Movements and Migration

The Golden Eagle is highly mobile throughout all stages of life after fledging. Nearly all movement is via flight, though individuals are capable of walking surprisingly long distances. Flight relies on thermal or orographic updraft, with flapping avoided except when necessary. Telemetry studies provide most of the information on the movements of individuals, although surprisingly large numbers of birds are counted at some migration count sites. Much of the knowledge about movement behavior comes from North America and Europe (e.g., 11 Haworth, P. F., M. J. McGrady, D. P. Whitfield, A. H. Fielding, and D. R. McLeod (2006). Ranging distance of resident Golden Eagles Aquila chrysaetos in western Scotland according to season and breeding status. Bird Study 53: 265–273. Close , 252 Brown, J. L., B. Bedrosian, D. A. Bell, M. A. Braham, J. Cooper, R. H. Crandall, J. DiDonato, R. Domenech, A. E. Duerr, T. E. Katzner, M. J. Lanzone, D. W. LaPlante, C. L. McIntyre, T. A. Miller, R. K. Murphy, A. Shreading, S. J. Slater, J. P. Smith, B. W. Smith, J. W. Watson, and B. Woodbridge (2017). Patterns of spatial distribution of Golden Eagles across North America: How do they fit into existing landscape-scale mapping systems? Journal of Raptor Research 51: 197–215. Close ), and comparatively less is known about movements of birds in Africa and Asia.

Natal Dispersal and Philopatry

Initial movements from a nesting site are strongly influenced by the migratory tendency of the population from which it originates. As such, we discuss separately migratory and non-migratory birds.

Dispersal in Migratory Populations

Post-independence movements of migrant individuals from interior Alaska include short to long-distance migrations that span a broad region of western North America (220 McIntyre, C. L., D. C. Douglas, and M. W. Collopy (2008). Movements of Golden Eagles (Aquila chrysaetos) from interior Alaska during their first year of independence. Auk 125: 214–224. Close , see Movement and Migration: Timing and Routes of Migration). A similar study in Norway of 25 nestlings from a partially migratory population recorded post-fledging movements of 10–1,500 km from the nest, with a median date of departure of 21 October (253 Nygård, T. (2016). Dispersal and survival of juvenile Golden Eagles (Aquila chrysaetos) from Finnmark, Northern Norway. Journal of Raptor Research 50(2): 144–160. Close ). Direct comparison of these two studies is difficult because of the partially migratory characteristics of the Norwegian population. Many of the eagles termed “dispersers” in that study traveled south and returned to their natal territory the following spring.

Dispersal in Non-migratory Populations

Post-independence movements at temperate latitudes involve nonlinear wandering beyond the natal area that sometimes follows topography (254 Steenhof, K., M. N. Kochert, and M. Q. Moritsch (1984). Dispersal and migration of southwestern Idaho raptors. Journal of Field Ornithology 55: 357–368. Close , 104 Murphy, R. K., J. R. Dunk, B. Woodbridge, D. W. Stahlecker, D. W. LaPlante, B. A. Millsap, and K. V. Jacobson (2017). First-year dispersal of Golden Eagles from natal areas in the southwestern United States and implications for second-year settling. Journal of Raptor Research 51(3): 216–233. Close ). First-year eagles banded (ringed) in Snake River Canyon, Idaho, dispersed from natal areas in nearly all directions (254 Steenhof, K., M. N. Kochert, and M. Q. Moritsch (1984). Dispersal and migration of southwestern Idaho raptors. Journal of Field Ornithology 55: 357–368. Close ). Most individuals encountered did not move beyond the boundaries of adjacent states. In fact, 78% of band encounters were < 100 km, and only 1% of band encounters were > 1,000 km from banding locations (254 Steenhof, K., M. N. Kochert, and M. Q. Moritsch (1984). Dispersal and migration of southwestern Idaho raptors. Journal of Field Ornithology 55: 357–368. Close ).

All 66 Golden Eagles telemetered as nestlings in the Colorado Plateau and southern Rocky Mountains left their natal territory within one year of fledging (104 Murphy, R. K., J. R. Dunk, B. Woodbridge, D. W. Stahlecker, D. W. LaPlante, B. A. Millsap, and K. V. Jacobson (2017). First-year dispersal of Golden Eagles from natal areas in the southwestern United States and implications for second-year settling. Journal of Raptor Research 51(3): 216–233. Close ). Most (67%) moved < 120 km from their natal nest in the first and second year of life. Another 17% moved moderate distances (120–500 km), and 13% moved long distances (> 500 km). Two eagles did not easily fit in the above classification scheme, as they regularly left and returned to their hatching site. In general, long distance travelers were from more arid areas and had lower survival rates than did eagles that moved short distances. Eagles that moved relatively short distances (< 350 km) traveled in apparently random directions. However, birds that moved longer distances tended to travel south, southeast, or east, to areas in northern Mexico or, in one case, Arkansas.

Natal Philopatry

Natal philopatry has been rarely recorded. Radio-telemetry and banding data from non-migratory eagles in Scotland suggest that as eagles reach breeding age, they tend to return to natal areas (255 Grant, J. R., and M. J. McGrady (1999). Dispersal of Golden Eagles Aquila chrysaetos in Scotland. Ringing and Migration 19: 169–174. Close ). Eight Golden Eagles banded in the Snake River Canyon nested 1–12 territory widths from their natal territories (254 Steenhof, K., M. N. Kochert, and M. Q. Moritsch (1984). Dispersal and migration of southwestern Idaho raptors. Journal of Field Ornithology 55: 357–368. Close ; USGS, unpublished data). Five of those eagles whose identity could be confirmed bred 7 to 65 km from their natal nests (mean 34 km ± 21 SD; 254 Steenhof, K., M. N. Kochert, and M. Q. Moritsch (1984). Dispersal and migration of southwestern Idaho raptors. Journal of Field Ornithology 55: 357–368. Close ; USGS, unpublished data).

There is some evidence that male may be more likely to nest near their natal areas than are females (256 Murphy, R. K., D. W. Stahlecker, B. A. Millsap, K. V. Jacobson, A. Johnson, C. S. Smith, K. J. Tator, and K. L. Kruse (2018). Natal dispersal distance of Golden Eagles in the southwestern United States. Journal of Fish and Wildlife Management 10(1): 213–218; e1944-687X. Close ). Six of seven eagles marked as nestlings in Snake River Canyon and later encountered there as breeders were identified as males (254 Steenhof, K., M. N. Kochert, and M. Q. Moritsch (1984). Dispersal and migration of southwestern Idaho raptors. Journal of Field Ornithology 55: 357–368. Close ; USGS, unpublished data). The female who returned to nest in the Snake River Canyon moved 44 km, farther than the average distance moved by males (32 km), but less than the maximum distance moved by a male (65 km). Two males banded in Utah bred 48 and 93 km from their natal nests (American Eagle Research Institute, unpublished data). A female banded in southwestern Montana first nested 61 km from its natal nest (R. Crandall, unpublished data), and three females banded in the Colorado Plateau-Southern Rocky Mountain region of the southwestern United States bred 19, 66, and 124 km from their natal nests (256 Murphy, R. K., D. W. Stahlecker, B. A. Millsap, K. V. Jacobson, A. Johnson, C. S. Smith, K. J. Tator, and K. L. Kruse (2018). Natal dispersal distance of Golden Eagles in the southwestern United States. Journal of Fish and Wildlife Management 10(1): 213–218; e1944-687X. Close ). In contrast, a genetic study in Scotland suggested that long-distance dispersal was male-biased (257 Ogden, R., E. Heap, R. McEwing, R. Tingay, and D. P. Whitfield (2015). Population structure and dispersal patterns in Scottish Golden Eagles Aquila chrysaetos revealed by molecular genetic analysis of territorial birds. Ibis 157(4): 837–848. Close ).

