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BLM/AK/ST-03/016+6501+023 

This document is also available on the the Northern Field Office (Alaska) Web site at 

http://aurora.ak.blm.gov/npra/wildlife 

Cover and title page photo by Ted Swem, U.S. Fish and Wildlife Service. 
Raptors 

By 

Bureau of Land Management 

Fairbanks, Alaska 99709 

Aerial Surveys of 

Cliff-Nesting 

in the National 

Petroleum Reserve–Alaska, 

1999, with Comparisons 

to 1977 

Robert J. Ritchie, 

Ann M. Wildman, and 

David A. Yokel 

Technical Note 413 

U.S. DEPARTMENT OF THE INTERIOR 

1150 University Avenue 

December 2003 
Suggested citation: 

Ritchie, Robert J., Ann M. Wildman, and David A. Yokel. 2003. Aerial surveys of cliff-nesting raptors in the 

National Petroleum Reserve–Alaska, 1999, with comparisons to 1977. Technical Note 413. Bureau of Land 

Management, Denver, Colorado. BLM/AK/ST-03/016+6501+023. 66 pp. 

ii Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 
Contents


Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

Study Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

Survey Conditions and Limitations . . . . . . . . . . . . . . . . . . . . . . . . .11

Peregrine Falcons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

Gyrfalcons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21

Golden Eagles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Rough-legged Hawks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

Nest Site Habitat Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29

Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

Peregrine Falcons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

Gyrfalcons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37

Golden Eagles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37

Rough-legged Hawks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40

Nest Site Habitat Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40

Survey Efficacy and Recommendations . . . . . . . . . . . . . . . . . . . . . .43

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45

Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47

Unpublished References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51

Appendix A. The Number of Sites Occupied by Peregrine Falcons 


in the National Petroleum Reserve–Alaska, 1952–1999 . . . . . . . . . .55

Appendix B. Description of Nesting Habitat for Cliff-Nesting 


Raptors in the Foothills and Mountains of the National Petroleum


Reserve–Alaska . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 iii
Figure 1.	 Map of the National Petroleum Reserve–Alaska showing the List of 

Northeast Planning Unit and major drainages surveyed for 

Figures
 raptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Figure 2.	 Comparison of the areas surveyed in 1977 and 1999, including 

a region of lakes surveyed in 1999 . . . . . . . . . . . . . . . . . . . . .6 

Figure 3.	 Distribution of peregrine falcon (Falco peregrinus tundrius) sites 

identified during fixed-wing aerial surveys in the National Petroleum Reserve–Alaska, July 1999 . . . . . . . . . . . . . . . . . . . . . .16

Figure 4.	 Photographs of (a) mud bank habitat on a large lake in the 

Oumalik Lakes area, northern Alaska; and (b) a portion of that 

bank used by peregrine falcons (Falco peregrinus tundrius) for 

nesting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

Figure 5.	 Distribution of gyrfalcon (Falco rusticolus) sites identified 

during fixed-wing aerial surveys in the National Petroleum 

Reserve–Alaska, July 1999 . . . . . . . . . . . . . . . . . . . . . . . . . .22

Figure 6.	 Distribution of golden eagle (Aquila chrysaetos) sites identified 

during fixed-wing aerial surveys in the National Petroleum 

Reserve–Alaska, July 1999 . . . . . . . . . . . . . . . . . . . . . . . . . .25

Figure 7.	 Distribution of rough-legged hawk (Buteo lagopus) sites identified 

during fixed-wing aerial surveys in the National Petroleum 

Reserve–Alaska, July 1999 . . . . . . . . . . . . . . . . . . . . . . . . . .28

Figure 8.	 Habitat assessment for cliff-nesting raptors in the Northeast 

Planning Unit, National Petroleum Reserve–Alaska (additions to 

mapping found in Ritchie 1979) . . . . . . . . . . . . . . . . . . . . .31

iv Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 
Figure 9.	 Distribution of peregrine falcon (Falco peregrinus tundrius) sites List of 

identified during fixed-wing aerial surveys in the National 

Petroleum Reserve–Alaska, July 1977 and July 1999 . . . . . . .32 Figures


(continued) Figure 10.	 Photographs of (a) typical low, soil bank used by nesting peregrine


falcons (Falco peregrinus tundrius) on drainages on the Arctic


Coastal Plain in the Northeast Planning Unit, National Petroleum


Reserve–Alaska; and (b) a ground nest site of peregrines at the


top of a bluff, upper Price River . . . . . . . . . . . . . . . . . . . . . .35

Figure 11. Distribution of gyrfalcon (Falco rusticolus) sites with pairs


observed during fixed-wing aerial surveys in the National


Petroleum Reserve–Alaska, July 1977 and July 1999 . . . . . .38

Figure 12.	 Distribution of golden eagle (Aquila chrysaetos) sites with pairs


observed during fixed-wing aerial surveys in the National


Petroleum Reserve–Alaska, July 1977 and July 1999 . . . . . . .41

Figure 13.	 Distribution of rough-legged hawk (Buteo lagopus) sites with


pairs observed during fixed-wing aerial surveys in the National


Petroleum Reserve–Alaska, July 1977 and July 1999 . . . . . . .42

Appendix Figure B.1. Distribution of habitat classes for cliff-nesting raptors


(Ritchie 1979) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64

Appendix Figure B.2. Habitat types, National Petroleum Reserve–Alaska . . .65

(a) Escarpment face (EF) on upper Kokolik River. . . . . . . . .65

(b) Shale banks (SB) on Ipnavik River. . . . . . . . . . . . . . . . . .65

(c) Soil and mud banks (MB) on lower Titaluk River. . . . . . .65

(d) Minaret outcrops (O) on Lisburne Ridge. . . . . . . . . . . . .65

(e) Rock cliffs (RC) along the Kiligwa River. . . . . . . . . . . . . .66

(f ) Scree and talus banks (ST) on the Kigalik River. . . . . . . .66

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 v
List of Table 1. Distribution, abundance, and productivity of peregrine falcons 

Tables 

(Falco peregrinus tundrius) by river drainage in the National 

Petroleum Reserve–Alaska, 1999 . . . . . . . . . . . . . . . . . . . . .12 

Table 2. Distribution, abundance, and productivity of cliff-nesting raptors in 1977 and 1999 in ecoregions of the National Petroleum 

Reserve–Alaska, 1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14 

Table 3a. Frequency (proportions) of use of different substrate types and 

mean elevation (in meters) of nest sites of peregrine falcons 

(Falco peregrinus tundrius), gyrfalcons (Falco rusticolus), golden eagles 

(Aquila chrysaetos), and rough-legged hawks (Buteo lagopus) in the 

National Petroleum Reserve–Alaska, 1999 . . . . . . . . . . . . . . . . .18 

Table 3b. Estimated dimensions of substrates at sites used by peregrine 

falcons (Falco peregrinus tundrius), gyrfalcons (Falco rusticolus), 

golden eagles (Aquila chrysaetos), and rough-legged hawks (Buteo 

lagopus) in the National Petroleum Reserve–Alaska, 1999 . . .18 

Table 4. Distribution, abundance, and productivity of gyrfalcons (Falco 

rusticolus) by river drainage in the National Petroleum 

Reserve–Alaska, 1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20 

Table 5. Distribution, abundance, and productivity of golden eagles 

(Aquila chrysaetos) by river drainage in the National Petroleum 

Reserve–Alaska, 1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24 

Table 6. Distribution, abundance, and productivity of rough-legged 

hawks (Buteo lagopus) by river drainage in the National Petroleum 

Reserve–Alaska, 1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26 

vi Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 
Table 7.	 Description of nesting habitat for cliff-nesting raptors in the List of 

transition region between the Arctic Foothills and the Arctic 

Coastal Plain of the Northeast Planning Unit, National Petroleum Tables 

Reserve–Alaska (areas are mapped in Figure 8) . . . . . . . . . . .30 (continued) 

Table 8.	 The number of occupied sites (single adults and pairs) of gyrfalcons 

(Falco rusticolus), golden eagles (Aquila chrysaetos), and rough-legged 

hawks (Buteo lagopus) in the National Petroleum Reserve–Alaska in 

1977 and 1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 vii

Abstract


In summer 1999, an extensive aerial survey of cliff-nesting raptors was 

conducted in the National Petroleum Reserve–Alaska (NPR–A) on Alaska’s 

North Slope. No similarly extensive survey had been conducted since 1977. 

In the interim, the regional population of the Arctic peregrine falcon (Falco 

peregrinus tundrius) had increased, as shown by monitoring along the 

Colville River. The 1999 survey assessed the present abundance and distribution of the peregrine falcon, as well as the gyrfalcon (Falco rusticolus), 

golden eagle (Aquila chrysaetos), and rough-legged hawk (Buteo lagopus) in 

most of the NPR–A. Specifically excluded from the 1999 survey were the 

Kogosukruk and Kikiakrorak Rivers and the Colville River below its junction with the Etivluk River. These areas had been included in other recent 

surveys. Peregrine falcons were found occupying 67 sites in 1999, 61 of 

which were in the area surveyed in 1977 and in which only four occupied 

sites were found. Gyrfalcons nest earlier than other raptor species in the 

NPR–A, and the 1999 survey was conducted too late in the season to determine occupancy of many sites. Gyrfalcons were located at only 19 sites in 

1999, down from 29 in 1977, but 41 sites showing evidence of gyrfalcon 

use were identified, whereas only 29 such sites were identified in 1977. 

Eleven pairs of golden eagles were found in 1999, which is similar to the 

10 pairs found in 1977. Rough-legged hawks were the most abundant and 

widespread cliff-nesting raptors in the NPR–A in both years. Their relative 

distribution was similar in the 2 years, but twice as many pairs were found 

in 1999 (109) as in 1977 (55). The difficulties of comparing the results of 

the two surveys are discussed. 

Photo by Ted Swem, U.S. Fish and Wildlife Service. 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 1

Introduction


In 1977, Ritchie (1979) conducted the first extensive aerial surveys 

specifically directed at locating and taking inventory of cliff-nesting raptors 

and evaluating habitats for these species in the National Petroleum 

Reserve–Alaska (NPR–A). The primary objectives of those surveys were to 

locate peregrine falcons (Falco peregrinus tundrius) outside the main 

Colville River corridor and evaluate habitat in the foothill and mountain 

provinces of the NPR–A for peregrine falcons, gyrfalcons (Falco rusticolus), 

golden eagles (Aquila chrysaetos), and rough-legged hawks (Buteo lagopus). Other 

raptor surveys in the area (Pegau 1975; Cade and White 1976) had been more 

limited in regional or species coverage. 

The Bureau of Land Management (BLM), during evaluations of the 

potential effects of oil leasing, exploration, and development on wildlife— 

including raptors in the northeastern portion of the NPR–A, identified 

the need for current distributional information on raptors in that region. 

