of individuals, it is not possible to make direct comparisons between our 

results and previous estimates of cuckoo numbers. Any declines that may have occurred are likely due to 

habitat alteration in the area, including the loss of riparian habitat, invasion of exotic species, and changes 

in adjacent land practices. See Chapter 6 for a discussion of some of the factors that may affect yellowbilled cuckoo distribution, abundance, and breeding along the lower Colorado River, as well as options to 

enhance cuckoo habitat in this region. 

There were several patterns in our detections that reinforce the idea that cuckoos within the study area can 

readily move between sites and outside of breeding habitat, such that not every location where a cuckoo is 

found should be considered a breeding site. For example, the habitats at several sites where cuckoos were 

detected were far outside the range of normal within this region and were probably not suitable for 

nesting; birds found there were likely non-breeding “wanderers” or birds breeding elsewhere but foraging 

within the patch. Also, we had several one-time detections of single cuckoos at smaller sites—where we 

were unlikely to have missed a cuckoo that was present during the other surveys. We believe these 

cuckoos did not attempt to breed within these patches, but instead were either migrants or non-breeding 

individuals who were visiting the patch only temporarily. 

Other Riparian Bird Detections 

We detected and documented 190 additional species during our surveys in 2006, including local breeders 

and many neotropical migratory birds (Appendix 5). These species were observed before, during, or after 

our cuckoo surveys. Because the focus of our efforts was on detecting cuckoos, no effort was made to 

quantify the abundance of these additional species, nor to track down and verify any species that were not 

readily identifiable or obvious to the surveyors. 
35 

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 may be used to help further refine and develop specific hypotheses that can be tested in the future. 

Tape playback 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). Playback has also been helpful in estimating population 

size and investigating avian social behavior and territoriality. Playback 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 they have also been employed on wintering grounds (Koronkiewicz et al. 

2006). 

The use of playback recordings can however 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 may alter their habits or their territorial boundaries if they believe that there are competing members 

of the same species holding a territory nearby. Studies of the use of playback recordings to survey spotted 

owls (Strix occidentalis) suggest that if surveyed too often, some individuals and/or species may become 

less responsive (Forsman et al. 1977). Also, the use of playback recordings can attract some individuals 

away from their territories, as in elegant trogons (Trogon elegans; Taylor 1978), resulting in inflated 

population density estimates. As with other monitoring techniques, playback surveys assume a constant 

probability of detection over time and space (Pollock et al. 2002), and frequent violation of this 

assumption can bias efforts to compare results among different areas or studies. 

 

The use of playback 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 territorially, and they vocalize relatively infrequently. Little is known about 

the functions of the cuckoo’s various calls, but it has been suggested that the kowlp call (used in playback 

surveys) may function as a spacing mechanism, and 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 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. 

Assessing the use of playback 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 may 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 playback 

recordings may 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. 2004, 2005). During a test of playback survey methods using adult cuckoos with radio 
36 

transmitters, Halterman (2004) found that only 30–50 percent (depending on breeding season stage) of the 

birds responded to the playback recordings. 

Methods 

To gain a better understanding of the efficacy of the yellow-billed cuckoo survey protocol, we compared 

patterns of cuckoo responses among sites and across the season to the number of playbacks, detection 

rates, and types of detections. We also examined whether the number of surveys conducted in an area 

increases the overall probability of detecting cuckoos at a site. 

Our survey method involves broadcasting five consecutive playbacks of the cuckoo kowlp call spaced one 

minute apart. Cuckoo detections were categorized as either “unsolicited” if birds called before initiation 

of the playback or “solicited” if they occurred after a playback (i.e., in response to the playback). 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. 

Results 

In 2006, across the lower Colorado River study region, the highest percentages of initial responses were 

either unsolicited or occurred after the first playback (Figure 3.1). The percentage of first responses 

decreased as the number of playbacks increased. However, most of the unsolicited responses occurred in 

the two areas with the largest number of yellow-billed cuckoos (Figure 3.2). Almost 65 percent of the 

unsolicited responses were in the Bill Williams River NWR, and 26 percent were in the Grand Canyon 

NP/Lake Mead NRA. The other unsolicited responses occurred at Imperial NWR, the Limitrophe North 

Site near Morelos Dam, and Cibola NWR. 

The Bill Williams River NWR and Grand Canyon NP/Lake Mead NRA areas differ from other areas in 

the lower Colorado River region (Figure 3.3). Most detected responses in these two areas were unsolicited 

or took place after the first playback. In contrast, the initial responses of cuckoos in areas with apparent 

lower densities (totaling < 10 detections) tended to occur after more playbacks (Figure 3.3). We are 

limited in how these data can be analyzed because the actual density of cuckoos per area is unknown, but 

it appears that cuckoos are calling unsolicited or responding after one playback more often at sites where 

there are more cuckoos present. Presumably, the birds vocalize more frequently when conspecific 

neighbors are nearby, and rarely engage in spontaneous calling when few or no cuckoos are in the 

proximity. 

Overall, the majority of cuckoo detections (72%) were solicited through playback at all study sites 

(Figure 3.4). The number of solicited detections peaked during the first half of July and then declined as 

the breeding season progressed; the number of unsolicited detections remained fairly constant. 

Sixty-four percent of cuckoo detections (solicited and unsolicited) were aural (Figure 3.5), 27 percent 

were both heard and seen, and 9 percent were visual only. The ratio of aural to visual detections was 

similar during the early and middle part of the breeding season, but the proportion of aural detections 

declined substantially in August. 
37 

Figure 3.1. Percentage of times that yellow-billed cuckoos first responded to survey vocalization playbacks, based 

on sequential order of broadcast (180 total responses). 

Figure 3.2. Percentage of unsolicited responses by yellow-billed cuckoos at individual survey areas (180 total 

responses). An unsolicited response is one in which the cuckoo vocalized prior to the first tape playback recording. 

0

10

20

30

40

50

60

70

Bill Williams 

River NWR

Grand Canyon

NP/Lake Mead 

NRA 

Cibola 

NWR 

Imperial 

NWR 

Limitrophe 

Division 

Percentage of Initial Responses

Survey Areas 

One Four 

Number of Playbacks

Unsolicited Two Three Five 

30

25

20

15

10

5

0

Percentage of Initial Responses 
38 

Figure 3.3. Percentage of times that yellow-billed cuckoos first responded to survey vocalization playbacks at (A) 

Bill Williams River NWR, (B) Grand Canyon NP/Lake Mead NRA and all sites with <10 detections, based on 

sequential order of response and detection types by season.

Unsolicited Four

45

40

30

35

25

20

15

10

5

0

One Two Three Five 

Percentage of Initial Responses 

(B)Grand Canyon NP/Lake 

Mead NRA; n=21 

Unsolicited One Three Two Four Five

Percentage of Initial Responses

Number of Playbacks 

50

45

40

35

30

25

20

15

10

5

0

(C)Sites with < 10 cuckoos 

detections; n=30 

Unsolicited One Two 

Percentage of Initial Responses

50 

45 

40 

35 

30 

25 

20 

15 

10 

5 

0 

Three Four Five

(A)Bill Williams River 

NWR; n=94 
39 

Figure 3.4. Number of yellow-billed cuckoo detections (solicited vs. unsolicited) by time period, from 15 June to 15 

August 2006. 

Figure 3.5. Number of yellow-billed cuckoo aural, visual, or both aural and visual detections by time period, from 

15 June to 15 August 2006. 

0

5

10

15

20

25

30

35

40

45

50

6/15 - 6/30 7/1 - 7/15 7/16 - 7/31 8/1 - 8/15

 Date Interval

Solicited

Unsolicited

Number of Cuckoo Detections

0

5

10

15

20

25

30

35

40

6/15 - 6/30 7/1 - 7/15 7/16 - 7/31 8/1 - 8/15

Date Interval

Number of Cuckoo Detections 

Aural

Both

Visual
40 

Discussion 

Song playback is commonly used to survey for bird species that are not readily detected visually and to 

increase response rate compared to passive surveys. With secretive species, song playback is often the 

only way to survey efficiently, especially if natural rates of vocalization are low (Legare et al. 1999). The 

method is thus appropriate for yellow-billed cuckoos, which are secretive and not readily detected 

visually, and vocalize infrequently, especially in areas with low cuckoo densities (as evidenced during 

this study). We had difficulty detecting cuckoos when we tried to locate them without the use of 

playback, even during attempts to relocate recently detected cuckoos immediately after surveys were 

finished. 

The number of playbacks required to solicit a response, which was variable, may be influenced by the 

abundance of cuckoos in an area. Nearest-neighbor distance has been shown to influence call response 

and duration in other species (Penteriani et al. 2002). In areas where we had the most detections (and 

presumably higher densities of cuckoos), cuckoos tended to call unsolicited or be first detected after the 

initial playback. In contrast, in areas with fewer cuckoos (< 10 detections), more detections were made 

after the third, fourth and final playback (Figure 3.3c). Repeated broadcasts at each point, at least up to 

the five playbacks we conducted, therefore increased the probability of a cuckoo being detected. 

The probability of detecting secretive species such as the yellow-billed cuckoo may depend on season, 

stage of nesting, and sex of the bird(s) present. In a study of Bicknell’s thrushes (Catharus bicknelli), 

birds called and sang consistently during the day in early to mid-June, but later in the season songs were 

infrequent and calls were concentrated at dawn and dusk (Rimmer et al. 1996). Some researchers have 

found that birds may be less likely to vocalize in response to playback after nesting has started (Sogge et 

al. 1997, Legare et al. 1999, Bogner and Baldassarre 2002), however Halterman (2005) found no 

noticeable decrease in vocalization frequency after nesting for two yellow-billed cuckoos that she tracked 

via telemetry throughout their nesting cycles. In contrast, we found that aural detections (both solicited 

and unsolicited) peaked somewhat during the middle of the breeding season, but dropped off across the 

season (Figure 3.4). 

Even though broadcasting vocalizations generally increases cuckoo detections, no survey methodology 

can guarantee a detection probability of 1.0, especially on any given survey. Evidence that birds may be 

present but not responding includes our observation that on some occasions, no detections were made at a 

survey point during the broadcast and listening period but a cuckoo vocalized several minutes after a 

surveyor left a point (but was still close enough to detect the bird calling). Also, Halterman (2003, 2005) 

conducted a test of the playback survey method where a researcher carried out a normal survey while 

another researcher with telemetry equipment located and monitored the response of birds to playback. 

Only 50 percent of birds responded to the broadcast calls, suggesting that any single survey may miss half 

the birds present at a site. 

The type of song a bird uses may vary through the season or throughout the year (Ritchison et al. 1988), 

and it may be possible to increase detection probabilities on any given survey by using different calls to 

elicit a response. The yellow-billed cuckoo has a diverse repertoire, which most commonly includes the 

kowlp call but also a variety of kuks, coos, and rattles. Playback during our surveys only used recordings 

of the kowlp call, and although this helps to ensure consistency across survey areas, it may fail to elicit 

responses in some birds. 

Even though the probability of detection on any given survey of a site is less than 1.0, our data confirm 

that conducting multiple surveys within an area increases the probability of detecting resident cuckoos 

(i.e., individuals that are consistently in an area throughout the breeding season) as the breeding season 

progresses. Also, the more cuckoos present at a site the more likely that surveyors will correctly 

determine that the site is occupied. 
41 

Our technique of spatially mapping detections across multiple surveys allowed us to use the spatiotemporal pattern of detections to infer the probable status of the detected cuckoo(s). For example, a clump 

of detections, which includes confirmation of two individuals during at least one survey period, may be 

interpreted as belonging to a pair of cuckoos. 

Survey Methodology Modifications for 2007 

Based on our experience during the 2006 breeding season, cuckoos may be more responsive to playback 

during the second and possibly third survey periods. Therefore, in 2007 we will attempt (dependent upon 

logistical constraints) to increase the number of second and third period visits to selected sites to 

determine if this increases the probability of detecting cuckoos during the peak period of breeding. To 

initiate efforts at determining the relative effectiveness of “edge-based” surveys compared to those 

conducted from within a habitat patch, we will conduct comparative surveys of each type at several of our 

existing survey sites and quantify the cuckoo response under each approach. Due to logistical 

considerations, this can be done at only a few sites in 2007; however, it will allow us to begin building the 

sample size needed for a more robust comparison of the influence of survey point location. 
42 

Chapter 4. Habitat Vegetation Characteristics 

To design an effective habitat restoration program under the Lower Colorado River Multi-Species 

Conservation Program, more information is needed regarding yellow-billed cuckoo habitat characteristics 

in this region. We currently know relatively little about the cuckoos’ specific breeding requirements along 

the Colorado River; much of the quantitative information available on breeding habitat characteristics of 

western yellow-billed cuckoos comes from studies conducted in California (e.g., Gaines 1974, Laymon et 

al. 1997, Halterman 1991), where riparian habitat can be considerably different from Arizona. 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). 

Western yellow-billed cuckoos generally breed in large blocks of riparian habitat, particularly woodlands 

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

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-willow-ashmesquite habitat with less than 75 percent tamarisk. Mesquite bosque–hackberry habitat also had a 

relatively high occupancy rate. Yellow-billed cuckoos were much less common in sycamore-cottonwood 

(46% occupancy), sycamore-alder (33% occupancy), and more than 75 percent tamarisk habitats (33% 

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, willow, velvet ash, Arizona walnut, mesquite, 

and tamarisk. 

Our objective was to improve the current knowledge of yellow-billed cuckoo habitat requirements 

specifically within the LCR MSCP study area by characterizing riparian habitat at the survey site–patch 

level. We sampled occupied and unoccupied sites in order to describe vegetation composition and 

structure, including characteristics of the canopy, and the distribution and density of woody species. 

Methods 

We considered this first year of data collection to be a pilot year during which to develop, assess, and 

refine our vegetation sampling study design and data collection. To develop field methodologies for 

vegetation sampling, we reviewed the sample designs and measurement techniques typically used in 

previous Western riparian bird-habitat studies. The majority of these studies used point-based sampling 

associated with point count survey locations, 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). We then evaluated potential measurement techniques based on our understanding of cuckoo 

habitat use and the physical features that might be most important in characterizing breeding habitat. For 

example, cuckoos have been observed using fairly large areas compared to typical songbird territories, so 

we selected point-based sampling measures that characterize riparian habitat at the survey site–patch 

level. Overall, measures were selected 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 6). Landscape-level measures of habitat attributes and 

measurement techniques were not addressed. 
43 

Vegetation Sampling Design 

During 2006 we were primarily interested in characterizing vegetation at the site level and in comparing 

vegetation between occupied and unoccupied sites. The survey region was stratified north to south from 

the Grand Canyon to the United States/Mexican International border, and 11 areas were selected (Table 

4.1) from the total list based on the presence of cuckoos (in 2005) and/or the feasibility of placing the 

microclimate data loggers (see Chapter 5) that were co-located with the vegetation sampling locations. 

For the preliminary analyses presented in this report, we focused only on the Grand Canyon NP/Lake 

Mead NRA, Bill Williams River NWR, and Cibola NWR sites. 

Within study areas, vegetation sampling plots were located in both occupied and unoccupied survey sites. 

Sites were initially selected and classified as occupied or not based on 2005 yellow-billed cuckoo surveys 

(Johnson et al. 2006); sites were then reclassified after the field season. Sites were categorized as 

occupied if cuckoos were detected during two or more survey periods in 2006 and unoccupied if cuckoos 

were detected during only one or no survey periods. 

Within sites, vegetation plots were centered on microclimate sampling locations that were selected in two 

ways: (1) At occupied sites, vegetation sampling locations included the estimated coordinates of cuckoo 

detection locations (see below) and one or more GIS-generated random points. (2) At unoccupied sites, 

locations included one or more random UTM coordinates generated from orthorectified aerial 

photographs of sites. 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 plot was established at the 

first patch of riparian vegetation along that compass bearing. 

The cuckoo locations used to designate sampling locations in occupied sites were of three types: (1) UTM 

coordinates for perches of observed cuckoos (i.e., a cuckoo was observed and a UTM was recorded in the 

field, from the point below the perch). (2) Detections in 2006, where a surveyor returned to the 

Table 4.1. Vegetation and microclimate study areas along the lower Colorado River and tributaries, 2006. Sites 

whose data were analyzed and presented in this report are marked with asterisks. 

Study Areas Plots in Occupied Sites Plots in Unoccupied Sites 

Pahranagat NWR 0 12 

Overton WMA 3 0 

Grand Canyon NP/Lake Mead NRA* 7 5 

Havasu NWR 0 3 

Bill Williams River NWR* 26 2 

Cibola NWR* 4 9 

Imperial NWR 1 0 

Mittry Lake WMA/Pratt Restoration 0 8 

Gila/Colorado Rivers Confluence 7 8 

Yuma West Wetlands 0 3 

Gila River/Quigley Pond WMA 0 2 
44 

survey location from where the cuckoo was detected, followed the stated bearing and distance until the 

approximate location of the bird was reached, and recorded the UTM for the plot center. (3) GIS-based 

estimates of cuckoo locations from 2005 detections. For example, if a cuckoo was detected from a known 

location in the Cibola NWR in 2005, and estimated to be 50 m away at a 200 compass bearing, we used 

GIS to determine the UTM coordinates for the estimated location. 

There were four sampling subplots—main, 100 m, 50 m, and 30 m (Figure 4.1)—within each vegetation 

sampling plot. The main subplot was located directly beneath the microclimate (HOBO) sensor 

coordinate. The first subplot was 100 m away from the main subplot’s center, on a randomly chosen 

bearing (but constrained so that the subplot fell within riparian vegetation). The second subplot was 50 m 

away from the main subplot, on a bearing 120° from the bearing to the first subplot. The third subplot was 

120° from the second subplot, and 30 m from the center of the main subplot. We sampled vegetation 

characteristics within both 5 m and 11.3 m radii circles (the former nested within the latter) at each of the 

four subplots. 

Vegetation Measures and Measurement Techniques 

Vegetation sampling was conducted during August and September of 2006. Within each subplot, we 

measured the density of woody species, canopy cover, ground cover, average top canopy height, and litter 

depth. We recorded the woody species density because they are functional and structural dominants in 

most riparian systems. We counted the stems of each species encountered (within size classes) within 

each 5 m and 11.3 m circle. Smaller size classes (< 2.5 cm, 2.5–8 cm at 10 cm above ground, < 8 cm dbh) 

were counted within the 5 m radius circle and larger size classes were counted within the 11.3 m radius 

circle. We also made a set of measurements based on the point-centered quarter method (MuellerDombois and Ellenberg 1974) for estimating densities of plants. Standing at the center of the subplot, the 

nearest live tree, live shrub, and snag (dead tree) were located within each of the quarters of the circle. We 

recorded the distance to each, the height, the maximum width and perpendicular width of the crown, the 

species, and canopy cover (using a spherical densiometer). 

Figure 4.1. Layout of vegetation subplots used to characterize yellow-billed cuckoo habitat in occupied and 

unoccupied sites. 
45 

Cover was estimated as the vertical projection of vegetation from the ground, as viewed from above. We 

used a spherical densiometer for measuring total canopy cover (which includes the high canopy), and 

from that made a visual estimate of the high canopy cover (i.e., the percent total canopy cover above 5 m 

in height). Eight measures (four each of total canopy and high canopy) were taken at the center of each 

vegetation subplot, standing at the center point and facing each of the cardinal directions. Counts from the 

densiometer were converted, after the field season, using the formula 

 

numberof covered dots

96 × 100 = percentcanopycover.

We also recorded the dominant and co-dominant plant species in the canopy and the percentage of the 

canopy accounted for by each species. We defined a dominant species as one that accounted for at least 

40 percent of the high canopy (visually estimated) within the 11.3 m radius subplot. Two species were 

considered co-dominant when each accounted for ≥ 40 percent of the high canopy present. If no single 

plant species comprised ≥ 40 percent of the high canopy, there were no dominant species. 

Average top canopy height was measured using a clinometer based on a point in the canopy that 

represented the estimated average height of the top canopy within the 11.3 m main subplot; lone trees that 

emerged far above the main canopy were not considered when estimating this average. 

We made ocular estimates of ground cover within each 5 m radius circle, for each of the following 

vegetation classes: all green vegetation, grass, sedge, shrub, dead woody vegetation, forb, cactus, moss, 

leaf litter, rock, log, marsh vegetation, water, and bare ground. The percent cover of each class was 

estimated independently of all other vegetation types (i.e., as if other vegetation types were absent). Thus, 

vegetative cover categories could sum to more than 100 percent because of vertical stratification of plant 

layers. 

We measured litter depth to the nearest millimeter at 2 m intervals along ropes that divided the 5 m radius 

circular subplot into quadrats (one 10 m rope placed north to south, with litter depth measured at 0 m, 2 

m, 4 m, 6 m, 8 m, and 10 m; one rope placed east to west). Thus, litter depth was measured at 12 points, 

and then averaged for the subplot. 

Given that 2006 was the pilot year for this study, our preliminary analyses focused on comparing patterns 

in woody plant structure and density in occupied and unoccupied sites. In doing so, we combined woody 

species into structurally similar categories (i.e., cottonwood, willow, mesquite, and tamarisk). Within the 

willow category, all plants in the larger size classes (> 23 cm dbh) and most in the smaller size classes (< 

23 cm dbh) were Goodding’s willow; a few small coyote willow were grouped in the latter, as they are 

structurally similar when of this size. The mean total stem count for occupied and unoccupied sites was 

then calculated for each of three geographical areas: the Grand Canyon NP/Lake Mead NRA, Bill 

Williams River NWR, and Cibola NWR. All sampling plots were a fixed size; thus, mean abundance also 

represents the relative density of each area. 

None of the areas included in these preliminary analyses had any woody plants in the 2.5–8 cm diameter 

at 10 m height category. The shrub/sapling size classes were therefore combined to examine patterns in 

the distribution of shrubs/saplings among the areas and within areas. Mean total shrub and sapling counts 

for areas were derived by summing counts in both size classes for each vegetation subplot and calculating 

the mean count per subplot (i.e., density) for each site, and the mean for the sites within each of the six 

areas. Likewise, the mean density of shrubs and saplings was calculated for occupied and unoccupied 

sites, for each area. 
46 

Results 

The following results are based on exploratory analyses of a subset of data from the initial pilot year of 

the study. Therefore, these results are preliminary, and are intended for use in identifying areas for further 

study or refinement of our vegetation study design and sampling methods. Additional data collection in 

2007 will yield further insights, and may lead to changes in the patterns described below. 

Characteristics of the Canopy 

Total canopy cover was higher at occupied sites than at unoccupied sites. This difference is attributed to 

more mid and lower canopy cover, as high canopy cover (i.e., the percent total canopy cover above 5 m in 

height) did not differ between the occupied and unoccupied sites (Table 4.2). 

Table 4.2. Mean percent canopy cover (and standard error) at all sites sampled. 

 Occupied Sites Unoccupied Sites 

 (n = 80) (n = 120) p value 

Total Canopy Cover 51 (3.8)* 41 (2.9) .044 

High Canopy Cover 19 (3.2) 19 (2.4) .968 

Density of Woody Species 

Mean total density of trees (i.e., mean total stem count, including all tree size classes) at occupied and 

unoccupied sites varied across the three geographical areas (Figure 4.2). Within each area, occupied sites 

had lower total densities of trees than did unoccupied sites. 

0

100

200

300

400

500

600

700

Grand Canyon Bill Williams Cibola

Mean Total Tree Stem Count

Occupied

Unoccupied

Figure 4.2. Mean tree densities for occupied (green bars) and unoccupied (red bars) yellow-billed cuckoo sites, 

within three geographic areas. Lines above each bar represent the standard error of each mean. 
47 

Patterns of tree abundance and size class (cm dbh) distribution in occupied and unoccupied sites differed 

across the areas (Figure 4.3). At all three sites, trees in the smallest size class were most abundant and 

there were few trees over 23 cm dbh. Small trees were particularly abundant at the Grand Canyon 

NP/Lake Mead NRA and Bill Williams River NWR areas, where unoccupied sites had higher tree 

densities than occupied sites. At the Cibola NWR, overall tree density was low; unoccupied sites were 

considerably denser, due almost entirely to the number of trees in the smallest size class (Figure 4.3). 

The Cibola and Grand Canyon NP/Lake Mead areas were characterized by overall denser understories of 

shrubs and saplings than found in the Bill Williams River NWR (Figure 4.4). In the Cibola NWR cuckoos 

were detected in locations with relatively sparse understory, with low densities of woody species in the 

shrub and sapling size class. Within the other two areas, occupied sites had denser understories on 

average than unoccupied sites (Figure 4.4). 

Grand Canyon

0

100

200

300

400

500

600

700

<8 8 to 23 23 to 38 >38

M ean Tree D en sity

Bill Williams

0

50

100

150

200

250

300

350

400

450

500

<8 8 to 23 23 to 38 >38

Mean Tree Density

Occupied

Unoccupied

Cibola

0

10

20

30

40

50

60

70

80

90

100

<8 8 to 23 23 to 38 >38

Mean Tree Density

Occupied

Unoccupied

Figure 4.3. Mean tree densities in different size classes (< 8, 8–23, 23–38, and > 38 cm dbh), for occupied (green 

bars) and unoccupied (red bars) yellow-billed cuckoo sites within three areas. Lines above each bar represent the 

standard error of each mean. 
48 

0

50

100

150

200

250

300

Grand Canyon Bill Williams Cibola

Mean Total Shrub/Sapling

Occupied

Unoccupied

Figure 4.4. Mean shrub/sapling densities for occupied (green bars) and unoccupied (red bars) yellow-billed cuckoo 

sites, within three areas. Lines above each bar represent the standard error of each mean. 

We also examined patterns in the distribution and abundance of the dominant trees found in the study 

areas (occupied and unoccupied sites combined). Among all the vegetation sampling areas, tamarisk was 

by far the most common tree; willow was the second most commonly recorded tree, and cottonwood and 

mesquite trees were encountered fairly equally during sampling. Small tamarisk trees (< 8 cm dbh) 

comprised the most abundant (Table 4.4) species and size class. 

The distribution and abundance of woody trees within size classes varied across the study areas (Figure 

4.5). The Grand Canyon NP/Lake Mead NRA sites had the densest trees, mostly tamarisk and willows in 

the smaller sizes. The Bill Williams River NWR area had, on average, relatively more large willows than 

the other areas. The Cibola NWR area is mainly tamarisks in the smallest size class and cottonwoods of 

8–38 cm dbh (Figure 4.5). 

Table 4.3. Number of each tree species encountered, by dbh size classes, during vegetation sampling at all yellowbilled cuckoo study areas in 2006. 

 Size Class (cm dbh) 

Tree < 8 8–23 23–38 > 38 Total 

Cottonwood 264 256 58 15 799 

Mesquite 771 50 4 0 781 

Tamarisk 9,742 487 106 49 10,224 

Willow 2,828 630 78 73 3597 
49 

Mean Abundance of Trees <8 cm dbh

0

50

100

150

200

250

300

Grand Canyon Bill Williams Cibola

Mean Abundance

Mean Abundance of Tress 8 to 23 cm dbh

0

10

20

30

40

50

60

Grand Canyon Bill Williams Cibola

Mean Abundance

cottonwood

mesquite

tamarisk

willow

Mean Abundance of Trees >38 cm dbh

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Grand Canyon Bill Williams Cibola

Mean Abundance

cottonwood

mesquite

tamarisk

willow

Figure 4.5. The mean abundance of trees of differing size classes at three yellow-billed cuckoo study areas, 

occupied and unoccupied sites combined, 2006. Note that the abundance scale (y axis) is different for each size 

class. Lines above each bar represent the standard error of each mean. 

The average density of each of the most abundant trees (cottonwood, willow, and tamarisk) for occupied 

and unoccupied locations varied among study areas. Cottonwoods in the two smallest size classes were 

found in much greater densities in occupied sites at the Cibola NWR, compared to unoccupied sites 

(Figure 4.6). The Grand Canyon NP/Lake Mead NRA sites had no cottonwoods. 

Occupied sites tended to have higher average densities of willows in the smallest size class. The Grand 

Canyon NP–Lake Mead area had many dense willows less than 8 cm dbh, particularly in occupied sites. 

Larger willows (> 23 cm dbh) were found only at Bill Williams River NWR (Figure 4.7). 

Tamarisk, especially in the smaller size classes, was widespread and abundant across the study region. 

Within the three areas, occupied sites had lower densities of small tamarisk, than unoccupied sites. This 

pattern is particularly evident in the areas that had relatively dense small tamarisks, including Bill 

Williams River NWR and the Grand Canyon NP/Lake Mead areas. Larger tamarisks (> 8 cm dbh) were 

recorded almost exclusively in occupied sites at Bill Williams River NWR (Figure 4.8). 