Adult Fidelity to Breeding Site and Dispersal

Adult eagles often show fidelity to breeding sites (176 Marzluff, J. M., S. T. Knick, M. S. Vekasy, L. S. Schueck, and T. J. Zarriello (1997). Spatial use and habitat selection of Golden Eagles in southwestern Idaho. Auk 114(4): 673–687. Close , TAM). Most telemetered adults repeatedly use the same nesting territory for the entire time their telemetry unit functions (TEK, CLM, TAM), but tagged birds occasionally switch territories (176 Marzluff, J. M., S. T. Knick, M. S. Vekasy, L. S. Schueck, and T. J. Zarriello (1997). Spatial use and habitat selection of Golden Eagles in southwestern Idaho. Auk 114(4): 673–687. Close ; G. Hunt, personal communication). One marked individual remained on the same nesting territory for ≥ 12 years in Idaho (Snake River Canyon, USGS, unpublished data). Closely related Imperial Eagle and Spanish Eagle are similarly faithful to nesting territories, with generally low rates of territory switching (258 Ferrer, M., and J. A. Donazar (1996). Density-dependent fecundity by habitat heterogeneity in an increasing population of Spanish imperial eagles. Ecology 77: 69–74. Close , 259 Rudnick, J. A., T. E. Katzner, E. A. Bragin, O. E. Rhodes Jr., and J. A. Dewoody (2005). Using naturally shed feathers for individual identification, genetic parentage analyses, and population monitoring in an endangered Eastern imperial eagle (Aquila heliaca) population from Kazakhstan. Molecular Ecology 14: 2959–2967. Close ). White-tailed Eagle, which is more distantly related and has different ecology, appears to switch nesting territories more frequently (260 Bulut, Z., E. A. Bragin, J. A. DeWoody, M. A. Braham, T. E. Katzner, and J. M. Doyle (2016). Use of non-invasive genetics to assess nest and space use by White-tailed Eagles. Journal of Raptor Research 50: 351–362. Close ).

There are few records of eagles moving from one nesting territory to another (i.e., breeding dispersal). This behavior may be under-appreciated and the reason for these movements are not well-understood. A radio-tracked female used nesting territories 15 km apart in consecutive years in Snake River Canyon (USGS, unpublished data). Three individual territory-holders (one female, two males) tracked by radio telemetry switched territories in California. These birds settled in different territories within 8 km of their old ones, generally 10 days to 3 months after leaving their original territories. Habitat change near the original nesting site may have precipitated one of these moves (G. Hunt, personal communication).

Fidelity to Overwintering Home Range

Both residents and migratory individuals often show fidelity to wintering areas (261 McKinley, J. O., and B. Mattox (2010). Winter site fidelity of migratory raptors in southwestern Idaho. Journal of Raptor Research 44(3): 240–243. Close ). For example, 10 eagles wintering in central Idaho were recaptured within 1.6 km of sites where they were first captured 1–5 winters earlier (EHC, T. Craig, unpublished data). Similarly, two adult migrants from Montana (n = 1 male) and Alaska (n = 1 female) returned to their respective wintering sites in Idaho for ≥ 2 consecutive years (EHC, M. Fuller, T. Craig, L. Schueck, J. McKinley, USGS unpublished data). Similarly, telemetered migratory eagles in eastern North America regularly returned to wintering sites they used the prior year (TAM, TEK, unpublished data).

Younger individuals appear to show more variable fidelity to summer and winter ranges than do older birds. Pre-adult eagles typically do not show strong winter site fidelity until the third or fourth winter (TAM, CLM, unpublished data). In many cases juveniles and some second winter eagles settle farther south and possibly explore other wintering sites during their first or second northward migration. In subsequent years they tend to settle in an area explored during a prior spring migration. However, as additional telemetry data are collected, variations on this strategy are apparent (CLM). For example, preliminary results based on a sample of ~75 individuals of all age classes (HY to adult) telemetered in Alaska suggests that there is substantial individual variation in fidelity to winter ranges. In this sample, some individuals used the same winter range each year, some individuals return to the same general area each year, and others use different winter ranges in different years (Alaska Department of Fish and Game, National Park Service, and U.S. Fish and Wildlife Service, unpublished data).

Populations may be non-migratory, partially migratory, or short- medium- or long-distance migratory. Island populations (e.g., the United Kingdom) are generally non-migratory, and birds tend to stay on or near territories year-round. Birds from non-migratory mainland continental populations may make longer-distance movements from territories more frequently than do their island counterparts. Migrants may cover short distances (e.g., within Scandinavia) or extremely long distances (e.g., from northern Alaska and Canada to southern United States and Mexico), and may travel in a north-south or south-north direction in either season.