It is important to note that the status and abundance of at least one 

species, the peregrine falcon, had changed substantially in northern Alaska 

since the 1977 survey (Ambrose et al. 1988). However, with the exception 

of annual monitoring of peregrines along the main Colville River, information from other areas in the NPR–A was scant, incomplete, outdated, 

or limited in accessibility (unpublished agency trip reports). The objectives 

of this study were to (1) duplicate, as closely as possible, aerial survey 

coverage and techniques employed in 1977 to compare cliff-nesting raptor 

populations between the two periods; (2) assess the present distribution, 

abundance, and degree of recovery of the peregrine falcon population in 

the region; and (3) identify and assess cliff-nesting habitats in areas not 

previously surveyed in the northeastern portion of the NPR–A. 

Peregrine falcons are emphasized in this report because of the role they 

have played in influencing the development of protection strategies for all 

raptors in northern Alaska, their special status (i.e., recently delisted endangered 

species), and because of dramatic increases in their populations recorded in other 

regions of northern Alaska (Ambrose et al. 1988). 

Photo by Jim Silva, Bureau of Land Management. 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 3
4 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977

Figure 1. Map of the National Petroleum Reserve–Alaska showing the Northeast Planning Unit and major drainages surveyed for raptors. (The dashed lines delineate the

three ecoregions: the Arctic Coastal Plain, the Arctic Foothills, and the Brooks Range.)
Study Area


The 1999 study area generally 

included all cliff habitats in the 

NPR–A, excluding the Kogosukruk 

and Kikiakrorak Rivers and the 

Colville River below its junction with 

the Etivluk River (Figures 1 and 2). 

This area is composed of three ecoregions (Figure 1): Arctic Coastal Plain, 

Arctic Foothills, and Brooks Range 

(including the De Long Mountains; 

Gallant et al. 1996). Figure 2 shows a 

comparison of the areas surveyed in 

1977 and 1999. 

Ritchie (1979) described six habitats 

used for nesting substrates by cliffnesting raptors in the Arctic Foothills 

and Brooks Range ecoregions of the 

NPR–A: shale banks, mud (soil) or 

sand banks, rock cliffs (along floodplains), outcrops (isolated rock 

exposures, removed from floodplains), scree and talus slopes, and 

escarpment faces (extensive cliffs 

associated with large, off-river mesas; 

Appendix B). These habitat types 

were used during the present study 

to describe areas in the NE Planning 

Unit not previously mapped. 

The Arctic Coastal Plain is the 

northernmost ecoregion, bounded by 

the Arctic Ocean and characterized 

by little topographical relief and 

low-gradient, meandering watercourses. Consequently, habitats are 

limited for cliff-nesting raptors. However, a few landforms in this region 

(i.e., pingoes [ice-cored hills or 

mounds], coastal bluffs, and dunes 

and mud banks along lake shorelines 

and some meandering rivers) offer 

potential habitat for cliff-nesting 

raptors—particularly peregrine falcons 

and rough-legged hawks. 

Most habitats for cliff-nesting raptors 

in the NPR–A occur in the Arctic 

Foothills ecoregion. This wide swath 

of rolling hills and plateaus, formed 

by the gentle warping of sedimentary 

beds into anticlines and synclines, 

grades from the Arctic Coastal Plain 

on the north to the Brooks Range on 

the south. Cliff habitat has been 

created in many areas where streams 

have crossed and eroded the geologic 

folds. The area can be separated 

into northern and southern sections. 

The northern section is dominated 

by loosely consolidated cutbanks 

(<600 m in elevation) and the 

southern section (<800 m in elevation) includes rock outcrops along 

fast, braided rivers and off-river sites 

Photo by Jim Silva, Bureau of Land Management. 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 5 
6 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977

Figure 2. Comparison of the areas surveyed in 1977 and 1999, including a region of lakes surveyed in 1999 (near center of map).
on cliffs and rock outcrops associated 

with mesas and buttes (Gallant et 

al. 1996). 

The Brooks Range ecoregion generally comprises several rugged mountain areas, including cliffs, in the 

western Brooks Range and De Long 

Mountains of the NPR–A. These 

areas provide nest sites for cliff-nesting 

raptors, particularly golden eagles and 

gyrfalcons. Most of this ecoregion 

in the NPR–A is dominated by 

talus and scree slopes, however, 

which are poor habitats for cliffnesting raptors. Furthermore, 

because cliff habitats in this 

ecogregion exceed general elevation 

limits for nesting by peregrine falcons 

(Cade 1960), they provide limited 

opportunities for peregrines. 

Photo by Ted Swem, U.S. Fish and Wildlife Service. 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 7 

Methods


Aerial surveys were conducted in the 

NPR–A between 23 and 29 July and 

on 2 August 1999. In 1977, aerial 

surveys were flown between 27 June 

and 11 July (Ritchie 1979), or about 

2 to 3 weeks earlier than surveys in 

1999. This difference in survey timing (i.e., 1977 surveys occurred 

earlier in the breeding cycle) needs 

to be considered when comparing 

results of the 2 years. 

A Piper Super Cub fixed-wing aircraft with a pilot and one observer 

was used for all surveys. Standard 

operating procedures involved flying 

at 120 kph and <200 m above 

ground level along drainages, ridgelines, and other areas where bank 

and cliff exposures suitable for nesting 

occurred. When suitable habitats were 

identified, we made slower (80 kph) 

passes at lateral distances of about 

50 m. Multiple passes (two to four) 

were often required to better determine occupancy and productivity, 

particularly where cliffs were large or 

complex. Except where tight maneuvering was hazardous because of the 

topography (e.g., invaginated cliffs), 

nesting habitats were approached 

as directly as possible to minimize 

surprising nesting birds (Fyfe and 

Olendorff 1976). In addition to limitations imposed by terrain, some cliffs 

could not be approached closely 

because of locally unsafe winds or 

the proximity of defensive and 

aggressive adults. 

At each suitable nesting habitat we 

searched for signs of raptor use, 

including the presence of stick 

nests and nesting ledges, whitewash 

(feces) deposits, and the presence 

of adult raptors or young. The following information was recorded at 

each site where at least one individual 

raptor was recorded or a definitive 

sign of raptor nesting use (e.g., stick 

nest, nest ledge) was identified: 

Unique site number (sequential 

for each U.S. Geological Survey 

[USGS] 1:250,000 map); 

Location (recorded on USGS 

1:250,000 map); 

Latitude and longitude (World 

Geodetic System 1984 [WGS-84] 

datum; recorded with onboard 

global positioning system [GPS]); 

Species present were the peregrine falcon, gyrfalcon, golden 

eagle, and rough-legged hawk; 

common raven (Corvus corax) 

nests were also noted, although 

this species was not a target of 

this study. At some sites only 

young were recorded and the 

Photo by Bruce Durtsche, Bureau of Land Management. 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 9 
species was determined by a 

combination of factors such 

as plumage (e.g., white down 

of falcons vs. gray [second] 

down in rough-legged hawks), 

nest type (e.g., large, regularly 

inaccessible stick nest of golden 

eagle vs. smaller, often more 

accessible hawk nest), and 

expected nest phenology differences (e.g., most gyrfalcons were fledged or nearly 

fledged vs. midnestling stage 

of peregrine falcons in late 

July) among species. If nests 

or nestlings could not be 

identified as to species, they 

were described as “unknown”; 

Number of adults (pairs 

were counted for sites where 

young were present); number 

and approximate age of young; 

presence of eggs; 

Occupancy: (1) Unoccupied— 

nest present but no adults 

observed; could include 

nests used before 1999; (2) 

Occupied—pair of adults or 

an aggressive single adult, in 

combination with other 

signs of use (e.g., nest); and 

(3) Occupied and Successful— 

at least one young present or 

recently fledged; 

Dimensions of the nesting 

habitat (e.g., height and 

length of cliffs) and height of 

nest in meters; (Estimated 

from the aircraft; these were 

crude estimations intended to 

provide a rough idea of the 

relative size of the substrate); 

General habitat category as 

defined in Ritchie (1979): shale 

banks, mud (also described as 

soil in this report) or sand 

banks, rock cliffs (along floodplains), outcrops (isolated rock 

exposures, removed from 

floodplains), scree and talus 

slopes, and escarpment faces 

(cliffs associated with large, 

off-river mesas); 

Location of riverine site on 

left or right bank when facing 

upstream; and 

Primary exposure of cliff and 

nest (nearest 45 degrees). 

Productivity values are presented 

for successful pairs and for all 

pairs. The values of young per 

pair for all pairs, however, are 

probably artificially high and 

should be used with caution. We 

conducted only one survey, 

whereas two surveys are essential 

for improving the accuracy of this 

calculation (Steenof 1987). 

That is, many pairs that did 

not nest or had failed nests 

probably departed their territories 

before the time of our survey, 

resulting in an inflated estimation 

of young per pair for all pairs 

according to our counts. 

Nonetheless, the calculations 

are included in the present 

report because they allow a 

gross comparison with other 

studies reporting this value. 

After surveys were completed, 

GPS location data were entered 

on GIS base maps with AtlasGIS Software (ESRI, Redlands, 

California). 

10 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 
Results


Survey Conditions and 

Limitations 

In the Brooks Range and Arctic 

Foothills ecoregions of the NPR–A, 

nearly all major drainages and their 

tributaries, as well as intervening 

off-river rock outcrops and ridges 

surveyed in 1977, were resurveyed 

for raptors in 1999 (Figure 2). 

Mid- to upriver portions of major 

streams on the Arctic Coastal 

Plain, however—especially those 

with their origins in the Foothills 

between the Meade and Colville 

Rivers—were surveyed more extensively in 1999 than in 1977. Also 

during the 1999 flights, a number 

of lakes with steep, eroding soil 

banks (>5 m in height), were noted 

in a transitional area between the 

northern edge of the Arctic Foothills 

and the southern edge of the Arctic 

Coastal Plain. A sample of these 

lakes was surveyed, primarily those 

between the Ikpikpuk and Titaluk 

Rivers, including the Oumalik Lakes 

area (Figure 2). 

The Kokolik River and its tributaries 

and portions of the Utukok, the 

Kogosukruk, and Kikiakrorak Rivers 

in the Arctic Foothills ecoregion were 

not surveyed in 1999. Dangerous 

winds thwarted attempts to fly the 

entire Utukok and Kokolik 

drainages. However, these two 

rivers were surveyed by Peter Bente 

(Alaska Department of Fish and 

Game [ADFG], personal communication; Appendix A) during the 

late incubation to early nestling 

stage (4–9 July 1999), and we 

summarize here some of his observations. We did not survey the 

Kogosukruk and Kikiakrorak Rivers 

because a complete helicopter survey 

of these rivers was conducted in 1997 

(T. Swem, U.S. Fish and Wildlife 

Service [USFWS], personal communication; Appendix A) that provided 

sufficient information for describing present raptor use. Similarly, 

the main Colville River, below its 

junction with the Etivluk River, 

was not included in this survey 

because it was surveyed by boat in 

1999 (T. Swem, USFWS, personal 

communication; Appendix A). 

Peregrine Falcons 

Peregrine falcons occupied 67 sites in 

the NPR–A in 1999 (Table 1). These 

sites were composed of a minimum of 

51 pairs and 16 single adults. Most 

(84%) of the pairs observed were successful, producing at least one young. 

For the entire study area, productivity 

averaged 2.3 young per successful pair 

(Table 1) and 2.0 young per pair for 

all pairs (Table 2). 