Mean Abundance of Trees 23 to 38 cm dbh

0

0.5

1

1.5

2

2.5

Grand Canyon Bill Williams Cibola

Mean Abundance
50 

Mean Abundance of Cottonwood <8 cm dbh

0

1

2

3

4

5

6

7

8

Grand Canyon Bill Williams Cibola

Mean Abundance

Mean Abundance of Cottonwood 8 to 23 cm dbh

0

5

10

15

20

25

Grand Canyon Bill Williams Cibola

Mean Abundance

Occupied

Unoccupied

Mean Abundance of Cottonwood >38 cm dbh

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Grand Canyon Bill Williams Cibola

Mean Abundance

Occupied

Unoccupied

Figure 4.6. Mean cottonwood abundance, by size class (cm dbh), of occupied (green bars) and unoccupied (red 

bars) sites in three yellow-billed cuckoo study areas. Lines above each bar represent the standard error of each 

mean. The lack of bars in the graph for cottonwoods >38 cm dbh reflects an absence of trees of that size class at all 

three sites. 

Mean Abundance of Cottonwood 23 to 38 cm dbh

0

0.5

1

1.5

2

2.5

Grand Canyon Bill Williams Cibola

Mean Abundance
51 

Mean Abundance of Willow <8 cm dbh

0

50

100

150

200

250

300

Grand Canyon Bill Williams Cibola

Mean Abundance

Mean Abundance of Willow 8 to 23 cm dbh

0

20

40

60

80

100

120

Grand Canyon Bill Williams Cibola

Mean Abundance

Occupied

Unoccupied

Mean Abundance of Willow 23 to 38 cm dbh

0

0.5

1

1.5

2

2.5

Grand Canyon Bill Williams Cibola

Mean Abundance

Mean Abundance of Willow >38 cm dbh

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Grand Canyon Bill Williams Cibola

Mean Abundance

Occupied

Unoccupied

Figure 4.7. Mean willow abundance, by size class (cm dbh), of occupied (green bars) and unoccupied (red bars) 

sites in three yellow-billed cuckoo study areas. Lines above each bar represent the standard error of each mean. 
52 

Mean Abundance of Tamarisk <8 cm dbh

0

50

100

150

200

250

300

350

400

Grand Canyon Bill Williams Cibola

Mean Abundance

Mean Abundance of Tamarisk 8 to 23 cm dbh

0

2

4

6

8

10

12

14

Grand Canyon Bill Williams Cibola

Mean Abundance

Occupied

Unoccupied

Mean Abundance Tamarisk 23 to 38 cm dbh

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

Grand Canyon Bill Williams Cibola

Mean Abundance

Mean Abundance of Tamarisk >38 cm dbh

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0.05

Grand Canyon Bill Williams Cibola

Mean Abundance

Occupied

Unoccupied

Figure 4.8. Mean tamarisk abundance, by size class (cm dbh), of occupied (green bars) and unoccupied (red bars) 

sites in three yellow-billed cuckoo study areas. Lines above each bar represent the standard error of each mean. 
53 

Discussion 

Our preliminary analysis of the vegetation data collected in 2006 focused on general patterns in the 

distribution and abundance of woody species within riparian habitats of the study region, including 

comparisons of occupied and unoccupied yellow-billed cuckoo survey sites. As noted earlier, this is a 

pilot year for vegetation analysis and the patterns observed in 2006 are preliminary; data from the 

upcoming 2007 season will provide additional insights. 

The density and composition of woody riparian vegetation varied considerably among the study areas. 

Much of the variation in tree density was due to the patterns of abundance of trees in the smallest size 

class (< 8 cm dbh). Differences in the woody plant species composition and vegetation physiognomy 

between native cottonwood/willow- and tamarisk-dominated habitats can lead to fundamental differences 

in structure, such as gallery forests versus riparian scrub or thicket habitats (Busch and Smith 1995). 

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 small (< 8 cm dbh) individuals. Larger trees were 

usually cottonwoods or willows, probably due to their morphology. Mesquite was not regularly 

encountered because most sampling occurred within riparian vegetation, with very few samples from 

adjacent habitat types, including mesquite. 

The Bill Williams River NWR sites have relatively more large willows. The Grand Canyon NP/Lake 

Mead NRA sites had the densest trees, mostly tamarisk and willows in the smaller size classes. The 

Cibola NWR is primarily a restoration site with planted native trees, and in general it does not resemble a 

“natural” riparian area (e.g., the cottonwoods were planted in rows). The area supports primarily 

tamarisks in the smallest size class and cottonwoods of 8–38 cm dbh. 

When occupied and unoccupied sites were compared, 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 was most often primarily cottonwood or willow trees. In addition, occupied sites in most 

areas had lower than average total tree density whereas unoccupied sites were denser than average. When 

densities of trees in different size classes were compared between occupied and unoccupied sites within 

areas, it appeared that cuckoos did not use areas with the highest density of small trees (< 8 cm dbh), 

mostly tamarisk. 

These results correspond with those of Corman and Magill (2000), who found that western yellow-billed 

cuckoo occupancy rates in Arizona were highest in sites dominated by native tree species, including 

cottonwood, willow, ash, and mesquite. Yellow-billed cuckoos were much less common in habitats with 

more than 75 percent tamarisk cover. Other studies of the western yellow-billed cuckoo in California 

found that dense understory foliage appears to be an important factor in nest site selection (Laymon et al. 

1997, USFWS 2002a), and this may be an important factor in habitat selection in our study sites as well. 

In addition, there may be a threshold of tree density, beyond which cuckoos select less dense sites. The 

influence of understory density and overall tree density will be further examined following the 2007 field 

season. 
54 

Chapter 5: Microclimate Analysis 

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. 2006) were conducted only in habitat that initially 

appeared suitable for cuckoos. 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 4,050 acres of yellow-billed cuckoo 

breeding habitat, including 1,350 acres created specifically for cuckoos (Lower Colorado River MultiSpecies Conservation Program 2004). Characterization of vegetation within currently occupied sites will 

help guide cuckoo habitat restoration and creation; however, cuckoos may select breeding habitat or nest 

sites based on specific microclimatic conditions (Hamilton and Hamilton 1965). Therefore, we designed a 

method to characterize the microclimate at occupied and unoccupied yellow-billed cuckoo survey sites, 

and collected preliminary data during the 2006 season. 

Although 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) noted that egg dehydration is sensitive to the hydric 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 may interact in the 

selection of nest sites (Holway 1991). 

In developing our methodology, all of the bird microclimate studies that we reviewed focused on 

characterizing the microclimate at nest locations rather than at the habitat patch level. Because yellowbilled cuckoo nests are very hard to find, and the focus of our 2006 surveys was on finding cuckoos rather 

than nests, we knew that a nest-based approach would not be feasible. However, given that there have 

been virtually no quantitative studies of even the most basic aspects of yellow-billed cuckoo habitat 

microclimate, a logical and useful starting point was to work at the habitat patch scale. It is reasonable to 

hypothesize that microclimate may differ between riparian habitats that are used or not used by cuckoos, 

so we focused in 2006 on comparing occupied and unoccupied cuckoo habitat is a first step towards 

understanding how microclimate affects habitat use within the riparian matrix. 

Ambient shade temperature is the most logical variable to measure in relation to occupied and unoccupied 

habitat. Summer temperatures along the lower Colorado River may approach 50° C (122° F), which can 

subject birds to severe heat loading. Other key microclimate properties are wind, radiation, and humidity. 

We examined how temperature and relative humidity varied between occupied and unoccupied sites, and 

we compared soil moisture at these same locations since this may affect the presence of cicada nymphs 

(Andersen 1994), which can be a very important food resource for cuckoos (Rosenberg et al. 1982). 

Finally, vegetation measurements (described in Chapter 4) were taken 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. Due to logistical considerations, we stratified our LCR MSCP survey region 

from north to south and selected 11 areas from the total list based on the presence of cuckoos and/or 

feasibility for the placement of microclimate data loggers (Table 5.1). 
55 

We collected microclimate data at both occupied and unoccupied study sites. Sites were initially selected 

and classified as occupied or not based on 2005 yellow-billed cuckoo surveys (Johnson et al. 2006); sites 

were then reclassified after the field season. 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. For 

microclimate analysis purposes, 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 do 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 during July and August and were removed during September and 

October. Our intended deployment in June did not occur due to delays in equipment purchases. Each 

logger was programmed to record an event (T/RH reading) every 6 minutes for 90 days. Twenty-five 

microclimate data loggers were deployed from the Bill Williams River NWR north, and 35 were deployed 

to the south, for a total of 60. Data loggers were placed in occupied or unoccupied patches within the 10 

microclimate data collection areas as described below. 

At unoccupied sites, loggers (n = 38) were typically placed in mixed native-exotic habitat or exotic 

habitat, but still 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 with housing was then deployed within 

vegetation at 3 m high (the mean nest height for yellow-billed cuckoos in this habitat; Halterman 2003). 

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. 

At occupied sites, loggers (n = 22) were initially deployed based on estimates of cuckoo locations from 

surveys conducted in 2005. We deployed data loggers as new cuckoos were detected throughout the 2006 

field season. For both 2005 and 2006 detections, loggers were placed at the approximate locations of 

detected cuckoos, based on the estimated bearing and distance from a surveyor to the cuckoo. As with the 

unoccupied locations, loggers (HOBOs) in occupied locations were hung at a height of 3 m. 

Table 5.1 Microclimate study areas along the lower Colorado River and adjacent locations (2006). Sites whose data 

were analyzed and presented in this report are marked with asterisks. 

Study Areas Plots in Occupied Sites Plots in Unoccupied Sites 

Pahranagat NWR 0 12 

Overton WMA 3 0 

Grand Canyon NP/Lake Mead NRA* 7 5 

Havasu NWR 0 3 

Bill Williams River NWR* 26 2 

Cibola NWR* 4 9 

Imperial NWR 1 0 

Mittry Lake WMA/Pratt Restoration 0 8 

Gila/Colorado Rivers Confluence 7 8 

Yuma West Wetlands 0 3 

Gila River/Quigley Pond WMA 0 2 
56 

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 (50° to –

30° C, accurate to ± 0.2° C at 21° C) and RH (0–100%, accurate to ± 3%) data at specified intervals. To 

protect each data logger from direct solar radiation, HOBOs were deployed in the field using a costeffective 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 (i.e., 0.5° C difference). Therefore, all data loggers 

were deployed within our homemade housings. 

Soil Moisture and Canopy Cover 

We measured soil moisture at each of the survey areas (listed in Table 5.1) using an ML2x ThetaProbe 

with a type HH2 ThetaMeter type (Delta-T Devices Ltd., Cambridge, UK). This instrument recorded 

percent volumetric water content to an accuracy of ± 1%. Soil moisture was recorded directly below each 

HOBO and also at distances of 1.0, 2.0, and 3.0 m from this spot in each cardinal direction, such that 13 

soil moisture readings were associated with each location, although at some locations dense vegetation or 

hard soil prevented us from collecting all 13 soil moisture readings. Soil type on the ThetaMeter was set 

to mineral soil, and measurements were taken at a depth of 60 mm. 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. Soil moisture was recorded at 

the same time that HOBO data loggers were deployed and retrieved. 

We used a spherical densiometer to measure total canopy cover, defined as the vertical projection of 

vegetation from the ground, as viewed from above. We recorded four measures of total canopy cover 

(standing at the center point and facing each of the cardinal directions) at the center of the vegetation 

sampling main subplot at the HOBO location, and at the centers of three satellite subplots associated with 

the data logger. Counts from the densiometer were converted, after the field season, using the formula 

 

number of covered dots

96 × 100 = percent canopy cover .

Occupied versus Unoccupied Sites 

HOBO data loggers were collected from field sites during September and October. One was destroyed in 

a fire at Cibola NWR, two were destroyed by heavy machinery at the Gila River confluence site, and one 

was missing at the West Wetlands Park in Yuma. In addition, two HOBOs at the Bill Williams River 

NWR failed to record data for the specified period of time. Data from the remaining 54 loggers (34 

unoccupied, 20 occupied) were downloaded and organized to allow comparison of occupied versus 

unoccupied sites for the following variables (based on McLeod et al. 2005): 

• Mean diurnal and nocturnal temperatures: we used local sunrise and sunset times to delineate cutoff 

times between night and day. 

• Mean diurnal and nocturnal relative humidity. 

• Mean soil moisture: we combined moisture readings from the first measurement period when 

HOBOs were deployed with those from the second when HOBOs were collected; little difference 

was found between early and late season soil moisture measurements. 
57 

• Mean number of 6-minute intervals above 41o C each day: 41o is a rough cutoff above which 

hyperthermic mortality of unattended eggs may increase (Webb 1987). 

• Mean daily temperature range: daily maximum minus daily minimum. 

For the preliminary analyses in this 2006 report, we restricted our investigation to the Bill Williams River 

NWR, the Cibola NWR, and the Grand Canyon NP/Lake Mead NRA. These three areas were selected 

because they are large and geographically distinct within the lower Colorado River region, and because 

they all had occupied sites. We placed data loggers at 8 occupied sites and 5 unoccupied sites (Table 5.2). 

Analyses included only data from 45 days, starting in early August and extending to mid-September, 

when all loggers were simultaneously active at all three areas. We examined the differences in diurnal and 

nocturnal relative humidity and temperature between occupied and unoccupied sites by calculating daily 

means per site, then calculating the overall means of diurnal and nocturnal relative humidity, and diurnal 

and nocturnal temperature at occupied and unoccupied sites. We used the canopy cover data collected at 

each data logger location to provide a broad characterization of occupied and unoccupied sites. 

Table 5.2. Number of sites and number of microclimate data loggers (HOBOs) within the three survey areas (Grand 

Canyon NP/Lake Mead NRA, Bill Williams River NWR, and Cibola NWR) from which data were used in the 

preliminary analysis of microclimate data. HOBOs were placed in occupied and unoccupied survey sites within the 

study areas. 

 Number of Sites Number of HOBOs 

Area Tota

l 

Occupied Unoccupied Total Occupied Unoccupied 

Three Areas Combined 13 8 5 19 11 8 

Grand Canyon/Lake Mead 4 3 1 6 4 2 

Bill Williams River NWR 5 3 2 7 3 4 

Cibola NWR 4 2 2 6 4 2 

Results 

The following microclimate results are based on exploratory analyses of a subset of data from the initial 

pilot year of the study. These results are therefore preliminary, but they may help identify aspects of our 

microclimate study design and sampling methods that need further study or refinement. Additional data 

collection in 2007 will yield further insights, and may lead to changes in the patterns described below. 

Relative Humidity and Temperature 

For all three microclimate areas combined, mean diurnal and nocturnal relative humidity measures were 

higher in unoccupied sites than in occupied sites; there were no significant differences in day or night 

temperatures (Table 5.3). Microclimate patterns were not consistent from area to area. For example, mean 

diurnal and nocturnal relative humidity values were higher in the unoccupied sites at the Grand Canyon 

NP/Lake Mead NRA area, lower at such sites in the Bill Williams River NWR, and not significantly 

different at Cibola NWR (Table 5.3). 
58 

Table 5.3. Descriptive statistics (means and standard errors, in parentheses) for microclimate data collected at Grand 

Canyon NP/Lake Mead NRA, Bill Williams River NWR, and Cibola NWR yellow-billed cuckoo study areas, 

August–September 2006. Microclimate data loggers were placed in occupied and unoccupied survey sites within the 

study areas. Means are given with their standard errors (+SE). Sig. is the 2-tailed p-value of independent sample Ttests for equality of means. 

Variable Occupied Unoccupied Sig. 

Mean Diurnal Relative Humidity 

 Grand Canyon/Lake Mead 32 (0.6) 44 (1.2) 0.00 

 Bill Williams River NWR 56 (1.3) 46 (1.0) 0.00 

 Cibola NWR 35 (0.6) 35 (1.0) 0.65 

 Three Areas Combined 39 (0.6) 43 (0.7) 0.00 

Mean Nocturnal Relative Humidity 

 Grand Canyon/Lake Mead 48 (1.2) 59 (1.7) 0.00 

 Bill Williams River NWR 69 (1.5) 65 (1.3) 0.03 

 Cibola NWR 56 (0.9) 55 (1.3) 0.24 

 Three Areas Combined 57 (0.7) 61 (0.9) 0.00 

Mean Diurnal Temperature 

 Grand Canyon/Lake Mead 32 (0.2) 30 (0.5) 0.00 

 Bill Williams River NWR 31 (0.2) 33 (0.2) 0.00 

 Cibola NWR 37 (0.2) 37 (0.2) 0.98 

 Three Areas Combined 34 (0.2) 33 (0.2) 0.14 

Mean Nocturnal Temperature 

 Grand Canyon/Lake Mead 24 (0.3) 22 (0.5) 0.02 

 Bill Williams River NWR 25 (0.2) 25 (0.2) 0.28 

 Cibola NWR 26 (0.2) 27 (0.3) 0.00 

 Three Areas Combined 25 (0.2) 25 (0.2) 0.88 

Soil Moisture and Canopy Cover 

When data from all sites were pooled, mean soil moisture was higher on average at occupied sites than at 

unoccupied sites (Table 5.4). Within individual areas, occupied sites had higher mean soil moisture when 

compared to unoccupied sites (though not significantly so at Cibola NWR). It is interesting that both 

occupied and unoccupied sites at the Cibola NWR had higher soil moisture than any Grand Canyon 

NP/Lake Mead NRA or Bill Williams River NWR sites. 

Overall, mean percent canopy cover did not differ significantly between occupied and unoccupied sites 

(Table 5.5). Within the Grand Canyon NP/Lake Mead area, we sampled only one unoccupied site and 

three occupied sites. The unoccupied site, Canyon Mile 274, is fairly unique in that it consists of a large 

patch of mostly very dense, low tamarisk whereas the occupied sites were comparatively more open. 

These observations are supported by our measures of canopy cover within the Grand Canyon NP/Lake 

Mead area. The occupied and unoccupied sites in Bill Williams River NWR had higher mean canopy 

cover than Grand Canyon NP/Lake Mead NRA and Cibola NWR sites. Occupied sites at Cibola had 

slightly higher mean canopy cover than unoccupied sites, but were highly variable (Table 5.5). 
59 

Table 5.4. Descriptive statistics (means and standard errors, in parentheses) for soil moisture data collected at 

yellow-billed cuckoo study areas within Grand Canyon NP/Lake Mead NRA, Bill Williams River NWR, and Cibola 

NWR. Means are given with their standard errors (+SE). Sig. is the 2-tailed p-value of independent sample T-tests 

for equality of means. 

 Mean Soil Moisture (%) 

Area Occupied Unoccupied Sig. 

Grand Canyon/Lake Mead 11 (1.1) 8 (0.8) 0.03 

Bill Williams River NWR 12 (1.4) 5 (0.9) 0.00 

Cibola NWR 19 (0.6) 16 (2.0) 0.11 

All Areas Combined 12 (0.6) 10 (0.4) 0.03 

Table 5.5. Descriptive statistics for percent canopy cover data from microclimate sampling sites in Grand Canyon 

NP/Lake Mead NRA, Bill Williams River NWR, and Cibola NWR yellow-billed cuckoo study areas in 2006. 

Means are given with their standard errors (+SE). Sig. is the 2-tailed p-value of independent sample T-tests for 

equality of means. 

 Mean % Canopy Cover 

Area Occupied Unoccupied Sig. 

Three Areas Combined 52 (4.8) 49 (6.4) 0.67 

Grand Canyon/Lake Mead 34 (7.9) 58 (11.7) 0.12 

Bill Williams River NWR 62 (5.5) 69 (7.3) 0.48 

Cibola NWR 46 (25.9) 30 (9.6) 0.59 

Discussion 

Our preliminary analysis of the microclimate data collected in 2006 focused on comparisons of a subset 

of occupied and unoccupied yellow-billed cuckoo survey sites. As noted earlier, this is a pilot year for 

data collection and analysis, and the patterns observed in 2006 are preliminary; data from the upcoming 

2007 season will provide additional insights. 

Over the three study areas examined, unoccupied sites had higher diurnal and nocturnal humidity and 

cooler mean daytime temperatures than occupied sites. This differs from what might be expected based on 

considerations of thermal tolerance and humidity as possible limiting factors in habitat use. However, at 

least part of our pattern may be driven by sample size and vegetation conditions at the Grand Canyon 

NP/Lake Mead NRA sites. There, the only unoccupied site sampled (Canyon Mile 274) consists of a large 

patch of mostly very dense, low tamarisk, whereas the occupied sites were comparatively more open. 

Occupied patches within the Bill Williams River NWR had higher mean diurnal and nocturnal relative 

humidity but also higher temperature; the latter runs counter to microclimate expectations. The one 

unoccupied site sampled here was a fairly open area with relatively sparse vegetation. Results for the 

Cibola NWR area are interesting in that there were no measurable differences in relative humidity and 

temperature between occupied and unoccupied sites with the exception of mean nocturnal temperature, 

which was lower at occupied sites. Overall, Cibola was also the hottest of the three areas. 

Mean soil moisture was consistently higher in occupied sites compared to unoccupied sites, when all 

areas were combined and when areas were considered separately. Cibola NWR was particularly 

interesting in that unoccupied sites there had higher mean soil moisture than the occupied sites at the 

Grand Canyon NP/Lake Mead NRA and Bill Williams River NWR. It appears that cuckoos may be using 

the moistest sites within each of the areas. 
60 

Yellow-billed cuckoos have been thought to favor humid habitats and to thus be confined to river bottom 

habitats in the arid Southwest (Hamilton and Hamilton 1965). Our data, though preliminary, provides 

limited indications that yellow-billed cuckoos along the lower Colorado River and adjacent drainages are 

occupying sites that have relatively high mean soil moisture within the area. Higher soil moisture may 

contribute to conditions that would be more favorable for breeding from a microclimate standpoint. 

However, at this point we are unable to discern any uniform patterns in microclimate differences between 

occupied versus unoccupied sites. High variation in local conditions, complex local and landscape 

interactions, and the small sample size of 2006 data may be masking general microclimate patterns. 

The reasons for differences in soil moisture between occupied and unoccupied sites are uncertain. One 

explanation may be moisture retention after flooding events, which may occur at Bill Williams River 

NWR; however, it is not a likely explanation at all other sites because they no longer receive natural flood 

pulses due to the altered hydrology of the Colorado River. Another possible factor may be the presence of 

Apache cicada (Diceroprocta apache) nymphs, which affect the spatial distribution of surface water by 

excreting unassimilated fluid obtained through feeding on xylem (Andersen 1994). However, the 

distribution of burrowing cicada nymphs is non-random and clustered (Ellingson and Andersen 2002), 

and we do not know where our soil moisture measurements were taken relative to cicada populations. 

Microclimate Evaluation – 2006 and 2007 

The variable patterns resulting from these preliminary microclimate analyses highlight the need to refine 

our microclimate sampling design and increase our overall sample sizes, in order to better compare 

microclimate characteristics between occupied and unoccupied sites. The 2006 evaluation of 

microclimate was limited by a small sample size and late deployment, and an uneven distribution of data 

loggers between unoccupied and occupied sites. This latter factor was due to the limited number of predesignated “occupied” detection sites available from the 2005 field season, and no previous cuckoo 

presence/absence data to work with from our northern survey areas. Furthermore, many data loggers were 

deployed late in the summer, which restricted our analyses to time intervals in August and September. All 

of these problems will be corrected in 2007. We will use 2006 yellow-billed cuckoo location data, aerial 

photography, and GIS in order to generate new sampling locations for 2007. We will attempt to evenly 

pair unoccupied and occupied sites within areas, and to deploy equal numbers of HOBOs within occupied 

and unoccupied sites. Additionally, HOBOs will be deployed in May and retrieved in September, in order 

to characterize microclimatic variables during the time span that yellow-billed cuckoos are normally 

present in the region. This should increase the power to detect differences in the microclimate variables 

we measure between occupied and unoccupied sites. 

Although our current project objectives do not include an analysis of cicada distribution, especially with 

regard to microclimate conditions, we believe this question is worth attention due to the potentially 

important role that cicadas may play in yellow-billed cuckoo distribution within the lower Colorado River 

region. Soil moisture may be an indication of the burrowing and feeding activities of cicada nymphs, and 

soil temperature may determine when adult cicadas emerge and are available as a food source for 

cuckoos. High soil temperatures may result in the earlier emergence of cicadas (Andersen 1994, Smith et 

al. 2006), and canopy cover affects soil temperature. Yellow-billed cuckoos arrive on their breeding 

grounds later than most neotropical-nearctic migrants, and high soil temperatures may increase the chance 

that cuckoos arrive after cicadas have emerged. Thus, further measurement of soil temperature in 

combination with additional vegetation analyses and examination of other microclimatic variables may 

provide useful information about the life cycle of this keystone resource in riparian habitat. Ultimately, 

soil temperature could become one of several easy-to-measure indicators of riparian restoration success. 
61 

Chapter 6. Riparian Habitat and the Status of Cuckoos in the 

Lower Colorado River Basin 

Given the lack of consistent long-term yellow-billed cuckoo survey information and the challenges of 

interpreting cuckoo detection data, we cannot make precise comparisons between the historical and 

current numbers of breeding cuckoos with the lower Colorado River project region. However, there are 

probably substantially fewer cuckoos and fewer breeding sites now than occurred in the early 1900s, and 

possibly fewer than during the 1970s and 1980s (see Chapter 1). Assessing the factors that may have 

contributed to declines can provide useful insight in developing conservation and restoration actions. 

Declines were likely due to substantial changes that have occurred in the riparian habitats of the area, 

including the loss of such habitat, the invasion of exotic species, and changes in adjacent land practices. 

It has been estimated that 85–98 percent of Arizona’s native riparian habitat has been destroyed or 

severely degraded since Euro-American settlement (Noss et al. 1995, Bogan et al. 1998). By the early 

1900s, extensive agriculture activities were occurring in Yuma, Arizona and in the Imperial Valley, 

California (Rosenburg et al. 1991), but annual flooding continued to devastate these farming efforts. To 

control the river for human use the U.S. Bureau of Reclamation began to develop the river for power 

generation, water storage, and flood control. This began with the construction of a series of dams—

Laguna Dam in 1907, Hoover Dam in 1936, Parker Dam and Imperial Dam in 1938, and Davis Dam in 

1954. Dam operations changed the natural flows of the lower Colorado River by ending the cycle of 

annual flooding, except when heavy runoff from local rains produced floods from the larger tributaries 

(e.g., Bill Williams River). Without these floods, new, rich alluvial seedbeds were no longer formed and 

the life history cycle of cottonwoods, willows, and mesquite were changed. With floods controlled and 

irrigation water readily available, large stands of natural floodplain vegetation were converted to 

agricultural uses. In the 1940s and 1950s wide portions of the floodplain near Yuma, Blythe, Parker, and 

Needles were cleared for agriculture. Extensive farm tracts, “clean” farming practices, and shifts to crops 

such as cotton and lettuce resulted in the removal of large tracts of cottonwood-willow forests and 

mesquite bosques and greatly reduced the extent of wildlife habitat, including habitat required by yellowbilled cuckoos to breed. The only large tracts of natural riparian vegetation that remained through the 

1970s were on the five Native American reservations and the four national wildlife refuges (Pahranagat, 

Havasu, Bill Williams River, Cibola, and Imperial; Rosenberg et al. 1991). 

In addition to reducing the amount of riparian habitat in the landscape, agricultural and urban 

development has also fragmented the remaining riparian areas. In this form of fragmentation, riparian 

forest tracts are progressively reduced to smaller and more isolated patches embedded within a relatively 

permanent matrix of largely unsuitable habitat (Saab 1999). Western yellow-billed cuckoos may be 

especially sensitive to fragmentation, as they require tracts of large contiguous and unfragmented patches. 

Laymon and Halterman (1989) have estimated that sites larger than 80 ha (200 acres) in extent and wider 

than 600 m (1950 feet) were the optimal patch size for yellow-billed cuckoos. 

Agricultural lands currently continue to dominate much of the riparian landscape within the region. Of the 

55 sites we surveyed for cuckoos in 2006, 65 percent are bordered on at least one side by agriculture 

fields; agricultural development on adjacent lands has been shown to affect riparian bird communities. 