Individuals from northern breeding areas are usually migratory (32 Brown, L. H., and D. Amadon (1968). Eagles, Hawks, and Falcons of the World. McGraw-Hill, New York, NY, USA. Close , 262 Kerlinger, P. (1989). Flight Strategies of Migrating Hawks. University of Chicago Press, Chicago, IL, USA. Close ), and northern territory holders tend to migrate longer distances than individuals nesting farther south (263 McGahan, J. (1966). Ecology of the Golden Eagle. M.S. thesis, University of Montana, Missoula, MT, USA. Close , 264 Mead, C. J. (1973). Movements of British raptors. Bird Study 20: 259–286. Close , 265 Miller, T. A., R. P. Brooks, M. J. Lanzone, D. Brandes, J. Cooper, J. A. Tremblay, J. Wilhelm, A. Duerr, and T. E. Katzner (2016). Limitations and mechanisms influencing the migratory performance of soaring birds. Ibis 158(1): 116–134. Close ). Northern eagles can migrate south > 5,000 km from breeding to wintering areas (266 Kuyt, E. (1967). Two banding returns for Golden Eagle and Peregrine Falcon. Bird-Banding 38: 78–79. Close , 220 McIntyre, C. L., D. C. Douglas, and M. W. Collopy (2008). Movements of Golden Eagles (Aquila chrysaetos) from interior Alaska during their first year of independence. Auk 125: 214–224. Close , 267 McIntyre, C. L. (2012). Quantifying sources of mortality and wintering ranges of Golden Eagles from interior Alaska using banding and satellite tracking. Journal of Raptor Research 46: 129–134. Close , 252 Brown, J. L., B. Bedrosian, D. A. Bell, M. A. Braham, J. Cooper, R. H. Crandall, J. DiDonato, R. Domenech, A. E. Duerr, T. E. Katzner, M. J. Lanzone, D. W. LaPlante, C. L. McIntyre, T. A. Miller, R. K. Murphy, A. Shreading, S. J. Slater, J. P. Smith, B. W. Smith, J. W. Watson, and B. Woodbridge (2017). Patterns of spatial distribution of Golden Eagles across North America: How do they fit into existing landscape-scale mapping systems? Journal of Raptor Research 51: 197–215. Close ). In eastern Canada, nearly all individuals are migratory (TAM, TEK). In western North America, it appears that individuals that nest south of 55°N often are not migratory, and those north of there often are migratory (the authors). In Scandinavia and Alaska, populations are partially or wholly migratory, likely in response to prey availability. For example, some eagles from Alaska may overwinter in interior and northern parts of the state when snowshoe hare (Lepus americanus) are abundant (172 Kessel, B. (1989). Birds of the Seward Peninsula, Alaska: Their Biogeography, Seasonality and Natural History. University of Alaska Press, Fairbanks, AK, USA. Close , CLM, EHC; T. Booms, personal communication). Individuals from south-central Alaska (T. Booms, unpublished data), western Alaska (CLM) and the Gaspé Peninsula of Quebec may stay close to northern breeding ranges some years and migrate south during other years (179 Miller, T. A. (2012). Movement ecology of Golden Eagles (Aquila chrysaetos) in eastern North America. Ph.D. dissertation, The Pennsylvania State University, University Park, PA, USA. Close , 265 Miller, T. A., R. P. Brooks, M. J. Lanzone, D. Brandes, J. Cooper, J. A. Tremblay, J. Wilhelm, A. Duerr, and T. E. Katzner (2016). Limitations and mechanisms influencing the migratory performance of soaring birds. Ibis 158(1): 116–134. Close ).

Migration patterns of eagles in arid areas of the southwestern North America appear different from those farther north. In these populations, pre-adults travel through New Mexico and western Texas at the beginning and end of winter (November and March; 268 Boeker, E. L., and T. D. Ray (1971). Golden Eagle population studies in the Southwest. Condor 73: 463–467. Close ). Tracking data suggest that northward movements of these birds may be considered migratory (103 Poessel, S. A., P. H. Bloom, M. A. Braham, and T. E. Katzner (2016). Age- and season-specific variation in local and long-distance movement behavior of Golden Eagles. European Journal of Wildlife Research 62: 377–393. Close , 104 Murphy, R. K., J. R. Dunk, B. Woodbridge, D. W. Stahlecker, D. W. LaPlante, B. A. Millsap, and K. V. Jacobson (2017). First-year dispersal of Golden Eagles from natal areas in the southwestern United States and implications for second-year settling. Journal of Raptor Research 51(3): 216–233. Close ). Published telemetry studies suggest extensive overlap in western North America between individuals from migratory and non-migratory populations (see Distribution: Non-breeding Range). There is no information as to whether eagles from arid areas of southern Europe and the Middle East engage in similar behaviors.

Post-breeding

Telemetry data suggest that Golden Eagle leaves northern areas of North America as early as August or as late as November. Date of departure appears to vary by age and social class. Specifically, non-territorial individuals often leave earlier than territorial individuals, failed breeders leave earlier than successful breeders, and young-of-the-year and territorial adults leave last (CLM, 265 Miller, T. A., R. P. Brooks, M. J. Lanzone, D. Brandes, J. Cooper, J. A. Tremblay, J. Wilhelm, A. Duerr, and T. E. Katzner (2016). Limitations and mechanisms influencing the migratory performance of soaring birds. Ibis 158(1): 116–134. Close ).

Individuals from Denali National Park and Preserve, Alaska, leave in September or October, soon after the onset of hibernation of ground squirrels and hoary marmot (Marmota caligata; 269 McIntyre, C. L., and M. W. Collopy (2006). Postfledging dependence period of migratory Golden Eagles (Aquila chrysaetos) in Denali National Park and Preserve, Alaska. Auk 123(3): 877–884. Close , 220 McIntyre, C. L., D. C. Douglas, and M. W. Collopy (2008). Movements of Golden Eagles (Aquila chrysaetos) from interior Alaska during their first year of independence. Auk 125: 214–224. Close ). Several cohorts of juveniles from this area initiated migration between mid-September and early October (mean departure date = 24 September ± 5 d [n = 43]; 269 McIntyre, C. L., and M. W. Collopy (2006). Postfledging dependence period of migratory Golden Eagles (Aquila chrysaetos) in Denali National Park and Preserve, Alaska. Auk 123(3): 877–884. Close , 220 McIntyre, C. L., D. C. Douglas, and M. W. Collopy (2008). Movements of Golden Eagles (Aquila chrysaetos) from interior Alaska during their first year of independence. Auk 125: 214–224. Close ). Those birds reach their southern wintering areas 28–58 days after departure (mean 44 d ± 9 d [n = 26]), arriving on winter ranges throughout western North America between 26 October and 19 November (mean 7 November ± 7 d [n = 16] 220 McIntyre, C. L., D. C. Douglas, and M. W. Collopy (2008). Movements of Golden Eagles (Aquila chrysaetos) from interior Alaska during their first year of independence. Auk 125: 214–224. Close ). Three second-year eagles in this study arrived on winter ranges from 1 to 8 October in 2000 (mean 5 October ± 3.9 d) (CLM).

Eagles tracked by telemetry from summering grounds in eastern Canada departed between 11 August and 17 December (265 Miller, T. A., R. P. Brooks, M. J. Lanzone, D. Brandes, J. Cooper, J. A. Tremblay, J. Wilhelm, A. Duerr, and T. E. Katzner (2016). Limitations and mechanisms influencing the migratory performance of soaring birds. Ibis 158(1): 116–134. Close ). Mean departure date was 15 October ± 15 d (SD) (n = 26) for adults; 5 October ± 23 d (n = 18) for sub-adults; and 12 October ± 15 d (n = 2) for juveniles (TAM, 265 Miller, T. A., R. P. Brooks, M. J. Lanzone, D. Brandes, J. Cooper, J. A. Tremblay, J. Wilhelm, A. Duerr, and T. E. Katzner (2016). Limitations and mechanisms influencing the migratory performance of soaring birds. Ibis 158(1): 116–134. Close ). Duration of migration of these birds is highly variable with large overlaps among age classes (265 Miller, T. A., R. P. Brooks, M. J. Lanzone, D. Brandes, J. Cooper, J. A. Tremblay, J. Wilhelm, A. Duerr, and T. E. Katzner (2016). Limitations and mechanisms influencing the migratory performance of soaring birds. Ibis 158(1): 116–134. Close ). Some individuals of each age class wander and use short-term stopover sites for several weeks during autumn migration (TAM). These eagles reached their wintering grounds in 17–153 d (mean 53 ± 28 d; n = 44) (TAM). Adults reached the wintering grounds in 52 ± 28 d (n = 24), arriving between 23 October and 16 February (mean 9 December ± 28 d). Pre-adults reached the wintering grounds in 56 ± 30 d (n = 18), arriving between 16 September and 2 February (mean 28 November ± 32 d). In another smaller study, radio-tagged adults (n = 4) from eastern Hudson Bay took 26–40 d to reach their wintering areas in central Michigan, eastern West Virginia, northwestern Pennsylvania, and northeastern Alabama, arriving in November or December (186 Brodeur, S., R. Décarie, D. M. Bird, and M. Fuller (1996). Complete migration cycle of Golden Eagles breeding in northern Quebec. Condor 98(2): 293–299. Close ).