Photo courtesy of the Bureau of Land Management. 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 11 
12 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977

Table 1. Distribution, abundance, and productivity of peregrine falcons (Falco peregrinus tundrius) by river

drainage in the National Petroleum Reserve–Alaska, 1999.

Single Successful Young per

Drainage All Sites Adults Pairs Pairs Young Successful Pair

Avalik 2 0 2 2 6 3.0

Awuna 0 0 0 0

Colville, Upper 9 1 8 7 18 2.6

Etivluk 2 0 2 1 2 2.0

Fish Creek 9 3 6 6 14 2.3

Ikpikpuk 5 2 13 12 29 2.4

Ipnavik 2 0 2 1 1 1.0

Ishuktak 2 1 1 1 2 2.0

Ketik 0 0 0 0

Kigalik 1 0 1 1 1 1.0

Kiligwa 3 1 2 2 6 3.0

Kokolik 0 0 0 0

Kuna 1 1 0 0

Meade 0 0 0 0

Nigu 0 0 0 0

Nuka 0 0 0 0

Oumalik Lakes 4 1 3 3 3 1.0

Oumalik River 1 1 0 0

Titaluk 5 2 3 2 6 3.0

Topagoruk 4 1 3 2 7 3.5

Usuktuk 2 1 1 1 1 1.0

Utukok 5 1 4 2 4 2.0

Total 67 16 51 43 100 2.3
Most peregrine falcon sites (61%) 

were found in a narrow belt of lowrelief tundra drained by meandering, 

slow-gradient rivers north of the 

Colville River (Figure 3), including 

the Ikpikpuk River and its primary 

tributaries, the Titaluk and Price 

Rivers, and Fry Creek. The area is 

rich in lakes, which are often bordered at their northern ends by 

rolling-to-steep exposed soil banks, 

caused by thermokarsting (erosion). Peregrines (three pairs, two 

of which were successful, and two 

single adults) were located at five 

lakes in this region (Figure 4). Additionally, a few sites (6%) were 

located in the northern Foothills 

and the rest (33%) were distributed 

in the lower reaches of the Colville 

tributaries that drain the northern 

side of the Brooks Range (Table 2). 

Peregrine falcons primarily nested 

on low mud and sand banks (69%) 

associated with low-gradient streams 

and lakes in a transitional zone 

between the Arctic Coastal Plain and 

northern Foothills, or shale bluffs 

(27%) associated with faster braided 

streams in the southern Foothills 

(Table 3a). Rock cliffs and scree 

slopes were also used to a limited 

degree. All sites were closely associated with riverine or lacustrine (i.e., 

deep, open lakes) habitats. No pairs 

or single birds were recorded at offriver rock outcrops. The mean elevation of nest sites with pairs was 

174 m (SD = 144; range 30–490 m; 

n = 51; Table 3a). Approximate 

dimensions of nest site substrates used 

by peregrine falcons are summarized 

in Table 3b. 

Photo by Alexander Reshetniak, Raptor Education Foundation. 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 13 
14 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977

Ecoregion

All Sites

Peregrine Falcon

(Falco peregrinus tundrius)

Table 2. Distribution, abundance, and productivity of cliff-nesting raptors in 1977 and 1999 in ecoregions of the National Petroleum

Reserve–Alaska, 1999.

(Falco rusticolus)

Gyrfalcon

Pairs

Young

Young per pair

All Sites

Pairs

Young

Young per pair

1977

Coastal Plain 0 0 0 1 1 0 0

Northern Foothills 1 0 0 7 4 7 1.8

Southern Foothills 2 2 0 0 21 16 27 1.7

and Brooks Range

Total 3 2 0 0 29 21 34 1.6

1999

Coastal Plain 41 29 60 2.1 2 1 3 3.0

Northern Foothills 4 4 9 2.3 5 4 7 1.8

Southern Foothills 22 18 31 1.7 34 11 15 1.4

and Brooks Range

Total 67 51 100 2.0 41 16 25 1.6

a ND = not detected; survey in 1977 mostly confined to incubation stage, and limited numbers of 

young could be detected.
Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 15

Csuti

et al.

19952

Hagar

and 

Stern

19773

Rough-legged Hawka

(Buteo lagopus)

0 0 0 1 1 ND ND

0 0 0 15 13 ND ND

25 10 17 1.7 44 41 ND ND

25 10 17 1.7 60 55 ND ND

0 0 0 7 7 14 2.0

0 0 0 30 18 35 1.9

35 11 13 1.2 145 84 161 1.9

35 11 13 1.2 182 109 210 1.9 All Sites Pairs Young Young per pair All Sites Pairs Young Young per pair

Golden Eagle

(Aquila chrysaetos)
Distribution of peregrine falcon (Falco peregrinus tundrius Figure 3. ) sites identified during fixed-wing aerial surveys in the National Petroleum Reserve–Alaska, July 1999. (The

dashed lines delineate the three ecoregions: the Arctic Coastal Plain, the Arctic Foothills, and the Brooks Range [see Figure 1].) 

16 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 
a 

b 

Figure 4. Photographs of (a) mud bank habitat on a large lake in the Oumalik Lakes area, northern 

Alaska; and (b) a portion of that bank used by peregrine falcons (Falco peregrinus tundrius) for nesting. 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 17
18 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977

Species

Table 3a. Frequency (proportions) of use of different substrate types and mean elevation (in meters) of nest sites of

peregrine falcons (Falco peregrinus tundrius), gyrfalcons (Falco rusticolus), golden eagles (Aquila chrysaetos), and roughlegged hawks (Buteo lagopus) in the National Petroleum Reserve–Alaska, 1999.

Mud Bank

Pairs

All Sites

Pairs

All Sites

Pairs

All Sites

Pairs

Peregrine Falcon 67 51 0 0 0.70 0.69 0.03 0.02

Gyrfalcon 41 16 0.10 0.06 0.02 0 0.76 0.69

Golden Eagle 35 11 0.03 0.09 0 0 0.83 0.82

Rough-legged Hawk 182 109 0.01 0.02 0.10 0.11 0.26 0.24

Escarpment Rock Outcrop

(floodplain) n

All Sites

Species

Table 3b. Estimated dimensions of substrates at sites used by peregrine falcons (Falco peregrinus tundrius), gyrfalcons

(Falco rusticolus), golden eagles (Aquila chrysaetos), and rough-legged hawks (Buteo lagopus) in the National Petroleum

Reserve–Alaska, 1999.

mean

SD

range

Peregrine Falcon 67 26 12 5–75 156 91 20–400 20 10 4–48

Gyrfalcon 41 43 30 7–150 130 139 20–800 25 16 3–75

Golden Eagle 35 53 28 10–125 138 157 20–800 33 20 7–90

Rough-legged Hawk 182 22 13 5–80 88 71 10–400 14 8 1–45

All Sites

Height (m) Length (m) Nest Height (m) mean SDrange mean SDrange

n
Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 19

0 0 0.25 0.27 0.01 0.02 169 146 30–490 174 144 30–490

0 0 0.12 0.25 0 0 398 201 60–730 368 203 60–670

0 0 0.06 0 0.09 0.09 597 162 150–820 615 173 180–790

0.02 0.02 0.43 0.48 0.17 0.14 364 163 30–730 364 157 30–670

Scree Slope

Pairs

All Sites

Pairs

All Sites

Pairs

mean

SD

Shale Bank Elevation (m) Rock Outcrop

(nonfloodplain) All Sites

All Sites Pairs range mean SD

range

51 27 10 8–50 152 79 20–400 20 10 4–48

16 36 26 7–100 159 194 25–800 22 14 3–50

11 47 19 20–75 155 227 30–800 30 14 17–60

109 24 12 5–80 91 61 15–400 16 8 1–45

Pairs

mean

SD

range

Height (m) Length (m) Nest Height (m) mean SDrange mean SDrange

n
Table 4. Distribution, abundance, and productivity of gyrfalcons (Falco rusticolus) by river drainage in the National 

Petroleum Reserve–Alaska, 1999. 

0 0 0 0 

2 0 2 2 4 

3 0 3 3 6 2.0 

1 0 1 0 

0 0 0 0 

2 0 0 0 

2 0 0 0 

0 0 0 0 

0 0 0 0 

Kigalik 1 0 1 1 2 

Kiligwa 5 0 2 2 2 

0 0 0 0 

8 0 2 2 3 

1 0 1 1 1 

3 0 0 0 

1 0 1 1 2 

0 0 0 0 

0 0 0 0 

1 0 1 1 3 3.0 

0 0 0 0 

0 0 0 0 

11 3 2 2 2a 2.0 

41 3 

Single Successful Young per 

Drainage All Sites Adults Pairs Pairs Young Successful Pair 

Avalik 

Awuna 2.0 

Colville, Upper 

Etivluk 

Fish Creek 

Ikpikpuk 

Ipnavik 

Ishuktak 

Ketik 

2.0 

1.0 

Kokolik 

Kuna 1.5 

Meade 1.0 

Nigu 

Nuka 2.0 

Oumalik Lakes 

Oumalik River 

Titaluk 

Topagoruk 

Usuktuk 

Utukok 

Total 16 15 25 1.8 

a The number of young was only determined at one of two successful sites on the 

Utukok River. 

20 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 
Gyrfalcons 

Forty-one sites or cliff locations 

(characteristically whitewash 

[feces]-covered nest ledges or ledges 

with adults or young present) 

probably used by gyrfalcons were 

identified during our aerial surveys 

in the NPR–A (Table 4). Many of 

these locations may not have been 

occupied in 1999. The timing of 

our surveys did not allow a determination of occupancy at many 

sites. Gyrfalcons occupied 19 of 

these sites, including 3 single adults 

and 16 pairs, whereas 22 sites were 

unoccupied. Most pairs (93%) were 

successful, and for the entire study 

area productivity averaged 1.8 young 

per successful pair (Table 4) and 1.6 

young per pair for all pairs (Table 2). 

Because we probably missed identifying some young because of the timing 

of our aerial survey (i.e., our surveys 

were flown after some gyrfalcons had 

already fledged), productivity values 

may be higher. 

Most gyrfalcon nest sites (83%) 

were on cliffs in the southern 

Foothills, particularly in the southwestern portion of the study area 

(Figure 5); sites on the Kiligwa, 

Kuna, and Utukok Rivers accounted for more than half (58%) of all 

recorded sites (Table 4). This area 

has the most well-developed cliff 

faces—both riparian and offriver—and relatively steep-gradient braided rivers cutting through 

moist tussock and alpine tundra. In 

contrast, only seven sites were 

located in the northern Foothills 

and its transition with the Arctic 

Coastal Plain (Table 2). 

Gyrfalcons primarily nested on 

rock cliffs (69%) and shale banks 

(25%) associated with the floodplains of rivers in the Arctic 

Foothills (Table 3a). A few sites 

(6%) were on off-river outcrops 

and on escarpment cliffs in the 

southern Foothills. No pairs were 

recorded on scree and talus slopes 

or on unconsolidated soil or mud 

banks often found in the northern 

Foothills and Coastal Plain, respectively. The mean elevation of nest 

sites with pairs was 368 m (SD = 

203 m; range 60–670 m; n = 16; 

Table 3a). Gyrfalcons generally 

used larger cliff habitats than peregrine falcons and rough-legged 

hawks (Table 3b). 