While studying habitat use by breeding birds in cottonwood riparian forests at multiple spatial scales 

along the South Fork of the Snake River in southeastern Idaho, Saab (1999) found that riparian patches 

surrounded by an agriculture matrix supported different bird assemblages than did patches surrounded by 

a natural habitat matrix. In addition, avian nest predators, brood parasites, and exotic species all 

responded positively to the human-altered landscapes resulting from agricultural development, 

fragmentation, residential areas, or all three factors (Saab 1999). 
62 

Agriculture and urban development and their attendant water capture, control, and distribution practices 

represent new types, or at least new scales, of disturbance for river systems in the Southwest (Stromberg 

and Chew 2002). Urban and agricultural demands throughout western North America are expected to 

result in increasingly scarce water resources, and altered flow regimes will negatively impact riparian 

cottonwood ecosystems (Lytle and Merritt 2004). In addition, tail-water from irrigated fields or urban 

sewage treatment plants is often enriched with nutrients and salt, which can negatively impact the river 

reaches that receive such water (Stromberg and Chew 2002). In contrast to the generally negative affects 

of water diversions and modifications at the landscape level, at a localized scale these activities may help 

support some riparian habitat patches. For example, the southwestern willow flycatcher recovery plan 

(USFWS 2002b) notes that most of the riparian patches in which the flycatcher breeds are supported by 

various types of supplemental water, including agricultural and urban runoff, treated water outflow, 

irrigation or diversion ditches, reservoirs, and dam outflows. The sustainability of habitats relying on such 

supplemental water is questionable, and these supplemental flows likely do not provide for the full array 

of ecological functions that occurred before the alteration of the local hydrology. 

These factors all have the potential to influence yellow-billed cuckoo habitat use. In arid regions such as 

those found along the lower Colorado River, yellow-billed cuckoos are restricted to river bottoms, ponds, 

swampy areas, and damp thickets with relatively high humidity (Gaines and Laymon 1984, Hughes 

1999). Most breeding pairs of western yellow-billed cuckoos have been found nesting in riparian patches 

within 100 m of water (Laymon and Halterman 1987a, Johnson et al. 2005, 2006). Surface water in 

cottonwood-willow groves may help lower the air temperature via evaporative cooling (Laymon and 

Halterman 1987b, Hughes 1999). Our habitat sampling in 2006 found that occupied sites were 

significantly closer than unoccupied sites to surface water (mean of 98 m versus 290 m, respectively). 

Changes in microclimate conditions resulting from development may also affect cuckoos. Large patches 

of mature cottonwood forest, with willows forming a subcanopy layer, are likely to provide the best 

shading of any riparian habitat. While foraging western yellow-billed cuckoos may be found in stands of 

smaller mesquite trees or even tamarisk, they usually do not nest there (Halterman 2004). Tamarisk and 

open mesquite bosques may be inadequate in buffering extreme high temperatures. Habitat attributes that 

provide cooler temperatures and higher humidity are likely especially important to cuckoos in the lower 

Colorado River basin where the cuckoo is one of the last migratory summer breeders to arrive. Cuckoos 

arrive in mid to late June and depart by the end of August or mid-September. Nesting cuckoos would thus 

be exposed to the extremely high midsummer temperatures common in this region (> 35–45° C; 100° F). 

In 2006 we found that locations occupied by yellow-billed cuckoos were more shaded and tended to be 

cooler and more humid on average compared to unoccupied locations, which tended to be more variable 

with respect to both temperature and relative humidity. 

The factors that most drastically changed the riparian vegetation structure and composition throughout the 

lower Colorado River basin were the introduction of the exotic tamarisk tree and the changes in riparian 

ecosystem processes that initially promote its establishment and persistence. In 1894, Means (1907) 

estimated that native riparian vegetation covered about 160,000–180,000 ha of alluvial bottomland 

between Fort Mohave and Fort Yuma. As of 1986, there were only about 40,000 ha of riparian 

vegetation—roughly 25 percent of the bottomland estimated by Means (Anderson and Ohmart 1984, 

Younker and Anderson 1986). Approximately 40 percent of the area remaining in 1986 was dominated by 

tamarisk, 16 percent by honey mesquite and/or native shrubs, and only 0.7 percent by mature cottonwood 

or willow habitat (Ohmart et al. 1988). 

Tamarisk and Russian olive are currently the third and fourth most frequently occurring woody riparian 

plants in the Southwest (Friedman et al. 2005). Although tamarisk was the most common tree in the study 

area, the canopy at occupied sites was usually dominated by cottonwood or willow trees. Occupied sites 

in most areas had lower than average total tree density, and it appears that cuckoos did not breed in areas 

with the highest density of small trees (< 8 cm dbh), which were mostly tamarisk. The exceptions to this 
63 

pattern were the northernmost sites and the southernmost sites, where overall tree density was relatively 

low and cuckoos were detected in sites with higher than average tree density. These results correspond 

with those of Corman and Magill (2000), who found that western yellow-billed cuckoo occupancy rates 

in Arizona were highest in sites dominated by native tree species and lower in habitats consisting of more 

than 75 percent tamarisk cover. We do not know if cuckoos are generally absent from areas of denser or 

smaller tamarisk because of the species composition or because the trees do not have the proper structure; 

these two factors are likely related. 

In sum, multiple factors such as water diversion and redistribution and agricultural and urban 

development have impacted riparian habitats and landscapes along the lower Colorado River in the 

previous 50–100 years. Riparian habitats have been lost, fragmented, and degraded. We found that 

yellow-billed cuckoos persist in the region mainly in riparian habitats with some native vegetation. Other 

factors such as the presence of surface water, microclimate conditions, and landscape-level habitat 

features may also play a role in cuckoo habitat selection. 

Restoring Riparian Habitat for the Yellow-Billed Cuckoo: Additional Research 

Needs 

Efforts to restore riparian habitats within the lower Colorado River basin have focused on the restoration 

of native vegetation through the removal of tamarisk and planting of native cottonwoods and willows. 

Revegetated stands have been established at Cibola NWR, Quigley WMA, Mittry Lake WMA/Pratt 

Restoration, and Imperial NWR, and in 2006 we detected unpaired non-breeding cuckoos in all of these 

areas. Each of the revegetated stands consists of mainly mature trees and they appear to have adequate 

plant species composition and structure to accommodate cuckoos. However, we observed only unpaired, 

presumably non-breeding cuckoos at the restoration sites, except that one cuckoo was seen carrying food 

within the restoration site at the Imperial NWR and flying to a nearby non-restored area, where it was 

likely breeding. Western yellow-billed cuckoos require large blocks of riparian habitat (Laymon and 

Halterman 1987a, Ehrlich et al. 1988, USFWS 2002a), and data are needed regarding the size and 

distribution of riparian habitat required for breeding within the lower Colorado River region. Such 

information is crucial for designing adequately sized riparian restoration projects that can accomplish the 

goal of providing breeding habitat for these birds. Additional information gaps include knowledge about 

habitat factors at other spatial scales, such as riparian patch connectivity, the effects of the landscape 

geomorphology, the amount of riparian habitat in the landscape, and the composition of the surrounding 

landscape matrix—all of which likely have substantial influence on yellow-billed cuckoo habitat 

selection. 

The distribution and population dynamics of many birds cannot be understood solely by studying the 

processes occurring within individual habitat patches (Freemark et al. 1995). A landscape comprises a 

heterogeneous mosaic of patches in which individual birds live and disperse (Dunning et al. 1992); 

landscapes thus represent an intermediate spatial scale between local habitat patches and larger-scale 

regions (Freemark et al. 1995). Since patterns in the mosaic of habitat patches on the landscape influence 

the distribution and dynamics of individuals, populations, and communities (Kotliar and Wiens 1990, 

Barrett 1992, Freemark et al. 1995), a landscape perspective is needed to adequately monitor lower 

Colorado River cuckoos, and to properly assess the effects from the dynamics of the surrounding 

landscape patterns on species, biotic interactions, and ecological processes (Freemark et al. 1995). 

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, and to identify the habitat features that cuckoos require. This knowledge about habitat 

selection patterns and identification of potential breeding habitat is essential to establishing effective 

conservation efforts, including prioritization of areas for conservation and restoration and areas for 

monitoring changes in habitat distribution and quality over time. 
64 

Other factors to consider in designing effective riparian restoration include the effects of such restoration 

on avian food resources. Many bird species that breed in riparian habitats are insectivorous, and the lush 

vegetation associated with riparian zones provides abundant food resources, especially when compared to 

surrounding upland habitats (Strong and Bock 1990). The Apache cicada, in particular, has been 

suggested as a keystone species in the lower Colorado riverine ecosystem, due to its herbivory (Karban 

1980, Andersen 1987) and role as a prey species for birds and mammals (Rosenberg et al. 1982, Krohne 

et al. 1991). 

Yellow-billed cuckoo habitat use in the Southwest does in fact appear to be linked to cicadas. Rosenberg 

et al. (1982) found that in cottonwood-willow habitat in the Colorado River valley, cuckoos concentrate 

on cicadas, a superabundant, seasonally predictable resource (Strong and Bock 1990). The relatively late 

nesting period of the western population of cuckoos 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 middle 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. 2006) that cottonwood density and cottonwood canopy 

cover are important factors in cicada emergence density and phenology; the age and health of a 

cottonwood stand have a smaller effect on emergence density. Cottonwood canopy was also correlated 

with lower soil temperatures, which are associated with later emergence dates (Smith et al. 2006). These 

findings suggest that the recovery and sustainability of yellow-billed cuckoo populations in the Southwest 

may depend to some extent on sustaining cicada populations. It may be possible to design riparian 

restoration to promote conditions that allow cicadas to emerge at densities and times that provide the 

greatest benefits to cuckoos. To do so, additional studies are needed to understand the relationships 

between vegetation associations and annual cicadas, and the effects of vegetation structure and climate on 

cicada emergence density and phenology in riparian habitats along the lower Colorado River. 

In addition to the LCR MSCP program, several other efforts are currently underway in the lower 

Colorado River basin and other areas of the Southwest to restore riparian habitats; these include the Clark 

County Nevada Multiple Species Plan, the Western Riverside Multi-Species Habitat Conservation Plan in 

California, the Colorado River Indian Tribes (CRIT) 1998 revegetation plan, and the Salt River Project 

Roosevelt Lake Habitat Conservation Plan. All have the goal of restoring riparian habitats and thus 

providing assistance to riparian wildlife, including the western yellow-billed cuckoo. Additional 

knowledge of the yellow-billed cuckoo’s habitat requirements in the Southwest, and what factors 

influence these habitats, can help lead to even more effective and efficient riparian restoration. Armed 

with this knowledge, there is great potential to restore considerable amounts of breeding habitat within 

the LCR MSCP region. 
65 

Acknowledgments 

This project was made possible by the support and cooperation of many persons, agencies and private 

companies. Funding was provided by the U.S. Bureau of Reclamation in Boulder City, Nevada, under the 

Multi-Species Conservation Plan, and the USGS Southwest Biological Science Center in Flagstaff, 

Arizona. 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 and Fred Wong 

(Bureau of Land Management) for his assistance in the field. Terry Arundel (USGS) assisted with GISrelated tasks and with the maps presented in this report. The success of the project is ultimately due to the 

efforts of the field personnel on the 2006 USGS field crew: Chris Calvo, Ivan Samuels, Laura Riley, 

Stefanie Krantz, Jimmy McMorran, Kristina Baker, Geoffrey Bland, Sarah Newell, Brandon Wilson, and 

Ken Etzel. Greg Clune, Theresa Olson, Susan Sferra, and John Swett (Bureau of Reclamation) provided 

insightful and helpful reviews on earlier drafts of this report, as did Sartor Williams. Louella Holter 

(Northern Arizona University) assisted with report production. Use of product trade names does not 

constitute U.S. Geological Survey endorsement of any product. 
66 

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74

Appendix 1 

Survey sites and survey dates for yellow-billed cuckoo surveys lower Colorado River Watershed 

along the along the Virgin and Muddy rivers, Nevada, lower Colorado, Bill Williams and Gila 

rivers, Arizona and California, 2006. Surveys took place during four survey periods in 2006. 

Survey Period 1 = 11 June–2 July, Period 2 = 3–23 July, Period 3 = 24 July–10 August, Period 4 = 

11 August–13 September. 

Geographic Area Site Name Period 1 Period 2 Period 3 Period 4 

Littlefield NV Littlefield Bridge 6/20 7/03, 7/15 7/28 9/07 

Mesquite NV Mesquite Bridge 6/20 7/03, 7/15 7/28 9/07 

Pahranagat NWR Pahranagat North 6/27 7/14 7/27 8/12,8/25 

Pahranagat East 6/27 7/14 7/27 8/12 

Pahranagat South 6/27 7/14 7/27 8/12 

Pahranagat West 6/27 7/14 7/27 8/11 

Overton WMA Honeybee Pond 6/21 7/03, 7/15 7/28, 8/10 8/27 

Overton North 6/21 no survey 7/28, 8/10 no survey 

Overton Tamarisk no survey no survey 8/10 no survey 

Overton Wildlife 6/21 7/03, 7/15 7/28, 8/10 8/27 

Grand Canyon NP– Spencer Canyon no survey no survey no survey 8/11,8/27 

Lake Mead NRA RM 274.5 6/29 7/13 8/10 8/26 

River Delta/RM 285.3N 6/29 no survey no survey no survey 

Cuckoo Beach 6/29 - 6/30 7/12 8/10 8/25 

Iceberg Ridge 6/29 7/12 8/10 8/25 

Chuckwalla Cove 6/29 - 6/30 7/12 8/09 8/25 

Lake Mohave Waterwheel Cove 7/02 no survey 7/25 9/07 

Mohave Patch 7/02 no survey 7/26 9/07 

Havasu NWR Pintail Slough 6/15, 6/29 7/11 7/26, 8/09 no survey 

North Dike 6/15, 6/29 7/11 7/26, 8/09 no survey 

Topock Marsh Restoration 6/15, 6/28 7/10 7/25, 8/10 no survey 

Sacramento Wash 6/18, 6/30 7/12 7/29 no survey 

Havasu Tamarisk 6/18, 6/30 7/12 7/29 no survey 

Topock Tamarisk 6/14, 6/28 7/10 7/24 no survey 

Bill Williams NWR Cave Wash no survey 7/05, 7/19 8/02 8/15 

Mineral Wash no survey 7/05, 7/19 8/01 8/15 

Big Bend no survey 7/05, 7/19 8/02 8/15 

Gibraltar Rock 6/17 7/04, 7/18 8/01 8/14 

Sandy Wash no survey 7/04, 7/18 7/31 8/13 

Fox Wash 6/17 7/04, 7/18 8/01 8/13 

Mosquito Flats 6/17 7/04, 7/18 7/30 8/13 

Saguaro Slot 6/17 7/18 7/30 8/13 

Bill Williams River Marsh no survey 7/05, 7/19 7/31 8/14 

Cibola NWR Cibola North Restoration 6/20 7/03, 7/17 7/318/12 

Cibola Nature Trail Restoration 6/20 7/03, 7/17 7/31 8/12 

Cibola Eucalyptus Restoration 6/20 7/03, 7/17 7/31 8/12 

Cibola South Restoration 6/20 7/03, 7/17 7/31 8/12 

Cibola Cross River 6/20 7/03, 7/17 7/31 8/12 

Cibola East Side 6/20 7/03, 7/17 7/31 8/12 

Picacho SRA Picacho SRA 6/21 7/03, 7/17 8/02 8/11 
75

Appendix 1 (continued) 

Geographic Area Site Name Period 1 Period 2 Period 3 Period 4 

Imperial NWR Imperial Paradise 6/21 7/03 8/02 8/11 

Imperial South Restoration 6/19, 7/02 7/15 7/30 8/12 

Mittry Lake WMA Mittry Lake WMA/ 6/14, 6/26 7/11 7/25, 8/07 no survey 

 Pratt Restoration 

Gila/Colorado River Colorado River 6/16, 7/01 7/14 7/27, 8/08 no survey 

Confluence Gila River 6/16, 7/01 7/14 7/27, 8/08 no survey 

Yuma West Wetlands Yuma West Wetlands 6/21, 6/01 7/16 7/29, 8/09 no survey 

Limitrophe Division Limitrophe Division North 6/18, 6/28 7/16 7/28, 7/29, 8/10 no survey 

Limitrophe Division South 6/17, 6/27 no survey 7/28, 8/10 no survey 

Gila River Highway 95 Gila 95 Bridge 6/13, 6/27 7/13 7/24, 8/07 no survey 

Gila 95 Canal 6/13, 6/27 7/13 7/24, 8/07 no survey 

Gila 95 Tall Tamarisk 6/13, 6/27 7/13 7/24, 8/07 no survey 

Gila River/Ligurta Gila River/Ligurta 6/26 7/11 7/30 8/11 

Gila River/Wellton Gila River/Wellton 6/26 7/11 7/30 8/11 

Gila River/Quigley Gila River/Quigley Pond WMA 6/14, 6/26 7/11 7/30 8/11 

Pond WMA 
76

Appendix 2 

Narrative description of each yellow-billed cuckoo detection in the lower Colorado River 

Watershed along the along the Virgin and Muddy rivers, Nevada, lower Colorado, Bill Williams 

and Gila rivers, Arizona and California, 2006. 

The following are descriptions of each yellow-billed cuckoo detection from the 2006 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, behavioral observations such as vocalization type, 

courtship behavior, and breeding status. 

We assigned breeding status based on observations of cuckoo behavior conducted across all four visits. 

Breeding was considered “confirmed” if an attended nest was found, copulation was observed, and/or 

recently fledged young were observed at the site. Breeding status was assigned as “probable” when a pair 

was observed during more than one visit, or agitated behavior (e.g., “knocker” call given, agitated adults) 

was observed that indicated a nest was nearby. Breeding status was classified as “Possible” when 

cuckoo(s) were detected in the same general area within the site on two or more visits, indicating that 

individuals had established a home range and were staying within the area long enough to breed. Sites 

that had only one detection within the season, or detections that were intermittent and/or observed 

behavior indicated the individual was solitary and not consistently detected in the same area were 

classified as “unknown” breeding status. If a site had no detections, it was classified as “unoccupied”. 

LITTLEFIELD BRIDGE, CITY OF LITTLEFIELD, AZ (VIRGIN RIVER, BEAVER DAM WASH) 

In 2006, no yellow-billed cuckoos were detected near Littlefield Bridge or in Beaver Dam Wash. 

MESQUITE BRIDGE, CITY OF MESQUITE, NV (VIRGIN RIVER) 

Mesquite Bridge - 07/03/2006 – 0925, 0760180 E, 4075671 N, 340°/180 m. Yellow-billed cuckoo 

responded with a knock and kowlp call, then a knock call from across river after the 1st playback. The 

vocalization came from one of three cottonwoods on possible private property. The observers were 

not sure that the calls were from a YBCU so they played the track a second time to verify the bird. 

The bird flew in and landed nearby in thick tamarisk, willow, and some larger cottonwoods, then 

proceeded to give the knock and kowlp call. After 40 minutes, the track was played again. The bird 

came into clear view for two surveyors and called approximately five times (first time was kowlp, 

then knock, successive calls were all knocks). This cuckoo reacted very aggressively. Aural and visual 

detections. Breeding classification: unconfirmed, no cuckoos were detected at this site during later 

surveys. 

PAHRANAGAT NATIONAL WILDLIFE REFUGE (WHITE RIVER) 

Pahranagat North 

Pahranagat NWR - Pahranagat North - 07/27/2006 – 0630, 0665808 E, 4131084 N, 190°/100 m. 

Yellow-billed cuckoo vocalized cooing then kowlping call after the 1st playback. Cuckoo cooed off 

and on for about one hour. Cuckoo was flying up and down the east part of the patch from point five 

to point two and the bird was also using the east corner of the thickest part of the patch. Yellow-billed 

cuckoo was observed after the survey at 0718. Aural and visual detections. Breeding classification: 

unconfirmed, no cuckoos were detected at this site during later surveys. 

Pahranagat East 

In 2006, no yellow-billed cuckoos were detected at this site.
77

Pahranagat South 

In 2006, no yellow-billed cuckoos were detected at this site. 

Pahranagat West 

In 2006, no yellow-billed cuckoos were detected at this site.

OVERTON WILDLIFE MANAGEMENT AREA (MUDDY RIVER) 

Honey Bee Pond 

Overton WMA – Honey Bee Pond – 07/15/2006, 0715, 0731456 E, 4045633 N, 172°/1000 m. 

Yellow-billed cuckoo vocalized by knocking after 4th playback, but it was almost inaudible, it 

seemed to be coming from S/SE. Completed final playback and waited a minute to see if it would call 

again, no response. Aural detection only. Breeding classification: unconfirmed. 

Overton WMA – Honey Bee Pond – 07/15/2006, 0725, 0731254 E, 4045702 N, 8°/35 m. 

Yellow-billed cuckoo flew in from the south and began calling from palm trees after 3rd playback 

then flew overhead and perched on willow snag. At 0744 cuckoo called again from palm trees. At 

0749 cuckoo vocalized knock/kowlp call from palm trees. UTM of palm trees; 0731247E / 4045736N. 

UTM of willow snag; 0731230E / 4045736N. At 0834 cuckoo vocalized knock/ kowlp call from 

willows. Aural and visual detections. Breeding classification: unconfirmed. 

Overton WMA – Honey Bee Pond – 07/28/2006, 0626, 0731152 E, 4045675, 240°/700 m. 

No response after 5th playback. Played coo call just to see what would happen and yellow-billed 

cuckoo vocalized coo call immediately after 2nd coo playback. Aural detection only. Breeding 

classification: unconfirmed, however, cuckoo detected during previous survey at this site on 

07/15/06. 

Overton North 

 In 2006, no yellow-billed cuckoos were detected at this site. 

Overton Tamarisk 

In 2006, no yellow-billed cuckoos were detected at this site. 

Overton Wildlife 

Overton WMA – Overton Wildlife – 06/21/2006, 0807, 0732038 E, 4044167 N, 200°/80 m. 

Yellow-billed cuckoo called after 2nd playback. Cuckoo detection was 100m from the end of the 

patch so observers ended survey and searched for the bird. Observed the cuckoo as it flew from lower 

tamarisk to upper willows. Cuckoo called often with both knocker and coo calls, flew up and down 

patch, observed only one cuckoo. Aural and visual detection. Breeding classification: unconfirmed. 

Overton WMA – Overton Wildlife – 07/03/2006, 0730, 0731971 E, 4044114 N, 348°/70 m. 

Yellow-billed cuckoo gave knocker call from willows at UTM 0731990E / 4044167N after 2nd 

playback. At 0753 cuckoo knocking about 40 m east of where originally detected. This is the same 

area where the cuckoo was followed during the last survey. At 0810 listened for about 10 min to be 

sure but suspected two cuckoos calling as one consistently called from willows near point two and 

another cuckoo seemed to call from different locations along other side of drainage ditch. At 0810 

cuckoos began to counter-call. Cuckoo1 and Cuckoo2 continued counter-call for about 10 minutes. 

Aural detection only. Breeding classification: unconfirmed, however, cuckoo detected at this site 

during previous survey on 06/21/06, also observed two cuckoos counter-calling at this site. 
78

GRAND CANYON NATIONAL PARK/LAKE MEAD NATIONAL RECREATION AREA 

(COLORADO RIVER AND LAKE MEAD) 

Spencer Canyon 

In 2006, no yellow-billed cuckoos were detected at this site. 

RM 274.5 

Grand Canyon NP – RM 274.5 – 08/10/2006, 1116, 0236073 E, 3999118 N, 228°/15 m. 

Yellow-billed cuckoo vocalized fast knocker call after 1st playback. Observer had a visual 

observation of cuckoo as it flew overhead, flew back to the tall willows on the edge of the patch. 

Aural and visual detections. Cuckoo continued knocking call for two minutes. Breeding 

classification: unconfirmed. 

River Delta/RM 285.3N 

In 2006, no yellow-billed cuckoos were detected at this site. 

Cuckoo Beach 

Lake Mead NRA – Cuckoo Beach – 06/29/2006, 0602, 0767482 E, 4009822 N, Cuckoo1 @ 

334°/13 m, Cuckoo2 @ 254°/150m, Cuckoo3 @ 292°/40m. Yellow-billed cuckoo (Cuckoo1) 

vocalized an unsolicited coo call. This patch is a willow gallery in different stages of growth. 

Cuckoo1 continued calling, while another yellow-billed cuckoo (Cuckoo2) vocalized a knocker call 

from 150 m downstream, 254 degrees. Cuckoo1 flushed, flew about 40 m, while another yellowbilled cuckoo (Cuckoo3) flew out after Cuckoo1. Cuckoo3 first observed at 40m, 292 degrees. Aural 

and visual detections. Breeding classification: unconfirmed. 

Lake Mead NRA – Cuckoo Beach – 06/29/2006, 0802, 0767020 E, 4009353 N, 46°/130 m. 

Yellow-billed cuckoo vocalized coo call after 1st playback. This detection is in same location as 

detected during the first survey. Aural detection only. Breeding classification: unconfirmed. 

Lake Mead NRA – Cuckoo Beach – 06/30/2006, 0600, 0766855 E, 4009097 N, 32°/140 m. 

Yellow-billed cuckoo vocalized unsolicited coo call from upstream. Cuckoo flew past observer and 

continued to call from downstream. Aural and visual detections. Breeding classification: 

unconfirmed. 

Lake Mead NRA – Cuckoo Beach – 06/30/2006, 0617, 0766613 E, 4008820 N, 30°/60 m. 

Yellow-billed cuckoo vocalized coo call after 1st playback. Cuckoo vocalized another coo and 

knocker call five minutes later. Aural detection only. Breeding classification: unconfirmed. 

Lake Mead NRA – Cuckoo Beach – 07/12/2006, 0729, 0767465 E, 4009818 N, Cuckoo1 @ 

272°/200m, Cuckoo2 @ unknown/100m. Yellow-billed cuckoo (Cuckoo1) gave unsolicited coo call 

at first point. Due to the bend in the river, observer could hear cuckoo from far away. Coo call was 

repeated every minute for six minutes. Next point will be greater than 300 m away. At 0748 cuckoo 

moved down patch nearer to where observer took the point. There is also another yellow-billed 

cuckoo (Cuckoo2) cooing about 100 m away from the west, did not get bearing. Aural detection only. 

Breeding classification: unconfirmed, however cuckoo detected at this site during previous survey on 

06/30/2006. 

Lake Mead NRA – Cuckoo Beach – 07/12/2006, 0757, 0767008 E, 4009348 N, 28°/30 m. 

Yellow-billed cuckoo flew out of the patch after 3rd playback, the observer visually observed the 

cuckoo. The cuckoo flew across the river to river right, disappearing out of sight. This bird flew from 

the Cuckoo Beach site to the direction of Chuckwalla Cove site. Visual detection only. Breeding 

classification: unconfirmed, however cuckoo detected at this site during previous survey on 

06/30/2006. 
79

Lake Mead NRA – Cuckoo Beach – 08/25/2006, 0755, 0767391 E, 4009808 N, 35°/65 m. Yellowbilled cuckoo vocalized a couple of soft rolling kowlps after 2nd playback. Cuckoo detected in second 

band of willow that is 5 m tall. Aural detection only. Breeding classification: unconfirmed, however, 

cuckoo detected at this site during previous surveys on 06/30/2006 and 07/12/2006 

Iceberg Ridge 

Lake Mead NRA – Iceberg Ridge – 06/29/2006, 0836, 0765731 E, 4008502 N, Cuckoo1 @ 

311°/65m, Cuckoo2 @ 40°/210m. Yellow-billed cuckoo (Cuckoo1) vocalized unsolicited coo call in 

willow, overstory of 6-7 m, tamarisk and willow understory. A second yellow-billed cuckoo 

(Cuckoo2) called with coo call across river. Aural detections only. Breeding classification: 

unconfirmed. 

Lake Mead NRA – Iceberg Ridge – 07/12/2006, 0931, 0765694 E, 4008450 N 252°/90 m. 

Yellow-billed cuckoo vocalized coo call after 3rd playback. This cuckoo is in the same location it was 

detected during first survey. Aural detection only. Breeding classification: unconfirmed, however, 

cuckoo detected at this site during previous survey on 06/29/2006. 

Chuckwalla Cove 

Lake Mead NRA – Chuckwalla Cove – 06/28/2006, 19:45, 0766211 E, 4009724 N, no 

direction/100m. Yellow-billed cuckoo gave a knocker call at dusk as the crew beached their boat to 

camp, call came from within the patch surrounding the camp, also vocalized a coo call 15 minutes 

later. Aural detection only. Breeding classification: unconfirmed. 

Lake Mead NRA – Chuckwalla Cove – 06/29/2006, 0430, 0765852 E, 4008952 N, 140°/150 m. 

Yellow-billed cuckoo gave unsolicited knocker calls. Aural detection only. Breeding classification: 

unconfirmed. 

Lake Mead NRA – Chuckwalla Cove – 06/29/2006, 0530, 0765852 E, 4008952 N, 70°, 175 m. 

Two yellow-billed cuckoos counter-calling after 1st playback. Aural detection only. Breeding 

classification: unconfirmed. 

Lake Mead NRA – Chuckwalla Cove – 06/29/2006, 0627, 0766076 E, 4009263 N, 27°/200 m. 

Yellow-billed cuckoo cooing after 3rd playback. Aural detection only. Breeding classification: 

unconfirmed. 

Lake Mead NRA – Chuckwalla Cove – 06/29/2006, 0645, 0766036 E, 4009565 N, 35°/150 m. 

Yellow-billed cuckoo cooing after 1st playback. Aural detection only. Breeding classification: 

unconfirmed. 

