Appendix_A_Craig_et_al___Results_of_2010_Dalton_Highway_Raptor_Survey_Redacted.pdf

RESULTS OF A CLIFF-NESTING RAPTOR INVENTORY ALONG THE DALTON

HIGHWAY, 2010

, Jim Herriges2, and Tim Craig3

2Bureau of Land Management, 1150 University Avenue, Fairbanks, AK 99709 3 US Fish &Wildlife Service, Kanuti National Wildlife Refuge, Fairbanks, AK 99701

Abstract

We conducted a helicopter survey for cliff-nesting raptors along a portion of the Dalton Highway in northern Alaska during summer 2010. The study area (~10,130 km2) extended from the Yukon River, northward ~ 395 km through the Brooks Range to Slope Mountain on the Arctic Plain. It was our goal to inventory as many nest sites (occupied and unoccupied) as possible during eight days of flights in the study area . Although cliff-nesters were the target species for this inventory, we also recorded raptor perch sites on cliffs, all other raptors and Common Ravens (Corvus corax) that we observed. We documented a minimum of 315 stick nests, 346 raptor perch sites and 55 occupied raptor nesting territories. We found occupied territories of 25 Golden Eagles (Aquila chrysaetos), ten Peregrine Falcons (Falco peregrinus) and 11 Gyrfalcons (Falco rusticolus). Successful Golden Eagle nests with the highest productivity were concentrated along river valleys on either side of the crest of the Brooks Range; the lowest productivity occurred in the southern Brooks Range. Number of currently occupied territories is far fewer than the number of existing eagle stick nests in the study area.

We have insufficient historic data to say whether this represents a decrease in number of nesting eagles in the area. However, our data do indicate that the distribution of nesting eagles in 2010 is different than in the past. Whether this shift in distribution pattern is in response to changes in availability of prey, differences in habitat, climate change, anthropogenic influences, a combination of these, or some other factor warrants further investigation.

Introduction

The Dalton Highway traverses northern interior Alaska, and is the only all-weather road in North America that accesses the Arctic Ocean. Because of the access it provides, many existing and proposed development activities occur along the highway. Most notable of these is the Trans- Alaska Pipeline (TAPS), which roughly parallels the Dalton. However, additional existing and proposed anthropogenic related activities and structures are concentrated along the highway, including other pipeline rights-of-way, mines, and research and recreational pursuits.

The Central Yukon Field Office of the Bureau of Land Management (BLM) administers much of the land along the highway north of the Yukon River. Golden Eagles (Aquila chrysaetos), Gyrfalcons (Falco rusticolus), and Peregrine Falcons (Falco peregrinus) are the primary cliff-nesting raptor species that occur on these lands, with the greatest densities in the more mountainous regions. Changes that have the potential to influence raptor populations are rapidly

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Redacted occurring in the Arctic due to such factors as climate change and energy development (Suter and Jones 1981, Schmidt et al. 2012, VanDerWal et al. 2012, ). For example, the Gyrfalcon is currently ranked as highly vulnerable to impending impacts related to climate change (Liebezeit 2012, The Climate Change Vulnerability Index--CCVI). In addition, multiple sources now indicate declines in eagle counts throughout the western portion of their range (Kochert and Steenhof 2002, Hoffman and Smith 2003, Good 2007) and possibly in Alaska (McIntyre and Schmidt 2012) at the same time that alterations to extensive tracts of eagle winter and breeding range are occurring (Kochert et al. 2002, Copeland et al. 2011). All of these changes have broad-scale implications for agencies responsible for land-use decisions within the ranges of these species (FWS 2009).

In summer 2010, we conducted a helicopter survey for cliff-nesting raptors primarily on BLM lands bordering the Dalton Highway north of the Yukon River. This effort was driven by agency policy to fulfill the Federal Land Policy and Management Act (FLPMA) of 1976, the National Environmental Policy Act, the Migratory Bird Treaty Act, and the Bald and Golden Eagle Protection Act. FLPMA specifies that the BLM manage public lands for multiple use and sustained yield of natural resources and directs the agency to inventory the resources on public lands it administers on a continuing basis (Olendorff and Kochert 1992). The survey we conducted was of particular importance to the BLM because of recent increases in proposed development related to pipelines, and mineral extraction in the study area. The results can inform and guide management in making land-use decisions (Olendorff et al. 1989). The objectives of our survey (in order of priority) were to 1) identify as many of the occupied cliff nesting raptor territories as possible in the survey area and within logistical constraints, 2) document important raptor use areas as evidenced by vacant stick nests, eyrie ledges and perch sites with whitewash (feces) on them, and 3) record incidental observations of all raptors we encountered.