Photo by Ted Swem, U.S. Fish and Wildlife Service. 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 21 
Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 

Figure 5. Distribution of gyrfalcon (Falco rusticolus) sites identified during fixed-wing aerial surveys in the National Petroleum Reserve–Alaska, July 1999. (The dashed lines

delineate the three ecoregions: the Arctic Coastal Plain, the Arctic Foothills, and the Brooks Range [see Figure 1].) 

22 
Golden Eagles 

We identified (by the presence of 

stick nests, adults, or young) 35 

cliff locations that golden eagles 

had used for nesting during our 

aerial surveys in the NPR–A (Table 

5). Many of these locations were 

probably not used in 1999, and 

some represent alternative nest sites 

for pairs nesting at other locations. 

Golden eagles occupied at least 12 

of these sites, including 11 successful pairs and a single adult. Productivity averaged 1.2 young per 

successful pair (Table 5; same for 

all pairs, Table 2) for the entire 

study area. 

In the southern Foothills, golden 

eagle nest sites were distributed in the 

same drainages, and golden eagles 

used substrate types similar to those 

used by gyrfalcons (i.e., generally 

large, vertical face cliffs; Tables 2 and 

3a, Figure 6). Nests on the Kiligwa, 

Kuna, and Utukok Rivers accounted 

for nearly three-fourths (71%) of 

all observed nests (Table 5). The 

southern Foothills have the most 

well-developed cliff faces, both on 

and off relatively steep-gradient, 

braided rivers that cut through 

moist tussock and alpine tundra. 

Golden eagles usually nested (82%) 

on the largest cliffs that were associated with rivers in the southern 

Foothills near the Brooks Range 

(Table 3a and b). A few sites were 

off-river on escarpment cliffs (9%) or 

on talus slopes along rivers (9%). 

Although no pairs or sites were 

identified on unconsolidated soil 

or mud banks in the northern 

Foothills or Arctic Coastal Plain, 

subadult eagles regularly were 

observed in these areas. The mean 

elevation of nest sites with pairs 

was 615 m (SD = 173 m; range 

180–790 m; n = 11). The lowest 

elevation nests were on the 

Utukok River. 

Photo by Alexander Reshetniak, Raptor Education Foundation. 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 23 
Table 5. Distribution, abundance, and productivity of golden eagles (Aquila chrysaetos) by river drainage in the 

National Petroleum Reserve–Alaska, 1999. 

0 0 0 0 

0 0 0 0 

2 0 2 2 2 1.0 

0 0 0 0 

0 0 0 0 

0 0 0 0 

3 0 1 1 2 

0 0 0 0 

0 0 0 0 

Kigalik 0 0 0 0 

Kiligwa 8 0 2 2 3 

2 1 1 1 1 

5 0 1 1 1 

0 0 0 0 

1 0 0 0 

2 0 0 0 

0 0 0 0 

0 0 0 0 

0 0 0 0 

0 0 0 0 

0 0 0 0 

12 0 4 4 4 1.0 

35 1 

Single Successful Young per 

Drainage All Sites Adults Pairs Pairs Young Successful Pair 

Avalik 

Awuna 

Colville, Upper 

Etivluk 

Fish Creek 

Ikpikpuk 

Ipnavik 2.0 

Ishuktak 

Ketik 

1.5 

Kokolik 1.0 

Kuna 1.0 

Meade 

Nigu 

Nuka 

Oumalik Lakes 

Oumalik River 

Titaluk 

Topagoruk 

Usuktuk 

Utukok 

Total 11 11 13 1.2 

24 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 
Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 

Figure 6. Distribution of golden eagle (Aquila chrysaetos) sites identified during fixed-wing aerial surveys in the National Petroleum Reserve–Alaska, July 1999. (The dashedlines delineate the three ecoregions: the Arctic Coastal Plain, the Arctic Foothills, and the Brooks Range [see Figure 1].) 25

Table 6. Distribution, abundance, and productivity of rough-legged hawks (Buteo lagopus) by river drainage in 

the National Petroleum Reserve–Alaska, 1999. 

3 0 1 1 1 1.0 

9 1 6 6 11 1.8 

1 16 16 29 1.8 

14 2 9 9 

2 0 2 2 3 1.5 

7 0 4 4 8 2.0 

22 0 

1 0 1 1 3 3.0 

1 0 0 0 

Kigalik 6 0 5 5 12 2.4 

Kiligwa 12 0 8 7 

2 0 2 2 3 1.5 

2 

7 0 4 4 7 1.8 

8 0 3 3 6 

8 1 4 4 8 2.0 

0 0 0 0 

0 0 0 0 

2 0 2 2 4 2.0 

0 0 0 0 

0 0 0 0 

39 4 

182 11 109 106 210 2.0 

Single Successful Young per 

Drainage All Sites Adults Pairs Pairs Young Successful Pair 

Avalik 

Awuna 

Colville, Upper 24 

Etivluk 20 2.2 

Fish Creek 

Ikpikpuk 

Ipnavik 13 12 26 2.2 

Ishuktak 

Ketik 

13 1.9 

Kokolik 

Kuna 15 10 10 19 1.9 

Meade 

Nigu 2.0 

Nuka 

Oumalik Lakes 

Oumalik River 

Titaluk 

Topagoruk 

Usuktuk 

Utukok 19 18 37 2.1 

Total 

26 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 
Rough-legged Hawks 

Rough-legged hawks were the most 

abundant and widespread cliff-nesting 

raptors in the NPR–A. We identified 

182 locations that had rough-legged 

hawk nests present (Table 6), of 

which 66% were occupied. A minimum of 106 nests (88% of occupied 

sites) were determined to be successful. Young may have fledged 

from a few nests, limiting our ability 

to determine the reproductive success 

of all nests. For the entire study 

area, productivity averaged 2.0 

young per successful pair (Table 6) 

and 1.9 young per pair for all pairs 

(Table 2). 

Most rough-legged hawk nest sites 

(80%) were found along cliffs in 

the southern Foothills (Table 2, 

Figure 7). Sixty-nine percent of all 

nests were located on six drainages, 

including the upper Colville River 

(Table 6). These same areas were 

commonly used by golden eagles 

and gyrfalcons. Rough-legged hawk 

nests were more sparsely distributed 

(16%) in the northern Foothills and 

were only occasionally observed 

(4%) on the Arctic Coastal Plain. 

Rough-legged hawks nested on a 

wide variety of cliff and bank substrates in the NPR–A (Table 3a). 

Shale bluffs and rock cliffs were 

used most often (72%), but scree 

and talus slopes and mud banks 

accounted for 25% of sites. A few 

sites (4%) were off-river on isolated 

rock outcrops and escarpments in 

the southern Foothills. The mean 

elevation of nest sites with pairs 

was 364 m (SD = 157 m; range 

30–670 m; n = 109; Table 3a). The 

lowest elevation nests were on Fish 

Creek on the Arctic Coastal Plain. 

Of the four raptor species surveyed, rough-legged hawks used 

some of the smallest banks and 

cliffs available (Table 3b). 

Photo by Ted Swem, U.S. Fish and Wildlife Service. 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 27 
Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 

Figure 7. Distribution of rough-legged hawk (Buteo lagopus) sites identified during fixed-wing aerial surveys in the National Petroleum Reserve–Alaska, July 1999. (The dashed

lines delineate the three ecoregions: the Arctic Coastal Plain, the Arctic Foothills, and the Brooks Range [see Figure 1].) 

28 
Nest Site Habitat Assessment 

An assessment of suitable nesting 

habitats for cliff-nesting raptors in 

most foothill and mountain 

drainages and their tributaries was 

made during aerial surveys in 1977 

(Ritchie 1979; Appendix B). Habitat values of some areas, particularly 

the transition zone between the 

Foothills and Coastal Plain, were 

only cursorily described in 1977 

as poor to fair on the basis of an 

apparent lack of good nesting substrates. Surveys in 1999, however, 

were extended farther north than 

in 1977, particularly in the NE 

Planning Unit, and this allowed a 

more thorough appraisal of habitats 

in this region. 

With the exception of a few rock 

cliffs in the upper reaches of rivers 

draining from the Foothills, all 

suitable nesting habitats for cliffnesting raptors in the NE Planning 

Unit are sand and mud banks, most 

of which occur along meandering 

portions of streams where they exit 

the Foothills. Habitat descriptions 

are summarized for these areas (Table 

7, Figure 8) according to classifications described in Ritchie (1979). In 

this area, substrates rarely exceed 

25 m and range from 5 to 40 m in 

height. A few nonvegetated, riverine bluffs and dunes extend onto 

the Coastal Plain, but do not exceed 

15 m in height. Many larger lakes 

between the Meade and Colville 

Rivers, especially in the Oumalik 

and Koluktak Lakes regions, have 

nesting habitat on steep-banked, 

primarily south-facing shorelines 

with partly vegetated soil bluffs 

5–20 m high. These lakes occur in 

a narrow band about 25 km wide 

along the northern edge of the 

Arctic Foothills. North of this 

band are a few more lakes with 

soil banks, but these are rarely 

more than 2–3 m high. Similar 

lake and riparian areas were not 

surveyed west of the Meade River, 

but it appears from topographic 

maps and aerial photos that this 

type of lacustrine habitat is more 

limited there than to the east. All of 

these habitats (lacustrine soil or 

mud banks and dunes) provide 

fair-to-good nesting substrates for 

peregrine falcons, poor-to-fair substrates for rough-legged hawks, and 

poor substrates for gyrfalcons. Golden 

eagles regularly use these elevated 

substrates for perches (Ritchie 1979), 

but these habitats are not suitable for 

nesting by this species. 

Photo by Ted Swem, U.S. Fish and Wildlife Service. 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 29 
Table 7. Description of nesting habitat for cliff-nesting raptors in the transition region between the Arctic 

Foothills and the Arctic Coastal Plain of the Northeast Planning Unit, National Petroleum Reserve–Alaska (areas are 

mapped in Figure 8). Substrate types: shale banks = SB, Mud or soil banks = MB, rock cliffs = RC, off-river outcrops 

= O, scree and talus slopes = ST, escarpment faces = EF. Height classes: 1 = >100 m, 2 = 50–100 m, 3 = <50 m (after 

Ritchie 1979). See Figure 8 for description of habitat assessment values. 