Lake Mead NRA – Chuckwalla Cove – 06/29/2006, 0705, 0765789 E, 4009734 N, 40°, 150 m. 

Yellow-billed cuckoo cooing after 5th playback. Aural detection only. Breeding classification: 

unconfirmed. 

Lake Mead NRA – Chuckwalla Cove – 06/30/2006. 0800, 0765876 E, 4009628 N, no bearing or 

distance. Yellow-billed cuckoo (Cuckoo1) began giving the ping-pong ball call and cooing

approximately five meters away from observer. Cuckoo1 then flew out of patch and called from 

further away. Cuckoo2 was in patch near Cuckoo1 and flew by observer flapping wings around a 

willow tree, this bird acting very agitated (hitting leaves, crashing into foliage) Cuckoo1 continued 

cooing out of patch, and then Cuckoo3 called from a downstream patch with a coo call. Observed 

visually three adult cuckoos at the same time in patch of willows. Observer backed away 10 m, and 

on his way out he noticed a juvenile yellow-billed cuckoo on a branch 2.5 m up in a willow. Its head 

and bill were pointed straight up to the sky, its feathers looked ragged and body pin feathers were still 

evident, the tail feathers were not fully developed either. Second visit at this site, no yellow-billed 

cuckoos were observed at this site. Aural and visual detections. Breeding classification: confirmed. 
80

Lake Mead NRA – Chuckwalla Cove – 06/30/2006, 0805, 0765929 E, 4009371 N, 62°/18 m. Yellowbilled cuckoo vocalized unsolicited knocker call. Aural and visual detections. Breeding classification: 

unconfirmed. 

Lake Mead NRA – Chuckwalla Cove – 06/30/2006, 0820, 0765930 E, 4009367 N, 335°/70 m. 

Yellow-billed cuckoo vocalized unsolicited coo call. Aural detection only. Breeding classification: 

unconfirmed. 

Lake Mead NRA – Chuckwalla Cove – 07/12/2006, 0733, 0764732 E, 4009773 N, 88°/30 m. 

Yellow-billed cuckoo was heard giving a series of knocking calls during the 5th playback. Aural 

detection only. Breeding classification: unconfirmed, however, cuckoo detected at this site during 

previous survey on 06/30/2006. 

Lake Mead NRA – Chuckwalla Cove – 07/12/2006, 0844, 0766012 E, 4009891 N, 20°/25 m. 

Yellow-billed cuckoo vocalized knocker and kowlps calls after the 2nd playback. A different tone and 

cadence to these calls. The call had more of a metallic type quality. The call also started with a long 

introduction of knocker calls before transitioning into kowlps. Aural detection only. Breeding 

classification: unconfirmed, however, cuckoo detected at this site during previous survey on 

06/30/2006. 

LAKE MOHAVE (COLORADO RIVER) 

Waterwheel Cove 

In 2006, no yellow-billed cuckoos were detected at this site.

Mohave Patch 

In 2006, no yellow-billed cuckoos were detected at this site.

HAVASU NATIONAL WILDLIFE REFUGE (COLORADO RIVER) 

Pintail Slough 

Havasu NWR – Pintail Slough – 06/29/2006, 0700, 0726188 E, 3858492 N, 258°/100 m. 

Yellow-billed cuckoo vocalized full rapid call with a lot of knocks at the beginning after the 3rd 

playback. It came from a patch of mesquite/tamarisk west across the canal from where the observer 

played the tape. The observer monitored the area for a while, but did not see or hear it again. Aural 

detection only. Breeding classification: unconfirmed, no cuckoos were detected at this site during 

later surveys. 

 

North Dike 

In 2006, there were no yellow-billed cuckoo detections at this site. 

Topock Marsh Restoration Site 

In 2006, there were no yellow-billed cuckoo detections at this site. 

Sacramento Wash 

In 2006, there were no yellow-billed cuckoo detections at this site. 

Havasu Tamarisk 

In 2006, there were no yellow-billed cuckoo detections at this site. 

Topock Tamarisk 

In 2006, there were no yellow-billed cuckoo detections at this site. 
81

BILL WILLIAMS NATIONAL WILDLIFE REFUGE (COLORADO & BILL WILLIAMS RIVERS) 

Cave Wash 

Bill Williams River NWR – Cave Wash – 07/05/2006, 0701, 0225080 E, 3794437 N, 164°/ 50 m. 

Yellow-billed cuckoo was observed flying overhead and perching briefly in a willow after 4th 

playback. There was no vocalization. Cuckoo flew out of sight behind vegetation. Visual detection 

only. Breeding classification: unconfirmed. 

Bill Williams River NWR – Cave Wash – 07/05/2006, 0732, 0225413 E, 3794655 N, 300°/ 120 m. 

Yellow-billed cuckoo vocalized knocker excitedly near previous point after 1st playback. This is the 

"end" of a good patch with very diverse avian and tree species. Aural detection only. Breeding 

classification: unconfirmed. 

Bill Williams River NWR – Cave Wash – 07/05/2006, 0757, 0225704 E, 3794725 N, 192°/ 60 m. 

Yellow-billed cuckoo vocalized unsolicited knocker call. Aural detection only. Breeding 

classification: unconfirmed. 

Bill Williams River NWR – Cave Wash – 07/05/2006, 0846, 0226290 E, 3794328 N, 60°/20 m. 

Yellow-billed cuckoo flew across river unsolicited, seen again flying back across and perching in 

cottonwood approximately 8 m tall. Visual detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR – Cave Wash – 07/05/2006, 0856, 0226594 E, 3794335 N, Cuckoo1 @ 

102°/25m, Cuckoo2 @ 194°/80m. Yellow-billed cuckoo (Cuckoo1) was observed perched in a 

willow after 3rd playback. At 0859 Cuckoo1 flew just down river into a cottonwood. Cuckoo1 was 

silent but finally vocalized more kowlp than knocker calls. At 0905 Cuckoo2 was vocalized knocker

and kowlp calls upstream. Visual and aural detections. Breeding classification: unconfirmed. 

Bill Williams River NWR – Cave Wash – 07/05/2006, 0910, 0226518 E, 3794322 N, 121°/ 50 m. 

Yellow-billed cuckoo was observed flying out of cottonwood after 3rd playback, then went back into 

patch, vocalizing a metallic sounding knocker call two different times. Visual and aural detection. 

Breeding classification: unconfirmed. 

Bill Williams River NWR – Cave Wash – 07/19/2006, 0657, 0225012 E, 3794388 N, 270°/ 35 m. 

Yellow-billed cuckoo vocalized unsolicited knocker call as surveyors neared the first survey point. 

Aural detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR – Cave Wash – 07/19/2006, 0707, 0225274 E, 3794527 N, 320°/ 130 m. 

Yellow-billed cuckoo vocalized knocker call after 3rd playback. Yellow-billed cuckoo (Cuckoo1) 

was observed flying from one cottonwood across river to another cottonwood. A second cuckoo 

(Cuckoo2) was vocalizing knocker and kowlp calls about 130 m away. Cuckoo1 than flew from the 

cottonwood to a willow closer to us, vocalizing knocker call. Cuckoo1 continues to call with long 

series of kowlps. Cuckoo2 was then observed flying across the river into the same cottonwood and 

same height as Cuckoo1. Cuckoo1 or 2 completed a food carry out of that cottonwood, and cuckoo1 

or 2 flew across river. Nest search turned up nothing. Aural and visual detection. Breeding 

classification: unconfirmed, however food carry was observed. 

Bill Williams River NWR – Cave Wash – 07/19/2006, 0738, 0225561 E, 3794674 N, Cuckoo1 @ 

170°/12m, Cuckoo2 @ 60°/80m. Yellow-billed cuckoo (Cuckoo1) vocalized very sharp, abrupt 

knocker calls, followed by a rolling kowlp call, after 1st playback. Vocalizations came from larger 

cottonwoods on river left, just off the bank. While Cuckoo1 began to coo call, Cuckoo2 vocalized 

sharp knocker calls upstream. Aural detections only. Breeding classification: unconfirmed, however, 

cuckoo detected at this site during previous survey on 07/05/2006. 

Bill Williams River NWR – Cave Wash – 08/02/2006, 0811, 0226967 E, 3794356 N, Cuckoo1 @ 

285°/40m, Cuckoo2 @ 30°/120m. Yellow-billed cuckoo (Cuckoo1) vocalized knocker calls after 1st 

playback. Seconds later, Cuckoo2 vocalized knocker calls. At this time a cuckoo? flushed from a 
82

cottonwood approximately seven meters up in tree and continued downstream quietly. Conducted a 

brief nest search and found nothing. Aural and visual detection. Breeding classification: unconfirmed. 

Bill Williams River NWR – Cave Wash – 08/02/2006, 0859, 0226669 E, 3794318 N, Cuckoo1 @ 

30°/70m, Cuckoo2 @ 0°/15m. Yellow-billed cuckoo (Cuckoo1) vocalized knocker calls after the 1st 

playback. Seconds later a second yellow-billed cuckoo (Cuckoo2) vocalized knocker calls very close. 

Aural detections only. Breeding classification: unconfirmed. 

Bill Williams River NWR – Cave Wash – 08/02/2006, 0929, 0226369 E, 3794334 N, 350°/5 m. 

A yellow-billed cuckoo observed not being fully developed (suggesting a juvenile) was seen perched 

in a small opening in a tamarisk after 1st playback. The tail was definitely not full length. Observer 

was almost confused on the identification of this bird. The bill was yellow-billed cuckoo, but the 

body didn't match up to be an adult, lighting was not clear. Visual detection only. Breeding 

classification: unconfirmed, however, it was a likely sighting of a juvenile. 

Bill Williams River NWR – Cave Wash – 08/15/2006, 0620, 0226384 E, 3794327 N, 22°/12 m. 

Yellow-billed cuckoo was observed flying into a cottonwood approximately 10-12 meters high after 

5th playback. The cuckoo then flew across the river into another cottonwood of the same height. 

Visual detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR – Cave Wash – 08/15/2006, 0725, 0225717 E, 3794728 N, 98°/50 m. 

Yellow-billed cuckoo vocalized knocker and kowlp calls after the 5th playback. Cuckoo was last 

observed flying over the river and out of sight. Aural and visual detections. Breeding classification: 

unconfirmed. 

Bill Williams River NWR – Cave Wash – 08/15/2006, 0803, 0225275 E, 3794525 N, 210°/8 m. 

Yellow-billed cuckoo was observed flying into a willow directly above us after 1st playback. Cuckoo 

continued to vocalize knocker and kowlp calls (very metallic sounding). Cuckoo then flew back 

across the river into willows. Cuckoo was spotted again low in a willow that was projecting out just 

above the waters surface. Visual and aural detections. Breeding classification: unconfirmed. 

Bill Williams River NWR – Cave Wash – 08/15/2006, 0844, 0224926 E, 3794386 N, 280°/ 100 m. 

Yellow-billed cuckoo vocalized a series of knocker calls after 2nd playback. The cuckoo was very 

distant. Aural detection only. Breeding classification: unconfirmed. 

Mineral Wash 

Bill Williams River NWR – Mineral Wash – 07/05/2006, 0546, 0775622 E, 3794379 N, 25°/50 m. 

Yellow-billed cuckoo vocalized knocker and rapid kowlp calls after 4th playback. Observer could not 

see into habitat where bird was calling due to dense willows. Aural detection only. Breeding 

classification: unconfirmed. 

Bill Williams River NWR – Mineral Wash – 07/05/2006, 0649, 0223800 E, 3794492 N, Cuckoo1 @ 

190°/12m, Cuckoo2 @ 230°/30m. Yellow-billed cuckoo (Cuckoo1) calling first with a knocker call 

then another knocker call then a coo call many times after 1st playback. Then another yellow-billed 

cuckoo (Cuckoo2) vocalizing knocker and kowlp call 30 m away @ 230 degrees. Tried to pursue 

Cuckoo1 (the cooing one) and found it in a large cottonwood tree about eight m from the bottom of 

the tree. The cuckoo flew when the observers got too close. One of the cuckoos continued the call 

sporadically with the knocker call. Did not see the cuckoos again although they were calling all 

around the area. Habitat here consists of cottonwood/willow/ tamarisk. Aural and visual detections. 

Breeding classification: unconfirmed. 

Bill Williams River NWR – Mineral Wash – 07/05/2006, 0809, 0224455 E, 3794340 N, 50°/50 m. 

Yellow-billed cuckoo vocalizing knocker and kowlp call after 2nd playback. Cuckoo called once from 

a willow/cottonwood stand. Aural detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR – Mineral Wash – 07/19/2006, 0544, 0775646 E, 3794384 N, 350°/ 13 m. 

Yellow-billed cuckoo vocalized knocker and kowlp calls after 1st playback, paused for 3 minutes, 
83

then called from 20 m at 80°, then 4 minutes later at 40°; Sarah stayed near this bird and watched it as 

it moved around and called until about 0615. Aural and visual detections. Breeding classification: 

unconfirmed. 

Bill Williams River NWR – Mineral Wash – 07/19/2006, 0623, 0776135 E, 3794399 N, 280°/ 45 m. 

Yellow-billed cuckoo called after 1st playback with knocker and kowlp call, then flew over to 20°, 10 

m from observer. The bird sat in a willow scanning for a while then went to back side of tree and out 

of sight. Waited for 20 minutes and did not see the bird again. It called again at 0641 with the same 

call as before and at 0642 with same call further upstream 50 meters. Habitat at detection location, 

dense willow along river with a tamarisk understory. Aural and visual detections. Breeding 

classification: unconfirmed. 

Bill Williams River NWR – Mineral Wash – 07/19/2006, 0750, 0224450 E, 3794344 N, 65°/ 100 m. 

Yellow-billed cuckoo giving knocker call after 1st playback from cottonwood/tamarisk area. Aural 

detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR – Mineral Wash – 07/19/2006, 0806, 0224751 E, 3794393 N, 45°/ 100 m. 

Yellow-billed cuckoo vocalized knocker and kowlp call after 3rd playback, then cuckoo called again 

two minutes later and 50 meters away at 265°. Observed cuckoo for about one minute perched in a 

tree 11 meters away; he then flew away into some willows. Aural and visual detections. Breeding 

classification: unconfirmed. 

Bill Williams River NWR – Mineral Wash – 08/01/2006, 0543, 0775340 E, 3794451 N, 15°/40 m. 

Yellow-billed cuckoo vocalized knocker call after 2nd playback from a small patch of willows with 

some tamarisk understory directly across from starting survey point and gate. Cuckoo was detected in 

willows 10 m high. Aural detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR – Mineral Wash – 08/01/2006, 0610, 0775633 E, 3794388 N, 53°/25 m. 

Yellow-billed cuckoo vocalized knocker and rapid kowlp calls after 1st playback from dense 

willow/tamarisk area, called only once. Then cuckoo flew across the river towards observers, landing 

in a willow at 250° then cuckoo flew to another willow at 240°, 5 m away, then flew back across river 

and out of sight. Aural and visual detections. Breeding classification: unconfirmed. 

Bill Williams River NWR – Mineral Wash – 08/01/2006, 0646, 0776033 E, 3794354 N, Cuckoo1 @ 

320°/11m, Cuckoo2 @ 73°/25 m. Two cuckoos observed, one cuckoo (Cuckoo1) flew into 14 m tall 

willow (11 m at 320°). Observers were not sure the cuckoo was there so they played the 5th playback. 

Cuckoo1 came out of the willow and flew across the river landing in another willow ( @ 158°/8 m). 

Another cuckoo (Cuckoo2) flew across the river with Cuckoo2 and the birds crossed paths in the air. 

Cuckoo2 went to a different tree ( @ 73°/25 m). Cuckoo1 vocalized a knocker and kowlp calls after it 

landed. Cuckoo1 then vocalized a knocker call and was continuously bobbing its tail. Cuckoo1 stayed 

in the willow, moving around to the back of the patch slowly then flying downstream and out of 

sight. Observer stayed to do further observations and followed cuckoos around this location 

eventually finding a nest but it was an old nest. There were some leaves in it and no eggs. Habitat 

here is mainly willow dominated with some taller willows here (15 m) and a tamarisk understory. 

Visual and aural detections. Breeding classification: unconfirmed, however, cuckoos detected at this 

site during previous surveys on 07/05/2006 and 07/19/2006. 

Bill Williams River NWR – Mineral Wash – 08/01/2006, 0839, 0224486 E, 3794347 N, 25°/35 m. 

Yellow-billed cuckoo vocalized knocker and kowlp call after 2nd playback. Cuckoo in 13 m 

cottonwood in cottonwood/willow stand then flew to cottonwood 2 m away @ 23° and then flew out 

of sight. Aural and visual detections. Breeding classification: unconfirmed. 

Bill Williams River NWR – Mineral Wash – 08/01/2006, 0856, 0224780 E, 3794408 N, 20°/22 m. 

Yellow-billed cuckoo vocalized knocker and kowlp call then continued to vocalize a soft three-part 

kowlp for two minutes. Cuckoo was barely visible in the willow from where it was kowlping. Habitat 

is mostly dense willow with some sparse tamarisk and a few taller (13 m) cottonwoods. Aural and 

visual detections. Breeding classification: unconfirmed. 
84

Bill Williams River NWR – Mineral Wash – 08/15/2006, 0920, 0224345 E, 3794468 N, 70°/40 m. 

Yellow-billed cuckoo vocalized knocker and kowlp calls after 3rd playback, called three times then 

moved 12 m away at 40°. Aural detection only. Breeding classification: unconfirmed. 

Big Bend 

Bill Williams River NWR – Big Bend – 07/05/2006, 0527, 0775328 E, 3794433 N, 70°/60m. 

Yellow-billed cuckoo vocalized kowlp call after 4th playback. Aural detection only. Breeding 

classification: unconfirmed. 

Bill Williams River NWR – Big Bend – 07/05/2006, 0632, 0774762 E, 3794887 N, 340°/40 m. 

Yellow-billed cuckoo called after 1st playback. Gave quite a few knocker and a couple kowlp calls. 

Cuckoo called again several more times after that from the same location. Aural detection only. 

Breeding classification: unconfirmed. 

Bill Williams River NWR – Big Bend – 07/05/2006, 0732, 0774376 E, 3795440 N, 10°/10m. 

Yellow-billed cuckoo flew in from downstream after 4th playback. Landed in cottonwood - observed 

bird in same tree a couple minutes later and watched it for a little while. Cuckoo left at 0744. At 0749 

observer heard cuckoo knocking from downstream. This could be another cuckoo but observer 

unsure. Aural and visual detections. Breeding classification: unconfirmed. 

Bill Williams River NWR – Big Bend – 07/05/2006, 0816, 0774332 E, 3795730 N, 128°/30 m. 

Yellow-billed cuckoo flew in silently from upstream - still within same large patch. Cuckoo silently 

foraging in upper cottonwood canopy. Observed cuckoo until 0945. Two cuckoos in same area – one 

cuckoo heard calling in distance (about 50m away) while watching this bird not calling within 20 m 

of observer. Unsolicited aural and visual detections. Breeding classification: unconfirmed. 

Bill Williams River NWR – Big Bend – 07/05/2006, 0909, 0773853 E, 3795831 N, 45°/100 m. 

Yellow-billed cuckoo called from next to where surveyors completed last point. Surveyors walked 

back upriver and observed cuckoo sitting in the open on a dead branch. Cuckoo then flew about 100m 

downriver and called (full call again). Observers did not get another visual on the bird, but a cuckoo 

called again at 0930. Unsolicited aural and visual detection. Breeding classification: unconfirmed. 

Bill Williams River NWR – Big Bend – 07/19/2006, 0530, 0775337 E, 3794455 N, 72°/100 m. 

Yellow-billed cuckoo vocalized a unsolicited kowlp from bend in river. Aural detection only. 

Breeding classification: unconfirmed. 

Bill Williams River NWR – Big Bend – 07/19/2006, 0618, 0774777 E, 3794872 N, 160°/30 m. 

Yellow-billed cuckoo flew in and landed after 5th playback, then vocalized full kowlp call. Cuckoo 

flew to high perch at 105°/45 m. Observed bill wiping. Cuckoo vocalized one more full kowlp call 

before flying off, then bird called once again from unseen perch. Visual and aural detections. 

Breeding classification: unconfirmed. 

Bill Williams River NWR – Big Bend – 07/19/2006, 0637, 0774548 E, 3795066 N, 15°/15 m. 

Yellow-billed cuckoo flew into mesquite after 4th playback where it was viewed at close range 

(15 m). Then cuckoo flew across river to 270°/ 35 m where it vocalized multiple knocker calls from 

within mesquite patch. Visual and aural detections. Breeding classification: unconfirmed. 

Bill Williams River NWR – Big Bend – 07/19/2006, 0708, 0774327 E, 3795613 N. 

Yellow-billed cuckoo observed carrying food (dragonfly) from north side of river to south side of 

river. Two individual cuckoo heard counter-calling. Nest search of area unsuccessful. Visual and 

aural detections. Breeding classification: unconfirmed, however, food carry was observed. 

Bill Williams River NWR – Big Bend – 07/19/2006, 0742, 0774220 E, 3795892 N, 260°/45 m. 

Yellow-billed cuckoo vocalized a muted kowlp without knocks after 2nd playback. Aural detection 

only. Breeding classification: unconfirmed. 

Bill Williams River NWR – Big Bend – 07/19/2006, 0758, 0773918 E, 3795885 N, 95°/100 m. 
85

Yellow-billed cuckoo vocalized a full kowlp call after 5th playback. Aural detection only. Breeding 

classification: unconfirmed. 

Bill Williams River NWR – Big Bend – 08/02/2006, 0708, 0774317 E, 3795656 N, 330°/15 m. 

Yellow-billed cuckoo vocalized an unsolicited full call at 0708. Then observer watched cuckoo perch 

in a cottonwood from 0718 - 0730. Cuckoo flew to a willow where two cuckoos were sitting, one 

adult and one juvenile. Aural and visual detection. Breeding classification: confirmed. 

Bill Williams River NWR – Big Bend – 08/02/2006, 0937, 0773764 E, 3795404 N, 136°/80 m. 

Aural detection after 3rd playback. Breeding classification: unconfirmed. 

Bill Williams River NWR – Big Bend – 08/15/2006, 0753, 0774537 E, 3795068 N, 339°/180 m. 

Yellow-billed cuckoo vocalized unsolicited series of knockers and kowlps. Aural detection only. 

Breeding classification: unconfirmed. 

Bill Williams River NWR – Big Bend – 08/15/2006, 0800, 0774316 E, 3795644 N, 30°/30 m. 

Yellow-billed cuckoo vocalized unsolicited soft kowlping from willows on east side of river. Cuckoo 

called a couple more times, then went silent. Aural detection only. Breeding classification: 

unconfirmed. 

Bill Williams River NWR – Big Bend – 08/15/2006, 0855, 0774185 E, 3795913 N, 144°/270 m. 

Yellow-billed cuckoo vocalized a full series of kowlps after 4th playback - rapid and repeated three 

times. Aural detection only. Same area where two adult and juvenile cuckoos were detected on 

08/02/2006. Breeding classification: unconfirmed, however, other breeding cuckoos were detected at 

this site during previous survey on 08/02/2006. 

Bill Williams River NWR – Big Bend – 08/15/2006, 0908, 773880 E, 3795838 N, no bearing and 

distance are at point. Yellow-billed cuckoo vocalized low rolling kowlps (four times) after 2nd 

playback. This GPS coordinate is directly below where the bird was observed. Aural detection only. 

Breeding classification: unconfirmed. 

Gibraltar Rock 

Bill Williams River NWR – Gibraltar Rock – 06/17/2006, 0640, 0771330 E, 3796306 N, 160°/120 m. 

Yellow-billed cuckoo vocalized coo call multiple times after 2nd playback. Aural detection only. 

Breeding classification: unconfirmed. 

Bill Williams River NWR – Gibraltar Rock – 07/04/2006, 0736, 0771850 E, 3796091 N, 300°/ 8 m. 

Yellow-billed cuckoo flew in quietly from direction of previous point. Landed in willow 

approximately five m tall, and approached observer after the 3rd playback. Observer watched cuckoo 

for quite a while as it hopped from branch to branch, being very elusive and quiet. Cuckoo flew off in 

a northern direction after about a minute. The observer never heard it give loud kowlps but thought 

they heard it making a very low, almost inaudible, clicking sound. It was two clicks click, click, 

repeated 2 times, with almost a question mark at the end (similar to Plumbeous Vireo). Aural and 

visual detections. Breeding classification: unconfirmed. 

Bill Williams River NWR – Gibraltar Rock – 07/18/2006, 0915, 0773399 E, 3794985 N, 350°/ 30 m. 

Yellow-billed cuckoo called five minutes after 5th tape playback. Cuckoo vocalized a rolling kowlp

and a knocker call. Aural detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR – Gibraltar Rock – 08/01/2006, 0600, 0771269 E, 3796320 N, 110°/300m. 

Yellow-billed cuckoo spontaneously cooing when the surveyors pulled up to the drop-off point for 

Gibraltar Rock and Sandy Wash. Technically this in the Gibraltar Rock survey area. Started survey 

300 m away, then moved another 100m away because cooing did not stop for another 10 minutes. 

Aural detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR – Gibraltar Rock – 08/14/2006, 0712, 0773302 E, 3794928 N, 280°/ 30 m. 

Yellow-billed cuckoo flew in silent front right in front of us across the river after the 4th playback. 
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The cuckoo flew into a willow about seven meters high, did not observe cuckoo again. Visual 

detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR – Gibraltar Rock – 08/14/2006, 0717, 0771920 E, 3795971 N, 229°/ 50 m. 

Yellow-billed cuckoo vocalized a hard, short, rolling kowlp given once after 5th playback. Observers 

weren't sure so they played the tape again for confirmation. They saw cuckoo in a willow 10m away 

and at 2°. Cuckoo then flew back to the willows it initially called from. After a minute, cuckoo flew 

to 74° and 80m away, then went behind some willows and disappeared. Aural and visual detections. 

Breeding classification: unconfirmed. 

Bill Williams River NWR – Gibraltar Rock – 08/14/2006, 0751, 0772825 E, 3795061 N, 192°/ 15 m. 

Yellow-billed cuckoo was observed perched in a willow looking at us after the 2nd playback. The 

cuckoo then flew to a willow next to it and then flew across the river into another willow. All willows 

were roughly 5-8 meters tall. Visual detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR – Gibraltar Rock – 08/14/2006, 0812, 0772828 E, 3795456 N, 168°/ 25 m. 

Yellow-billed cuckoo was visually observed after the 3rd playback. No vocalization from the cuckoo. 

Cuckoo was observed flying from a cottonwood over the river into a tamarisk. Visual detection only. 

Breeding classification: unconfirmed. 

Sandy Wash 

Bill Williams River NWR – Sandy Wash – 07/04/2006, 0755, 0771866 E, 3796385 N, Cuckoo1 @ 

230°/30m, Cuckoo2 @ 350°/150m, Cuckoo3? @ 20°/200m. Yellow-billed cuckoo (Cuckoo1) flew 

immediately after 1st playback, Cuckoo1 gave knocker call from nearby patch at 230° and 30 m 

away. After Cuckoo1 called, Cuckoo2 knocked from further downstream at 350° and 150 m away. At 

0759 a cuckoo gave a rolling kowlp call from area where Cuckoo1 originally called. At 0801, heard 

knocker call in same area as Cuckoo1. At 0803 a possible third cuckoo (Cuckoo3?) gave fast kowlps

at 20°, 200 m away. At 0804, a possible forth cuckoo (that was extremely small looking), flew in 

from due South. Flew right overhead of observer and into the patch. This patch with diverse stages of 

willow growth and older tall cottonwoods. Aural and visual detections. Breeding classification: 

unconfirmed. 

Bill Williams River NWR – Sandy Wash – 07/04/2006, 0816, 0771770 E, 3796578 N, 32°/ 50 m. 

Yellow-billed cuckoo vocalized an unsolicited knocker call. Aural detection only. Breeding 

classification: unconfirmed. 

Bill Williams River NWR – Sandy Wash – 07/18/2006, 0627, 0771823 E, 3796249 N, Cuckoo1 @ 

350°/20m, Cuckoo2 @ 50°/40m. Two yellow-billed cuckoos (Cuckoo1 and Cuckoo2) vocalizing full 

calls while the observers heard each bird vocalize several times. One observer got a visual on one 

cuckoo perched in a willow, cuckoo then flew up the river channel. Aural and visual detection. 

Breeding classification: unconfirmed. 

Bill Williams River NWR – Sandy Wash – 07/18/2006, 0703, 0771792 E, 3796546 N, 310°/30 m. 

Yellow-billed cuckoo vocalized a full call after 5th playback. Called again at 0719, called again right 

after 2nd vocalization, call came from further downstream. Aural detection only. Breeding 

classification: unconfirmed. 