Study Area

Our survey area included lands with appropriate cliff-nesting habitat adjacent to the Dalton Highway and the TAPS. It extended from ~ latitude 65.9° at the Yukon River, north to ~68.7° at Slope Mountain and included the foothills and mountains of both the north and south slopes of the Brooks Range (Figure 1); the crest of the Brooks Range is the Continental Divide in our study area. While our efforts focused primarily on BLM administered lands, we also occasionally surveyed cliffs that were located close to the BLM boundary or that were continuous across administrative boundaries. These parcels may have included small segments of lands administered by the State of Alaska, US Fish and Wildlife Service (FWS) and National Park Service (NPS).

Six major river valleys and their tributaries incise the study area: The Kanuti, Jim, South and Middle Fork of the Koyukuk, Dietrich, and Atigun Rivers. The best nesting habitat for cliff-nesting raptors in the study area is found in the latter three of these river valleys, which bisect the Brooks Range. For ease of interpretation in this report, we refer to the study area in five separate sections; they include the three drainages in the mountains and foothills of the Brooks Range and two rolling tundra hills areas just to the north and the south of the Brooks Range. The first two drainages are on the south slope of the Brooks Range: the Middle Fork of the Koyukuk River (MFK) from where it enters the mountains (~14 km south of the village of Coldfoot, Alaska), north to its confluence with the Dietrich River, and the Dietrich River (DR), which has its headwaters at the crest of the Brooks Range. The third drainage includes the Atigun River (AR) from its headwaters on the north slope of the Brooks Range, to its confluence with the Sagavanirktok River. Common habitat types in the area include montane tundra communities, shrub-dominated riparian areas and patchy coniferous and deciduous forests (Gallant et al. 1996).

The elevation ranges from 126 to > 1700 m with glacier-carved mountain valleys and rugged peaks in the north-central part of the study area and rolling, tundra-covered hills in its southern and northern reaches.

Cliffs with potential raptor nesting sites occur throughout the study area; they range from isolated monoliths (tors) or small outcrops less than 100 m tall in the rolling tundra areas, to nearly continuous rocky mountain slopes and massive escarpments more than 500 m tall in the Brooks Range (see Appendix A for examples). Other cliff-nesting raptor habitat in the region includes escarpments bordering drainages, limestone/marble and granite cliffs and eroded alluvial bluffs along watercourses.

Relatively warm temperatures and continuous daylight characterize the study area’s Arctic climate in the summer, which contrasts with extreme cold temperatures and abbreviated daylight in the winter. Temperatures in the central part of the study area (Wiseman, Alaska) average 14.1° C during July, (62 year means; Weatherbase 2012) and precipitation averages about 35.7 cm/year (64 year mean of annual totals; Western Regional Climate Center 2013).

Methods

Cliff-nesting raptors and their nests were the primary focus of this inventory; however, all raptors observed were recorded. We also report Common Ravens (Corvus corax) because they build stick nests on cliffs and occupy an ecological niche similar to raptors (Boarman and Heinrich 1999). Their stick nests can also provide nesting substrate for raptors that do not build their own nests (White and Cade 1971).

We conducted the aerial surveys from 25 June through 2 July 2010 when the opportunity to identify occupied raptor territories was maximized. The inventory occurred during the late incubation/early nestling period for most Peregrine Falcons and during the mid to late nestling period for most Golden Eagles and Gyrfalcons. Common Raven young had already fledged during our survey. In all, we spent eight survey days and ~50 hours of helicopter flights, including ferry time within the study area. We summed the daily track logs to calculate total length of the route traveled; they also provide a record of areas not covered for future inventory efforts. A conservative minimum estimate of total area inventoried was calculated by assuming an average coverage of approximately 300 m either side of the ship. Budgetary constraints prevented a complete inventory or more than one survey during the nesting season.

We determined areas to be surveyed through pre-flight analyses of likely cliff-nesting habitats using expert opinion, historic data, and Geographic Information System (GIS) examination of terrain. Because historic nest locations were highly variable in their accuracy, we did not rely heavily on these for selecting our survey routes. However, if we were in the vicinity of a waypoint for a historic site during the survey, we used that information to alert us to a potential nest there. In addition, when in the field, we adjusted survey routes to include areas with the most likely nesting substrate, and/or which were closest to the Dalton Highway and therefore most likely to be impacted by future or current development activities. The Dietrich and Atigun River Valleys contain extensive cliffs with appropriate raptor habitat but because of time constraints, we focused our survey efforts in these areas to the best habitat within ~2.0 km either side of the highway (Appendix B). Coverage of these areas in the Brooks Range was more intensive than in the less mountainous southern and northernmost tundra portions of the study area. In these areas because cliff nesting habitat was fragmented, we flew at higher altitude and searched for the isolated outcroppings and river cliffs/bluffs that occurred there. In this broad area, the survey was likely less complete in coverage than in the Central Brooks Range.