III–IV 

III–IV 

III–IV 

dominant 

III–IV 

IV 

III–IV 

especially along south side 

IV 

III–IV 

III–IV 

Drainage or Area Substrate Types and Occurrence Habitat Assessment 

Fish Creek Occasional 3 MBs on Coastal Plain upriver from 

junction with Judy Creek (<25 m) 

Inigok Creek Occasional 3 MBs (<25 m) 

Key, Judy, Wolf, Scattered 3 MBs (<25 m) between 69° 35' and 

and Alice Creeks from Foothills to 69° 47' N in lake transition Coastal 

Plain; little habitat in Foothills where rolling hills 

Price River Occasional 3 MBs with some >25 m 

Koluktak Lakes Some small MBs less than 10 m along some deep 

lake fronts 

Oumalik Lakes Numerous deep lakes with MBs up to 20 m, 

Oumalik River Limited low soil bluffs (3 MBs) 

Ishuktak Creek MBs between 69° 45' N and 70° 00' N 

Usuktuk River A few MBs between 69° 50' N and 70° 00' N IV 

Topagoruk River A few MBs between 69° 50' N and 70° 00' N 

30 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 
Figure 8. Habitat assessment for cliff-nesting raptors in the Northeast Planning Unit, National Petroleum Reserve–Alaska (additions to 

mapping found in Ritchie 1979). 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 31
32 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 

Figure 9. Distribution of peregrine falcon (Falco peregrinus tundrius) sites identified during fixed-wing aerial surveys in the National Petroleum Reserve–Alaska, July 1977 and

July 1999. Locations are from Ritchie (1977), Bente (1999, unpublished data), and the present study. Excludes sites located on the Colville River below the Etivluk River in all

years. (The dashed lines delineate the three ecoregions: the Arctic Coastal Plain, the Arctic Foothills, and the Brooks Range. [see Figure 1].)
Discussion


Peregrine Falcons 

A comparison of the 1999 survey 

with surveys of the 1970s (Pegau 

1975; Cade and White 1976; Ritchie 

1979) reveals that numbers of peregrine falcons have increased dramatically in the NPR–A (Figure 9). 

Excluding areas on the Coastal Plain, 

which were not surveyed in 1977 

(about 16 locations with peregrines), 

and the Kogosukruk and Kikiakrorak 

Rivers, the number of sites occupied by at least one adult has 

increased from 4 in 1977 to 61 in 

1999. The 1999 total includes 51 

sites we identified and an additional 10 sites located during a separate 

survey on the Utukok and Kokolik 

Rivers (P. Bente, ADFG, personal 

communication; Appendix A). The 

1977 total includes two dark falcons 

identified on nests on Fay and Cutaway Creeks (Figure 9). Because these 

birds were incubating late in the season (not typical of gyrfalcons), and 

because of the nesting habitats they 

occupied, they probably were 

peregrines (Ritchie 1979) and have 

been included in this total. The two 

sites that were definitely occupied by 

peregrines in 1977—a site on the 

upper Colville River above the 

mouth of the Kiligwa River (a pair) 

and a site on Anuk Creek (a single, 

incubating adult), were revisited in 

1999, but only the Colville River 

site was occupied. 

In addition, about 100 pairs of 

peregrine falcons also occur in 

other areas of the NPR–A. Surveys 

conducted on the Kogosukruk and 

Kikiakrorak Rivers in 1997 identified 28 sites occupied by at least 

one adult (Swem 1997; Appendix 

A). Only one site was found occupied by peregrines in 1977 (Ritchie 

1979). In addition, the Colville 

River, below the Etivluk River, had 

56 sites occupied by at least one 

adult peregrine in 1999 (T. Swem, 

USFWS, personal communication). 

In 1977, aerial surveys were incomplete along this portion of the 

Colville River (three occupied sites 

identified during partial surveys; 

Ritchie 1979). Finally, our survey 

did not identify peregrines in some 

drainages with a recent history of 

use, such as the Awuna and Nigu 

Rivers (M. Kunz, BLM, personal 

communication; Silva and Masinton 

1987; Appendix A), suggesting the 

potential for additional nesting pairs. 

Nesting success and productivity of 

peregrine falcons in the study area 

exceeded or were within the range 

of other populations in northern 

Alaska (Swem 1997; Wright and 

Bente 1999). In our study area, 

Photo by Skip Ambrose, National Park Service. 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 33 
84% of pairs were successful, 

compared with 39% and 71% 

of pairs on the Colville (T. Swem, 

USFWS, personal communication) and Sagavanirktok (J. 

Wright, ADFG, personal communication) Rivers, respectively. 

Productivity for our study was 

2.3 young per successful pair, 

whereas productivity was 2.4 

young per successful pair on the 

main Colville River. Because we 

were limited to a single visit late 

in the season, however, our 

observations were probably 

biased toward successful pairs 

(i.e., nonnesting or failed pairs 

may have departed the area 

before our survey or were less 

conspicuous). Two surveys, one 

during incubation and a second 

during the nestling stage, are 

essential for an accurate calculation 

of nesting success (Steenof 1987). 

We were somewhat surprised to 

locate most peregrine falcon sites 

in the transitional area between 

the Arctic Coastal Plains and 

Arctic Foothills ecoregions and 

not along the braided drainages 

of the southern Foothills. This 

result may partly reflect the lack 

of surveys conducted during the 

1970s in the transitional area, 

rather than an actual change in 

distribution. Additionally, this 

area generally offers more valuable and denser wetland habitats 

used by primary prey species of 

peregrine falcons, including 

waterfowl and shorebirds, than 

the foothills region. Indeed, 

waterbird surveys conducted in 

the Coastal Plain and Foothills 

regions have clearly shown greater 

numbers of ducks and shorebirds, 

important prey of peregrines, in 

the transition area than in any 

areas south (King 1979). 

The transitional area is also closer 

to the densest component of the 

population (lower Colville, Kogosukruk, and Kikiakrorak Rivers). 

Greater densities of peregrine 

falcons in the transitional areas 

may reflect characteristics of a 

recovering population if, as 

peregrines expand, they are 

occupying habitats closest to 

their core population centers 

(i.e., main Colville River). It 

may be difficult for new pairs to 

colonize areas farther from their 

origins because social behavior 

of this species places a high premium on previous experience by 

one member of a pair (White 

and Cade 1971). 

Peregrine falcons seem to be 

nesting on the most common 

substrates in this portion of the 

study area. No cliffs occur on 

the Arctic Coastal Plain or in 

the transition area between the 

Coastal Plain and Foothills. 

Peregrines are essentially 

ground nesters in these areas, 

nesting on the tops of sand and 

mud banks cut by meandering 

rivers (Figure 10), beneath willow bushes on the tops or slopes 

of steep, willow-covered soil and 

mud banks, or less frequently in 

abandoned stick nests of roughlegged hawks or on mud banks 

along lake shorelines. The use of 

lacustrine habitats for nesting 

has not previously been recorded 

for the tundrius subspecies in 

Alaska, and may reflect the use 

of more marginal habitats close 

to core habitats in the Coastal 

Plain–Arctic Foothills transition 

area. However, a few isolated 

instances of another North 

American subspecies (F. p. anatum) nesting on cliffs near lakes 

have been identified in interior 

Alaska (Mindell 1983). Additionally, ground nesting has 

been described in parts of Canada 

(F. p. tundrius) and boggy wetlands in Russia (F. p. calidris), 

Fennoscandia, and Europe (F. p. 

peregrinus; Hickey and Anderson 

1979). 

Many seemingly suitable cliffs 

in the Arctic Foothills, however, 

have never been observed to be 

occupied during surveys in the 

past 15 years (Appendix A). In 

the northern portion of this 

ecoregion, the absence of cliff 

and bank habitats is obvious, 

but explanations for low densities 

of peregrines in the southern 

Foothills, where cliff structures 

and improvements such as 

abandoned stick nests of other 

34 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 
a 

b 

Figure 10. Photographs of (a) a typical low, soil bank used by nesting peregrine falcons (Falco peregrinus tundrius) on drainages on the Arctic Coastal Plain in the Northeast Planning Unit, National Petroleum 

Reserve–Alaska; and (b) a ground nest site of peregrines at the top of a bluff, upper Price River (center right). 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 35
raptors are numerous, are not 

apparent and are probably related 

to a number of ecological factors. Peregrine falcons may be 

avoiding golden eagles (Poole 

and Bromley 1988). Although 

peregrines occasionally nest 

close to golden eagles along 

interior rivers of Alaska, little 

overlap is seen with nesting 

eagles in the NPR–A (Figures 3 

and 6). Alternatively, this 

apparent avoidance of some 

cliffs may be due to altitudinal 

limits of peregrines nesting in 

northern Alaska. Cade (1960) 

noted that the distribution of peregrine nest sites in Alaska is almost 

consistently limited by altitude at 

about 610 m (2,000 feet). A few 

peregrine nests have been located 

at higher elevations in northern 

Alaska (Cade 1960), but such 

observations are rare. In addition 

to the presence of eagles and 

elevation, competition may 

occur with gyrfalcons or common 

ravens for nesting substrates or 

resources, but few data support 

this hypothesis (White and 

Cade 1971). Finally, habitat 

quality (e.g., prey availability) 

probably differs as one moves 

inland and may influence peregrine distribution (e.g., increased 

diversity of wetlands on the 

Coastal Plain vs. tussock tundra 

inland). 

36 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 
Gyrfalcons 

Adult or young gyrfalcons were 

located at only 19 sites in 1999, 

down from 29 in 1977 (Table 8; 

Ritchie 1979). However, a greater 

number of sites used by gyrfalcons 

(41 vs. 29) were documented in 

1999 than in 1977 (Table 2). 

Because of the difference in survey timing noted previously, we 

cannot be certain whether these 

observations resulted from population fluctuations or from adult 

and young birds leaving the nest 

before our survey was undertaken 

in 1999. An estimate of the 

number of gyrfalcon territories 

in the NPR–A study area would 

probably range from 30 to 40, 

excluding those on the main 

Colville River below its junction 

with the Etivluk River, where 

about 40 territories are known 

(Swem et al. 1994). Both the 

number of occupied territories 

and productivity may fluctuate 

widely in this species (Cade 

1960; Shank and Poole 1994), 

depending on prey availability— 

especially ptarmigan—and spring 

weather conditions (Poole 1987). 

Furthermore, nonbreeding or 

failed gyrfalcons are not often 

encountered at nesting territories 

during brief aerial surveys (Roseneau 1972), complicating an 

assessment of territory occupancy. 

The distribution of gyrfalcon 

sites in 1999 was similar to that 

recorded in 1977 (Figure 11), 

with most sites occurring along 

drainages in the upper Colville 

River area (Table 8). As in 

1977, gyrfalcons nested on sizable 

cliffs in the southern Foothills in 

1999, and less often on shale 

bluffs and smaller rock outcrops 

north of the Colville River. 

Golden Eagles 

The number of golden eagle 

nest sites located in the NPR–A 

was greater in 1999 than in 

1977, but in both years less 

than half of the nests were 

occupied (Tables 2 and 8). Ten 

pairs (or incubating adults) were 

found in 1977 and 11 in 1999. 

Some of the unoccupied nest 

locations probably represent 

golden eagle territories, but 

their status could not be determined from a single aerial survey. The number of territories 

probably exceeds our counts of 

successful nests, however. 

The NPR–A is at the northern 

limit of the breeding range of 

the golden eagle (Johnson and 

Herter 1989). In the past, climatic conditions north of the 

Brooks Range were believed to 

be too severe for consistent and 

successful breeding by golden 

eagles (Hobbie and Cade 1962). 

But after systematic, multiyear 

surveys were conducted in the 

Arctic National Wildlife Refuge 

in 1988–1990, Young et al. 

(1995) concluded that golden 

eagles breed consistently and 

successfully on the North Slope. 

The number of young per successful pair in 1999 (1.2) was 

similar to results from other 

studies conducted in arctic 

areas. In the Arctic National 

Wildlife Refuge, Young et al. 