Bill Williams River NWR – Sandy Wash – 07/18/2006, 0801, 0771636 E, 3796737 N, 180°/10 m. 

Yellow-billed cuckoo vocalized a full, unsolicited call as observer came out of survey trail. Aural 

detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR – Sandy Wash – 07/31/2006, 0625, 0771701 E, 3796093 N, 140°/10 m. 

Yellow-billed cuckoo flew across path in N/NE direction, this was an unsolicited visual detection. A 

couple minutes later, observed cuckoo again near where it was originally seen. Soon after this 

observation another cuckoo kowlped softly from the other side of the patch. Cuckoo continued to 
87

move around and kowlp. Aural and visual detections. Breeding classification: unconfirmed, however 

cuckoo detected at this site during previous survey on 07/04/2006 and 07/18/2006. 

Bill Williams River NWR – Sandy Wash – 07/31/2006, 0734, 0771844 E, 3796410 N, 302°/50 m. 

Yellow-billed cuckoo was kowlping from cottonwoods after 1st playback. Aural detection only. 

Breeding classification: unconfirmed. 

Bill Williams River NWR – Sandy Wash – 07/31/2006, 0751, 0771690 E, 3796681 N, 129°/10 m. 

Yellow-billed cuckoo vocalized a unsolicited call right before the observer was about to play the 

recording. Observed yellow-billed cuckoo flying. Then heard cuckoo calling cross the wash. Later 

during survey saw a cuckoo across the wash near head of research trail and also observed cuckoo with 

a grasshopper in it’s beak in a willow patch. Aural and visual detections. Breeding classification: 

unconfirmed, however, cuckoo detected at this site during previous surveys on 07/04/2006, and 

07/18/2006, and a food carry was observed. 

Fox Wash 

Bill Williams River NWR – Fox Wash – 06/17/2006, 0652, 0771529 E, 3796659 N, 210°/100 m. 

Yellow-billed cuckoo vocalized kowlp call after 1st playback, did not hear it again. Aural detection 

only. Breeding classification: unconfirmed. 

Mosquito Flats 

Bill Williams River NWR - Mosquito Flats – 06/17/2006, 0722, 0769851 E, 3797146 N, 350°/100 m. 

Yellow-billed cuckoo vocalized kowlp call rapidly after 4th playback; played 5th playback because 

observer was not sure they were hearing cuckoo. Cuckoo called once/sec for two minutes. Aural 

detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR - Mosquito Flats – 06/17/2006, 0758, 0769936 E, 3797114 N, 345°/200 m. 

Yellow-billed cuckoo vocalizing kowlp call after 3rd playback may have been the same bird detected 

at 0722, observer accidentally walked only 100 m before doing playback. Aural detection only. 

Breeding classification: unconfirmed. 

Bill Williams River NWR - Mosquito Flats – 06/17/2006, 0904, 0770449 E, 3796998 N, 325°/125 m. 

Yellow-billed cuckoo vocalized once after 1st playback. Aural detection only. Breeding 

classification: unconfirmed. 

Bill Williams River NWR - Mosquito Flats – 06/17/2006, 1055, 0771194 E, 3796635 N, 18°/ 130 m. 

Yellow-billed cuckoo called after 4th and 5th playback (verified with 5th playback). Aural detection 

only. Breeding classification: unconfirmed. 

Bill Williams River NWR - Mosquito Flats – 07/04/2006, 0614, 0769769 E, 3797196 N, 345°/ 40 m. 

Yellow-billed cuckoo vocalized knocker and kowlp from willow after 1st playback, just called once. 

Very dense patch with tamarisk, willow, and mesquite. Aural detection only. Breeding classification: 

unconfirmed. 

Bill Williams River NWR - Mosquito Flats – 07/04/2006, 0700, 0770209 E, 3797027 N, 25°/ 75 m. 

Yellow-billed cuckoo vocalizing knocker and kowlp call after 3rd playback from a thick willow stand. 

Only called once. Aural detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR - Mosquito Flats – 07/04/2006, 0735, 0770627 E, 3797061 N, 320°/ 65 m. 

Yellow-billed cuckoo vocalizing knocker and kowlp call after 2nd playback. Called from 

willow/cottonwood with tamarisk and mesquite understory. Only called once. Aural detection only. 

Breeding classification: unconfirmed. 

Bill Williams River NWR - Mosquito Flats – 07/04/2006, 0753, 0770797 E, 3796836 N, 20°/ 50 m. 

Yellow-billed cuckoo vocalizing knocker call after 2nd playback, knocking call six to seven times. 

Cuckoo called from willow/tamarisk. Aural detection only. Breeding classification: unconfirmed. 
88

Bill Williams River NWR - Mosquito Flats – 07/18/2006, 0608, 0769860 E, 3797118 N, 59°/ 35 m. 

Yellow-billed cuckoo vocalized knocker and kowlp call after 2nd playback. Cuckoo called from 

willow/cottonwood stand. Aural detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR - Mosquito Flats – 07/18/2006, 0654, 0770412 E, 3797025 N, 40°/ 60 m. 

Yellow-billed cuckoo vocalized loud and extended kowlp after 3rd playback, one minute later cuckoo 

called successive knocker calls. Cuckoo call came from cottonwood stand. Aural detection only. 

Breeding classification: unconfirmed. 

Bill Williams River NWR - Mosquito Flats – 07/18/2006, 0712, 0770716 E, 3796997 N, 318°/100 m. 

Yellow-billed cuckoo vocalized rapid knocker call then kowlp call after 1st playback, cuckoo call 

sounding very aggressive, called again 45 seconds later with same kind of call. Cuckoo call coming 

from cottonwood stand. Aural detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR - Mosquito Flats – 07/18/2006, 0758, 0771062 E, 3796691 N, 350°/ 75 m. 

Yellow-billed cuckoo vocalized rapid knocker call, at least two times, after 1st playback. Aural 

detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR - Mosquito Flats – 07/18/2006, 0814, 0771332 E, 3796566 N, 76°/ 25 m. 

Observer took no notes for this detection. Aural detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR - Mosquito Flats – 07/30/2006, 0701, 0770033 E, 3797029 N, 343°/ 65 m. 

Yellow-billed cuckoo responded 10 sec. after 1st playback with a knocker and rapid kowlp calls. 

Calling coming from one of two large (13 m) cottonwood trees that are standing alone in 

mesquite/willow shrubby area just south of the large patch of cottonwoods. Cuckoo called again for 

four minutes. Aural detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR - Mosquito Flats – 07/30/2006, 0955, 0771291 E, 3796569 N, 62°/ 50 m. 

Yellow-billed cuckoo responded after 1st playback with many coo calls. They continued for about 

two minutes. Calling from dense cottonwood/ willow/tamarisk stand just NE of survey trail. Aural 

detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR - Mosquito Flats – 08/13/2006, 0614, 0769767 E, 3797202 N, 340°/ 35 m. 

Yellow-billed cuckoo vocalized knocker call after the 4th playback. Aural detection only. Breeding 

classification: unconfirmed. 

Bill Williams River NWR - Mosquito Flats – 08/13/2006, 0720, 0770450 E, 3796994 N, 327°/ 80 m. 

Yellow-billed cuckoo responded with knocker and kowlps calls after the 1st playback. Aural detection 

only. Breeding classification: unconfirmed. 

Bill Williams River NWR - Mosquito Flats – 08/13/2006, 0806, 0771026 E, 3796703 N, 60°/ 60 m. 

Unsolicited visual detection of yellow-billed cuckoo perching and then flying. Cuckoo stayed around 

small clump of mostly willow with some tamarisk. Cuckoo slowly turning head around, looking all 

around, up and down. Visual detection only. Breeding classification: unconfirmed. 

Saguaro Slot 

Bill Williams River NWR – Saguaro Slot - 06/17/2006, 0656, 0769110 E, 3797902 N, 22°/25 m. 

Yellow-billed cuckoo responded after 2nd playback, flew overhead after 5th playback. Aural 

detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR – Saguaro Slot - 06/17/2006, 1230, 0769322 E, 3797724 N, 320°/ 60 m. CD 

player accidentally played in backpack, yellow-billed cuckoo called right after accidental playback. 

Aural detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR – Saguaro Slot – 07/18/2006, 0547, 0769519 E, 3797574 N, 10°/35 m. 

Yellow-billed cuckoo vocalized a quiet unsolicited knocking call. Observer heard call only one time. 

Aural detection only. Breeding classification: unconfirmed, however cuckoo detected at this site 

during previous survey on 06/17/2006. 
89

Bill Williams River NWR – Saguaro Slot – 07/18/2006, 0611, 0769597 E, 3797406 N, 62°/25 m. 

Yellow-billed cuckoo was heard knocking one time unsolicited. Aural detection only. Breeding 

classification: unconfirmed, however cuckoo detected at this site during previous survey on 

06/17/2006. 

Bill Williams River NWR – Saguaro Slot – 07/18/2006, 0711, 0769679 E, 3797370 N, 130°/ 45 m. 

Yellow-billed cuckoo vocalizing unsolicited knocking and kowlps calls. This call came from where 

previous detection was. Aural detection only. Breeding classification: unconfirmed, however cuckoo 

detected at this site during previous survey on 06/17/2006. 

Bill Williams River NWR – Saguaro Slot – 07/30/2006, 0730, 0769543 E, 3797526 N, Cuckoo1 @ 

42°/40m, Cuckoo2 @ 154°/100m. Observer thought they heard a yellow-billed cuckoo knocking to 

the south as they were marking the point, but it was too far off to know so played two playbacks. A 

yellow-billed cuckoo (Cuckoo1) responded from the northeast. About one minute later cuckoo 

(Cuckoo2) called from the south. Aural detection only. Breeding classification: unconfirmed, 

however cuckoo detected at this site during previous surveys on 06/17/2006 and 07/18/2006. 

Bill Williams River NWR – Saguaro Slot – 07/30/2006, 0948, 0769054 E, 3797997 N, 17°/ 140 m. 

Yellow-billed cuckoo called after 4th playback. Aural detection only. Breeding classification: 

unconfirmed, however cuckoo detected at this site during previous surveys on 06/17/2006 and 

07/18/2006. 

Bill Williams River NWR – Saguaro Slot – 08/13/2006, 0850, 0769391 E, 3797781 N, 224°/ 60 m. 

Yellow-billed cuckoo called after survey was completed. Unsolicited aural detection only. Breeding 

classification: unconfirmed, however cuckoo detected at this site during previous survey on 

06/17/2006 07/18/2006, and 07/30/2006. 

Saguaro Slot Yellow-billed cuckoo Nest (documentation of the one nest found) 

Bill Williams River NWR – Saguaro Slot Nest – 0769377 E, 3797779 N (GPS accuracy 6 m) 

07/18/2006 - YBCU Nest was found during trail maintenance at the Saguaro Slot site in Bill Williams 

NWR. Location: 0769377E, 3797779N, GPS Accuracy was 6 m (Zone 11, Nad 83). Yellow-billed 

While nest searching, heard cuckoo vocalize soft knocker call, which was repeated many times. While 

walking on freshly cut survey trail, flushed cuckoo off the nest. The cuckoo flew 10 m and perched 

on a branch above the trail. Observer got a good look at the cuckoo, then the bird flew off. Nest 

contents, two eggs. Cuckoo nest was located within an impenetrable patch, approx 50 m from the 

river, but near various washes. The nest itself is comprised of mostly tamarisk branches with a few 

willows, loosely constructed. 

07/27/2006 - Revisit – During nest check, the adult cuckoo flushed from the nest and flew to the 

tallest Cottonwood tree in the area (about 25 m away). From the top of the cottonwood, the cuckoo 

began to knock frequently and repeatedly. Nest checkers decided not to use the mirror pole, since the 

cuckoo was obviously distressed, but observers could see at least two eggs from the bottom of the 

nest as they walked under it to exit area. 

07/30/2006 – Revisit – Yellow-billed cuckoo off the nest upon approaching, used mirror pole was 

and observed two white eggs, one appears smaller than the other. Also one nestling, feathers in pin, 

nestling did not lift head or move while observers at the nest. Estimated age of nestling, 5-6 days. 

08/01/2006 - Revisit – Yellow-billed cuckoo on nest, did not flush. Did not disturb cuckoo any 

further. Nest contents unknown. 

08/13/2006 - Revisit - Two eggs still in the nest, one smaller than the other, waited for about 5 min, 

didn't see or hear adult cuckoo or nestling. Did playback; no response; waited 10 minutes no cuckoo 

detected. As surveyor was walking away from nest a cuckoo called, at 224 degrees and 60 m away, 

did not get a visual observation of the bird. 

09/10/2006 - Revisit - Nest still had the one smaller egg in it. No cuckoos were detected near the nest. 
90

Bill Williams River Marsh 

Bill Williams River NWR – Bill Williams River Marsh - 07/05/2006 – 0718, 0768759E 3798405N, 9°, 

60 m. Yellow-billed cuckoo vocalized a knocker call after the 1st playback. Aural detection only. 

Breeding classification: unconfirmed. 

Bill Williams River NWR – Bill Williams River Marsh - 07/05/2006 – 0838, 0769547E 3797742N, 

Cuckoo1 @ 325°/60 m, Cuckoo2 @ 108°/40 m. Yellow-billed cuckoo (Cuckoo1) vocalized an 

unsolicited knocker call. Did not get distance or bearing so played one cuckoo playback. Cuckoo gave 

kowlp call at 60 m and 325°. One minute later a second yellow-billed cuckoo (Cuckoo2) called at 40 

m and 108° in the opposite direction. Aural detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR – Bill Williams River Marsh - 07/19/2006 – 0704, 0769212 E, 3798054 N, 

104°/180 m. Yellow-billed cuckoo called 10 sec after 1st playback. Aural detection only. Breeding 

classification: unconfirmed. 

Bill Williams River NWR – Bill Williams River Marsh - 07/19/2006 – 0722, 0769451 E, 3797863 N, 

Cuckoo1 @ 342°/30 m, Cuckoo2 @ 150°/160 m. Yellow-billed cuckoo (Cuckoo1) responded after 

1st playback with one kowlp call, yellow-billed cuckoo (Cuckoo2) responded to 1st cuckoo after it 

vocalized one kowlp call. Aural detection only. Breeding classification: unconfirmed, however 

cuckoo detected at this site during previous survey on 07/05/2006. 

Bill Williams River NWR – Bill Williams River Marsh - 07/19/2006 – 0759, 0769549 E, 3797750 N, 

274°/60 m. Unsolicited yellow-billed cuckoo calling, came from where 2nd cuckoo detected earlier. 

Aural detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR – Bill Williams River Marsh – 07/31/2006 – 0801, 0769544 E, 3797740 N, 

Cuckoo1 @ 2°/30m, Cuckoo2 @ 287°/45m. Two yellow-billed cuckoos responded tape playback. 

Yellow-billed cuckoo (Cuckoo1) responded after 2nd playback with several coo calls. Cuckoo1 

vocalized coo call off and on for several minutes. After the 5th playback another yellow-billed 

cuckoo (Cuckoo2) responded with knocker call lasting about three seconds from nearby patch of 

willows. This bird only called once. Cuckoo1 gave "coo" call again after the 5th playback. Aural 

detection only. Breeding classification: unconfirmed, however cuckoo detected at this site during 

previous survey on 07/05/2006, and 07/19/2006. 

Bill Williams River NWR – Bill Williams River Marsh – 07/31/2006 – 0946, 0769563 E, 3797573 N, 

Cuckoo1 @ 15°/50m, Cuckoo2 @ 75°/40m. Yellow-billed cuckoo (Cuckoo1) vocalized an 

unsolicited call. Cuckoo2 responded to Cuckoo1 after about one minute with knocker call. Aural 

detection only. Breeding classification: unconfirmed. 

Bill Williams River NWR – Bill Williams River Marsh – 08/14/2006 – 0752, 0769571 E, 3797765 N, 

Cuckoo1 @ 140°/65m, Cuckoo2 @ 170°/45m. Yellow-billed cuckoo (Cuckoo1) vocalized an 

unsolicited knocking call (3-4 times) then gave two kowlp calls, five minutes later yellow-billed 

cuckoo (Cuckoo2) responded with one kowlp call. Aural detection only. Breeding classification: 

unconfirmed, however cuckoos detected at this site during previous survey on 07/05/2006, 

07/19/2006, and 07/31/2006. 

CIBOLA NATIONAL WILDLIFE REFUGE (COLORADO RIVER) 

Cibola North Restoration 

In 2006, there were no yellow-billed cuckoo detections at this site. 

Cibola Nature Trail Restoration 

Cibola NWR – Cibola Nature Trail Restoration - 6/20/06 – 0608, 3694479 N, 716055 E, 290o/30 m. 
91

Yellow-billed cuckoo vocalized after 1st recording. The bird was never seen, but appeared to have 

called from the edge of cottonwoods at the north border of the restoration site. Breeding 

classification: unconfirmed, however cuckoo detected at this site during previous survey on 7/17/06. 

Cibola NWR – Cibola Nature Trail Restoration - 7/17/06 – 0723, 3694204 N, 715965 E, 216o/5 m. 

Yellow-billed cuckoo visually detected after 2nd playback. Bird silently flew towards observer and 

landed nearly above observer. Remained on first perch for approximately 1.5 minutes, then cuckoo 

flew to two other nearby perches before flying out of sight. Appeared very agitated, and bird 

vocalized as surveyor was leaving site. Visual and aural detections. Breeding classification: 

unconfirmed, however cuckoo detected at this site during previous survey on 6/20/06. 

Cibola Eucalyptus Restoration 

In 2006, there were no yellow-billed cuckoo detections at this site. 

Cibola South Restoration 

Cibola NWR – South Restoration - 7/3/06 – 0727, 3684684 N, 715869 E. Yellow-billed cuckoo 

observed flying over trail into mesquite when observer leaving site; thus no bearing or distance taken. 

Detection was visually only, and only seen in flight. Detection location at border of cottonwood 

restoration site. Visual detection only. Breeding classification: unconfirmed. 

Cibola Cross River 

In 2006, there were no yellow-billed cuckoo detections at this site. 

Cibola East Side 

In 2006, there were no yellow-billed cuckoo detections at this site. 

PICACHO STATE RECREATION AREA (COLORADO RIVER) 

Picacho SRA - 8/2/06 – 0729, 3656439 N, 722720 E, 45o/35 m. Yellow-billed cuckoo vocalized 

kowlp call after 1st playback, cuckoo then cooed for five minutes from one spot. The bird then flew 

north into lower willow/mesquite matrix. This bird may have been detected at the next survey point at 

0745. Aural and visual detections. Breeding classification: unconfirmed. 

IMPERIAL NATIONAL WILDLIFE REFUGE (COLORADO RIVER) 

Imperial Paradise 

 In 2006, there were no yellow-billed cuckoo detections at this site. 

Imperial South Restoration 

Imperial NWR – Imperial South Restoration - 6/19/06 – 0536, 3653855 N, 734396 E, 40o/110 m. 

Yellow-billed cuckoo vocalized after 4th playback. While writing notes on this bird, a cuckoo called 

one time at 0544 from within the cottonwood restoration site. While looking for bird in restoration 

site, another cuckoo (or same bird) vocalized from approximately 50 m north of the restoration site in 

what is mostly marsh with scattered trees. Observer suspected that this was the same bird all three 

times moving around in response to playback. Aural detection only. Breeding classification: 

unconfirmed, however cuckoo detected at this site during previous survey on 7/2/06, 7/15/06 and 

07/26/06. 

Imperial NWR – Imperial South Restoration - 7/2/06 – 0619, 3653863 N, 734398 E, 88o/100 m. 

Yellow-billed cuckoo vocalized near opposite side of the restoration site after 3rd playback. Aural 

detection only. Breeding classification: unconfirmed, however cuckoo detected at this site during 

previous survey on 6/19/06 and 7/15/06. 
92

Imperial NWR – Imperial South Restoration - 7/12/06 – 1800, 3654083 N, 734774 E. 

Cuckoo seen by G. Bland at drip (bird bath with drip) near FEMA trailers; sitting on ground, flew up 

into tree upon approach and then flew across clearing towards other buildings, landed in mesquite, 

then flew out over marsh; seen at this spot last year by the WIFL crew. Unsolicited visual detection 

only. 

Imperial NWR – Imperial South Restoration - 7/15/06 – 0610, 3653872 N, 734267 E. 

Surveyor was near the restoration site after cancelling the survey due to high wind when yellowbilled cuckoo was visually detected at edge of restoration site. Bird was seen with food in bill 

(possible cicada?). While perched, the bird gave a quiet series of knocker calls before flying across 

the marsh with food. Unable to relocate bird, but suspected that food was being carried to nest. Visual 

and aural detections. Breeding classification: unconfirmed, however food carry was observed. 

This detection was followed up with non-survey based efforts to confirm the breeding status of the 

bird. On 07/26/2006, two birds were confirmed to be present in the refuge by surveyors using 

vocalizations and radios to pinpoint individual birds. Please see the following entries. 

Imperial NWR – Imperial South Restoration - 7/26/2006 – 0627, 3653837 N, 734406 E. 

One cuckoo seen in restoration site; heard at 0548 vocalized full series of knocker and kowlp calls; 

cuckoo not visually observed until 0627; 35 meters at 316 degrees, very windy. Aural and visual 

detections. Breeding classification: unconfirmed, however cuckoo detected at this site during previous 

survey on 6/19/06 and 7/15/06 and food carry was observed on 07/15/2006. 

Imperial NWR – Imperial South Restoration - 7/26/2006 – 0816, 3654086 N, 734294 E. 

Did playback in marsh at two points; one near cottonwood restoration site, one inside 12 foot tall 

tamarisk patch in marsh; got response at second point from within tamarisk; a few moments earlier 

the second surveyor had heard a cuckoo across the road from main restoration site; approximately 

300-400 meters from where the first cuckoo was heard; Surveyors thought this meant there were two 

birds but on 07/30/06 survey efforts, but did not yield detections. 40 meter at 316 and 333 degrees. 

Aural detection only. Breeding classification: unconfirmed, however cuckoo detected at this site 

during previous survey on 6/19/06 and 7/15/06 and food carry was observed on 07/15/2006. 

MITTRY LAKE STATE WMA/PRATT RESTORATION (COLORADO RIVER) 

In 2006, there were no yellow-billed cuckoo detections at this site. 

GILA/COLORADO RIVER CONFLUENCE (GILA AND COLORADO RIVER) 

Colorado River 

Gila/Colorado River Confluence - Colorado River - 7/1/06 – 0817, 3625239 N, 731334 E, 

Cuckoo188o/60 m, Cuckoo2 350o/40 m. Yellow-billed cuckoo (Cuckoo1) vocalized after 1st 

playback. This bird continued calling several more times, and 40 seconds after it stopped calling a 

second cuckoo (Cuckoo2) was heard calling 80 meters away at 350o on the other side of the river. 

Two minutes after that call the first bird called again from the same exact spot. No bird was seen to 

cross the river, so these are considered different birds. Aural detection only. Breeding classification: 

unconfirmed, however cuckoo detected at this site during previous survey on 7/14/06. 

Gila/Colorado River Confluence - Colorado River - 7/1/06 – 1014, 3623855 N, 730639 E, 10o/100 m. 

Shortly after the 5th playback and after leaving the point, a yellow-billed cuckoo responded near the 

point where the surveyor had been. The bird called three separate times. Aural detection only. 

Breeding classification: unconfirmed. 

Gila/Colorado River Confluence - Colorado River - 7/1/06 – 1121, 3623065 N, 729526 E, Cuckoo1 

342o/120 m, Cuckoo2 290o/40 m. Yellow-billed cuckoo (Cuckoo1) vocalized after 2nd playback. 

While that bird was calling, a different cuckoo (Cuckoo2) flew out of the cottonwoods directly in 

front of the observer at 290o/40 m and proceeded to fly across the river where it perched in a small 
93

willow. This bird then flew back across the river to a cottonwood where it originally came from. Just 

after landing, it called quietly one time and ascended into the canopy and out of sight. While that bird 

was being watched, the other cuckoo was heard calling two different times in the same area where it 

was first detected. This confirms that two birds were present. Aural and visual detections. Breeding 

classification: unconfirmed. 

Gila/Colorado River Confluence - Colorado River - 7/14/06 – 0708, 3625378 N, 731386 E, 250o/45 

m. Yellow-billed cuckoo vocalized knocker calls after 4th playback. This bird was also heard 

spontaneously calling by another surveyor that passed this location at 0601 on the same morning. 

Aural detection only. Breeding classification: unconfirmed, however cuckoo detected at this site 

during previous survey on 7/1/06. 

Gila/Colorado River Confluence - Colorado River - 7/14/06 – 0914, 3623317 N, 730021 E, 335o/10 

m. A yellow-billed cuckoo was heard calling between survey points. The bird was fairly close to one 

point, and likely was a delayed response to broadcasted recordings. Bird gave quiet series of knocks 

twice, then was silent. Aural detection only. Breeding classification: unconfirmed. 

Gila River 

Gila/Colorado River Confluence - Gila River - 6/16/06 – 0721, 3623021 N, 731460 E, 30o/100 m. 

Yellow-billed cuckoo initially heard at previous point, but bird was distant with construction noise in 

background, so identification uncertain. At next point, a cuckoo was heard more clearly after third 

recording, and bird approached surveyor and continued calling while remaining out of sight. Aural 

detection only. Breeding classification: unconfirmed. 

YUMA WEST WETLANDS (COLORADO RIVER) 

In 2006, no yellow-billed cuckoos were detected at this site. 

LIMITROPHE DIVISION (COLORADO RIVER) 

Limitrophe Division North 

Limitrophe Division North - 6/18/06 – 0623, 3615483 N, 710533 E, 283o/25 m. Yellow-billed cuckoo 

observed flying into tree on riparian edge after 3rd playback. Bird perched out of site and was not 

seen again. One surveyor remained at site and heard bird call once after five minutes. Visual and aural 

detections. Breeding classification: unconfirmed. 

Limitrophe Division North - 6/18/06 – 0640, 3615653 N, 710781 E, 315o/65 m. Yellow-billed cuckoo 

vocalized cooing calls repeatedly after 4th playback. Could not see bird; may have been on the 

Mexico side of river. Aural detection only. Breeding classification: unconfirmed. 

Limitrophe Division North - 6/28/06 – 0530, 3620561 N, 712919 E, 276o/50 m. As surveyors were 

walking to next point, a yellow-billed cuckoo was heard vocalizing a series of two knocker calls 

unsolicited. This bird was then heard again at 0540 from the next survey point after 4th playback. 

Aural detection only. Breeding classification: unconfirmed, however cuckoo detected at this site 

during previous survey on 7/16/06 and 7/28/06. 

Limitrophe Division North - 7/16/06 – 0954, 3620234 N, 712854 E, 301o/25 m. Yellow-billed cuckoo 

flew from surveyor side of road from low bush. Bird flew over road and dropped down into 

vegetation. Unable to relocate bird. Visual detection only. Breeding classification: unconfirmed, 

however cuckoo detected at this site during previous survey on 6/28/06 and 7/28/06. 

Limitrophe Division North - 7/28/06 – 0612, 3620633 N, 712951 E, 187o/75 m. Yellow-billed cuckoo 

vocalized two kowlp calls on side of the road that is away from the best habitat. Aural detection only. 

Breeding classification: unconfirmed, however cuckoo detected at this site during previous survey on 

6/28/06 and 7/16/06. 
94

Limitrophe Division South 

In 2006, no yellow-billed cuckoos were detected at this site. 

GILA RIVER HIGHWAY 95 (GILA RIVER) 

Gila 95 Bridge 

In 2006, there were no yellow-billed cuckoo detections at this site. 

Gila 95 Canal 

In 2006, there were no yellow-billed cuckoo detections at this site. 

Gila 95 Tall Tamarisk 

In 2006, there were no yellow-billed cuckoo detections at this site. 

GILA RIVER/LIGURTA (GILA RIVER) 

In 2006, no yellow-billed cuckoos were detected in the Ligurta Patch. 

GILA RIVER/WELLTON (GILA RIVER) 

Gila River/Wellton - 6/26/06 – 0943, 3619183 N, 762891 E, 2o/80 m. Yellow-billed cuckoo vocalized 

cooing call (five times) after 4th playback. The bird then moved closer and vocalized one knocker

call. Surveyors searched the area for 20 minutes, but did not find the bird, however, heard one more 

knocker call. Aural detection only. Breeding classification: unconfirmed. 