Because we conducted a single survey we may not have detected 1) early nesters that occupied territories but failed, 2) territories that may have already fledged young prior to the survey, 3) later-nesting raptors such as Peregrine Falcons, that were still incubating eggs, when raptors are typically more secretive (Steenhof and Newton 2007), and 4) post-survey mortality in the nest prior to fledging (Steenhoff and Newton 2007). These factors likely biased our estimates of nest success upward and underestimated the total number of occupied cliff-nesting raptor territories in the study area. Similarly, the estimates of productivity for Golden Eagles and Gyrfalcons are probably inflated because our calculations are based on the number of nestlings observed at the time of the survey, regardless of nestling age (Steenhoff and Newton 2007).

We used a Robinson R-44 II helicopter for the survey and two experienced observers. The observer in the rear seat also served as a recorder, and the pilot functioned as a third observer when flying conditions permitted. The flights were conducted when winds were calm to moderate and when there was good visibility, with little to no precipitation. Whenever possible, cliff faces were surveyed with the sun behind the helicopter. Sighting conditions were generally excellent, but shadows during early morning hours and light rain occasionally reduced visibility.

On larger slopes with multiple outcrops we made two or more passes in the helicopter, loosely following slope contours. Large escarpments requiring multiple passes were surveyed from top to bottom. In some cases, long narrow outcrops were surveyed by slowly descending from top to bottom.

The recorder collected GPS waypoints and track logs (WGS-84), using a Garmin 76csx GPS with an external antenna mounted on roof plexiglass and recorded data related to each waypoint on a field survey form (see Appendix C). The pilot also recorded tracklogs. Waypoints for nest and perch locations were generally recorded slightly above and away from from the nest site on the cliff. The GPS waypoint elevation was assumed to be the elevation of the nest site or perch, leading to an error of ~10 – 20 m for our location data, in addition to the inherent elevation error associated with GPS units (up to + 120 m; Garmin Support 2012).

Because helicopters can disturb nesting raptors (Watson 1993), we hovered near occupied nest sites only long enough to determine occupancy, and record observations at the nest. Approaches to nest cliffs were as direct as possible in order to minimize startling raptors on nests. We generally flew no closer than ~30 m from a cliff face and further away in windy conditions. We photographed nests from a distance using a telephoto lens to later verify the number of young or eggs and/or used binoculars to examine nests . Photos were geo-tagged with GPS coordinates using GPS-photolink software (Geospatial Experts, Inc.)

We attempted to record every stick nest encountered, as well as ledges or cavities that showed evidence of having been used by raptors because they can provide evidence of both recent and historic raptor distribution. When we encountered multiple nests very close together in a single cliff complex, we did not always record each one as an individual waypoint. Therefore, the number of vacant stick nests that we record should be considered a minimum estimate of the actual number of nests in the study area. We attributed vacant stick nests to different species based on their size, physical appearance, location, and physical setting. In general, large nests we encountered were attributed to Golden Eagles and smaller and sloppily built nests to ravens or buteos. While there was some subjectivity in this classification scheme, we are confident that errors in attribution were small. We also recorded raptor perch sites, evidenced by whitewash, as an additional measure of raptor use areas. Similar to our records for stick nests, our records of raptor perch sites are an underestimate of raptor perching activity. Waypoints taken often represent multiple perches in a single area and we did not record perches that contained only a few dribbles of whitewash.

We used the following terminology in classifying nesting territories.

Occupied—observation of an adult incubating, an adult or adults exhibiting nesting behavior (e.g. vocalizing at the approach of the helicopter), eggs, nestlings, or a family group of recently fledged young perched near a nest site, (Steenhof and Newton 2007). In addition, for Golden Eagles, we considered a territory occupied if 1) a nest contained fresh greenery, even if we observed no nestlings or eggs, and 2) was more than 2.2 km from another nest containing nestlings (minimum distance observed between successful Golden Eagle nests in the study area).

• Successful—an occupied territory containing at least one nestling or recently fledged young regardless of age.

• Unsuccessful—an occupied territory containing no nestlings (determined for Golden Eagles and Gyrfalcons only, since the nesting fate of Peregrine Falcons could not be determined due to their later nesting chronology).

Unoccupied—stick nest or eyrie ledge where we did not observe adults, nestlings, eggs, fresh greenery or fresh whitewash evidence of nesting in 2010.