(1995) found 1.1–1.3 young 

per successful pair from 1988 to 

1990; in the Northwest Territories, Poole and Bromley (1988) 

reported 1.1–1.5 young per successful pair from 1983 to 1986. 

The number of young per successful pair in the NPR–A in 

1977 (1.7) was higher than 

these, but similar to upper values found in other studies in 

Alaska south of the Brooks 

Range (1.3–1.6 young per successful pair, Porcupine River, 

Ritchie and Curatolo 1982; 

1.3–1.7 young per successful 

pair, Denali National Park, 

McIntyre 1995). The overall 

population’s productivity (i.e., 

young per total pairs) and occupancy data for 1999, however, 

are limited for comparison with 

other areas because a single, 

late-season survey results in 

underestimating total pairs 

occupying territories. 

The distribution of golden eagle 

nests in 1999 was similar to 

their distribution in 1977 in 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 37 
Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 

Figure 11. Distribution of gyrfalcon (Falco rusticolus) sites with pairs observed during fixed-wing aerial surveys in the National Petroleum Reserve–Alaska, July 1977 and July 1999. Locations are from Ritchie (1977) and the present study. (The dashed lines delineate the three ecoregions: the Arctic Coastal Plain, the Arctic Foothills, and the Brooks Range

[see Figure 1].) 

38 
Table 8. The number of occupied sites (single adults and pairs) of gyrfalcons (Falco rusticolus), golden eagles 

(Aquila chrysaetos), and rough-legged hawks (Buteo lagopus) in the National Petroleum Reserve–Alaska in 1977 

and 1999. 

a 1999b 1977a 1999b 1977a 1999b 

0 0 0 0 0 1 

2 2 1 0 5 7 

2 3 0 2 12 17 

1 1 0 0 3 

0 0 0 0 1 2 

1 0 0 0 0 4 

4 0 2 1 8 

NSc 0 0 1 

0 0 0 0 0 0 

Kigalik 0 1 0 0 1 5 

2 0d 0 0 d 0 5d 

Kiligwa 3 2 1 2 2 8 

2 0d 0 0d 7 d 

2 0 1 2 0 2 

3 2 2 1 8 

1 1 0 0 2 4 

0 0 0 0 3 3 

0 1 1 0 1 5 

NS 0 0 NS 0 

0 NS 0 0 

0 1 0 0 0 2 

NS 0 0 NS 0 

NS 0 0 NS 0 

6 5 7 4 7 

29 19 15 12 60 146 

Gyrfalcon Golden Eagle Rough-legged Hawk 

Drainage 1977 

Avalik 

Awuna 

Colville, Upper 

Etivluk 11 

Fish Creek 

Ikpikpuk 

Ipnavik 13 

Ishuktak NS NS 

Ketik 

Kikiakrorak 

Kogosukruk 21

Kokolik 

Kuna 12 

Meade 

Nigu 

Nuka 

Oumalik Lakes NS 

Oumalik River NS NS 

Titaluk 

Topagoruk NS 

Usuktuk NS 

Utukok 23 

Total 

a Data from 1977 survey by Ritchie (1979). 

b Data from present survey, except where noted. 

NS = indicates that the drainage was not surveyed. 

d Data from 1997 survey by Swem (1997). 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 39

c 
that most nests were found in 

the southern Foothills (Figure 

12). Three active nest sites in 

1999 were close to sites that 

were active in 1977 (Figure 12). 

Historically and in recent years, 

subadult (excluding young-ofyear) golden eagles have been 

observed across a wide area of 

the Arctic Coastal Plain and the 

northern Foothills region, but 

nesting has been found only in 

the southern Foothills region 

and the Brooks Range (Kessel 

and Cade 1958; Roseneau 1974; 

Ritchie 1979; Mauer 1985; 

Young et al. 1995). The most 

northerly nests located in the 

NPR–A during both the 1977 

and 1999 surveys were about 

latitude 69.25°N, and both sites 

were on the Utukok River or its 

tributary, Carbon Creek (Ritchie 

1977). In the eastern NPR–A, a 

nest was located on the Colville 

River at its intersection with 

Siksikpak Ridge (69.07°N; T. 

Swem, USFWS, personal communication). In the Arctic 

National Wildlife Refuge, where 

the mountains extend farther 

north than in the NPR–A, 

occupied golden eagle nest sites 

occurred between latitudes 

69.36° and 69.64°N (Young et 

al. 1995). 

Rough-legged Hawks 

In both 1977 and 1999, roughlegged hawks were the most 

abundant and widespread cliffnesting raptor in the NPR–A 

(Table 8). However, twice as 

many pairs were found in 1999 

than in 1977 (Table 2). Nesting 

densities seemed to be lower in 

1977 than in recent years, according to observations made on the 

lower Colville River (Ritchie 

1979). The size and productivity 

of breeding populations of 

rough-legged hawks has been 

shown to vary considerably 

among years (Kuyt 1980; Poole 

and Bromley 1988; Swem 1996b). 

Studies on the lower Colville 

River between the Etivluk River 

and Ocean Point showed that 

the number of pairs occupying 

territories varied from 53 to 

106 (mean=90) over an 11-year 

period (Swem 1996a). 

Because of the difference in timing 

of the 1977 and 1999 surveys, 

comparisons of productivity cannot be made. However, the 

timing of the 1999 survey fell 

within the period of Swem’s 

(1996a) productivity surveys on 

the lower Colville River, and 

the number of young per total 

pairs found in 1999 (1.9) in 

the NPR–A was within the 

range of values (1.6–2.1 young 

per total pairs) found on the 

lower Colville River during 

years when rough-legged hawk 

numbers were moderate. The 

overall population’s productivity 

(i.e., young per total pairs) and 

occupancy data for 1999, however, are limited for comparison 

with other areas because a single, late-season survey results in 

underestimating total pairs 

occupying territories. 

The relative distribution of 

rough-legged hawks in the 

NPR–A was similar in 1977 

and 1999 (Table 2, Figure 13). 

About 75% of the pairs nested 

in the southern Foothills south 

of the Colville River in both 

years. Most nests were on shale 

bluffs, riverine cliffs, or scree 

slopes, which are common substrates along the braided streams 

of the southern Foothills. Few 

nests were found on the Arctic 

Coastal Plain (Figure 13). 

Nest Site Habitat 

Assessment 

Surveys conducted in 1999 

identified many sand and mud 

banks north of the Arctic 

Foothills in a transition area 

between the Foothills and 

Coastal Plain. These habitats 

were considered marginal for 

raptors, including peregrine falcons, in the 1970s because so 

few birds had been recorded 

there. However, results of our 

1999 survey suggest that earlier 

appraisals were inaccurate and 

that fair-to-good habitat does 

extend into the Coastal Plain at 

elevations under 100 m and 

40 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 
Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 

Figure 12. Distribution of golden eagle (Aquila chrysaetos) sites with pairs observed during fixed-wing aerial surveys in the National Petroleum Reserve–Alaska, July 1977 andJuly 1999. Locations are from Ritchie (1977) and the present study. (The dashed lines delineate the three ecoregions: the Arctic Coastal Plain, the Arctic Foothills, and theBrooks Range [see Figure 1].) 41

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 

Figure 13. Distribution of rough-legged hawk (Buteo lagopus) sites with pairs observed during fixed-wing aerial surveys in the National Petroleum Reserve–Alaska, July1977 and July 1999. Locations are from Ritchie (1977) and the present study. (The dashed lines delineate the three ecoregions: the Arctic Coastal Plain, the ArcticFoothills, and the Brooks Range [see Figure 1].) 

42 
south of about 70°N latitude. 

Waterfowl surveys north of 

about 70°N latitude between 

the Meade and Colville Rivers 

have not encountered nesting 

peregrines (R. Ritchie, unpublished notes) in this portion of 

the Coastal Plain, but occasional 

bluffs associated with lakes and 

rivers might attract peregrine 

falcons for nesting. In addition, 

some riverine and lacustrine 

areas west of the Meade River 

may have occasional banks 

suitable for nesting. This area 

requires better survey coverage. 

A nest was recorded in this 

region on the Kaolak River 

(R. King, USFWS, personal 

communication) and peregrines 

have been observed at Dewline 

Sites and on steep coastal mud 

banks west of Barrow. Peregrines 

have also been found nesting in 

coastal areas in northwestern 

Alaska and near Kaktovik on 

the Arctic Coast (F. Mauer, 

USFWS, personal communication). These observations suggest 

nesting may occur even farther 

north than 70°N latitude. With 

a recovered and perhaps still 

expanding peregrine falcon 

population in northern Alaska, 

it would not be prudent to 

conclude the absence of these 

falcons in any northern areas 

until demonstrated by more 

intensive surveys. 

Survey Efficacy 

Recommendations 

The quality of data collected 

from fixed-wing aircraft for raptors, particularly falcons, can be 

influenced greatly by the complexity of nesting substrates, 

experience of the observer, and 

the timing of the surveys. In 

regard to timing, questions arise 

about the comparability of our 

aerial surveys conducted during 

different phases of the breeding 

season. For instance, surveys in 

1977 coincided with the incubation through early nestling 

stage of peregrine falcons, whereas 

surveys in 1999 were conducted 

during the midnestling period 

for this species. What effect this 

difference in survey timing has 

on comparable results probably 

varies by species, but it influences most the comparison of 

occupancy for all species. That 

is, given the later surveys in 

1999, occupancy estimates may 

have been lower for each species 

because failed and nonbreeding 

pairs would be absent or less 

conspicuous on their territories 

later in the season. 

In 1977, our surveys occurred 

at a time when peregrine falcon 

adults sit more tightly (i.e., late 

in the incubation through early 

nestling period) and may not be 

as conspicuous from an aircraft 

platform as they are later in the 

year. Most incubating adults 

should have been detected, 

however, because small cliffs 

typical of the region can be 

thoroughly searched by fixedwing aircraft. Cade and White 

(1976) searched much of the 

southern Foothills in 1975 and 

were convinced that only the 

occasional pair occurred in the 

area even if they had missed half 

of the incubating peregrines. 

Numbers of peregrine falcons 

were lowest during the mid1970s in their core breeding 

areas in northern Alaska 

(Colville and Sagavanirktok 

Rivers; Ambrose et al. 1988), 

and aerial survey results in this 

period support a general consensus that peregrine falcons 

were even more greatly reduced 

in tributaries and smaller 

drainages in northern Alaska 

than along the main rivers 

(Cade and White 1976). 

In 1999, in an effort to get the 

most information on relative 

distribution, abundance, and 

productivity, we conducted our 

surveys during a period when 

young peregrines were more 

obvious and adults were regularly 

defensive of their young (i.e., 

midnestling period). As mentioned previously, we probably 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 43 
missed some failed or nonbreeding 

pairs of peregrine falcons at this 

time, which may have been absent 

or inconspicuous during our visit. 

Despite this limitation, conducting 

this survey was a cost-effective 

way to verify the extent of recovery 

of peregrine falcons in the region 

and to create a map of the present 

distribution and relative abundance 

of peregrines, as well as other 

raptors, in the NPR–A. 