GILA RIVER/QUIGLEY POND WMA (GILA RIVER) 

Gila River/Quigley Pond WMA - 6/26/06 – 0646, 3625636 N, 222511 E (zone 12), 217o/18 m. After 

5th playback, surveyor was walking between points when a silent yellow-billed cuckoo was visually 

detected. The bird was foraging along a scrubby edge of mixed willows and tamarisk. The bird flew 

in the direction of the place where the playback was completed, perched in vegetation at the edge of 

the riparian zone, then flew into a field of 1m tall cotton (Malvaceae spp.) row crops where it 

appeared to be foraging before flying back into riparian. Visual detections only. Breeding 

classification: unconfirmed. 
95

Appendix 3 

Incidental yellow-billed cuckoo observations in the lower Colorado River Watershed along the 

Virgin and Muddy rivers, Nevada, lower Colorado, Bill William and Gila rivers, Arizona and 

California, 2006. 

Throughout the 2006 field season yellow-billed cuckoos were occasionally detected independent of 

surveys. Many of 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 Ehrenberg, 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. However, SWCA detected at least two cuckoos at the Limitrophe Division 

South site; we did not detect any cuckoos here. This is likely due to a large patch of riparian habitat away 

from the road at this site that we did not survey because of security concerns. Also, our incidental 

sightings at Imperial NWR helped determine that cuckoos probably breed at this site. 

Date Time Observer No. Location UTM* Comments 

6/13/2006 NA SWCA 1 Lake Mead/Grand NA Heard calling (kowlp) for approx. 

 Canyon 10 minutes; RM 286N 

7/3/2006 NA SWCA 1 Lake Mead/Chuckwalla NA Observed singing throughout 

 Cove morning from top of willow. 

7/17/2006 NA SWCA 1 Lake Mead/Chuckwalla NA Individual observed and heard 

 Cove calling. 

7/13/2006 NA SWCA NA Bill Williams/Cave NA Calls heard. 

 Wash

7/13/2006 NA SWCA NA Bill Williams River NA Calls heard in a large cottonwood. 

 NWR/Mineral Wash

6/20/2006 NA SWCA 1 Bill Williams River NA Individual observed skulking 

 NWR/Site 2 through vegetation. 

7/2/2006 NA SWCA NA Bill Williams River NA Calls heard at a distance. 

 NWR/Site 3 

6/19/2006 NA SWCA 1 Ehrenberg, Arizona NA Individual observed flying over 

 Colorado River; one vocalization 

 heard.

NA NA SWCA 1 Near Blythe NA SWCA employee saw a cuckoo 

 fly across the road approx. 3 miles 

 south of Blythe. 

7/3/2006 NA SWCA NA Cibola NWR/Nature NA NA 

 Trail 

7/4/2006 NA SWCA NA Cibola NWR/Site 2 NA NA 

7/5/2006 700 SWCA 1 Picacho SRA E722493, SWCA employee heard YBCU 

 N3656587 calling. 

6/28/2006 1753 U of AZ 1 Imperial NWR E734892, Cuckoo heard calling in evening 

 N3652768 while in transit to a rail survey. 
96

Appendix 3 (continued) 

Date Time Observer No. Location UTM* Comments 

7/12/2006 1800 USGS 1 Imperial NWR E734744, YBCU seen by G. Bland at water 

 N3654083 drip near Imperial NWR staff 

 housing, then flew out over 

 marsh. Seen at this spot last year 

 by SWCA crew. 

7/26/2006 627 USGS 1 Imperial NWR E734406, One YBCU gave full series of 

 N3653837 knocks and kowlps at 0548 in 

 restoration site; seen 

 at 0627 by G. Bland and 

 S. Krantz.

7/26/2006 816 USGS 2 Imperial NWR E734294, Did playback in marsh at 2 points 

 N3654086 and YBCU responded at second 

 point from within tamarisk. A few 

 moments later a second YBCU 

 was heard back across the road 

 from restoration site. 

6/28/2006 NA SWCA 2 Gila/Colorado Confluence NA At least two individuals heard 

 counter singing. 

6/29/2006 1001 USGS 2 Gila/Colorado Confluence E731880, Two YBCU flew across road 

 N3623536 while on cuckoo relocation 

 mission; heard one give muted 

 series of knocks. Seen near 

 survey.

6/17/2006 NA SWCA 1 Limitrophe Division NA Individual heard calling for 

 South approx. 10 min., then observed in 

 willow. Playback by USGS crew 

 may have been conducted simul- 

 taneously with this detection. 

6/20/2006 NA SWCA NA Limitrophe Division E707398, Heard calling in the distance. 

 South N3604281 

7/1/2006 NA SWCA 2 Limitrophe Division NA At least two individuals heard 

 South counter singing, one of which was 

 observed. 

* Zone 11, NAD 83 
97

Appendix 4 

Appendices 4.1 through 4.20 include aerial photographs of yellow-billed cuckoo survey points, and 

detections according to survey period at sites along the Virgin and Muddy rivers, Nevada, lower Colorado 

and Gila rivers, Arizona and California 2006. 

Appendix 4.1. Littlefield Bridge, NV 

The following orthorectified aerial photo shows the Littlefield Bridge, NV, Yellow-billed Cuckoo survey 

area, 2006. 
98

Appendix 4.1. Littlefield Bridge, NV (continued) 

The following orthorectified aerial photo shows Yellow-billed Cuckoo survey points at Littlefield Bridge, 

NV, 2006. No cuckoos were detected at this area in 2006. Red boundary line represents yellow-billed 

cuckoo survey habitat patch. 
99

Appendix 4.2. Mesquite Bridge, NV 

The following orthorectified aerial photo shows the Mesquite Bridge NV, Yellow-billed Cuckoo survey 

area, 2006. 
100

Appendix 4.2. Mesquite Bridge, NV (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Mesquite Bridge NV, 2006. Red boundary line represents yellow-billed cuckoo survey 

habitat patch. 
101

Appendix 4.3. Pahranagat National Wildlife Refuge, NV 

The following orthorectified aerial photo shows the Pahranagat National Wildlife Refuge NV yellowbilled cuckoo survey area, 2006. 
102

Appendix 4.3. Pahranagat National Wildlife Refuge, NV (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Pahranagat National Wildlife Refuge, NV, Pahranagat North, 2006. Red boundary line 

represents yellow-billed cuckoo survey habitat patch. 
103

Appendix 4.3. Pahranagat National Wildlife Refuge, NV (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Pahranagat 

National Wildlife Refuge, NV, Pahranagat East, 2006. No cuckoos were detected at this site in 2006. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 
104

Appendix 4.3. Pahranagat National Wildlife Refuge, NV (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Pahranagat 

National Wildlife Refuge, NV, Pahranagat West, 2006. No cuckoos were detected at this site in 2006. 

Red boundary line represents yellow-billed cuckoo survey habitat patch. 
105

Appendix 4.3. Pahranagat National Wildlife Refuge, NV (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Pahranagat 

National Wildlife Refuge, NV, Pahranagat South, 2006. No cuckoos were detected at this site in 2006. 

Red boundary line represents yellow-billed cuckoo survey habitat patch. 
106

Appendix 4.4. Overton Wildlife Management Area, NV 

The following orthorectified aerial photo shows the Overton Wildlife Management Area, NV yellowbilled cuckoo survey area, 2006. 
107

Appendix 4.4. Overton Wildlife Management Area, NV (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Overton Wildlife Management Area, NV, Honeybee Pond, 2006. Red boundary line 

represents yellow-billed cuckoo survey habitat patch. 
108

Appendix 4.4. Overton Wildlife Management Area, NV (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Overton Wildlife 

Management Area, NV, Overton North, 2006. No cuckoos were detected at this site in 2006. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 
109

Appendix 4.4. Overton Wildlife Management Area, NV (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Overton Wildlife 

Management Area, NV, Overton Tamarisk, 2006. No cuckoos were detected at this site in 2006. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 
110

Appendix 4.4. Overton Wildlife Management Area, NV (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Overton Wildlife Management Area, NV, Overton Wildlife, 2006. Red boundary line 

represents yellow-billed cuckoo survey habitat patch. 
111

Appendix 4.5. Grand Canyon National Park/Lake Mead National Recreation Area, AZ 

The following orthorectified aerial photo shows the Grand Canyon National Park/ Lake Mead National 

Recreation Area, AZ, yellow-billed cuckoo survey area, 2006. 
112

Appendix 4.5. Grand Canyon National Park/Lake Mead National Recreation Area, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Grand Canyon 

National Park/Lake Mead National Recreation Area, AZ, Spencer Canyon, 2006. No cuckoos were 

detected at this site in 2006. Red boundary line represents yellow-billed cuckoo survey habitat patch. 
113

Appendix 4.5. Grand Canyon National Park/Lake Mead National Recreation Area, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Grand Canyon National Park/Lake Mead National Recreation Area, AZ, RM 274.5, 2006. 

Red boundary line represents yellow-billed cuckoo survey habitat patch. 
114

Appendix 4.5. Grand Canyon National Park/Lake Mead National Recreation Area, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Grand Canyon 

National Park/Lake Mead National Recreation Area, AZ, River Delta/RM 285.3N, 2006. No cuckoos 

were detected at this site in 2006. Red boundary line represents yellow-billed cuckoo survey habitat 

patch. 
115

Appendix 4.5. Grand Canyon National Park/Lake Mead National Recreation Area, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Grand Canyon National Park/Lake Mead National Recreation Area, AZ, Cuckoo Beach, 

2006. Red boundary line represents yellow-billed cuckoo survey habitat patch. 
116

Appendix 4.5. Grand Canyon National Park/Lake Mead National Recreation Area, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Grand Canyon National Park/Lake Mead National Recreation Area, AZ, Iceberg Ridge, 2006. 

Red boundary line represents yellow-billed cuckoo survey habitat patch. 
117

Appendix 4.5. Grand Canyon National Park/Lake Mead National Recreation Area, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Grand Canyon National Park/Lake Mead National Recreation Area, AZ, Chuckwalla Cove, 

2006. Red boundary line represents yellow-billed cuckoo survey habitat patch. 
118

Appendix 4.6. Lake Mohave, AZ 

The following orthorectified aerial photo shows Lake Mohave, AZ yellow-billed cuckoo survey area, 

2006. 
119

Appendix 4.6. Lake Mohave, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Lake Mohave, AZ, 

Waterwheel Cove, 2006. No cuckoos were detected at this site in 2006. Red boundary line represents 

yellow-billed cuckoo survey habitat patch. 
120

Appendix 4.6. Lake Mohave, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Lake Mohave, AZ, 

Mohave Patch, 2006. No cuckoos were detected at this site in 2006. Red boundary line represents yellowbilled cuckoo survey habitat patch. 
121

Appendix 4.7. Havasu National Wildlife Refuge, AZ 

The following orthorectified aerial photo shows the Havasu National Wildlife Refuge, AZ yellow-billed 

cuckoo survey area, 2006. 
122

Appendix 4.7. Havasu National Wildlife Refuge, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Havasu National Wildlife Refuge area, AZ, Pintail Slough, 2006. Red boundary line 

represents yellow-billed cuckoo survey habitat patch. 
123

Appendix 4.7. Havasu National Wildlife Refuge, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Havasu National 

Wildlife Refuge area, AZ, North Dike, 2006. No cuckoos were detected at this site in 2006. Red boundary 

line represents yellow-billed cuckoo survey habitat patch. 
124

Appendix 4.7. Havasu National Wildlife Refuge, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Havasu National 

Wildlife Refuge area, AZ, Topock Marsh Restoration, 2006. No cuckoos were detected at this site in 

2006. Red boundary line represents yellow-billed cuckoo survey habitat patch. 
125

Appendix 4.7. Havasu National Wildlife Refuge, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Havasu National 

Wildlife Refuge area, AZ, Sacramento Wash, 2006. No cuckoos were detected at this site in 2006. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 
126

Appendix 4.7. Havasu National Wildlife Refuge, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Havasu National 

Wildlife Refuge area, AZ, Havasu Tamarisk, 2006. No cuckoos were detected at this site in 2006. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 
127

Appendix 4.7. Havasu National Wildlife Refuge, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Havasu National 

Wildlife Refuge area, AZ, Topock Tamarisk, 2006. No cuckoos were detected at this site in 2006. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 
128

Appendix 4.8. Bill Williams National Wildlife Refuge, AZ 

The following orthorectified aerial photo shows the Bill Williams National Wildlife Refuge, AZ, survey, 

2006. 
129

Appendix 4.8. Bill Williams National Wildlife Refuge, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Bill Williams National Wildlife Refuge, AZ, Cave Wash, 2006. Red boundary line represents 

yellow-billed cuckoo survey habitat patch. 
130

Appendix 4.8. Bill Williams National Wildlife Refuge, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Bill Williams National Wildlife Refuge, AZ, Mineral Wash, 2006. Red boundary line 

represents yellow-billed cuckoo survey habitat patch. 
131

Appendix 4.8. Bill Williams National Wildlife Refuge, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Bill Williams National Wildlife Refuge, AZ, Big Bend, 2006. Red boundary line represents 

yellow-billed cuckoo survey habitat patch. 
132

Appendix 4.8. Bill Williams National Wildlife Refuge, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Bill Williams National Wildlife Refuge, AZ, Gibraltar Rock, 2006. Red boundary line 

represents yellow-billed cuckoo survey habitat patch. 
133

Appendix 4.8. Bill Williams National Wildlife Refuge, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Bill Williams National Wildlife Refuge, AZ, Sandy Wash, 2006. Red boundary line 

represents yellow-billed cuckoo survey habitat patch. 
134

Appendix 4.8. Bill Williams National Wildlife Refuge, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Bill Williams National Wildlife Refuge, AZ, Fox Wash, 2006. Red boundary line represents 

yellow-billed cuckoo survey habitat patch. 
135

Appendix 4.8. Bill Williams National Wildlife Refuge, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Bill Williams National Wildlife Refuge, AZ, Mosquito Flats, 2006. Red boundary line 

represents yellow-billed cuckoo survey habitat patch. 
136

Appendix 4.8. Bill Williams National Wildlife Refuge, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Bill Williams National Wildlife Refuge, AZ, Saguaro Slot, 2006. Red boundary line 

represents yellow-billed cuckoo survey habitat patch. 
137

Appendix 4.8. Bill Williams National Wildlife Refuge, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Bill Williams National Wildlife Refuge, AZ, Bill Williams River Marsh, 2006. Red boundary 

line represents yellow-billed cuckoo survey habitat patch. 
138

Appendix 4.9. Cibola National Wildlife Refuge, AZ 

The following orthorectified aerial photo shows the Cibola National Wildlife Refuge area, AZ yellowbilled cuckoo survey, 2006. 
139

Appendix 4.9. Cibola National Wildlife Refuge, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Cibola National 

Wildlife Refuge area, AZ, Cibola North Restoration, 2006. No cuckoos were detected at this site in 2006. 

Red boundary line represents yellow-billed cuckoo survey habitat patch. 
140

Appendix 4.9. Cibola National Wildlife Refuge, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Cibola National Wildlife Refuge area, AZ, Cibola Nature Trail Restoration, 2006. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 
141

Appendix 4.9. Cibola National Wildlife Refuge, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Cibola National 

Wildlife Refuge area, AZ, Cibola Eucalyptus Restoration, 2006. No cuckoos were detected at this site in 

2006. Red boundary line represents yellow-billed cuckoo survey habitat patch. 
142

Appendix 4.9. Cibola National Wildlife Refuge, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Cibola National Wildlife Refuge area, AZ, Cibola South Restoration, 2006. Red boundary 

line represents yellow-billed cuckoo survey habitat patch. 
143

Appendix 4.9. Cibola National Wildlife Refuge, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Cibola National 

Wildlife Refuge area, AZ, Cibola Cross River, 2006. No cuckoos were detected at this site in 2006. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 
144

Appendix 4.9. Cibola National Wildlife Refuge, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Cibola National 

Wildlife Refuge area, AZ, Cibola East Side, 2006. No cuckoos were detected at this site in 2006. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 
145

Appendix 4.10. Picacho State Recreation Area, CA 

The following orthorectified aerial photo shows the Picacho SRA, CA yellow-billed cuckoo survey site, 

2006. 

 
146

Appendix 4.10. Picacho State Recreation Area, CA (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Picacho SRA, CA along the lower Colorado River, CA, 2006. Red boundary line represents 

yellow-billed cuckoo survey habitat patch. 
147

Appendix 4.11. Imperial National Wildlife Refuge, AZ 

The following orthorectified aerial photo shows the Imperial National Wildlife Refuge, AZ yellow-billed 

cuckoo survey area, 2006. 
148

Appendix 4.12. Imperial National Wildlife Refuge, CA (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Imperial National 

Wildlife Refuge, CA, Imperial Paradise, 2006. No cuckoos were detected at this site in 2006. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 
149

Appendix 4.11. Imperial National Wildlife Refuge, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Imperial National Wildlife Refuge, AZ, Imperial South Restoration, 2006. Red boundary line 

represents yellow-billed cuckoo survey habitat patch. 
150

Appendix 4.13. Mittry Lake WMA/Pratt Restoration, AZ 

The following orthorectified aerial photo shows the Mittry Lake WMA/Pratt Restoration, AZ yellowbilled cuckoo survey area, 2006. 
151

Appendix 4.13. Mittry Lake WMA/Pratt Restoration, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Mittry Lake 

WMA/Pratt Restoration, AZ, 2006. No cuckoos were detected at this site in 2006. Red boundary line 

represents yellow-billed cuckoo survey habitat patch. 
152

Appendix 4.14. Gila/Colorado River Confluence, AZ 

The following orthorectified aerial photo shows the Gila/Colorado River Confluence, AZ yellow-billed 

cuckoo survey area, 2006. 
153

Appendix 4.14. Gila/Colorado River Confluence, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Gila/Colorado River Confluence, AZ, Colorado River, 2006. Red boundary line represents 

yellow-billed cuckoo survey habitat patch. 
154

Appendix 4.14. Gila/Colorado River Confluence, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

locations at Gila/Colorado River Confluence, AZ, Gila River, 2006. Red boundary line represents yellowbilled cuckoo survey habitat patch. 
155

Appendix 4.15. Yuma West Wetlands, AZ 

The following orthorectified aerial photo shows the Yuma West Wetlands, AZ, yellow-billed cuckoo 

survey area, 2006. 
156

Appendix 4.15. Yuma West Wetlands, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

location at Yuma West Wetlands, AZ, 2006. Red boundary line represents yellow-billed cuckoo survey 

habitat patch. 
157

Appendix 4.16. Limitrohpe Division, AZ 

The following orthorectified aerial photos shows the Limitrophe Division, AZ yellow-billed cuckoo 

survey area, 2006. 
158

Appendix 4.16. Limitrohpe Division, AZ (continued) 

The following orthorectified aerial photos shows yellow-billed cuckoo survey points and detection 

locations at Limitrophe Division, AZ, Limitrophe Division North, 2006. Red boundary line represents 

yellow-billed cuckoo survey habitat patch. 

 
159

Appendix 4.16. Limitrohpe Division, AZ (continued) 

The following orthorectified aerial photos shows yellow-billed cuckoo survey points at Limitrophe 

Division, AZ, Limitrophe Division South, 2006. No cuckoos were detected at this site in 2006. Red 

boundary line represents yellow-billed cuckoo survey habitat patch. 
160

Appendix 4.17. Gila River Highway 95, AZ 

The following orthorectified aerial photo shows the Gila River Highway 95, AZ yellow-billed cuckoo 

survey area, 2006. 
161

Appendix 4.17. Gila River Highway 95, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Gila River 

Highway 95, AZ, Gila 95 Bridge, 2006. No cuckoos were detected at this site in 2006. Red boundary line 

represents yellow-billed cuckoo survey habitat patch. 
162

Appendix 4.17. Gila River Highway 95, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Gila River 

Highway 95, AZ, Gila 95 Canal, 2006. No cuckoos were detected at this site in 2006. Red 

boundary line represents yellow-billed cuckoo survey habitat patch.
163

Appendix 4.17. Gila River Highway 95, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Gila River 

Highway 95, AZ, Gila 95 Tall Tamarisk, 2006. No cuckoos were detected at this site in 2006. 

Red boundary line represents yellow-billed cuckoo survey habitat patch.
164

Appendix 4.18. Gila River/Ligurta, AZ 

The following orthorectified aerial photo shows the Gila River/Ligurta, AZ yellow-billed cuckoo survey 

area, 2006. 
165

Appendix 4.18. Gila River/Ligurta, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points at Gila River/ 

Ligurta, AZ, 2006. No cuckoos were detected at this site in 2006. Red boundary line represents 

yellow-billed cuckoo survey habitat patch.
166

Appendix 4.19. Gila River/Wellton, AZ 

The following orthorectified aerial photo shows the Gila River/Wellton, AZ yellow-billed cuckoo survey 

area, 2006. 
167

Appendix 4.19. Gila River/Wellton, AZ (continued) 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and detection 

location at Gila River/Wellton, AZ, 2006. Red boundary line represents yellow-billed cuckoo survey 

habitat patch.
168

Appendix 4.20. Gila River/Quigley Pond WMA, AZ 

The following orthorectified aerial photo shows the Gila River/Quigley Pond WMA, AZ yellow-billed 

cuckoo survey area along the Gila River, 2006. 
169

Appendix 4.20. Gila River/Quigley Pond WMA, AZ 

The following orthorectified aerial photo shows yellow-billed cuckoo survey points and cuckoo detection 

location at Gila River/Quigley Pond WMA, AZ, along the Gila River, 2006. Red boundary line represents 

yellow-billed cuckoo survey habitat patch. 

 
170

Appendix 5 

List of other bird species observed during 2006 yellow-billed cuckoo surveys, in the lower 

Colorado River Watershed along the Virgin and Muddy rivers, Nevada, lower Colorado, Bill 

William and Gila rivers, Arizona and California. 

Common Name Scientific Name 1 2 3 4 

Littlefield Bridge, City of Littlefield (Virgin River) 

Great Blue Heron Ardea herodias - X - - 

White-faced Ibis Plegadis chihi - - X - 

Common Black Hawk** Buteogallus anthracinus X X X - 

Red-tailed Hawk Buteo jamaicensis - X - - 

Peregrine Falcon Falco peregrinus - - X - 

Gambel’s Quail Callipepla gambelii - - X - 

Killdeer Charadrius vociferus - X - - 

Greater Yellowlegs Tringa melanoleuca - - X - 

Spotted Sandpiper Actitus macularia - X X - 

Long-billed Curlew Numenius americanus - X - - 

Rock Pigeon Columba livia - X X - 

Mourning Dove Zenaida macroura X X - - 

White-winged Dove Zenaida asiatica - - X - 

Greater Roadrunner Geococcyx californianus - X - - 

Ladder-backed Woodpecker Picoides scalaris - - X - 

Black Phoebe Sayornis nigricans X X X - 

Say’s Phoebe Sayornis saya - X - - 

Brown-crested Flycatcher Myiarchus tyrannulus X X X - 

Western Kingbird Tyrannus verticalis X X X - 

Bell’s Vireo Vireo bellii - X - - 

Common Raven Corvus corax X - - - 

Violet-green Swallow Tachycineta thalassina X - - - 

Cliff Swallow Petrochelidon pyrrhonota - X - - 

Northern Rough-winged Swallow Stelgidopteryx serripennis X X - - 

Canyon Wren Catherpes mexicanus X X X - 

Rock Wren Salpinctes obsoletus - - X - 

Black-tailed Gnatcatcher Polioptila melanura - X - - 

Yellow Warbler Dendroica petechia X X - - 

Common Yellowthroat Geothlypis trichas X - X - 

Yellow-breasted Chat Icteria virens X X X - 

Summer Tanager Piranga rubra - X X - 

Abert’s Towhee Pipilo aberti - X - - 

Song Sparrow Melospiza melodia X X X - 

Red-winged Blackbird Agelaius phoeniceus - X - - 

Great-tailed Grackle Quiscalus mexicanus - - X - 

Brown-headed Cowbird Molothrus ater - X X - 

Bullock’s Oriole Icterus bullockii X - - - 

House Finch Carpodacus mexicanus X X - - 

Lesser Goldfinch Carduelis psaltria - X X - 

Mesquite Bridge, City of Mesquite (Virgin River) 

Mallard Anas platyrynchos - X X - 

Green-winged Teal Anas creeca - - X - 

Northern Shoveler Anas clypeta - - - - 

Cinnamon Teal Anas cyanoptera - - - - 
171

Appendix 5 (continued) 

Common Name Scientific Name 1 2 3 4 

Mesquite Bridge (continued) 

Green Heron Butorides virescens - X X - 

Snowy Egret Egretta thula - X X - 

Great Blue Heron Ardea herodias X X X - 

White-faced Ibis Plegadis chihi - X X - 

Turkey Vulture Cathartes aura - - X - 

Northern Harrier Circus cyaneus X X - - 

Prairie Falcon Falco mexicanus - - - - 

Gambel’s Quail Callipepla gambelii - X X - 

Clapper Rail Rallus longirostris - X - - 

Killdeer Charadrius vociferous X X X - 

Spotted Sandpiper Actitus macularia X X X - 

Mourning Dove Zenaida macroura X X X - 

Yellow-billed Cuckoo Coccyzus americanus - X - - 

Greater Roadrunner Geococcyx californianus - - - - 

Lesser Nighthawk Chordeiles acutipennis - - - - 

Rufous Humminbird Selasphorus rufus - - - - 

Northern Flicker (red-shafted) Colaptes auratus - - - - 

Ladder-backed Woodpecker Picoides scalaris - X X - 

Black Phoebe Sayornis nigricans - X X - 

Ash-throated Flycatcher Myiarchus cinerascens - X - - 

Western Kingbird Tyrannus verticalis - X X - 

Loggerhead Shrike Lanius ludovicianus - - - - 

Bell’s Vireo Vireo bellii X X - - 

American Crow Corvus brachyrhynchos - - - - 

Common Raven Corvus corax - X X - 

Tree Swallow Tachycineta bicolor - - - - 

Cliff Swallow Petrochelidon pyrrhonota - X X - 

Northern Rough-winged Swallow Stelgidopteryx serripennis - X X - 

Barn Swallow Hirundo rustica - - - - 

Verdin Auriparus flaviceps - X - - 

Black-tailed Gnatcatcher Polioptila nigriceps - X - - 

American Robin Turdus migratorius - - - - 

Crissal Thrasher Toxostoma crissale - - - - 

Lucy’s Warbler Vermivora luciae - X - - 

Yellow Warbler Dendroica petechia X X X - 

Wilson’s Warbler Wilsonia pusilla - - - - 

Common Yellowthroat Geothlypis trichas X X X - 

Yellow-breasted Chat Icteria virens X X X - 

Green-tailed Towhee Pipilo chlorurus - X - - 

Abert’s Towhee Pipilo aberti - X - - 

Chipping Sparrow Spizella passerine - - - n/a 

Song Sparrow Melospiza melodia X X X n/a 

Vesper Sparrow Pooecetes gramineus - - - n/a 

Blue Grosbeak Guiraca caerulea - X X n/a 

Lazuli Bunting Passerina amoena - - - n/a 

Red-winged Blackbird Agelaius phoeniceus X X X n/a 

Great-tailed Grackle Quiscalus mexicanus X X X n/a 

Brown-headed Cowbird Molothrus ater X X X n/a 

House Finch Carpodacus mexicanus - X X n/a 

Lesser Goldfinch Carduelis psaltria X - X n/a 
172

Appendix 5 (continued) 

Common Name Scientific Name 1 2 3 4 

Pahranagat National Wildlife Refuge (White River) 

Canada Goose Branta canadensis X X - X 

Mallard Anas platyrynchos - X - X 

Northern Pintail Anas acuta - - - X 

American Wigeon Anas Americana - - - X 

Northern Shoveler Anas clypeata - - - X 

Blue-winged Teal Anas discors - - X X 

Cinnamon Teal Anas cyanoptera - - - X 

Ruddy Duck Oxyura jamaicensis - - - X 

Pied-billed Grebe Podilymbus podiceps - X X X 

Western Grebe Aechmophorus occidentalis X X X X 

Clark’s Grebe Aechmophorus clarkii - X X X 

Black-crowned Night Heron Nycticorax nycticorax X X X - 

Snowy Egret Egreta thula - - X X 

Great Egret Ardea alba - - - X 

Great Blue Heron Ardea herodias X X X X 

White-faced Ibis Plegadis chihi - - X X 

Turkey Vulture Cathartes aura X X X X 

Northern Harrier Circus cyaneus X - X X 

Sharp-shinned Hawk Accipiter striatus - - - X 

Cooper’s Hawk Accipiter cooperii X - - X 

Red-shouldered Hawk Buteo lineatus - - - X 

Red-tailed Hawk Buteo jamaicensis X X X X 

American Kestrel Falco sparverius X X - X 

Peregrine Falcon Falco peregrinus - X - - 

Gambel’s Quail Callipepla gambelii X - X X 

Clapper Rail Rallus longirostris - X - X 

Common Moorhen Gallinula chloropus - X - X 

American Coot Fulica Americana X X X X 

Killdeer Charadrius vociferus - - X X 

American Avocet Recurvirostra Americana - X - X 

Greater Yellowlegs Tringa melanoleuca - - - X 

Solitary Sandpiper Tringa solitaria - - - X 

Spotted Sandpiper Actitus macularia - - - X 

Western Sandpiper Calidris mauri - - - X 

Least Sandpiper Calidris minutilla - - - X 

Baird’s Sandpiper Caladris bairdii - - - X 

Long-billed Dowitcher Limnodromus scolopaceus - - - X 

Wilson’s Phalarope Phalaropus tricolor - - - X 

Red-necked Phalarope Phalaropus lobatus - - - X 

Ring-billed Gull Larus delewarensis - - X X 

Caspian Tern Sterna caspia - - - X 

Forster’s Tern Sterna forsteri - - - X 

Black Tern Chlidonias niger - - - X 

Rock Pigeon Columa livia - - - X 

Mourning Dove Zenaida macroura X - - X 

Eurasian Collared-Dove Streptopelia chinensis - - - X 

Yellow-billed Cuckoo Coccyzus americanus - - X - 

Greater Roadrunner Geococcyx californianus - - X X 

Barn Owl Tyto alba - - X X 

Great Horned Owl Bubo virginianus - - - X 

Lesser Nighthawk Chordeiles acutipennis - X - X 

Belted Kingfisher Ceryle alcyon - - X X 
173

Appendix 5 (continued) 