Additional terminology is as follows:

Active Nest—the nest within an occupied territory that contains eggs or nestlings or an incubating adult.

Vacant Nest—a nest that contains no eggs, nestlings, fresh greenery, or incubating adult.

A vacant nest can be an alternate nest in an occupied territory.

At sites where no adults were present and only young were observed, we determined the species based on nestling plumage, other physical characteristics (e.g. head and beak shape) and nest site location and characteristics. If occupancy of a large falcon territory was documented, we spent little additional time attempting to identify the actual nest “scrape” or ledge. Although both American Kestrels and Merlins can sometimes nest on cliffs (Warkentin et al. 2005, TC) and were detected during our survey, we made no effort to determine occupancy or locate nest sites if they were not immediately apparent.

All spatial analyses of data were conducted in ArcMap 10.0 and were performed only for Golden Eagle territories, stick nests, and distribution of raptor perches; we had insufficient sample sizes to perform these analyses for Gyrfalcons and Peregrine Falcons. The tools used in our analyses are located in the ArcMap Toolbox (ESRI 2011). Layers were projected into Albers North American Datum 1983 prior to analyses; additional metadata for layers accompany the electronic geodatabases provided to BLM with this report. We used the Average Nearest Neighbor (NN) Tool in Spatial Statistics to test whether occupied nests were randomly distributed throughout the area surveyed (estimated to be ~2510 km2), and α = 0.05 for this and all other statistical tests. We used the Integrate Tool (Data Management) and a radius of 2.2 km (the minimum distance between successful Golden Eagle nests observed in this survey) to weight point data for perch and nest site locations and then used the Collect Events Tool (Spatial Statistics) to create a weighted point layer. The weighted point layer was loaded into the Hot Spot Analysis Tool (Spatial Statistics) to identify spatial clusters of stick nests or perches that differ significantly from an expected random distribution of the same set of features. The Hot Spot Analysis Tool calculates the Getis-Ord Gi* statistic, which is output as a z score. To determine statistical significance the z score is compared to the values for the selected confidence level (e.g., for α = 0.05, z is significant if it is greater than 1.96 or less than -1.96). A high or low negative z score and low p value indicate either a hotspot where points are clustered or a coldspot where points do not occur.

Descriptive statistics were performed in Excel (Microsoft 2003); means are reported + SD. We used Single Factor ANOVA to test for differences in mean Golden Eagle productivity among the three valleys in the Brooks Range; two nests located north and south of the Brooks Range, respectively, were not included in analyses of nest data for the valleys in the Brooks Range but were included in calculations of overall productivity in the study area . We used the minimum distance between successful Golden Eagle nests to determine if a nest that contained fresh greenery was an alternate nest within an eagle territory that contained another successful nest.

Any nest containing greenery that was further than the minimum distance from another, successful Golden Eagle nest was considered to be in a separate, occupied and unsuccessful territory.

Results

Survey Overview. The total survey route was ~4200 km in length and covered an estimated minimum area of ~2510 km2. We encountered 11 and possibly 12 different species of raptors (a likely Northern Goshawk (Accipiter gentilis) was glimpsed briefly among trees as the helicopter flew over), 55 occupied raptor territories, two Common Raven family groups and a minimum of 285 vacant stick nests (Table 1). We classified most of the stick nests as unoccupied Golden Eagle nests. Condition of the vacant stick nests ranged from very good, with whitewash evidence of recent use, to ancient nests that were in disrepair. Golden Eagles, Gyrfalcons and Peregrine Falcons were the most common nesters in the survey area with Golden Eagles occupying more than twice the number of territories than either of the large falcons.

Golden Eagles. Golden Eagles comprised more than half of the 70 raptors sightings we made that were not associated with an occupied territory. Only two of those eagles were sub-adult birds. Most of these sightings occurred in the Dietrich and Atigun River Drainages, the same general areas in which many of the nests and 64% of the occupied territories were located.

Average NN distance of active Golden Eagle nests in the Brooks Range was 6.4 km ( Table 2).

These occupied nests were not randomly distributed but exhibited significant dispersion (z = - 4.247, p = 0.000; expected mean distance = 5.1 km; Figure 2a – 2d). However, all stick nests on cliffs (occupied and unoccupied) tended to be clustered, primarily in the mountainous terrain of the three river valleys in the Brooks Range (MFK, DR, and AR; Figure 3). There were significant hotspots in the MFK (z = 3.583, p = 0.000) and in the upper DR (z = 3.583, p = 0.000). Three other areas, two at MFK and one in the DR had nearly significant values (z = 1.909, p = 0.056).