Substantial (> 1,000 individuals) numbers of migrating Golden Eagle are counted at multiple count sites in the eastern and western United States during autumn migration. Some of these count sites have been operating for many years or decades (i.e., Hawk Mountain Sanctuary, Pennsylvania; Bridger Mountain in western Montana; Mt. Lorette in southern Alberta), and others only for a few years (i.e., Big Belt Mountains in Montana). Together, counts at these sites provide insight into the magnitude and timing of Golden Eagle migration. In general, autumn flights occur from early September through December at count sites in southern Canada and the northern United States. Peak flights are in October in western North America, but in November in eastern parts of the continent.

Median dates of peak passage as recorded at migration count sites in western North America tend to be in October, with adults often migrating a few days later than pre-adults. In Glacier National Park, Montana, maximum passage rates occur in early October (270 Yates, R. E., B. R. McClelland, P. T. McClelland, C. H. Key, and R. E. Bennetts (2001). The influence of weather on Golden Eagle migration in northwestern Montana. Journal of Raptor Research 35(2): 81–90. Close ). The largest numbers of migrating Golden Eagles are detected at Mount Lorette in the Front Ranges of the Rocky Mountains in southern Alberta (243 Dekker, D. (1985). Hunting behaviour of Golden Eagles, Aquila chrysaetos, migrating in southwestern Alberta. Canadian Field-Naturalist 99: 383–385. Close ). Median passage dates for all migrating Golden Eagles detected at this site from 2012 to 2018 range from 12–15 October (P. Sherrington, unpublished data; and Eagle Watch). Eagles arrive on wintering areas in New Mexico and western Texas in October, reaching peak numbers from December to February (268 Boeker, E. L., and T. D. Ray (1971). Golden Eagle population studies in the Southwest. Condor 73: 463–467. Close ).

Finally, there appears to be within-day variation in timing of fall migration. In western Montana, younger birds are seen more frequently early the morning and late in the day than are older birds (271 Omland, K. S., and S. W. Hoffman (1996). Seasonal, diel, and spatial dispersion patterns of Golden Eagle autumn migration in southwestern Montana. Condor 98: 633–636. Close ).

Pre-breeding

Exhibits age-structured seasonal timing of migration, with adults leaving wintering areas earlier than juveniles. This is reflected in both telemetry and observational data, and in eastern and western North America.

Telemetry data suggest that adults begin to migrate from wintering areas in southwestern Idaho between about 4 March and 13 April (mean 19 March ± 12 d [n = 8]; ECH; M. Fuller, USGS, T. Craig, unpublished data). Juvenile eagles originally telemetered in the nest in Denali National Park and Preserve, Alaska, depart wintering areas between 6 April and 8 May of their first winter (mean 21 April ± 12 d [n = 12; 220 McIntyre, C. L., D. C. Douglas, and M. W. Collopy (2008). Movements of Golden Eagles (Aquila chrysaetos) from interior Alaska during their first year of independence. Auk 125: 214–224. Close ]). These first-year eagles return to northern latitudes from 10 May to 13 June, up to 12 weeks after territory holders in the same region (220 McIntyre, C. L., D. C. Douglas, and M. W. Collopy (2008). Movements of Golden Eagles (Aquila chrysaetos) from interior Alaska during their first year of independence. Auk 125: 214–224. Close ). Travel time between Idaho wintering areas and breeding areas in Alaska and northwestern Canada, ranges from 6 to 27 days (mean 17 d ± 7 d [n = 8]; EHC, M. Fuller, T. Craig, unpublished data). Travel time between wintering areas and summering areas in Alaska and northwestern Canada ranges from 22 to 47 days (mean 35 d ± 6 d [n = 12]; CLM).

In eastern North America, there is little temporal overlap in timing of spring migration between territorial and non-territorial individuals, and no overlap between adults and juveniles (265 Miller, T. A., R. P. Brooks, M. J. Lanzone, D. Brandes, J. Cooper, J. A. Tremblay, J. Wilhelm, A. Duerr, and T. E. Katzner (2016). Limitations and mechanisms influencing the migratory performance of soaring birds. Ibis 158(1): 116–134. Close ). Adults migrate earliest, beginning migration between 4 February and 13 April (mean 10 March ± 11 d; n = 47); subadults migrate from 14 February to 15 May (mean 29 March ± 18 d; n = 41), and juveniles on their first northbound migration migrate from 22 March to 10 May (mean 19 April ± 13 d; n = 18) (TAM). Adults arrive on their breeding grounds after 29 d ± 18 d (range 4–92 d; n = 26), between 20 February and 21 July (mean 13 April ± 21 d; n = 28). These arrival dates are likely determined in part by latitude and breeding status. Subadults arrive on their summering grounds after 32 d ± 23 d (range 7–123 d; n = 24) between 3 March and 12 July (mean 1 May ± 25 d; n = 24). Juveniles on their first northbound migration arrive on their summering grounds after 37 d ± 14 d (range 20–55 d; n = 7), between 7 May and 23 June (mean 30 May ± 14 d; n = 8). These later migrating pre-adults travel different migratory pathways than the adults (239 Duerr, A. E., T. A. Miller, K. L. C. Duerr, M. J. Lanzone, A. Fesnock, and T. E. Katzner (2015b). Landscape-scale distribution and density of raptor populations wintering in anthropogenic-dominated desert landscapes. Biodiversity Conservation 24: 2365–2381. Close , 265 Miller, T. A., R. P. Brooks, M. J. Lanzone, D. Brandes, J. Cooper, J. A. Tremblay, J. Wilhelm, A. Duerr, and T. E. Katzner (2016). Limitations and mechanisms influencing the migratory performance of soaring birds. Ibis 158(1): 116–134. Close ), and this can explain why age-ratio data from spring migration count sites may not be accurate indicators of demographic trends.