Common Name Scientific Name 1 2 3 4 

Pahranagat National Wildlife Refuge (continued) 

Ladder-backed Woodpecker Picoides scalaris X X X X 

Olive-sided Flycatcher Contopus cooperi - - - X 

Western Wood-Pewee Contopus sordidulus - - - X 

Willow Flycatcher Empidonax traillii - X X - 

Black Phoebe Sayornis nigricans - X X X 

Vermillion Flycatcher Pyrocephalus rubinus X - X X 

Brown-crested Flycatcher Myiarchus tyrannulus X X X - 

Ash-throated Flycatcher Myiarchus cinerascens X X X - 

Western Kingbird Tyrannus verticalis X X X X 

Loggerhead Shrike Lanius ludovicianus - - - X 

Bell’s Vireo Vireo bellii X X - - 

American Crow Corvus brachyrynchos X X - X 

Common Raven Corvus corax X - - X 

Tree Swallow Tachycineta bicolor - - - X 

Cliff Swallow Petrochelidon pyrrhonota - - - X 

Northern Rough-winged Swallow Stelgidopteryx serripennis - X X X 

Verdin Auriparus flaviceps - - - X 

Bushtit Psaltriparus minimus X - - - 

Marsh Wren Cistothorus palustris - X X - 

Bewick’s Wren Thryomanes bewickii X X X X 

American Robin Turdus migratorius - X X X 

Northern Mockingbird Mimus polyglottos - X X X 

Cedar Waxwing Bombycilla cedrorum - - - X 

Yellow Warbler Dendroica petechia X X X X 

Common Yellowthroat Geothlypis trichas X X X X 

Yellow-breasted Chat Icteria virens X X - - 

Summer Tanager Piranga rubra - - - X 

Western Tanager Piranga ludoviciana - - - X 

Green-tailed Towhee Pipilo chlorurus - X - - 

Spotted Towhee Pipilo maculates - - - X 

Chipping Sparrow Spizella passerina - - - X 

Brewer’s Sparrow Spizella breweri - - - X 

Lark Sparrow Chondestes grammacus - - - X 

Black-throated Sparrow Amphispiza bilineata - - - X 

Song Sparrow Melospiza melodia X X X X 

White-crowned Sparrow Zonotrichia leucophrys - - - X 

Black-headed Grosbeak Pheucticus melanocephalus - - - X 

Blue Grosbeak Guiraca caerulea - X - X 

Lazuli Bunting Passerina ciris - - - X 

Yellow-headed Blackbird Xanthocephalus xanthocephalus X X - X 

Red-winged Blackbird Agelaius phoeniceus X X X X 

Great-tailed Grackle Quiscalus mexicanus X X - X 

Brown-headed Cowbird Molothrus ater X - - X 

Bullock’s Oriole Icterus bullockii X X - X 

Hooded Oriole Icterus cucullatus - - - X 

House Finch Carpodacus mexicanus X X X X 

American Goldfinch Carduelis tristis X - - X 

Lesser Goldfinch Carduelis psaltria - X X X 
174

Appendix 5 (continued) 

Common Name Scientific Name 1 2 3 4 

Overton Wildlife Management Area (Muddy River) 

Canada Goose Branta canadensis X X X - 

Mallard Anas platyrynchos - - X X 

Northern Shoveler Anas clypeata - - - X 

Pied-billed Grebe Podilymbus podiceps X - - X 

Double-crested Cormorant Phalacrocorax auritus - - - X 

Black-crowned Night Heron Nycticorax nycticorax - - - X 

Snowy Egret Egreta thula X - - X 

Great Blue Heron Ardea herodias - - - X 

White-faced Ibis Plegadis chihi - - - X 

Northern Harrier Circus cyaneus - - X X 

Red-tailed Hawk Buteo Jamaicensis - - - X 

American Kestrel Falco Sparverius - X - X 

Wild Turkey Meleagris gallopavo X - X - 

Gambel’s Quail Callipepla gambelli X - - X 

Virginia Rail Rallus limicola - - - X 

American Coot Fullica Americana - - - X 

Killdeer Charadrius vociferus X - X X 

Greater Yellowlegs Tringa melanoleuca - - - X 

Marbled Godwit Limosa fedoa - - - X 

Least Sandpiper Calidris minutilla - - - X 

Baird’s Sandpiper Calidris bairdii - - - X 

Wilson’s Snipe Gallinago gallinago - - - X 

Forster’s Tern Sterna forsteri - - - X 

Mourning Dove Zenaida macroura X X X X 

White-winged Dove Zenaida asiatica - X X X 

Eurasian Collared-Dove Streptopelia decaocto - - - X 

Rock Pigeon Columba livia - - - X 

Yellow-billed Cuckoo Coccyzus americanus X - - - 

Greater Roadrunner Geococcyx californianus - - - X 

Barn Owl Tyto alba - - - X 

Great Horned Owl Bubo virginianus - X - - 

Lesser Nighthawk Chordeiles acutipennis - - - X 

Costa’s Hummingbird Calypte costae - X - - 

Ladder-backed Woodpecker Picoides scalaris - - - X 

Western Wood-Pewee Contopus sordidulus - - - X 

Willow Flycatcher Empidonax traillii X X - X 

Ash-throated Flycatcher Myiarchus cinerascens - X - X 

Western Kingbird Tyrannus verticalis - - - X 

Loggerhead Shrike Lanius ludovicianus - - X X 

Bell’s Vireo Vireo bellii X X - - 

Common Raven Corvus corax - - - X 

Tree Swallow Tachycineta bicolor X - - X 

Violet-green Swallow Tachycineta thalassina X - - - 

Cliff Swallow Petrochelidon pyrrhonota - - - X 

Northern Rough-winged Swallow Stelgidopteryx serripennis X - - X 

Verdin Auriparus flaviceps - - - X 

Bewick’s Wren Thryomanes bewickii - - - X 

Black-tailed Gnatcatcher Polioptila nigriceps - - X X 

Northern Mockingbird Mimus polyglottos - - X - 

Lucy’s Warbler Vermivora luciae X - - - 

Yellow Warbler Dendroica petechia - - X X 

Common Yellowthroat Geothlypis trichas X X X X 
175

Appendix 5 (continued) 

Common Name Scientific Name 1 2 3 4 

Overton Wildlife Management Area (continued) 

Yellow-breasted Chat Icteria virens - X X X 

Western Tanager Piranga ludoviciana - - - X 

Abert’s Towhee Pipilo aberti - X - X 

Brewer’s Sparrow Spizella breweri - - - X 

Lark Sparrow Chondestes grammacus - - - X 

Black-throated Sparrow Amphispiza bilineata - - - X 

Song Sparrow Melospiza melodia - - - X 

Black-headed Grosbeak Pheucticus melanocephalus - - - X 

Western Meadowlark Sternella neglecta X - - X 

Red-winged Blackbird Agelaius phoenieus X - - X 

Great-tailed Grackle Quiscalus mexicanus X X - X 

Brown-headed Cowbird Molothrus ater X - - X 

Bullock’s Oriole Icterus bullockii - - - X 

House Finch Carpodacus mexicanus X - - - 

Lesser Goldfinch Carduelis psaltria - - - X 

Grand Canyon National Park/Lake Mead National Recreation Area 

(Lake Mead and Colorado River) 

Mallard Anas platyrynchos - - - - 

Eared Grebe Podiceps nigricollis - - - - 

Pied-billed Grebe Podilymbus podiceps - - - - 

Clark’s Grebe Aechmophorus occidentalis - X X X 

Western Grebe Aechmophorus clarkia - X X X 

American White Pelican Pelecanus erythrorhynchos - - - 

Double-crested Cormorant Phalacrocorax auritus - X X X 

Great Blue Heron Ardea herodias - X X X 

Turkey Vulture Cathartes aura X X X - 

Osprey Pandion haliaetus X - X - 

Sharp-shinned Hawk Accipiter striatus - - - - 

Cooper’s Hawk Accipiter cooperii - - - - 

Red-tailed Hawk Buteo jamaicensis X - X - 

Killdeer Charadrius vociferus - - - X 

Solitary Sandpiper Tringa solitaria - - X - 

Spotted Sandpiper Actitus macularia - X X 

Ring-billed Gull Larus delewarensis - X X 

Inca Dove Columbina inca - - - - 

Yellow-billed Cuckoo Coccyzus americanus X X X X 

Greater Roadrunner Geococcyx californianus - - X - 

Western Screech Owl Otus kennicotti - - - X 

White-throated Swift Aeronautes saxatalis - X X - 

Belted Kingfisher Ceeryle alcyon - - - - 

Ladder-backed Woodpecker Picoides scalaris - X X - 

Willow Flycatcher Empidonax traillii - - X - 

Black Phoebe Sayornis nigricans - - X X 

Say’s Phoebe Sayornis saya - - X - 

Ash-throated Flycatcher Myiarchus cinerascens X - X - 

Western Kingbird Tyrannus verticalis - - X - 

Loggerhead Shrike Lanius ludovicianus - X X X 

Bell’s Vireo Vireo bellii - X X X 

Warbling Vireo Vireo gilvus X - X - 
176

Appendix 5 (continued) 

Common Name Scientific Name 1 2 3 4 

Grand Canyon National Park/Lake Mead National Recreation Area (continued) 

Western Scrub-Jay Aphelocoma californica - - X - 

Horned Lark Eremophila alpestris - X - - 

Tree Swallow Tachycineta bicolor - - X 

Violet-green Swallow Tachycineta thalassina X - - - 

Cliff Swallow Petrochelidon pyrrhonota - X X - 

Verdin Auriparus flaviceps - X X - 

Bewick’s Wren Thryomanes bewickii - - X - 

Rock Wren Salpinctes obsoletus - - X - 

Canyon Wren Catherpes mexicanus - X X X 

Black-tailed Gnatcatcher Polioptila melanura - - X X 

Orange-crowned Warbler Vermivora celata - - - - 

Nashville Warbler Vermivora ruficapilla - - - 

Magnolia Warbler Dendroica magnolia - - - - 

Black-and-white Warbler Mniotilta varia - - - - 

Yellow Warbler Dendroica petechia X - X X 

Common Yellowthroat Geothlypis trichas X X X X 

Yellow-breasted Chat Icteria virens X X X X 

Summer Tanager Piranga rubra - X X - 

Hepatic Tanager Piranga flava - - - - 

Western Tanager Piranga ludoviciana - - - - 

Black-throated Sparrow Amphispiza bilineata - X X X 

Song Sparrow Melospiza melodia X X X X 

Black-headed Grosbeak Pheucticus melanocephalus - - X - 

Blue Grosbeak Guiraca caerulea - X X X 

Indigo Bunting Passerina cyanea - X - - 

Western Meadowlark Sternella neglecta - X X - 

Brown-headed Cowbird Molothrus ater X - X - 

Bullock’s Oriole Icterus bullockii - - X - 

House Finch Carpodacus mexicanus X - X - 

Lesser Goldfinch Carduelis psaltria - - X - 

Lake Mohave (Colorado River) 

Mallard Anas platyrhynchos - n/a X - 

Common Loon Gavia immer - n/a X - 

Pied-billed Grebe Podilymbus podiceps X n/a X - 

Green Heron Butorides virescens X n/a X - 

Great Blue Heron Ardea herodias X n/a X - 

Turkey Vulture Cathartes aura - n/a - - 

American Kestrel Falco sparverius - n/a X - 

Gambel’s Quail Callipepla gambelli - n/a - - 

American Coot Fulica Americana - n/a X - 

Killdeer Charadrius vociferus - n/a X - 

Ring-billed Gull Larus delawarenis - n/a X - 

Sabine’s Gull Xema sabini - n/a - - 

Mourning Dove Zenaida macroura X n/a X - 

White-winged Dove Zenaida asiatica X n/a X - 

Greater Roadrunner Geococcyx californianus - n/a X - 

Lesser Nighthawk Chordeiles acutipennis X n/a X - 

Belted Kingfisher Ceryle alcyon - n/a - - 

Ladder-backed Woodpecker Picoides scalaris X n/a X - 
177

Appendix 5 (continued) 

Common Name Scientific Name 1 2 3 4 

Lake Mohave (continued) 

Black Phoebe Sayornis nigricans X n/a X - 

Ash-throated Flycatcher Myiarchus cinerascens X n/a X - 

Brown-crested Flycatcher Myairchus tyrannulus - n/a X - 

Western Kingbird Tyrannus verticalis - n/a X - 

Loggerhead Shrike Lanius ludovicianus - n/a X - 

Bell’s Vireo Vireo bellii X n/a X - 

Common Raven Corvus corax X n/a X - 

Horned Lark Eremophila alpestris - n/a X - 

Tree Swallow Tachycineta bicolor - n/a X - 

Cliff Swallow Petrochelidon pyrrhonota - n/a X - 

Northern Rough-winged Swallow Stelgidopteryx serripennis - n/a X - 

Verdin Auriparus flaviceps - n/a X - 

Black-tailed Gnatcatcher Polioptila melanura X n/a X - 

Yellow Warbler Dendroica petechia X n/a X - 

Common Yellowthroat Geothlypis trichas X n/a X - 

Yellow-breasted Chat Icteria virens X n/a X - 

Abert’s Towhee Pipilo aberti - n/a X - 

Song Sparrow Melospiza melodia X n/a X - 

Yellow-headed Blackbird Xanthocephalus xanthocephalus - n/a X - 

Red-winged Blackbird Agelaius phoeniceus X n/a X - 

Great-tailed Grackle Quiscalus mexicanus X n/a X - 

Brown-headed Cowbird Molothrus ater X n/a X - 

Bullock’s Oriole Icterus bullockii - n/a X - 

Havasu National Wildlife Refuge (Colorado River) 

Greater White-fronted Goose Anser albifrons - - - X 

Green-winged Teal Anas crecca - - X - 

Blue-winged Teal Anas discors - - - X 

Clark’s Grebe Aechmophorus clarkii X - X X 

Western Grebe Aechmophorus occidentalis - - X 

Double-crested Cormorant Phalacrocorax auritus - - X X 

Green Heron Butorides virescens - - X X 

Snowy Egret Egretta thula - - X - 

Great Egret Ardea alba X X X - 

Great Blue Heron Ardea herodias X X X X 

White-faced Ibis Plegadis chihi - - X X 

Turkey Vulture Cathartes aura X X X - 

Cooper’s Hawk Accipiter cooperii - - X - 

American Kestrel Falco sparverius - X X X 

Prairie Falcon Falco mexicanus - - - X 

Gambel’s Quail Callipepla gambelii X X X X 

American Coot Fulica Americana X - X - 

Killdeer Charadrius vociferus X X X X 

Greater Yellowlegs Tringa melanoleuca - - X X 

Solitary Sandpiper Tringa solitaria - X - - 

Spotted Sandpiper Actitus macularia - - X X 

Long-billed Dowitcher Limnodromus scolopaceus - - X - 

Wilson’s Phalarope Phalaropus tricolor - - X - 

Mourning Dove Zenaida macroura X X X X 

Eurasian Collared-Dove Streptopelia chinensis - - - X 
178

Appendix 5 (continued) 

Common Name Scientific Name 1 2 3 4 

Havasu National Wildlife Refuge (continued) 

White-winged Dove Zenaida asiatica X X X X 

Yellow-billed Cuckoo Coccyzus americanus X - - - 

Greater Roadrunner Geococcyx californianus X X X - 

Great Horned Owl Bubo virginianus - - X - 

Lesser Nighthawk Chordeiles acutipennis X X X - 

Costa’s Hummingbird Calypte costae - X - - 

Anna’s Hummingbird Calypte anna X - X - 

Gila Woodpecker Melanerpes uropygialis X X X - 

Ladder-backed Woodpecker Picoides scalaris X X X X 

Black Phoebe Sayornis nigricans X X X X 

Say’s Phoebe Sayornis saya - - - X 

Brown-crested Flycatcher Myiarchus tyrannulus X - - - 

Ash-throated Flycatcher Myiarchus cinerascens X X X - 

Western Kingbird Tyrannus verticalis X X X X 

Loggerhead Shrike Lanius ludovicianus X X X X 

Bell’s Vireo Vireo bellii X X X X 

Warbling Vireo Vireo gilvus - - X X 

Common Raven Corvus corax X X X - 

Tree Swallow Tachycineta bicolor - X X - 

Cliff Swallow Petrochelidon pyrrhonota X X X - 

Northern Rough-winged Swallow Stelgidopteryx serripennis - X X - 

Verdin Auriparus flaviceps - X X X 

Black-tailed Gnatcatcher Polioptila melanura X X X X 

Northern Mockingbird Mimus polyglottos - X X - 

Crissal Thrasher Toxostoma crissale - - X X 

European Starling Sturnus vulgaris X - X - 

Lucy’s Warbler Vermivora luciae X - X - 

Yellow Warbler Dendroica petechia X X X - 

Common Yellowthroat Geothlypis trichas X X X X 

Yellow-breasted Chat Icteria virens X X X - 

Summer Tanager Piranga rubra X X X - 

Western Tanager Piranga ludoviciana - - X - 

Abert’s Towhee Pipilo aberti X X X X 

Song Sparrow Melospiza melodia X X X - 

Black-headed Grosbeak Pheucticus melanocephalus - - X - 

Blue Grosbeak Guiraca caerulea - X X X 

Indigo Bunting Passerina cyanea X - - - 

Yellow-headed Blackbird Xanthocephalus xanthocephalus - X X - 

Red-winged Blackbird Agelaius phoeniceus X X X - 

Great-tailed Grackle Quiscalus mexicanus X X X - 

Brown-headed Cowbird Molothrus ater X X X - 

Bullock’s Oriole Icterus bullockii X X X - 

House Finch Carpodacus mexicanus X X X - 

Lesser Goldfinch Carduelis psaltria - - X - 

Bill Williams National Wildlife Refuge (Bill Williams River) 

Northern Shoveler Anas clypeata - - - X 

Pied-billed Grebe Podilymbus podiceps - - X X 

Clark’s Grebe Aechmophorus clarkii - X X X 

Western Grebe Aechmophorus occidentalis - - X X 
179

Appendix 5 (continued) 

Common Name Scientific Name 1 2 3 4 

Bill Williams National Wildlife Refuge (continued) 

Double-crested Cormorant Phalacrocorax auritus X X - - 

Least Bittern Ixobrychus exilis - X - X 

Green Heron Butorides virescens X X X X 

Snowy Egret Egretta thula - - X - 

Great Egret Ardea alba X - X X 

Great Blue Heron Ardea herodias X X X X 

White-faced Ibis Plegadis chihi - - X X 

Turkey Vulture Cathartes aura - X X X 

Sharp-shinned Hawk Accipiter striatus - - - 

Cooper’s Hawk Accipiter cooperii - - - X 

Red-tailed Hawk Buteo jamaicensis X X X X 

American Kestrel Falco sparverius - - - X 

Peregrine Falcon Falco Peregrinus - - - X 

Gambel’s Quail Callipepla gambelii X X X X 

Virginia Rail Rallus limicola - - X - 

Black Rail Laterallus jamaicensis - - X - 

American Coot Fulica Americana - X X X 

Killdeer Charadrius vociferus - X X X 

Spotted Sandpiper Actitus macularia - - X X 

Least Sandpiper Calidris minutilla - - X X 

California Gull Larus californicus - X - - 

Forster’s Tern Sterna forsteri - - - X 

Least Tern Sterna antillarum - - - X 

Mourning Dove Zenaida macroura X X X X 

White-winged Dove Zenaida asiatica X X X X 

Common Ground-Dove Columbina passerina - X X - 

Yellow-billed Cuckoo Coccyzus americanus X X X X 

Greater Roadrunner Geococcyx californianus X X X X 

Barn Owl Tyto alba - - X X 

Great Horned Owl Bubo virginianus - X X X 

Elf Owl Micrathene whitneyi - X - - 

Lesser Nighthawk Chordeiles acutipennis - X X X 

Vaux’s Swift Chaetura vauxi - - - X 

White-throated Swift Aeronautes saxatalis - X X X 

Black-chinned Hummingbird Archilochus alexandri - X X - 

Belted Kingfisher Ceryle alcyon - - - - 

Gila Woodpecker Melanerpes uropygialis X X X X 

Gilded Flicker Colaptes chrysoides - X X X 

Ladder-backed Woodpecker Picoides scalaris X X X X 

Western Wood-Pewee Contopus sordidulus - - - X 

Willow Flycatcher Empidonax traillii X X X X 

Pacific-slope Flycatcher Empidonax difficilis - - - X 

Black Phoebe Sayornis nigricans X X X X 

Say’s Phoebe Sayornis saya X X X X 

Vermillion Flycatcher Pyrocephalus rubinus - X - X 

Brown-crested Flycatcher Myiarchus tyrannulus - X X X 

Ash-throated Flycatcher Myiarchus cinerascens X X X X 

Western Kingbird Tyrannus verticalis - X X X 

Loggerhead Shrike Lanius ludovicianus - X X X 

Bell’s Vireo Vireo bellii X X X X 

Plumbeous Vireo Vireo plumbeus - - - X 
180

Appendix 5 (continued) 

Common Name Scientific Name 1 2 3 4 

Bill Williams National Wildlife Refuge (continued) 

Warbling Vireo Vireo gilvus - - X X 

Common Raven Corvus corax - X X X 

Tree Swallow Tachycineta bicolor - - X X 

Violet-green Swallow Tachycineta thalassina X - - X 

Cliff Swallow Petrochelidon pyrrhonota - X X - 

Northern Rough-winged Swallow Stelgidopteryx serripennis X - X X 

Verdin Auriparus flaviceps X X X X 

House Wren Troglodytes aedon - - - X 

Bewick’s Wren Thryomanes bewickii X X X X 

Cactus Wren Campylorhynchus brunneicapillus - X X X 

Rock Wren Salpinctes obsoletus - - X X 

Canyon Wren Catherpes mexicanus X X X X 

Marsh Wren Cistothorus palustris - X X X 

Black-tailed Gnatcatcher Polioptila melanura X X X X 

Northern Mockingbird Mimus polyglottos - X X X 

Crissal Thrasher Toxostoma crissale - - X X 

Phainopepla Phainopepla nitens - - X X 

Tennessee Warbler Vermivora peregrina - - - X 

Orange-crowned Warbler Vermivora celata - - - X 

Nashville Warbler Vermivora ruficapilla - - - X 

Lucy’s Warbler Vermivora luciae - X - X 

Black-and-white Warbler Mniotilta varia - - - X 

Black-throated Gray Warbler Dendroica nigrescens - - - X 

Hermit Warbler Dendroica occidentalis - - - X 

Yellow Warbler Dendroica petechia X X X X 

Wilson’s Warbler Wilsonia pusilla - - - X 

Common Yellowthroat Geothlypis trichas X X X X 

Yellow-breasted Chat Icteria virens X X X X 

Summer Tanager Piranga rubra - X X X 

Western Tanager Piranga ludoviciana X - X X 

Abert’s Towhee Pipilo aberti X X X X 

Spotted Towhee Pipilo maculates X - - X 

Chipping Sparrow Spizella passerina X - - - 

Lark Sparrow Chondestes grammacus - - X - 

Black-throated Sparrow Amphispiza bilineata - X X X 

Song Sparrow Melospiza melodia X X X X 

Dark-eyed Junco “Oregon” Junco hyemalis - - X - 

Rose-breasted Grosbeak Pheucticus ludovicianus - - - X 

Black-headed Grosbeak Pheucticus melanocephalus - - X X 

Blue Grosbeak Guiraca caerulea X X X X 

Indigo Bunting Passerina cyanea - - X X 

Lazuli Bunting Passerina amoena - - X X 

Yellow-headed Blackbird Xanthocephalus xanthocephalus X X X X 

Red-winged Blackbird Agelaius phoeniceus X X X X 

Great-tailed Grackle Quiscalus mexicanus X X X X 

Brown-headed Cowbird Molothrus ater X X X X 

Bullock’s Oriole Icterus bullockii X X X X 

House Finch Carpodacus mexicanus X X X X 

Lesser Goldfinch Carduelis psaltria - - X X 
181

Appendix 5 (continued) 

Common Name Scientific Name 1 2 3 4 

Cibola National Wildlife Refuge (Colorado River) 

Northern Shoveler Anas clypeata - - X - 

Brown Pelican Pelecanus occidentalis X - - - 

Double-crested Cormorant Phalacrocorax auritus - - X - 

White-faced Ibis Plegadis chihi X - - - 

Turkey Vulture Cathartes aura - - X - 

White-tailed Kite Elanus leucurus - X - - 

Northern Harrier Circus cyaneus - - - - 

Sharp-shinned Hawk Accipiter striatus - - - - 

Cooper’s Hawk Accipiter cooperii - X - - 

Red-tailed Hawk Buteo Jamaicensis X - - - 

American Kestrel Falco Sparverius - - X - 

Prairie Falcon Falco mexicanus - - X - 

Gambel’s Quail Callipepla gambelii - - X - 

Killdeer Charadrius vociferus - - - - 

Solitary Sandpiper Tringa solitaria - - - - 

Spotted Sandpiper Actitus macularia - - - - 

Mourning Dove Zenaida macroura X - X - 

White-winged Dove Zenaida asiatica X - X - 

Common Ground-Dove Columbina passerina X - - - 

Yellow-billed Cuckoo Coccyzus americanus X X - - 

Greater Roadrunner Geococcyx califorianus - - X - 

Barn Owl Tyto alba - - - - 

Lesser Nighthawk Chordeiles acutipennis X - X - 

Vaux’s Swift Chaetura vauxi - - - - 

Black-chinned Hummingbird Archilochus alexandri X - X - 

Ladder-backed Woodpecker Picoides scalaris X - X - 

Western Wood-Pewee Contopus sordidulus - - - - 

Willow Flycatcher Empidonax traillii - - - X 

Black Phoebe Sayornis nigricans X - - - 

Brown-crested Flycatcher Myiarchus tyrannulus X - X - 

Ash-throated Flycatcher Myiarchus cinerascens X - X - 

Western Kingbird Tyrannus verticalis X - X - 

Cassin’s Kingbird Tyrannus vociferans - - - - 

Scissor-tailed Flycatcher Tyrannus forficatus - X - - 

Loggerhead Shrike Lanius ludovicianus X - X - 

Warbling Vireo Vireo gilvus - - - - 

Tree Swallow Tachycineta bicolor - - - - 

Cliff Swallow Petrochelidon pyrrhonota - - X - 

Northern Rough-winged Swallow Stelgidopteryx serripennis - - - - 

Barn Swallow Hirundo rustica - - - - 

Verdin Auriparus flaviceps X - X - 

Cactus Wren Campylorhynchus brunneicapillus - - X - 

House Wren Troglodytes aedon - - - - 

Black-tailed Gnatcatcher Polioptila melanura X - X - 

Northern Mockingbird Mimus polyglottos - - X - 

Orange-crowned Warbler Vermivora celata - - - - 

Lucy’s Warbler Vermivora luciae X X X - 

Townsend’s Warbler Dendroica townsendi - - - - 

Yellow Warbler Dendroica petechia - - - - 

MacGillivray’s Warbler Oporornis tolmiei - - - - 

Wilson’s Warbler Wilsonia pusilla - - - - 
182

Appendix 5 (continued) 

Common Name Scientific Name 1 2 3 4 

Cibola National Wildlife Refuge (continued) 