A total of 315 stick nests were counted at 266 locations on cliffs. Forty-seven (20%) of the vacant eagle stick nests (239) and 61 (18%) of the 346 raptor perch sites fell within 2.2 km of an active nest in an occupied eagle territory. The number of nests recorded in each occupied territory ranged from 1 – 11 (mode = 1 and mean ~ 2 nests).

Raptor perch sites, an indication of recent raptor use, were scattered throughout the study area;

two significant hotspots for perching activity were in the AR on the north slope of the Brooks Range (z = 3.520, p = 0.000, Figure 4). Both hotspots were further than 2.2 km from an occupied Golden Eagle territory. Perches were not restricted to nesting areas and covered a broader geographic and elevational range than nest sites in the study area (126 – 1718 m; mean: 978 + 319 m). Eagle stick nests had the widest range in elevation of any of the species’ nest sites we surveyed (mean elevation of vacant nests = 879 + 238; range: 257-1535 m).

We found 31 nestlings in the 19 successful Golden Eagle territories (1.6 nestlings/successful nest and 1.2 nestlings/occupied territory; Table 3). Of the 6 unsuccessful territories, four were in the MFK. Five of the unsuccessful nests contained only fresh greenery, but one had an egg in it that we presumed was addled. We observed two different pairs of Golden Eagles soaring high overhead within 2 km of the latter nest that were not near another occupied territory. It is possible that one of these pairs was associated with this unsuccessful territory.

There was a significant difference in productivity among the three river valleys in the Brooks Range (nestlings/occupied territory: F = 9.6778, df = 2, p = 0.001). Productivity and occupancy in the MFK area was lower than the other two river valleys. Habitats differ among the three areas, with the MFK being more forested (Black, Picea mariana, and White Spruce, Picea glauca ) than the areas further north. The seven occupied territories in the MFK were located within 20 km of the only two villages in the study area, near the highest density of mining claims and ~ 20 km north of an estimated 70,000 hectares that burned in 2005. Four current or proposed gravel pits along the Dalton Highway in the MFK are within a mile of eagle stick nests that were vacant in 2010. The southernmost occupied territory, was also unsuccessful. It was located more than 65 km from the nearest town, on a cliff in the rolling tundra hills south of the Brooks Range.

There is little mining activity in this area, with the closest mining claim more than 30 km away;

it is within 8-25 km of over 280,000 hectares that burned in 2004 and 2005.

The most productive eagle nests in the study area were in the Dietrich and Atigun River Valleys.

Both survey segments had an equal number of occupied territories, and similar productivity, with nests furthest north in the AR having slightly higher productivity than in the DR. The DR is the most remote part of the survey area; the closest village, mining claim and burned areas were 40, 17, and 50 km away, respectively. Current and proposed gravel pits occur along the highway in both of these valleys. Six sites in the DR are within a mile of eagle stick nests that were vacant in 2010. Three sites in the AR are less than a mile from golden eagle nests that were occupied in 2010 and one of these pits, if fully developed, will destroy an eagle nest that was occupied in 2010. In addition, the TAPS Pump Station No.4, Galbraith Lake airport, a campground, and a scientific research station, which is the largest village along the Dalton Highway are within ~2.5 km, 3.5 km and 18 km, respectively from the nearest occupied Golden Eagle territory in the AR .

We observed both Dall’s Sheep (Ovis dalli) and Willow Ptarmigan (Lagopus lagopus) in the same general areas where clusters of eagle nests occurred in the MFK, the DR and the AR.

Arctic Ground Squirrels (Spermophilus parryii), Snowshoe Hares (Lepus americanus), and other known prey of Golden Eagles in the Arctic (Young et al. 1995, McIntyre and Adams 1999) are also known to occur in the study area.

The northernmost territory in the study area was on a rock outcrop in the rolling tundra north of the Brooks Range; it contained one nestling. Similar to the AR nests, it was remote from towns, recently burned fires and mining activity. It is ~ 33 km from Galbraith Lake, Pump Station 4 and ~25 km from the Toolik Lake Field Station.

Nestlings in the study area ranged in age from ~two weeks of age, to near fledging. All of the nestlings in the MFK area were still downy chicks, while nestlings varied greatly in age in the nests that were located further north. One occupied eagle nest containing one nestling was ~770 meters from a Gyrfalcon eyrie that contained three nestlings. The closest Peregrine Falcon eyrie to an eagle nest was ~5 km away and the next closest was ~ 15 km away.