Observational data suggest that Golden Eagle leaves wintering areas in the southwestern United States in March (268 Boeker, E. L., and T. D. Ray (1971). Golden Eagle population studies in the Southwest. Condor 73: 463–467. Close ). Median passage date at Sandia Mountains, New Mexico (1985–2008) was 20 March ± 3 d (± 95% CI; 272 Smith, J. P., and M. C. Neal (2009b). Spring 2009 raptor migration study in the Sandia Mountains of central New Mexico. HawkWatch International Annual Report. Salt Lake City, UT, USA. Close ). Farther north in the Rocky Mountains, maximum passage rates occur during the second and third weeks of March in Glacier National Park, Montana (270 Yates, R. E., B. R. McClelland, P. T. McClelland, C. H. Key, and R. E. Bennetts (2001). The influence of weather on Golden Eagle migration in northwestern Montana. Journal of Raptor Research 35(2): 81–90. Close ) and from 8 to 27 March at Rogers Pass, Montana (273 Tilly, F. C., and C. R. Tilly (1998). Spring 1998 raptor migration study in West-central Montana near Rogers Pass. HawkWatch International, Salt Lake City, UT. Close ). Farther north again, at Mount Lorette in western Alberta, spring migration spans ≥ 92 days (274 Sherrington, P. (1997). Canadian Rockies and plains region. Hawk Migration Association of North America, Hawk Migration Studies 22: 50–51. Close ). The first migrants are seen in mid-February, followed by large movements of pre-adults from mid-April to May (274 Sherrington, P. (1997). Canadian Rockies and plains region. Hawk Migration Association of North America, Hawk Migration Studies 22: 50–51. Close ). Peak passage there is from 19 to 25 March (275 Sherrington, P. (1998). Canadian Rockies and plains. Hawk Migration Association of North America, Hawk Migration Studies 23: 16–19. Close ). Finally, over two seasons of observations at Gunsight Mountain in south-central Alaska, peak passage of breeding age Golden Eagles occurred between from 22–31 March and, in one of those years, 95% of all birds were detected before 10 April (276 Paprocki, N. (2016). Spring 2016 raptor migration report, Gunsight Mountain Hawkwatch – Alaska. Hawkwatch International Annual Report. Salt Lake City, UT, USA. Close ).

Count data also indicate that adults in western North America usually migrate earlier in spring than pre-adults. Median passage date from 1992–2001 for adults at Sandia Mountains, New Mexico was 9 March ± 2 d, significantly earlier than for pre-adults, whose median passage date was 5 April ± 4 d (277 Smith, J. P. (1999). Spring 1999 raptor migration study in the Sandia Mountains of central New Mexico. HawkWatch International, Salt Lake City, UT, USA. Close ). The proportion of pre-adults migrating at Glacier National Park increased with time from mid-March to mid-April (270 Yates, R. E., B. R. McClelland, P. T. McClelland, C. H. Key, and R. E. Bennetts (2001). The influence of weather on Golden Eagle migration in northwestern Montana. Journal of Raptor Research 35(2): 81–90. Close ). Adults move through northwestern Alberta earlier than pre-adults, with adults common in March and younger birds more frequently seen in April (275 Sherrington, P. (1998). Canadian Rockies and plains. Hawk Migration Association of North America, Hawk Migration Studies 23: 16–19. Close ). Finally, observations during spring migration in 2016 and 2017 at Gunsight Mountain in south-central Alaska suggest that most birds were adults that pass by over a period of 3 to 4 weeks starting about the second week of March (278 Paprocki, N. (2018). Spring 2017 raptor migration report Gunsight Mountain HawkWatch – Alaska. HawkWatch International Annual Report. Salt Lake City, UT, USA. Close ; P. Fritz, personal communication). This suggests that counts of migrants at Gunsight Mountain are composed primarily of territory-holders and these timing data may not be applicable to other age classes who migrate later, possibly across a broader area (CLM).

Territory holders and older pre-adults in Alaska arrive earlier than other individuals, with most coming to the breeding range in a narrow window from late February to early April (172 Kessel, B. (1989). Birds of the Seward Peninsula, Alaska: Their Biogeography, Seasonality and Natural History. University of Alaska Press, Fairbanks, AK, USA. Close , 131 Young, D. D., Jr., C. L. McIntyre, P. J. Bente, T. R. McCabe and R. E. Ambrose (1995). Nesting by Golden Eagles on the north slope of the Brooks Range in northeastern Alaska. Journal of Field Ornithology 66: 373–379. Close , CLM, Alaska Department of Fish and Game [AFG], National Park Service [NPS], USFWS, unpublished data). A second pulse of migrants, usually younger birds, return to Alaska from late March into early June.

In eastern North America, median passage dates at Tussey Mountain, Pennsylvania are 10 March (9–11 March; 95% CI) for adults and 19 March (19–21 March 95% CI) for pre-adults (N. Bolgiano, unpublished data). Golden Eagle migration through the Mackinac Straits, Michigan occurs from 7 March–17 May, with median passage of adults from 9 March–3 April (range 7 March–27 April) and median passage date of pre-adults from 17 April–9 May (range 28 March–17 May) (E. Pike, personal communication).

Routes

Major migratory routes of North American Golden Eagles occur along the Pacific Coast Ranges, the Rocky Mountains, the Appalachian Mountains, and through the Great Lakes region (252 Brown, J. L., B. Bedrosian, D. A. Bell, M. A. Braham, J. Cooper, R. H. Crandall, J. DiDonato, R. Domenech, A. E. Duerr, T. E. Katzner, M. J. Lanzone, D. W. LaPlante, C. L. McIntyre, T. A. Miller, R. K. Murphy, A. Shreading, S. J. Slater, J. P. Smith, B. W. Smith, J. W. Watson, and B. Woodbridge (2017). Patterns of spatial distribution of Golden Eagles across North America: How do they fit into existing landscape-scale mapping systems? Journal of Raptor Research 51: 197–215. Close ). Details about these migrations vary by season. This seasonal variation in use of routes is likely driven by corresponding variation in availability of updrafts that facilitate flight and in the motivation for migration. For example, in the Appalachians, thermals become more available as spring progresses adults are driven to return to nesting grounds sooner than are subadults (246 Duerr, A. E., T. A. Miller, M. Lanzone, D. Brandes, J. Cooper, K. O’Malley, C. Maisonneuve, J. A. Tremblay, and T. Katzner (2015). Flight response of slope-soaring birds to seasonal variation in thermal generation. Functional Ecology 29:779–790. Close , 265 Miller, T. A., R. P. Brooks, M. J. Lanzone, D. Brandes, J. Cooper, J. A. Tremblay, J. Wilhelm, A. Duerr, and T. E. Katzner (2016). Limitations and mechanisms influencing the migratory performance of soaring birds. Ibis 158(1): 116–134. Close ).