We recommend at least three 

changes in procedure to improve 

the value of future fixed-wing 

aircraft raptor surveys in the 

region. First, two surveys—one 

during incubation and a second 

during the nestling stage— 

would improve the accuracy of 

calculations of occupancy and 

productivity (Steenof 1987). 

Second, “truthing” fixed-wing 

coverage with helicopter or 

ground techniques would provide 

a means for more accurately 

obtaining a census of the population and would provide a better 

baseline for continued population 

monitoring. Finally, with 

increased oil exploration interest 

on the Arctic Coastal Plain, 

lakeshore nesting habitats for 

peregrine falcons, such as those 

identified in the Oumalik Lakes 

area, should be identified and 

mapped. Beyond improving our 

understanding of the recovery of 

peregrines in the region, identification of these habitats would be 

important for planning activities 

outside floodplain cliffs and banks 

normally considered primary 

raptor habitats. 

44 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 
Acknowledgments


This project was funded by the 

Bureau of Land Management 

(BLM). Additional logistics support was provided by the Fairbanks 

and Anaktuvuk Pass offices of the 

National Park Service (NPS) and 

the Ivotuk field camp of the Polar 

Ice Coring Group (PICO). We 

thank Scott Hillard, Camp Manager for PICO at Ivotuk, and Mike 

Haubert and Shelly Swanson 

(NPS) for their help in the field. 

Peter Bente (Alaska Department of 

Fish and Game) and Ted Swem 

(U.S. Fish and Wildlife Service) 

provided records from their survey 

work on the Utukok and Colville 

Rivers, respectively. Both Peter and 

Ted, in addition to Tim Craig 

(BLM), provided critical reviews of 

earlier drafts of this report. Mike 

Kunz (BLM) generously opened 

his field camp at Inigok to offer 

rest and a break from flying. 

Devonee Harshburger, Will Lentz, 

Alice Stickney, and Allison ZusiCobb from ABR, Inc., provided 

graphic, editorial, and word processing assistance for the final 

report, which preceded this technical report. Sandy Hamilton, Arctic 

Air Alaska, provided his companionship, good humor, and incredible skill at piloting his aircraft. His 

expertise greatly contributed to the 

success of this program. 

Photo courtesy of the Bureau of Land Management. 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 45 

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and map. 1 pp. 

Dittrick, R., and L. Moorehead. 1983. Productivity and status of cliff nesting raptors along the Colville 

River and selected tributaries, Alaska, 1983. Unpublished report prepared for the U.S. Fish and 

Wildlife Service, Office of Endangered Species, Anchorage, Alaska, by Biological Investigative 

Research Services. 37 pp. 

Dittrick, R., and T. Swem. 1981. Productivity and status of cliff nesting raptors along the Colville 

River and selected areas within the National Petroleum Reserve–Alaska. Unpublished report 

prepared for U.S. Fish and Wildlife Service, Office of Endangered Species, Anchorage, Alaska, by 

Biological Investigative Research Services. 45 pp. 

Hunter, R. E 1984. Colville River raptor survey, 1984. Unpublished field notes. U.S. Fish and 

Wildlife Service, Anchorage, Alaska. 19 pp. 

Karlen, R. R., and R. L. Masinton. 1991. The 1991 peregrine falcon/raptor survey, Kiligwa and 

Etivluk Rivers, Alaska. Unpublished report. U.S. Department of the Interior, Bureau of Land 

Management, Arctic District Office, Fairbanks, Alaska. 12 pp. 

King, R. 1978. Kogosukruk River raptor survey, July 20–27, 1978. Unpublished memorandum. U.S. 

Fish and Wildlife Service, Fairbanks, Alaska. 3 pp. + map 

Pegau, R. E. 1975. Raptor nesting in the western Brooks Range. Letter of 13 June to R. A. Hinman, 

State of Alaska, Division of Game, from R. E. Pegau, State of Alaska, Division of Game, Nome. 

3 pp. 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 51
Ritchie, R. J. 1986. Raptor surveys of the Ikpikpuk, Nanushuk-Anaktuvuk, Toolik, Ivishak, Canning, 

and Jago Rivers, 1986. Letter of 26 August to R. E. Ambrose, U.S. Fish and Wildlife Service, 

Fairbanks, Alaska, from R. J. Ritchie, Alaska Biological Research, Inc., Fairbanks, Alaska. 6 pp. 

Ritchie, R. J. 1988. Peregrine falcon survey of the Central Brooks Range, 1988. Unpublished survey 

map. Alaska Biological Research, Inc., Fairbanks, Alaska. 1 p. [map] 

Ritchie, R. J. 1989. Peregrine falcon survey of the Central Brooks Range, 1989. Letter of 20 November to 

R. E. Ambrose, U.S. Fish and Wildlife Service, Fairbanks, Alaska, from R. J. Ritchie, Alaska Biological 

Research, Inc., Fairbanks, Alaska. 4 pp. 

Ritchie, R. J. 1992. Peregrine falcon survey of the Central Brooks Range, 1992. Letter of 13 August to 

T. Swem, U.S. Fish and Wildlife Service, Fairbanks, Alaska, from R. J. Ritchie, Alaska Biological 

Research, Inc., Fairbanks, Alaska. 14 pp. 

Silva, J. 1984. 1984 peregrine falcon/raptor survey, preliminary status report. Unpublished report. 

U.S. Department of. Interior, Bureau of Land Management, Fairbanks, Alaska. 2 pp. + maps 

Silva, J. B. 1985a. The 1985 peregrine falcon/raptor survey, preliminary status report. Unpublished 

report. U.S. Department of the Interior, Bureau of Land Management, Fairbanks, Alaska. 2 pp. 

+ maps

Silva, J. B., and R. L. Masinton. 1986. The 1986 peregrine falcon/raptor survey along the Colville 

(Ipnavik River to Ocean Point) and Sagavanirktok Rivers, including portions of the Killik, 

Etivluk, and Kogosukruk Rivers. Unpublished report. U.S. Department of the Interior, Bureau 

of Land Management, Fairbanks, Alaska. 29 pp. 

Silva, J. B., and R. L. Masinton. 1987. The 1987 peregrine falcon/raptor survey along the Colville, 

Utukok, and Sagavanirktok Rivers, including selected tributaries. Unpublished report. U.S. 

Department of the Interior, Bureau of Land Management, Fairbanks, Alaska. 28 pp. 

Silva, J. B., and R. L. Masinton. 1988. The 1988 peregrine falcon/raptor survey, Central Arctic Alaska. 

Unpublished report. U.S. Department of the Interior, Bureau of Land Management, Fairbanks, 

Alaska. 23 pp. 

Silva, J. B., and R. L. Masinton. 1990. The 1990 peregrine falcon/raptor survey, Ipnavik River, Alaska. Unpublished report. U.S. Department of. Interior, Bureau of Land Management, Fairbanks, Alaska. 11 pp. 

Swem, T. R. 1985. The 1985 Colville River raptor survey. Unpublished report. U.S. Department of. 

Interior, Bureau of Land Management, Fairbanks, Alaska. 22 pp. + appendixes 

52 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 
Swem, T. R. 1987. The 1987 Colville River raptor survey. Unpublished report. U.S. Department of 

the Interior, Bureau of Land Management, Fairbanks, Alaska. 19 pp. 

Swem, T. R. 1988. The 1988 Colville River raptor survey. Unpublished report. U.S. Department of 

the Interior, Bureau of Land Management, Fairbanks, Alaska. 17 pp. 

Swem, T. R. 1989. 1989 Colville River raptor survey. Unpublished survey summary. U.S. Fish and 

Wildlife Service, Fairbanks, Alaska. 4 pp. 

Swem, T. R. 1990. 1990 Colville River raptor survey. Unpublished survey summary. U.S. Fish and 

Wildlife Service, Fairbanks, Alaska. 4 pp. 

Swem, T. R. 1991. 1991 Colville River raptor survey. Unpublished survey summary. U.S. Fish and 

Wildlife Service, Fairbanks, Alaska. 5 pp. 

Swem, T. R. 1992. 1992 Colville River raptor survey. Unpublished survey summary. U.S. Fish and 

Wildlife Service, Fairbanks, Alaska. 5 pp. 

Swem, T. R. 1993. 1993 Colville River raptor survey. Unpublished report. U.S. Fish and Wildlife 

Service, Fairbanks, Alaska. 8 pp. 

Swem, T. R. 1994. 1994 Colville River raptor survey. Unpublished report. U.S. Fish and Wildlife 

Service, Fairbanks, Alaska. 8 pp. 

Swem, T. R. 1995. 1995 Colville River raptor survey. Unpublished report. U.S. Fish and Wildlife 

Service, Fairbanks, Alaska. 10 pp. 

Swem, T. R. 1996a. 1996 Colville River raptor survey. Unpublished report. U.S. Fish and Wildlife 

Service, Fairbanks, Alaska. 10 pp. 

Swem, T. R. 1997. 1997 Colville River raptor survey. Unpublished report. U.S. Fish and Wildlife 

Service, Fairbanks, AK. 13 pp. 

Swem, T. R., B. Dittrick, and J. Silva. 1982. The 1982 peregrine falcon/raptor survey in Central Arctic 

Alaska. Unpublished report. U.S. Department of the Interior, Bureau of Land Management, 

Fairbanks, Alaska. 30 pp. + maps 

Todd, C. T. 1978. Surveillance of the Colville River, 1978. Unpublished report. U.S. Fish and 

Wildlife Service, Fairbanks, Alaska. 17 pp. 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 53
Watts, A. B. 1995. Raptor observations on the Colville, Kurupa, Etivluk, Chandler, Anaktuvuk Rivers, 

and September and Prince Creeks, 1995. Letter of 17 October to T. Swem, U.S. Fish and 

Wildlife Service, Fairbanks, Alaska, from A. B. Watts, ARCO Alaska, Inc., Anchorage. 3 pp. 

Watts, A. B. 1997. Raptor observations on the Colville, Kiligwa, Kukpowruk, Utukok Rivers, 1997. 

Letter of 12 March to T. Swem, U.S. Fish and Wildlife Service, Fairbanks, Alaska, from A. B. 

Watts, ARCO Alaska, Inc., Anchorage. 1 p. 

54 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 
Appendix A


The number of sites occupied by peregrine falcons 

(Falco peregrinus tundrius) in the National Petroleum 

Reserve–Alaska, 1952–1999. 

Numbers in bold text indicate years when complete surveys of drainages were 

conducted. Numbers in regular text indicate years when partial surveys of 

drainages were conducted or when incidental observations of peregrine falcons at territories were reported. A zero indicates that a survey was conducted, but no peregrine falcons were found occupying a territory. Surveys 

included aircraft, ground, and boat techniques. Data for complete surveys of 

the Lower Colville River are from Swem (unpublished data); other source 

information is noted. 