Gyrfalcons. We found 11 occupied territories with nestlings and four additional areas that may have been occupied this year based on fresh whitewash evidence on perches and ledges at the cliff. The number of nestlings per occupied territory ranged from 1 – 4 (mean: 2.4 + 0.9); they varied in age from ~2 weeks to fully feathered and near fledging. Six of the 11 active nests were in old Golden Eagle stick nests. Occupied Gyrfalcon territories were spread across the entire study area but usually occurred at the higher elevations; one territory was less than a mile from a current or proposed gravel pit site in the MFK. We did not find any occupied territories in the upper ends of the Dietrich or Atigun River Valleys although there were eyrie sites in these areas that had been used in the past. Falcon perches, on the other hand, were scattered throughout the study area, including the upper ends of those two valleys. The elevation range for falcon perches was 126 -1496 m (mean: 902 + 336 m, n = 134).

Peregrine Falcons. The timing of our survey was during the early nesting phase for Peregrine Falcons and so was not optimum for detecting birds. We documented ten occupied territories:

three contained eggs or an incubating adult, five held nestlings less than a week old, and two contained birds exhibiting defensive behavior at a cliff site where we did not find eggs or young.

In addition, there were three other sites with either birds present (n = 2) and/or whitewash (n = 1) evidence of occupancy but for which we could not verify occupancy; we considered these as likely to be occupied. The number of nestlings at eyries ranged from 2- 4 (mean: 2.6 + 0.9). Five of the eight active nests were on ledges and the remaining three were in old stick nests. Active nests were generally at the lower elevations in the study area. All but one of the occupied territories were scattered in the southern half of the study area and all but two were on bluffs or cliffs bordering rivers or streams. The territory at the northern end of the study area that was near the Toolik Lake Field Station contained a defensive pair of birds with no eggs or young in evidence. This territory was also less than a mile from an existing or proposed gravel pit.

Other raptor species. We found two Rough-legged Hawk nests on small rock outcrops north of 68° latitude and saw birds in four other areas where we did not find nests. All of these observations were made in the northern end of the study area: elevations of the sightings of Rough-legged Hawks ranged from 730 -1521 m (mean = 1017 + 250 m). All of the Harlan’s Hawk nests we found occurred south of the Brooks Range (south of ~67° Latitude). We located three nests in trees and two adults vigorously defended a vacant stick nest on a cliff overlooking a river at a third location. Common Ravens had already fledged when we conducted our survey.

However, we observed two family groups near nests and five other nests that likely had already fledged young, based on the amount of whitewash at the nest site. Other incidental non-cliff nesting raptor sightings during the survey are presented in Table 1. They included a Bald Eagle nest with one nestling in a cottonwood tree (Populus spp )at the edge of a river.

Discussion

Golden Eagles. We located more occupied Golden Eagle, territories and many more vacant eagle stick nests during our inventory than were previously found in the study area (Craig and Hamfler 2002, Roseneau and Bente 1979). This may be all or partially related to differences in survey effort expended between the current and previous surveys. We found that eagle nests spanned a wider elevational range than any of the other cliff-nesting species we encountered but the maximum elevation at which we found them nesting was consistent with reports by other researchers (maximum elevation: 1281 m, Craig and Hamfler 2002; 1340 m, Roseaneau et al.

1981).

Hobie and Cade (1962) suggested that the north slope of the Brooks Range is marginal nesting habitat for Golden Eagles because the harsh Arctic environment at the northern latitudes limits reproduction (Hobie and Cade 1962). However, surveys in the 1970’s and 1980’s, identified the mountains and foothills of the Brooks Range along the Dalton Highway to be prime habitat for nesting Golden Eagles (White and Streater 1970, Roseneau and Bente 1979, Roseneau et al.

1980, FWS unpublished data, Ritchie and Curatolo 1981). Similarly, our results from the Atigun River Valley further support these observations. In fact, we found more nesting Golden Eagles in the northern part of the study area than in the southern part.

Roseneau and Bente (1979) and Ritchie and Curatolo (1981) recorded 11 occupied (or likely occupied) Golden Eagle territories between the Yukon River and the northern boundary of the study area. The latter authors did not record vacant nests, but Roseneau and Bente (1979) report 54 vacant stick nests in this area. White and Streater (1970), who surveyed for Peregrine Falcons in the Brooks Range, also reported that the area was used by nesting Golden Eagles, although they made no attempt to estimate numbers. All of these earlier surveys reported fewer nesting eagles in the Atigun River Valley in the northern part of the study area, than in the Dietrich and Middle Fork Koyukuk Rivers south of the Continental Divide. In fact, literature accounts verify only one occupied Golden Eagle territory in the Atigun River Valley in 1979 and 1981 (Roseneau and Bente 1979, Ritchie and Curatolo 1981). In contrast, we found eight occupied territories and the greatest evidence of raptor perch activity in this valley in 2010 and 16 from the Crest of the Brooks Range to the Kanuti River where Craig and Hamfler (2003) found five occupied eagle territories and 76 unoccupied golden eagle stick nests between 1999 and 2002.