Common Yellowthroat Geothlypis trichas X - - - 

Yellow-breasted Chat Icteria virens X - X - 

Summer Tanager Piranga rubra X - - - 

Western Tanager Piranga ludoviciana - - - - 

Abert’s Towhee Pipilo aberti X - X - 

Sage Sparrow Amphispiza belli - - - - 

Song Sparrow Melospiza melodia X - - - 

Black-headed Grosbeak Pheuticus melanocephalus X - - - 

Blue Grosbeak Guiraca caerulea X - X - 

Yellow-headed Blackbird Xanthocephalus xanthocephalus X - - - 

Red-winged Blackbird Agelaius phoeniceus X - - - 

Brown-headed Cowbird Molothrus ater X - X - 

Great-tailed Grackle Quiscalus mexicanus X - X - 

Bullock’s Oriole Icterus bullockii X - X - 

House Finch Carpodacus mexicanus - - X - 

Picacho State Recreation Area (Colorado River) 

Northern Shoveler Anas clypeata - - X - 

Green Heron Butorides virescens - - X - 

Turkey Vulture Cathartes aura - X - - 

Peregrine Falcon Falco peregrinus X - - - 

Gambel’s Quail Callipepla gambelii - X X - 

Black Rail Laterallus jamaicensis - X - - 

American Coot Fulica Americana - X - - 

Killdeer Charadrius vociferus - X - - 

Long-billed Curlew Numenius americanus X - - - 

Mourning Dove Zenaida macroura - X X - 

White-winged Dove Zenaida asiatica - X X - 

Lesser Nighthawk Chordeiles acutipennis - X X - 

Gila Woodpecker Melanerpes uropygialis - X X - 

Ladder-backed Woodpecker Picoides scalaris - X X - 

Ash-throated Flycatcher Myiarchus cinerascens - X - - 

Western Kingbird Tyrannus verticalus - X X - 

Loggerhead Shrike Lanius ludovicianus - X - - 

Bell’s Vireo Vireo bellii X X X - 

Verdin Auriparus flaviceps - - X - 

Cactus Wren Campylorhynchus brunneicapillus - - X - 

Black-tailed Gnatcatcher Polioptila melanura - X X - 

Common Yellowthroat Geothlypis trichas - X - - 

Yellow-breasted Chat Icteria virens - X X - 

Abert’s Towhee Pipilo aberti - X - - 

Black-headed Grosbeak Pheuticus melanocephalus - X - - 

Blue Grosbeak Guiraca caerulea - X - - 

Great-tailed Grackle Quiscalus mexicanus - - X - 

Brown-headed Cowbird Molothrus ater - X X - 

Bullock’s Oriole Icterus bullockii - - X - 

Lesser Goldfinch Carduelis psaltria - - X - 
183

Appendix 5 (continued) 

Common Name Scientific Name 1 2 3 4 

Imperial National Wildlife Refuge (Colorado River) 

Mallard Anas platyrhynchos X - - - 

Gadwall Anas strepera X - - - 

American Wigeon Anas americana X - - - 

Northern Shoveler Anas clypeata X - X - 

Cinnamon Teal Anas cyanoptera X - - - 

Redhead Aythya americana X - - - 

Ruddy Duck Oxyura jamaicensis X - - - 

Pied-billed Grebe Podilymbus podiceps X - - - 

Clark’s Grebe Aechmophorus occidentalis X - - - 

Western Grebe Aechmophorus clarkia X - - - 

Double-crested Cormorant Phalacrocorax auritus X - - - 

Least Bittern Ixobrychus exilis X - - - 

Black-crowned Night Heron Nycticorax nycticorax X - - - 

Green Heron Butorides virescens X - X - 

Snowy Egret Egretta thula X - - - 

Great Egret Ardea alba X - X - 

Great Blue Heron Ardea herodias X - X - 

White-faced Ibis Plegadis chihi - - - - 

Turkey Vulture Cathartes aura X - - - 

Osprey Pandion haliaetus - - - - 

Red-tailed Hawk Buteo jamaicensis X - - - 

American Kestrel Falco sparverius X - - - 

Gambel’s Quail Callipepla gambelii X - X - 

Clapper Rail Rallus longirostris X - - - 

Black Rail Laterallus jamaicensis X - - - 

Common Moorhen Gallinula chloropus X - - - 

American Coot Fulica americana X - X - 

Killdeer Charadrius vociferus X - - - 

Snowy Plover Charadrius alexandrinus - - X - 

American Avocet Recurvirostra americana - - - - 

Black-necked Stilt Himantopus mexicanus - - X - 

Willet Catoptrophorus semipalmatus X - - - 

Greater Yellowlegs Tringa melanoleuca - - - - 

Lesser Yellowlegs Tringa flavipes - - - - 

Western Sandpiper Calidris mauri - - X - 

Least Sandpiper Calidris minutilla - - X - 

Long-billed Dowitcher Limnodromus scolopaceus - - X - 

Short-billed Dowitcher Limnodromus griseus - - - - 

Wilson’s Phalarope Phalaropus tricolor - - X - 

Caspian Tern Sterna caspia X - - - 

Mourning Dove Zenaida macroura X - - - 

White-winged Dove Zenaida asiatica X - - - 

Yellow-billed Cuckoo Coccyzus americanus X - - - 

Greater Roadrunner Geococcyx californianus X - - - 

Barn Owl Tyto alba X - - - 

Great Horned Owl Bubo virginianus X - - - 

Western Screech-Owl Otus trichopsis X - - - 

Lesser Nighthawk Chordeiles acutipennis X - - - 

Common Poorwill Phalaenoptilus nuttallii X - - - 

Black-chinned Hummingbird Archilochus alexandri X - - - 

Belted Kingfisher Ceryle alcyon - - - - 
184

Appendix 5 (continued) 

Common Name Scientific Name 1 2 3 4 

Imperial National Wildlife Refuge (continued) 

Gila Woodpecker Melanerpes uropygialis X - - - 

Ladder-backed Woodpecker Picoides scalaris X - - - 

Western Wood-Pewee Contopus sordidulus - - - - 

Pacific-slope Flycatcher Empidonax difficilis - - - - 

Black Phoebe Sayornis nigricans X - X - 

Say’s Phoebe Sayornis saya - - - - 

Brown-crested Flycatcher Myiarchus tyrannulus X - - - 

Ash-throated Flycatcher Myiarchus cinerascens X - - - 

Western Kingbird Tyrannus verticalis X - X - 

Loggerhead Shrike Lanius ludovicianus X - - - 

Bell’s Vireo Vireo bellii X - - - 

Warbling Vireo Vireo gilvus - - - - 

Common Raven Corvus corax X - - - 

Cliff Swallow Petrochelidon pyrrhonota X - - - 

Barn Swallow Hirundo rustica X - - - 

Verdin Auriparus flaviceps X - - - 

Black-tailed Gnatcatcher Polioptila melanura X - - - 

Northern Mockingbird Mimus polyglottos X - X - 

American Pipit Anthus rubescens - - - - 

Orange-crowned Warbler Vermivora celata - - - - 

Nashville Warbler Vermivora ruficapilla - - - - 

Lucy’s Warbler Vermivora luciae X - - - 

Townsend’s Warbler Dendroica townsendi - - - - 

Yellow Warbler Dendroica petechia X - - - 

Wilson’s Warbler Wilsonia pusilla - - - - 

Common Yellowthroat Geothlypis trichas X - X - 

Yellow-breasted Chat Icteria virens X - - - 

Summer Tanager Piranga rubra X - X - 

Western Tanager Piranga ludoviciana - - X - 

Abert’s Towhee Pipilo aberti X - - - 

Song Sparrow Melospiza melodia X - - - 

Black-headed Grosbeak Pheucticus melanocephalus - - - - 

Blue Grosbeak Guiraca caerulea X - X - 

Lazuli Bunting Passerina amoena - - X - 

Western Meadowlark Sturnella neglecta X - - - 

Yellow-headed Blackbird Xanthocephalus xanthocephalus X - - - 

Red-winged Blackbird Agelaius phoeniceus X - - - 

Great-tailed Grackle Quiscalus mexicanus X - X - 

Brewer’s Blackbird Euphagus cyanocephalus - - - - 

Brown-headed Cowbird Molothrus ater X - - - 

Bronzed Cowbird Molothrus aeneus X - - - 

Hooded Oriole Icterus cucullatus X - - - 

Bullock’s Oriole Icterus bullockii X - - - 

House Finch Carpodacus mexicanus X - - - 

Lesser Goldfinch Carduelis psaltria X - - - 

Mittry Lake Wildlife Management Area (Colorado River) 

Mourning Dove Zenaida macroura - - X - 

White-winged Dove Zenaida asiatica - - X - 

Black-chinned Hummingbird Archilochus alexandri - - X - 
185

Appendix 5 (continued) 

Common Name Scientific Name 1 2 3 4 

Mittry Lake Wildlife Management Area (continued) 

Ash-throated Flycatcher Myiarchus cinerascens - - X - 

Verdin Auriparus flaviceps - - X - 

Western Tanager Piranga ludoviciana - - X - 

Black-headed Grosbeak Pheucticus melanocephalus - - X - 

Great-tailed Grackle Quiscalus mexicanus - - X - 

Brewer’s Blackbird Euphagus cyanocephalus - - X - 

Brown-headed Cowbird Molothrus ater - - X - 

Bullock’s Oriole Icterus bullockii - - X - 

Gila/Colorado River Confluence (Gila and Colorado River) 

Pied-billed Grebe Podilymbus podiceps - - X - 

Brown Pelican Pelecanus occidentalis - - X - 

Great Blue Heron Ardea herodias - - X - 

White-faced Ibis Plegadis chihi - - X - 

Clapper Rail Rallus longirostris - - X - 

Common Moorhen Gallinula chloropus - - X - 

American Coot Fulica americana - - X - 

Killdeer Charadrius vociferus - - X - 

Black Tern Chlidonias niger - - X - 

Mourning Dove Zenaida macroura - - X - 

White-winged Dove Zenaida asiatica - - X - 

Common Ground-Dove Columbina passerina - - X - 

Yellow-billed Cuckoo Coccyzus americanus - - X - 

Greater Roadrunner Geococcyx californianus - - X - 

Great Horned Owl Tyto alba X - X - 

Lesser Nighthawk Chordeiles acutipennis - - X - 

Black Phoebe Sayornis nigricans - - X - 

Loggerhead Shrike Lanius ludovicianus - - X - 

Cliff Swallow Petrochelidon pyrrhonota - - X - 

Verdin Auriparus flaviceps - - X - 

Common Yellowthroat Geothlypis trichas - - X - 

Abert’s Towhee Pipilo aberti - - X - 

Blue Grosbeak Guiraca caerulea - - X - 

Yellow-headed Blackbird Xanthocephalus xanthocephalus - - X - 

Red-winged Blackbird Agelaius phoeniceus - - X - 

Great-tailed Grackle Quiscalus mexicanus - - X - 

Brown-headed Cowbird Molothrus ater - - X - 

Yuma West Wetlands (Colorado River) 

Yellow-billed Cuckoo Coccyzus americanus - X - - 

Burrowing Owl Athene cunicularia X X X X 

Cactus Wren Campylorhynchus brunneicapillus X X - - 

Warbling Vireo Vireo gilvus - - - - 

Yellow Warbler Dendroica petechia X - - - 

Common Name Scientific Name 1 2 3 4 

MacGillivray’s Warbler Oporornis tolmiei - - - - 

Black-headed Grosbeak Pheucticus melanocephalus X - - - 

Blue Grosbeak Guiraca caerulea X - - - 

Great-tailed Grackle Quiscalus mexicanus X - - - 
186

Appendix 5 (continued) 

Common Name Scientific Name 1 2 3 4 

Limitrophe Division (Colorado River) 

Mallard Anas platyrynchos - - X - 

Northern Shoveler Anas clypeata - - X - 

Brown Pelican Pelecanus occidentalis - X - - 

Double-crested Cormorant Phalacrocorax auritus X - X - 

Black-crowned Night Heron Nycticorax nycticorax X - X - 

Green Heron Butorides virescens X - X - 

Cattle Egret Bubulcus ibis X - X - 

Snowy Egret Egretta thula X - X - 

Great Egret Ardea alba X - X - 

Great Blue Heron Ardea herodias X - X - 

White-faced Ibis Plegadis chihi X - X - 

Turkey Vulture Cathartes aura X - X - 

White-tailed Kite Elanus leucurus X - X - 

Red-tailed Hawk Buteo jamaicensis X - X - 

American Kestrel Falco sparverius X - X - 

Ring-necked Pheasant Phasianus colcichus X - X - 

Gambel’s Quail Callipepla gambelii X - X - 

American Coot Fulica americana X - X - 

Killdeer Charadrius vociferus X - X - 

Black-necked Stilt Himantopus mexicanus X - X - 

Mourning Dove Zenaida macroura X - X - 

White-winged Dove Zenaida asiatica X - X - 

Common Ground-Dove Columbina passerine X - X - 

Yellow-billed Cuckoo Coccyzus americanus X X X - 

Greater Roadrunner Geococcyx californianus X - X - 

Barn Owl Tyto alba X - - - 

Burrowing Owl Athene cunicularia X - X - 

Lesser Nighthawk Chordeiles acutipennis X - X - 

Anna’s Hummingbird Calypte anna X - X - 

Black-chinned Hummingbird Archilochus alexandri X - X - 

Gila Woodpecker Melanerpes uropygialis X - X - 

Ladder-backed Woodpecker Picoides scalaris X - X - 

Willow Flycatcher Empidonax traillii X - X - 

Black Phoebe Sayornis nigricans X - X - 

Ash-throated Flycatcher Myiarchus cinerascens X - X - 

Western Kingbird Tyrannus verticalis X - X - 

Loggerhead Shrike Lanius ludovicianus X - X - 

Warbling Vireo Vireo gilvus - - X - 

Common Name Scientific Name 1 2 3 4 

Cliff Swallow Petrochelidon pyrrhonota X - X - 

Northern Rough-winged Swallow Stelgidopteryx serripennis X - X - 

Verdin Auriparus flaviceps X - X - 

Cactus Wren Campylorhynchus brunneicapillus X - X - 

Black-tailed Gnatcatcher Polioptila melanura X - X - 

Northern Mockingbird Mimus polyglottos X - X - 

Crissal Thrasher Toxostoma crissale X - X - 

Virginia’s Warbler Vermivora virginiae - - X - 

Lucy’s Warbler Vermivora luciae X - X - 

Yellow Warbler Dendroica petechia X - X - 

Common Yellowthroat Geothlypis trichas X - X - 

Yellow-breasted Chat Icteria virens X - X - 
187

Appendix 5 (continued) 

Common Name Scientific Name 1 2 3 4 

Limitrophe Division (continued) 

Summer Tanager Piranga rubra X - X - 

Western Tanager Piranga ludoviciana X X X - 

Abert’s Towhee Pipilo aberti X - X - 

Black-throated Sparrow Amphispiza bilineata X - X - 

Song Sparrow Melospiza melodia X - X - 

Black-headed Grosbeak Pheucticus melanocephalus X X X - 

Northern Cardinal Cardinalis cardinalis X X - - 

Blue Grosbeak Guiraca caerulea X - X - 

Red-winged Blackbird Agelaius phoeniceus X - X - 

Great-tailed Grackle Quiscalus mexicanus X - X - 

Brown-headed Cowbird Molothrus ater X - X - 

House Finch Carpodacus mexicanus X - X - 

House Sparrow Passer domesticus X - X 

Gila River Highway 95 (Gila River) 

Mallard Anas platyrhynchos - X - - 

Northern Shoveler Anas clypeata - - X - 

Brown Pelican Pelecanus occidentalis - X X - 

Black-crowned Night Heron Nycticorax nycticorax - X - - 

Green Heron Butorides virescens - X X - 

Cattle Egret Bubulcus ibis - - X - 

Snowy Egret Egretta thula - X X - 

Great Egret Ardea alba - X X - 

Great Blue Heron Ardea herodias - X X - 

Turkey Vulture Cathartes aura - X - - 

Osprey Pandion haliaetus - X - - 

Red-tailed Hawk Buteo jamaicensis - - X - 

American Kestrel Falco sparverius - - - - 

Prairie Falcon Falco mexicanus X - - - 

Gambel’s Quail Callipepla gambelii - X X - 

Killdeer Charadrius vociferous - X X - 

Black-necked Stilt Himantopus mexicanus - X - - 

Mourning Dove Zenaida macroura - X X - 

White-winged Dove Zenaida asiatica - X X - 

Common Ground-Dove Columbina passerina - - X - 

Inca Dove Columbina inca X - - - 

Greater Roadrunner Geococcyx californianus - - X - 

Great Horned Owl Bubo virginianus X X X - 

Lesser Nighthawk Chordeiles acutipennis - X - - 

Black-chinned Hummingbird Archilochus alexandri - X - - 

Ladder-backed Woodpecker Picoides scalaris - X X - 

Black Phoebe Sayornis nigricans - - X - 

Ash-throated Flycatcher Myiarchus cinerascens - X X - 

Western Kingbird Tyrannus verticalis - X X - 

Loggerhead Shrike Lanius ludovicianus - - X - 

Cliff Swallow Petrochelidon pyrrhonota - X X - 

Verdin Auriparus flaviceps - X X - 

Cactus Wren Campylorhynchus brunneicapillus - - X - 

Black-tailed Gnatcatcher Polioptila melanura X - X - 

Northern Mockingbird Mimus polyglottos - - X - 

Crissal Thrasher Toxostoma crissale X - - - 
188

Appendix 5 (continued) 

Common Name Scientific Name 1 2 3 4 

Gila River Highway 95 (continued) 

Lucy’s Warbler Vermivora luciae - X X - 

Western Tanager Piranga ludoviciana - - X - 

Abert’s Towhee Pipilo aberti - X X - 

Lark Sparrow Chondestes grammacus X - X - 

Black-throated Sparrow Amphispiza bilineata - - X - 

Song Sparrow Melospiza melodia - X X - 

Black-headed Grosbeak Pheucticus melanocephalus - - X - 

Blue Grosbeak Guiraca caerulea - X X - 

Lazuli Bunting Passerina amoena - - X - 

Western Meadowlark Sternella neglecta - - X - 

Yellow-headed Blackbird Xanthocephalus xanthocephalus - - X - 

Red-winged Blackbird Agelaius phoeniceus - X X - 

Great-tailed Grackle Quiscalus mexicanus - X X - 

Brown-headed Cowbird Molothrus ater - X X - 

House Finch Carpodacus mexicanus - X X - 

Lesser Goldfinch Carduelis psaltria - - X - 

Gila River/Ligurta (Gila River) 

White-winged Dove Zenaida asiatica - - X - 

Greater Roadrunner Geococcyx californianus - - X - 

Blue Grosbeak Guiraca caerulea - - X - 

Red-winged Blackbird Agelaius phoeniceus - - X - 

Lesser Goldfinch Carduelis psaltria - - X - 

Gila River/Wellton (Gila River) 

Yellow-billed Cuckoo Coccyzus americanus X - - - 

Black-headed Grosbeak Pheucticus melanocephalus X - - - 

Quigley Wildlife Management Area (Gila River) 

White-faced Ibis Plegadis chihi X - X - 

Gambel’s Quail Callipepla gambelii - X X - 

Killdeer Charadrius vociferous - X - - 

Mourning Dove Zenaida macroura - X X - 

White-winged Dove Zenaida asiatica - X X - 

Common Ground Dove Columbina passerine - X - - 

Yellow-billed Cuckoo Coccyzus americanus X - - - 

Greater Roadrunner Geococcyx californianus - X - - 

Lesser Nighthawk Chordeiles acutipennis - - X - 

Black-chinned Hummingbird Archilochus alexandri - - X - 

Willow Flycatcher Empidonax traillii X - X - 

Vermillion Flycatcher Pyrocephalus rubinus X - - - 

Western Kingbird Tyrannus verticalis X X X - 

Loggerhead Shrike Lanius ludovicianus X X - - 

Bell’s Vireo Vireo belli X X - - 

Cliff Swallow Petrochelidon pyrrhonota - - X - 

Yellow-breasted Chat Icteria virens - X - - 

Western Tanager Piranga ludoviciana - - X - 

Abert’s Towhee Pipilo aberti - - X - 
189

Appendix 5 (continued) 

Common Name Scientific Name 1 2 3 4 

Quigley Wildlife Management Area (continued) 

Black-headed Grosbeak Pheucticus melanocephalus - - X - 

Blue Grosbeak Guiraca caerulea - X X - 

Lazuli Bunting Passerina amoena - - X - 

Red-winged Blackbird Agelaius phoeniceus - X X - 

Great-tailed Grackle Quiscalus mexicanus - - X - 

Brown-headed Cowbird Molothrus ater - X X - 

Bullock’s Oriole Icterus bullockii X X - - 

House Finch Carpodacus mexicanus - X X - 

Lesser Goldfinch Carduelis psaltria - - X - 
190

Appendix 6 

Habitat photos of yellow-billed cuckoo survey areas and sites in the lower Colorado River 

Watershed along the Virgin and Muddy rivers, Nevada, lower Colorado, Bill Williams and Gila 

rivers, Arizona and California, 2006. Listed with each photo are area name and site name when 

applicable. 

 

Littlefield Bridge, NV 

 

 

Mesquite Bridge, NV 

Littlefield Bridge Littlefield Bridge 

Mesquite Bridge Mesquite Bridge 
191

Pahranagat National Wildlife Refuge, NV 

 

 

 

Pahranagat NWR, Pahranagat North Pahranagat NWR, Pahranagat North 

Pahranagat NWR, Pahranagat East Pahranagat NWR, Pahranagat East 

Pahranagat NWR, Pahranagat South Pahranagat NWR, Pahranagat West 
192

Overton Wildlife Management Area, NV 

 

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

\ 

Overton WMA, Overton Wildlife Overton WMA, Overton Wildlife 

Grand Canyon NP, Spencer Canyon. 

Photo taken from helicopter. 

Overton WMA, Honey Bee Pond Overton WMA, Overton North 

Grand Canyon NP, Spencer Canyon
193

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

 

 

Lake Mead NRA, Chuckwalla Cove Lake Mead NRA, Chuckwalla Cove 

Lake Mead NRA, Cuckoo Beach Lake Mead NRA, Iceberg Ridge 

Grand Canyon NP, RM 274.5. Grand Canyon NP, RM 274.5 

Photo taken from helicopter. 
194

Lake Mohave, AZ 

 

 

 

Havasu National Wildlife Refuge, AZ 

 

 

 

Havasu National Wildlife Refuge, Arizona 

Lake Mohave, Waterwheel Cove Lake Mohave, Waterwheel Cove

Lake Mohave – Mohave Patch Lake Mohave – Mohave Patch 

Havasu NWR, Pintail Slough Havasu NWR, Pintail Slough 
195

Havasu National Wildlife Refuge, AZ (continued) 

 

 

 

 

Havasu NWR, North Dike Havasu NWR, North Dike 

Havasu NWR, Topock Marsh Restoration Havasu NWR, Topock Marsh Restoration 

Havasu NWR – Topock Tamarisk Havasu NWR – Topock Tamarisk 
196

Havasu National Wildlife Refuge, AZ (continued) 

 

 

 

 

Bill Williams River National Wildlife Refuge, AZ 

 

Havasu NWR, Sacramento Wash Havasu NWR, Sacramento Wash 

Havasu NWR, Havasu Tamarisk Havasu NWR, Havasu Tamarisk 

Bill Williams River NWR, Cave Wash. 

Photo taken from helicopter. 

Bill Williams River NWR, Cave Wash. 

Photo taken from helicopter. 
197

Bill Williams River National Wildlife Refuge, AZ (continued) 

 

 

 

 

Bill Williams River NWR, Gibraltar Rock Bill Williams River NWR, Gibraltar Rock 

Bill Williams River NWR, Mineral Wash Bill Williams River NWR, Mineral Wash 

Bill Williams River NWR, Big Bend. 

Photo taken from helicopter. 

Bill Williams River NWR, Big Bend 
198

Bill Williams River National Wildlife Refuge, AZ (continued) 

 

 

 

Bill Williams River NWR, Sandy Wash Bill Williams River NWR, Sandy Wash 

.

Bill Williams River NWR, Fox Wash Bill Williams River NWR, Fox Wash. 

Photo taken from helicopter. 

Bill Williams River NWR, Mosquito Flats Bill Williams River NWR, Mosquito Flats 
199

Bill Williams River National Wildlife Refuge, AZ (continued) 

 

 

Cibola National Wildlife Refuge, AZ 

Bill Williams River NWR, Bill Williams River 

 Marsh. 

Bill Williams River NWR, Bill Williams River 

Marsh. 

Bill Williams River NWR, Saguaro Slot Bill Williams River NWR, Saguaro Slot 

Cibola NWR, Cibola North Restoration Cibola NWR, Cibola North Restoration 
200

Cibola National Wildlife Refuge, AZ (continued) 

 

 

 

Cibola NWR, Cibola Nature Trail Restoration Cibola NWR, Cibola Nature Trail Restoration 

Cibola NWR, Cibola Nature Trail Restoration Cibola NWR, Cibola Nature Trail Restoration. 

 Photo taken from helicopter.

Cibola NWR, Cibola Eucalyptus Restoration Cibola NWR, Cibola Eucalyptus Restoration 
201

Cibola National Wildlife Refuge, AZ (continued) 

 

 

Cibola NWR, Cibola South Restoration 

Cibola NWR, Cibola South Restoration Cibola NWR, Cibola South Restoration. 

Photo taken from helicopter. 

Cibola NWR, Cibola South Restoration 

Cibola NWR, Cibola Eucalyptus Restoration Cibola NWR, Cibola Eucalyptus Restoration 
202

Cibola National Wildlife Refuge, AZ (continued) 

 

Cibola NWR, Cibola Cross River. 

West side of site before fire. 

Cibola NWR, Cibola Cross River. 

West side of site after fire. 

Cibola NWR, Cibola Cross River Cibola NWR, Cibola Cross River 

Cibola NWR, Cibola East Side Cibola NWR, Cibola East Side 
203

Picacho State Recreation Area, CA 

 

 

 

Imperial National Wildlife Refuge, AZ and CA 

\ 

 Imperial NWR, Imperial Paradise. 

overview from River. 

Imperial NWR, Imperial Paradise. 

Photo taken from helicopter. 

Picacho SRA, overview. Picacho SRA 

Picacho SRA. 

Photo taken from helicopter. 

Picacho SRA. 

Photo taken from helicopter. 
204

Imperial National Wildlife Refuge, AZ and CA (continued) 

 

 

Mittry Lake WMA/Pratt Restoration, AZ 

 

 

Yuma West Wetlands Park, Y Mittry Lake WMA at Betty’s Kitchen 

Mittry Lake WMA/Pratt Restoration. 

 Photo taken from helicopter. 

Mittry Lake WMA/Pratt Restoration. 

 Photo taken from helicopter. 

Inside the Mittry Lake WMA/Pratt Restoration 

Imperial NWR, Imperial South 

Restoration 

Imperial NWR, Imperial South Restoration, 

overview from Refuge Headquarters. 
205

Gila/Colorado River Confluence, AZ and CA 

 

Gila/Colorado River Confluence, AZ and CA 

Gila/Colorado River Confluence, 

Colorado River 

Gila/Colorado River Confluence, 

Colorado River 

Gila/Colorado River Conluence, Colorado 

River. Photo taken from helicopter. 

Gila/Colorado River Confluence, 

Colorado River 

Gila/Colorado River Confluence, Gila River Gila/Colorado River Confluence, Gila River 
206

Gila/Colorado River Confluence, AZ and CA (continued)

 

Yuma West Wetlands, AZ 

Yuma West Wetlands Yuma West Wetlands 

Yuma West Wetlands, 

inside restoration site. 

Yuma West Wetlands, 

inside restoration site. 

Gila/Colorado River Confluence, Gila River Gila/Colorado River Confluence, Gila River 
207

Limitrophe Division, AZ 

 

Limitrophe Division North Sites (continued) 

 

 

 

 

Limitrophe Division North 

Limitrophe Division North Limitrophe Division North 

Limitrophe Division South

Limitrophe Division North. 

Photo taken from helicopter. 

Limitrophe Division South Site. 

Photo taken from helicopter.
208

Limitrophe Division (continued) 

Gila River Highway 95, AZ 

 

 

 

 

Gila River Highway 95, Gila 95 Canal Gila River Highway 95, Gila 95 Canal 

Gila River Highway 95, Gila 95 Tall Tamarisk Gila River Highway 95, Gila 95 Tall Tamarisk 

Limitrophe Division South Limitrophe Division South 
209

Gila River Highway 95, AZ (continued) 

 

Gila River/Ligurta, AZ 

Gila River/Wellton, AZ 

Gila River/Wellton Gila River/Wellton 

Gila River/Ligurta Gila River/Ligurta 

Gila River Highway 95, Gila 95 Bridge Gila River Highway 95, Gila 95 Bridge. 

Photo taken from helicopter. 
210

Gila River/Quigley Pond WMA, AZ 

 

 

 

 

 

Gila River/Quigley Pond WMA Gila River/Quigley Pond WMA 

Gila River/Quigley Pond WMA Gila River/Quigley Pond WMA