Migration routes across the interior and south-central regions of Alaska and the southern portion of the Yukon, Canada, tend to run east-west and northwest-southeast (247 Eisaguirre, J. M., T. L. Booms, C. P. Barger, C. L. McIntyre, S. B. Lewis, and G. A. Breed (2018). Local meteorological conditions reroute a migration. Proceedings of the Royal Society B 285: 20181779. Close ). However, starting in northern British Columbia, migration routes are predominantly north-south to northern Mexico. Autumn and spring migration corridors in the northwestern portion of North America in Alaska, Yukon and Northwest Territories generally tend to be broad (220 McIntyre, C. L., D. C. Douglas, and M. W. Collopy (2008). Movements of Golden Eagles (Aquila chrysaetos) from interior Alaska during their first year of independence. Auk 125: 214–224. Close , 252 Brown, J. L., B. Bedrosian, D. A. Bell, M. A. Braham, J. Cooper, R. H. Crandall, J. DiDonato, R. Domenech, A. E. Duerr, T. E. Katzner, M. J. Lanzone, D. W. LaPlante, C. L. McIntyre, T. A. Miller, R. K. Murphy, A. Shreading, S. J. Slater, J. P. Smith, B. W. Smith, J. W. Watson, and B. Woodbridge (2017). Patterns of spatial distribution of Golden Eagles across North America: How do they fit into existing landscape-scale mapping systems? Journal of Raptor Research 51: 197–215. Close , 279 Bedrosian, B. E., R. Domenech, A. Shreading, M. M. Hayes, T. L. Booms, and C. R. Barger (2018). Migration corridors of adult Golden Eagles originating in northwestern North America. PLoS ONE 13(11): e0205204. Close , 247 Eisaguirre, J. M., T. L. Booms, C. P. Barger, C. L. McIntyre, S. B. Lewis, and G. A. Breed (2018). Local meteorological conditions reroute a migration. Proceedings of the Royal Society B 285: 20181779. Close ; NPS, USFWS, AFG, unpublished data; Figure 2). For example, the migration corridor spans about 400 miles across the southern Yukon, northern British Columbia, and northwestern Alberta (220 McIntyre, C. L., D. C. Douglas, and M. W. Collopy (2008). Movements of Golden Eagles (Aquila chrysaetos) from interior Alaska during their first year of independence. Auk 125: 214–224. Close , 279 Bedrosian, B. E., R. Domenech, A. Shreading, M. M. Hayes, T. L. Booms, and C. R. Barger (2018). Migration corridors of adult Golden Eagles originating in northwestern North America. PLoS ONE 13(11): e0205204. Close ). At 55°N latitude, the migration corridor spans ~300 miles from central British Columbia to the eastern slopes of the Rocky Mountains in Alberta. The corridor becomes broader again 49°N latitude at the border of Canada and the coterminous United States.

There is also good evidence of a migration corridor along the coastline of southeastern Alaska and western British Columbia (220 McIntyre, C. L., D. C. Douglas, and M. W. Collopy (2008). Movements of Golden Eagles (Aquila chrysaetos) from interior Alaska during their first year of independence. Auk 125: 214–224. Close ; NPS, USFWS, USGS, unpublished data; TEK, TAM, EHC). Numbers of eagles migrating through this area are probably far less than those migrating inland to the east of the Coast Mountains (CLM).

Data from telemetry and years of visual observations clearly show that large numbers of migrating eagles concentrate at specific sites. In Alaska and Canada, these sites include the Matanuska-Susitna Valley and Gunsight Mountain in south-central Alaska (280 Fritz, P., and C. Fritz (2011). The hawks of Gunsight Mountain, Alaska. Birding 2011: 30–36. Close , 276 Paprocki, N. (2016). Spring 2016 raptor migration report, Gunsight Mountain Hawkwatch – Alaska. Hawkwatch International Annual Report. Salt Lake City, UT, USA. Close ; B. Dittrick and T. Swem, personal communication); the Mentasta Mountains in eastern interior Alaska (281 McIntyre, C. L., and S. B. Lewis (2016). Observations of migrating Golden Eagles (Aquila chrysaetos) in eastern interior Alaska offer insights of population size and migration monitoring. Journal of Raptor Research 50: 254–264. Close ); the Shakwak and Tintina Trenches, Kluane Lake and Ruby Range regions in southern Yukon, Canada (Sinclair et al. 2013); the northern Rocky Mountains including the Cassiar Mountains in northern British Columbia; and the northern Rocky Mountains and Canadian Rocky Mountains in western Alberta, including Mt. Lorrette in the southern portion of the Canadian Rocky Mountains in Alberta (Rocky Mountain Eagle Foundation, unpublished data). There are also a number of concentration areas in the conterminous United States (for details, see 282 Smith, J., C. J. Farmer, S. W. Hoffman, G. S. Kaltenecker, K. Z. Woodruff, and P. F. Sherrington (2008b). Trends in autumn counts of migratory raptors in western North America. In The State of North American Birds of Prey (K. L. Bildstein, J. P. Smith, and E. Ruelas-Inzuena, Editors). American Ornithologists' Union and Nuttall Ornithological Club, Cambridge, MA, USA. pp. 217–252. Close ).

Telemetry studies have provided detailed information on autumn migration routes in eastern North America (186 Brodeur, S., R. Décarie, D. M. Bird, and M. Fuller (1996). Complete migration cycle of Golden Eagles breeding in northern Quebec. Condor 98(2): 293–299. Close , 265 Miller, T. A., R. P. Brooks, M. J. Lanzone, D. Brandes, J. Cooper, J. A. Tremblay, J. Wilhelm, A. Duerr, and T. E. Katzner (2016). Limitations and mechanisms influencing the migratory performance of soaring birds. Ibis 158(1): 116–134. Close , 252 Brown, J. L., B. Bedrosian, D. A. Bell, M. A. Braham, J. Cooper, R. H. Crandall, J. DiDonato, R. Domenech, A. E. Duerr, T. E. Katzner, M. J. Lanzone, D. W. LaPlante, C. L. McIntyre, T. A. Miller, R. K. Murphy, A. Shreading, S. J. Slater, J. P. Smith, B. W. Smith, J. W. Watson, and B. Woodbridge (2017). Patterns of spatial distribution of Golden Eagles across North America: How do they fit into existing landscape-scale mapping systems? Journal of Raptor Research 51: 197–215. Close ). Adults nesting in Quebec and Labrador typically migrate south, concentrating along the north shore of the Gulf of St. Lawrence and along the ridges of the Appalachian Mountains. Some individuals, especially younger birds, move down the Atlantic coast. Golden Eagles from western Quebec migrate through the Great Lakes region, passing by the Mackinac Straits, Michigan, through the Michigan Upper Peninsula into Wisconsin or along the north shore of Lake Erie. Individuals from Ontario and Manitoba typically migrate south to the north shore of Lake Superior and pass by Hawk Ridge, Duluth, Minnesota, but some pass through the Mackinac Straits as do birds nesting farther east. Migration through the Midwest south of the Great Lakes is typically dispersed but appears to follow forested and riparian corridors (TAM).