We found almost three times the number of unoccupied stick nests in the same area in the 2010.

Interestingly, we also found the highest productivity for golden eagles in the Atigun River Valley (2.0 nestlings/successful pair); this estimate is higher than reported for other Arctic nesting populations found at a similar latitude. Young et al. (1995) and Poole and Bromley (1988) report the number of nestlings/successful pair as 1.22 and 1.30, respectively for latitudes 68° and northward. However, it is important to note that the productivity values from our survey are likely inflated because we: 1) only conducted a single survey, 2) used the number of nestlings in the nest at the time of our survey in calculating productivity estimates, regardless of their age, and 3) may have missed nestling mortality subsequent to our visit (Steenhoff and Newton 2007).

Nonetheless, our most interesting results are the differences we noted within the study area. Even though the number of occupied territories in each of the three cliff-rich mountain valleys of the Brooks Range were nearly identical, the most productive territories and the most evidence of recent raptor use (perches) were on the north slope of the Brooks Range. These results are converse to findings from previous surveys and the tenet that golden eagle productivity in Arctic regions declines with increasing latitude (Hobie and Cade 1962, Young et al. 1995, McIntyre and Adams 1999, Ritchie et al. 2003). It is also in contrast to the results of our analyses on the distribution of eagle stick nests in our study area; significant clusters of nests were found only south of the Continental Divide, with most clusters concentrated in the southernmost valley of the Brooks Range.

Comparison of our results with historic survey data suggest that nesting golden eagles in the study area have increased rather than decreased. However, caution must be used when comparing these data for two reasons. First, methods used in the different surveys were not identical; there was variability in the number of trained observers in the helicopters, experience of the pilot, survey timing, intensity of survey effort, and area covered. Secondly, golden eagle nest attendance and success can be influenced by many variables, especially the distribution and availability of prey, particularly for prey species that are cyclic in abundance (Young et al. 1995, Kochert et al. 2002). An analysis of the influence of various factors such as prey distribution, abundance and availability in different parts of the study area and among years, anthropogenic influences, and climate change, and their concomitant effects on eagles could help clarify our findings. However, that type of analysis is beyond the scope of the present study.

Regardless of whether the occupied territories reflect an increase over historic numbers, there is significance to the hundreds of vacant eagle nests in the study area. Eagle nests are persistent in the environment and so may represent decades or even centuries of past nesting attempts (Reimer et al. 2004). It is common for there to be multiple, unoccupied nests within a golden eagle nesting territory (Kochert et al. 2002). However, only a small fraction of the vacant nests we recorded were likely alternate nests in a nesting territory; in fact, several hundred nests were not near any occupied territories. The presence of these vacant nests implies that there may have been more nesting golden eagles in our study area in the past than we documented in 2010.

However, the available survey data from 1979-2002 do not support this notion. Golden eagles show fidelity to nesting areas, some even occupying territories during low prey years but not nesting (Steenhof et al. 1997, McIntyre and Adams 1999). However, golden eagles in western Alaska have been documented to use not only alternate nests in the same territory, but sometimes move to and nest in entirely different territories in successive years (P. Bente, Alaska Dept. of Fish and Game, Nome, pers. comm.). It is possible that the superfluous nests in our study area reflect changes in population distribution patterns over time, rather than changes in nesting densities.

In any case, our data indicate that the mountains and foothills of the Brooks Range are an important nesting location for golden eagles. Our results also indicate three specific things about nesting golden eagles in the study area: 1) the Middle Fork of the Koyukuk River Valley was more important in the past than in 2010, 2) the Dietrich River Valley has always been an important nesting area, and 3) the Atigun River Valley appears to be more important in 2010 than in the past. There are several possible explanations for these differences. First, there is more anthropogenic disturbance in the MFK than the other two surveyed areas and much of it was initiated subsequent to the early surveys. White and Streater (1970) noted that golden eagle nests in the mouths of canyons along the TAPS corridor were vacant and that occupied nests were located further back in the side canyons. They suggested this may have resulted from eagles attempting to avoid the human activity associated with the TAPS, which is located in the valley bottoms. Second, changes among years in Snowshoe Hare, Arctic Ground Squirrel and other prey species populations may have influenced the distribution of occupied eagle territories.