Photo by Jim Silva, Bureau of Land Management. 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 55
1952

1967

1969

1973

1977

1979

1981 

0 

0 0 

32 35 27 32 33 25 14 3 15 16 21 24 26 

8 0 3 1 2 

2 2 1 1 2 

0 

0 

0 0 0 

0 0 

Kigalik 0 0 

0 1 1 

Kiligwa 0 0 

1 2 4 3 

0 1 

0 1 

0 0 0 

0 0 

0 0 

0 

1 0 0 0 

40 35 27 32 33 26 14 5 9 19 16 21 29 34 

a b c d e f g 

Drainage 

1959

1968

1971

1975

1978

1980

1982

Avalik 

Awuna 

Colville - Lower 

Colville - Upper 

Etivluk 

Fish Creek 

Ikpikpuk 

Ipnavik 

Ishuktak 

Ketik 

Kikiakrorak 

Kogosukruk 

Kokolik 

Kuna 

Meade 

Nigu 

Nuka 

Oumalik Lake 

Oumalik River 

Titaluk 

Topagoruk 

Usuktuk 

Utukok 

Total 

Sources 

a Cade and White 1976 

b Cade et al. 1971, McGowan 1973 

c Pegau 1975, White and Cade 1975 

d White and Boyce 1978, Ritchie 1979 

e King 1978, Todd 1978 

f Dittrick and Swem 1981 

g Swem et al. 1982 

h Dittrick and Moorehead 1983, Silva 1985b 

i Hunter 1984, Silva 1984 

j Silva 1985a, Swem 1985 

k Ritchie 1986, Silva and Masinton 1986 

l Silva and Masinton 1987, Swem 1987 

m Ritchie 1988, Silva and Masinton 1988, Swem 1988 

56 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 
2 

0 1 0 

26 31 29 33 36 46 53 50 55 56 58 61 56 57 57 62 56 

0 1 3 1 4 1 2 1 1 1 1 2 1 9 

2 1 1 0 3 2 1 1 1 2 

9 

2 2 6 

1 1 2 2 

2 

0 

1 

1 1 1 2 2 1 7 

1 0 0 3 

2 2 3 2 3 3 9 1 1 1 3 2 2 4 21 

1 1 2 

2 1 1 

0 

0 0 1 0 0 

0 

4 

1 

1 5 

4 

2 

0 0 2 2 1 1 13 

30 35 34 37 54 57 71 55 59 66 62 64 62 65 87 62 133 

h i j k l m n o p q r s t u v w 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 

15 

n Bente 1989, Ritchie 1989, Swem 1989 t Swem 1995, Watts 1995 

o Dittrick 1990, Silva and Masinton 1990, Swem 1990 u Swem 1996a, Watts 1997 

p Karlen and Masinton 1991, Swem 1991 v Swem 1997, Kunz 1998 (maps) 

q Ritchie 1992, Swem 1992 w Present study, Bente (unpublished notes) and Swem 

r Swem 1993 (unpublished data) 

s Swem 1994 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 57

Appendix B


Description of nesting habitat for cliff-nesting raptors in 

the foothills and mountains of the National Petroleum 

Reserve–Alaska. 

Height (in meters) is referred to by numeric height classes.a Area numbers are 

keyed to the map (Appendix Figure B.1) following this table (Ritchie 1979); 

photo samples (Appendix Figure B.2) of these substrate types follow the map. 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 59
b 

1. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

Cade (1971) 

2 

Drainage or Area Substrate Types and Occurrence 

Anuk Creek South-facing 2-3 SB along lower 10 km; 1-3 RC–O in upper reaches 

2. Archimedes and Lookout Ridges 3 EF fractured rock near tops of these ridges 

Avalik River 3 MB at boundary of northern foothills extending into coastal plains 

Avingak Creek Not extensively surveyed but probably limited, small O–ST 

Awuna River 3 SB and 2-3 RC along 270 km of river; large RC at lat 69°06', long 156°43' 

Brooks Range (Central) Fairly gentle topography between the upper Kuna and Nigu; 1-2 ST slopes 

Brooks Range (De Long Mtns) West of Kuna there are more 1-3 RC–O than Central portion, but restricted 

Carbon Creek South-facing 2-3 SB–EF nearly entire 60 km of river 

Colville River (upper Kiligwa River Scattered 2-3 SB, some 1-2 RC, downriver from the mouth of the Nuka River 

10. Colville River Widely scattered 3 SB and ST 

(between Kiligwa and Etivluk Rivers) 

11. Colville River 2-3 SB, RC above Umiat; 1-3 MB with RC below Umiat described in White and 

(Etivluk River to Ocean Pt.) 

12. Cula Creek Few O–SB in upper Cula 

13. Cutaway Creek Scattered 2-3 RC and smaller O in upper portion 

14. Driftwood Creek A few 3 SB along the river 

15. East Fork Etivluk River Scattered east-facing 3 SB in upper portion 

16. Ekakevik Mountain Approximately 30 km with scattered 2-3, O–RC 

17. Etivluk River uplands and western edge Rolling tundra with occasional O 

of Ivotuk Hills 

60 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 
b 

lat 69°30' and 69°45' 

Drainage or Area Substrate Types and Occurrence 

18. Grayling Creek A few 3 SB; a single 2 SB–RC near confluence with Colville 30km 

19. Ikpikpuk River Scattered 3 MB–SB in upper portions; rock exposure on bank at Little Supreme Bluff 

(lat 69°36', long 154°57'); lower soil banks and sand dunes increase beneath this point 

20. Ipnavik River (lower) Similar to main Etivluk; numerous and widely spaced 3 SB 

21. Ipnavik River (mid-upper) ST in upper reaches; numerous 2 RC–SB (with at least three 1 RC between 

Memorial Creek and north of Crassico Creek); Memorial, Bupto, Ekakevik and Taffy 

Creeks have 1-2 RC 

22. Iteriak Creek Approximately 5 km of west-facing 3 SB 

23. Iteriak Ridge Approximately 5 km of O 

24. Judy, Wolf, Alice, and Fry Creeks 3 MB common up to 25 m in height as creeks leave foothills; most common between 

25. Kaksu River (tributary of Meade) upper 20 km scattered EF and 2-3 RC 

26. Ketik River 3 EF in headwaters; 3 MB where river enters coastal plains 

27. Kigalik River Lower 90 km has only a few SB–ST less than 15 m in height; however, a small canyon 

12 km in length near VABM 937 (Kigal) includes 2 RC, SB, and EF 

28. Kikiakrorak River Numerous 2-3 MB, with 3 RC in headwaters of main Kikiakrorak; MB not as high as 

those on Kogosukruk (generally less than 25 m) 

29. Kiligwa River (lower) Scattered 3 SB 

30. Kiligwa River (upper) Canyon between Rolling Pin Creek and Strident Creek providing 1-2 RC; above 

Rolling Pin Creek more ST and fewer RC; RC on Jubilee, Rolling Pin, and Panic Creeks 

31. Knifeblade, Kimipak, and other ridges Occasional 3 O–EF, mostly rolling tundra 

north of Colville but east of the Ikpikpuk 

32. Kogosukruk River Numerous 2-3 MB, some with limited rock outcropping; rock increases as headwaters 

are approached; 3 RC in west fork headwaters of his river 

33. Kokolik River Numerous 2 RC and EF above Avingak Creek and extending outside boundary of 

NPR-A; below Avingak Creek three 3 RC–ST with ledges 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 61
b 

2-3 O, amidst steep ST slopes 

Drainage or Area Substrate Types and Occurrence 

34. Kulugra, Shaningarok, and other ridges No O or EF; rolling tundra 

north of Colville, but west of Ikpikpuk 

35. Kuna River Lower section a broad valley with scattered 2-3 SB, with occasional O north of 

Monument Ridge. Upper Kuna has few RC, similar to upper Ipnavik, with ST prevailing 

36. Kutchaurak Creek Few scattered 3 SB–RC 

37. Liberator Ridge-Swayback Numerous but scattered 1-2 RC–O 

Mountain-Cockscomb Ridge 

38. Lily Creek (tributary of Meade) Upper 10 km has scattered EF and 2-3 RC 

39. Lisburne Ridge 

40. Lookout River Two main stretches, each approximately 2 km long, of 2 SB on north side of river; 

slumping 3 MB in headwaters; occasional SB near confluence with Awuna 

41. Lost Temper Creek Approximately 5 km of 2-3 SB along upper portion 

42. Main Etivluk River Numerous 2-3 SB with occasional RC on lower Etivluk; ST in the Howard Pass area; 

small 2-4 km canyons with 2 RC on Fay and Tukuto Creeks 

43. Main Utukok River Lower river between lat 69°45' and Eskimo Hill has at least five 3 RC and ST; above 

Carbon Creek and below Driftwood 2-3 RC and EF in two major canyons; 2-3 SB 

between these canyons 

44. Maybe Creek and tributaries 3 MB with some rock exposure; single 3 RC and 1-km stretch of SB near head of 

September Creek 

45. Meade River 2-3 MB and ST along river at northern edge of foothills; few 3 RC on upper Meade; 

single 2 RC at lat 69°32', long 157°52' 

46. Mesas from Meat Mountain to the 3 EF of highly fractured rock; rolling tundra 

Kiligwa River 

47. Monument Ridge-Rim Butte-Mt. Bupto Scattered 1-3 RC–O with some areas of ST 

48. Nigu River A few RC and SB such as Nigu Bluff in foothills section; ST in mountains with a few 

rock exposures 

62 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 
b 

less than 15 m 

a

2 = 50 to 100 m (165 to 330 feet) 

3 = less than 50 m (165 feet) 

b

Escarpment faces = EF 

Drainage or Area Substrate Types and Occurrence 

49. Nuka River (lower) Occasional 3 SB 

50. Nuka River (upper) Above Pilly Fork, scattered 1-3 RC and O in constricted valley, similar terrain in 

Mechanic and Sorepaw Creeks 

51. Otuk Creek 2 SB; large isolated RC lat 68°39', long 155°45' 

52. Prince Creek Numerous north-facing 3 MB 

53. Puvakrat Mountain A few 2-3 O 

54. Shaningarok Creek No exposures along creek; limited rock exposure along ridgelines in headwaters 

55. Smith Mountain Rolling tundra with some ST, no RC 

56. Swayback Creek 5-km stretch of 1-2 RC near confluence with Kuna 

57. Titaluk River Upper River featureless; area approximately 35 km upriver from confluence with 

Ikpikpuk contains 2 MB (50 m); lower Bronx Creek similar 

58. Tributaries on north side of Awuna Lower sections of these creeks (about 20 km) contain a few scattered 3 SB, EF, and RC 

Height classes: 

1 = more than 100 m (330 feet) 

Substrate types: 

Shalebanks = SB 

Mud or sand banks = MB 

Scree and Talus slopes = ST 

Rock cliffs = RC 

Outcrops = O 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 63
Appendix Figure B.1. Distribution of habitat classes for cliff-nesting raptors (Ritchie 1979). 

64 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 
Appendix Figure B.2. Habitat types, National Petroleum Reserve–Alaska. 

(a) Escarpment face (EF) on upper Kokolik River. (b) Shale banks (SB) on Ipnavik River. 

(c) Soil and mud banks (MB) on lower (d) Minaret outcrops (O) on Lisburne Ridge. 

Titaluk River. 

Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 65
(e) Rock cliffs (RC) along the Kiligwa River. 

(f) Scree and talus banks (ST) on the Kigalik River. 

66 Aerial surveys of cliff-nesting raptors in the National Petroleum Reserve–Alaska, 1999, with comparisons to 1977 
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