Spring migration corridors in the eastern United States occur primarily along the ridges of the Appalachian and Allegheny Mountains, especially early in the season. The corridor widens as spring progresses due to higher thermal activity that promotes soaring away from ridgelines (246 Duerr, A. E., T. A. Miller, M. Lanzone, D. Brandes, J. Cooper, K. O’Malley, C. Maisonneuve, J. A. Tremblay, and T. Katzner (2015). Flight response of slope-soaring birds to seasonal variation in thermal generation. Functional Ecology 29:779–790. Close , 265 Miller, T. A., R. P. Brooks, M. J. Lanzone, D. Brandes, J. Cooper, J. A. Tremblay, J. Wilhelm, A. Duerr, and T. E. Katzner (2016). Limitations and mechanisms influencing the migratory performance of soaring birds. Ibis 158(1): 116–134. Close ). Regularly recorded at migration count sites in Pennsylvania, western Maryland, Virginia, West Virginia, North Carolina, Tennessee, and along the shores of Lake Ontario in New York (186 Brodeur, S., R. Décarie, D. M. Bird, and M. Fuller (1996). Complete migration cycle of Golden Eagles breeding in northern Quebec. Condor 98(2): 293–299. Close , 283 Brandes, D. (1998). Spring Golden Eagle passage through the northeast U.S. – evidence for a geographically concentrated flight? Hawk Migration Association of North America, Hawk Migration Studies 23: 38–42. Close ). Spring migration also occurs in the Great Lakes region. At Whitefish Point, Michigan, increasing numbers were observed for several years after 1986 (284 Nicoletti, F. J. (1998). Western Great Lakes. Hawk Migration Association of North America, Hawk Migration Studies 23: 21–23. Close ). The highest spring counts in eastern North America occur at the Mackinac Straits in Michigan and at Tussey Mountain in central Pennsylvania. Golden Eagles are rare at coastal migration count sites (i.e., Sandy Hook, New Jersey; Cape Henlopen, Delaware; Plum Island, Massachusetts) and at migration count sites in Massachusetts, Vermont, and Maine (283 Brandes, D. (1998). Spring Golden Eagle passage through the northeast U.S. – evidence for a geographically concentrated flight? Hawk Migration Association of North America, Hawk Migration Studies 23: 38–42. Close , 285 Kellog, S. (2000). Eastern continental flyway. Hawk Migration Association of North America, Hawk Migration Studies 26: 76–83. Close ).

Age-Related and Inter-Seasonal Differences in Migratory Routes

Migration pathways of younger age classes, particularly juveniles, from Alaska may be more diverse and dispersed than those of older age classes (220 McIntyre, C. L., D. C. Douglas, and M. W. Collopy (2008). Movements of Golden Eagles (Aquila chrysaetos) from interior Alaska during their first year of independence. Auk 125: 214–224. Close , Alaska Department of Fish and Game, U.S. Fish and Wildlife Service, National Park Service, unpublished data). Route fidelity is variable, with some individuals using the same route repeatedly across years and others changing routes over time (CLM; T. Booms, personal communication).

Spring migration routes of territorial individuals are often similar to routes taken during autumn migration (CLM). Spring migration routes of non-territorial individuals are often similar to autumn routes, but routes become more dispersed at the northern end of the migration corridor as eagles approach the terminus of their migration in Alaska (220 McIntyre, C. L., D. C. Douglas, and M. W. Collopy (2008). Movements of Golden Eagles (Aquila chrysaetos) from interior Alaska during their first year of independence. Auk 125: 214–224. Close ; U.S. Fish and Wildlife Service, National Park Service, unpublished data). First-winter birds from Denali National Park and Preserve, Alaska tended to reverse their autumn migration route until reaching central Alberta, where they veer east of the Rocky Mountains, flying north through Alberta, across central Yukon, and to summer ranges throughout Alaska and the northern Yukon (220 McIntyre, C. L., D. C. Douglas, and M. W. Collopy (2008). Movements of Golden Eagles (Aquila chrysaetos) from interior Alaska during their first year of independence. Auk 125: 214–224. Close ).

Telemetry data suggest that more experienced (≥ third-year) eagles in eastern North America follow a similar route in spring as they do in autumn, but tend not to concentrate along the southern shores of the Great Lakes. Migration becomes more dispersed in April and May when thermals are stronger, allowing birds to stray from ridgelines, and when young, inexperienced birds are migrating north. For these reasons, more individuals, especially of younger age classes, are counted at Lake Ontario migration count sites (Braddock Bay and Derby Hill, New York) during April. Most older Golden Eagles are counted in March at ridge top migration count sites in the Appalachian Mountains (265 Miller, T. A., R. P. Brooks, M. J. Lanzone, D. Brandes, J. Cooper, J. A. Tremblay, J. Wilhelm, A. Duerr, and T. E. Katzner (2016). Limitations and mechanisms influencing the migratory performance of soaring birds. Ibis 158(1): 116–134. Close ).

Age Ratios along Migration Routes

Age ratios of eagles recorded at autumn migration count sites vary geographically. Mean pre-adult:adult ratio are 0.27 in Alberta (P. Sherrington, unpublished data), 1.03 at Hawk Mountain, Pennsylvania (Hawk Mountain Sanctuary, unpublished data), 1.2 ± 0.8 at Bridger Mountain, Montana (± 95% C.I.; 286 Davis, B., S. Hoffman, and D. Oleyar (2017). Fall 2016 raptor migration study in the Bridger Mountains, Montana. Montana Audubon and HawkWatch International, Helena, MT and Salt Lake City, UT, USA. Close ), 1.38 ± 0.37 at Wellsville Mountains, Utah (287 Smith, J. P., and M. C. Neal (2009a). Fall 2008 raptor migration studies in the Wellsville Mountains of northern Utah. HawkWatch International Annual Report. Salt Lake City, UT, USA. Close ), 2.19 ± 0.361 at Goshute Mountains, Nevada (288 Hawks, S., and M. Mika (2013a). Fall 2012 raptor migration studies in the Goshute Mountains of northeastern Nevada. HawkWatch International Annual Report. Salt Lake City, UT, USA. Close ), and 2.3 ± 0.42 in Manzano Mountains, New Mexico (289 Hawks, S., and M. Mika (2013d). Fall 2012 raptor migration studies in the Manzano Mountains of central New Mexico. HawkWatch International Annual Report. Salt Lake City, UT, USA. Close ). Most individuals observed at coastal migration count sites in the eastern United States are juveniles (290 Greenstone, E. (1996). Mid-Atlantic Region. Hawk Migration Association of North America, Hawk Migration Studies 22: 28–35. Close ) adults and subadults tend to migrate farther inland (5 Katzner, T., B. W. Smith, T. A. Miller, D. Brandes, J. Cooper, M. Lanzone, D. Brauning, C. Farmer, S. Harding, D. E. Kramar, C. Koppie, C. Maisonneuve, M. Martell, E. K. Mojica, C. Todd, J. A. Tremblay, M. Wheeler, D. F. Brinker, T. E. Chubbs, R. Gubler, K. O'Malley, S. Mehus, B. Porter, R. P. Brooks, B. D. Watts, and K. L. Bildstein (2012). Status, biology, and conservation priorities for North America's eastern Golden Eagle (Aquila chrysaetos) population. Auk 129: 168–176. Close ).