Third, changes in weather patterns associated with climate change may have resulted in a northward shift in nesting eagles in the study area, similar to what has been observed for other species of birds (Hitch and Leberg 2007). Whether the patterns in distribution of vacant and occupied eagle nests represents a short-term redistribution of eagle territories in response to changes in prey, or long-term changes in eagle distribution in response to anthropogenic influences and climate change is unknown.

Gyrfalcons and Peregrine Falcons. Like Golden Eagles, we recorded more Gyrfalcons and Peregrine Falcons nesting in the study area than did the historical surveys and actual numbers of occupied territories are likely higher than what we found because of the timing of our survey (Steenhof and Newton 2007). Roseneau and Bente (1979) found both Gyrfalcons and Peregrine Falcons nesting north of our study area, but none in it. Craig and Hamfler (2002) recorded three gyrfalcon and 2 peregrine falcon nests in their 1999-2001 surveys.

Gyrfalcon eyries occurred from ~ 66.4° latitude northward in our study area. We generally found them at higher elevations than Peregrine Falcons and, like Golden Eagles, over a wider range in elevations. This may have resulted because more than half of the occupied Gyrfalcon eyries we found were located in old eagle stick nests. While Peregrine Falcon eryies were restricted to the lower elevations in our study area, like Ritchie and Shook (2011) we found them nesting higher than the 610 m upper boundary suggested by Cade (1960). White and Streater (1970) hypothesized that Peregrine Falcons did not nest at higher elevations in the Brooks Range because they avoided Golden Eagle nesting territories; we also found Peregrine Falcons to occur primarily where the density of nesting eagles was lowest. Others have also noted that there is little overlap in the distribution of the two species (Poole and Bromley 1988, Ritchie et al. 2003).

We do not know if the increased number of Gyrfalcon nests we report represents an overall increase in the Gyrfalcon population at a landscape scale because, like Golden Eagles, they prey on irruptive prey (Booms et al. 2008). However, it is likely that the increased number of Peregrine Falcon territories in our study area reflects the increase in nesting Peregrine Falcons observed across Alaska since DDT restrictions were implemented in the early 1970’s (Ritchie and Shook 2011).

Notes of interest on other raptor species encountered. The single Bald Eagle nest that we encountered was in a cottonwood tree(Populus spp.) on a river bank at ~ 66.8° N latitude. This nest is among the furthest north records of nesting Bald Eagles in North America (US Fish and Wildlife Service, Migratory Bird Management-Raptors, Juneau, Alaska; Bald Eagle nest database). The Rough legged Hawks in our study area were nesting at the extreme southern end of their range in north-central Alaska. Similar to Roseneau and Bente (1979) who found only one nesting pair, we located only two pairs nesting in our study area. The American Kestrels we observed were in the upper reaches of the Middle Fork of the Koyukuk River Valley and in the Dietrich River Valley. The furthest north observation of a kestrel was on the Continental Divide at 68.1° N latitude and 1381 m elevation. The range of the American Kestrel is reported to be south of the Brooks Range; this may be one of the furthest north records for this species (Smallwood and Bird 2002).

Management Recommendations. We recommend that the Dalton Highway corridor between the Yukon River and Slope Mountain be identified by the pertinent land management agencies as an index area for monitoring cliff-nesting raptors in the Arctic. There are a number of reasons that this area should be considered for long-term monitoring. The area supports a high concentration of nesting Golden Eagles and other cliff-nesting raptors at a high latitude but is logistically less complicated than most Arctic study areas because of accessibility from the highway.

Furthermore, anthropogenic influences are concentrated along the Dalton and are accelerating with national demands for energy and minerals; the Dalton Highway is the only all-weather road that accesses the Arctic Circle, the Brooks Range and the Arctic Ocean. Lastly, climate change is expected to have a profound impact on Arctic regions (Chapman and Walsh 2007, Lawrence et

al. 2008, VanDerWal et al. 2012). Monitoring is an important component of conservation management for these species; the unique characteristics of this study area are ideal for tracking potential responses of these cliff-nesting raptors to changes within their environment.

We also recommend a preliminary analysis of existing data to help identify factors influencing the distribution and abundance of the species in question. This initial investigation can be useful in designing a successful monitoring program that provides information valuable to natural resource managers in making land management decisions.

Acknowledgements

This project was funded by the Bureau of Land Management; special thanks to Cara Staab, BLM-Alaska State Office for providing funding. We would also like to thank the many personnel from the BLM-Central Yukon Field Office, U.S. Fish and Wildlife Service, National Park Service and Alaska Department of Fish and Game, for providing help with the logistics involved in conducting this survey; and especially to our pilot, Mark Shelton, whose expert flying and excellent observational skills immeasurably enhanced what we were able to accomplish.

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