Pre-adult:adult ratios in spring are 0.08 at Rogers Pass, Montana (273 Tilly, F. C., and C. R. Tilly (1998). Spring 1998 raptor migration study in West-central Montana near Rogers Pass. HawkWatch International, Salt Lake City, UT. Close ), 0.12 in Alberta (P. Sherrington, unpublished data), 0.16 at Gunsight Mountain, Alaska, (but individuals were difficult to age accurately; 276 Paprocki, N. (2016). Spring 2016 raptor migration report, Gunsight Mountain Hawkwatch – Alaska. Hawkwatch International Annual Report. Salt Lake City, UT, USA. Close ), and 1.56 ± 0.46 (95% CI) in the Sandia Mountains, New Mexico (272 Smith, J. P., and M. C. Neal (2009b). Spring 2009 raptor migration study in the Sandia Mountains of central New Mexico. HawkWatch International Annual Report. Salt Lake City, UT, USA. Close ). Differences between pre-adult:adult ratio in fall and spring at raptor migration count sites might reflect age-specific differences in survival rates, migration routes, or detection probability, or even the difficulty of accurately aging a migrating eagle. Alternatively, these differences also may reflect differences in flight strategies of earlier migrating older birds (who use more orographic updraft to subsidize flight and thus are more visible to migration counters) versus later migrating younger birds (who migrate when thermals are more prevalent and thus may be harder for counters to see; 246 Duerr, A. E., T. A. Miller, M. Lanzone, D. Brandes, J. Cooper, K. O’Malley, C. Maisonneuve, J. A. Tremblay, and T. Katzner (2015). Flight response of slope-soaring birds to seasonal variation in thermal generation. Functional Ecology 29:779–790. Close , 265 Miller, T. A., R. P. Brooks, M. J. Lanzone, D. Brandes, J. Cooper, J. A. Tremblay, J. Wilhelm, A. Duerr, and T. E. Katzner (2016). Limitations and mechanisms influencing the migratory performance of soaring birds. Ibis 158(1): 116–134. Close ).

Flight Behavior During Migration

The Golden Eagle is a diurnal migrant. It does not migrate in flocks (271 Omland, K. S., and S. W. Hoffman (1996). Seasonal, diel, and spatial dispersion patterns of Golden Eagle autumn migration in southwestern Montana. Condor 98: 633–636. Close ), but may join small “kettles” near thermals (245 Sherrington, P. (1993). Golden Eagle migration in the front ranges of the Alberta Rocky Mountains. Birder's Journal 2: 195–204. Close ); at eastern migration count sites it is often observed in groups of 2–3 individuals (TAM) and in eastern Alaska up to 30 individuals have been noted using thermals during spring migration (CLM).

Up to 137 eagles/hr have been counted in northwestern Montana in autumn (270 Yates, R. E., B. R. McClelland, P. T. McClelland, C. H. Key, and R. E. Bennetts (2001). The influence of weather on Golden Eagle migration in northwestern Montana. Journal of Raptor Research 35(2): 81–90. Close ). Mean number of eagles seen/hr (± 95% C.I.) in autumn are 0.06 at Hawk Mountain, Pennsylvania; 0.25 ± 0.03 in the Manzano Mountains, New Mexico; 0.39 ± 0.03 at the Goshute Mountains, Nevada; 0.45 ± 0.12 at the Wellsville Mountains, Utah; 5.2 ± 0.56 at Bridger Mountain, Montana; and 5.4 near Mount Lorrette, Alberta (291 Rossman, D. J. (1999). Fall 1998 raptor migration study in the Manzano Mountains of central New Mexico. HawkWatch International, Inc., Salt Lake City, UT, USA. Close , 292 Davis, B., K. Baughan, M. Mika, and S. Hoffman (2013). Fall 2012 raptor migration studies in the Bridger Mountains, Montana. HawkWatch International Annual Report. Salt Lake City, UT, USA. Close , 293 Hawks, S., and M. Mika (2013b). Fall 2012 raptor migration studies at Chelan Ridge, Washington. HawkWatch International Annual Report. Salt Lake City, UT, USA. Close , 289 Hawks, S., and M. Mika (2013d). Fall 2012 raptor migration studies in the Manzano Mountains of central New Mexico. HawkWatch International Annual Report. Salt Lake City, UT, USA. Close ; Hawk Mountain, unpublished data; P. Sherrington, personal communication). Peak hourly counts of > 100 Golden Eagles were made repeatedly in early October in eastern Alaska (281 McIntyre, C. L., and S. B. Lewis (2016). Observations of migrating Golden Eagles (Aquila chrysaetos) in eastern interior Alaska offer insights of population size and migration monitoring. Journal of Raptor Research 50: 254–264. Close ). Within-season variation in hourly rates of passage is known to be related to movement of weather systems in eastern North America. Count data suggest that eagle passage rates peak one day after a cold front and subsequently decline steadily for the next three days (294 Allen, P. E., L. J. Goodrich, and K. L. Bildstein (1996). Within- and among-year effects of cold fronts on migrating raptors at Hawk Mountain, Pennsylvania, 1934–1991. Auk 113: 329–338. Close ).

Golden Eagle migration responds to the physiographic environment over which the birds pass. Golden Eagles use orographic and thermal updraft (262 Kerlinger, P. (1989). Flight Strategies of Migrating Hawks. University of Chicago Press, Chicago, IL, USA. Close ) along ridges , but also migrate over large flat or featureless terrain using thermal updraft and continuous gliding flight (270 Yates, R. E., B. R. McClelland, P. T. McClelland, C. H. Key, and R. E. Bennetts (2001). The influence of weather on Golden Eagle migration in northwestern Montana. Journal of Raptor Research 35(2): 81–90. Close ). Flight altitude and behavior of migrating eagles varies with weather and topography (5 Katzner, T., B. W. Smith, T. A. Miller, D. Brandes, J. Cooper, M. Lanzone, D. Brauning, C. Farmer, S. Harding, D. E. Kramar, C. Koppie, C. Maisonneuve, M. Martell, E. K. Mojica, C. Todd, J. A. Tremblay, M. Wheeler, D. F. Brinker, T. E. Chubbs, R. Gubler, K. O'Malley, S. Mehus, B. Porter, R. P. Brooks, B. D. Watts, and K. L. Bildstein (2012). Status, biology, and conservation priorities for North America's eastern Golden Eagle (Aquila chrysaetos) population. Auk 129: 168–176. Close , 295 Lanzone, M. J., T. A. Miller, P. Turk, C. Halverson, C. Maisonneuve, J. A. Tremblay, J. Cooper, K. O’Malley, R. P. Brooks, and T. E. Katzner (2012). Flight responses by a migratory soaring raptor to changing meteorological conditions. Biology Letters 8: 710–713. Close ). Golden Eagles fly lower over summits and cliffs and typically subsidize flight with orographic updraft. In contrast, when flying over side slopes, gentle hills, and flats, they use thermal updraft to subsidize flight and can obtain altitudes to just below the boundary layer (296 Shannon, H. D., G. S. Young, M. A. Yates, M. R. Fuller, and W. S. Seegar (2002). American White Pelican soaring flight times and altitudes relative to changes in thermal depth and intensity. Condor 104: 679–683. Close , 297 Katzner, T. E., P. J. Turk, A. E. Duerr, T. A. Miller, M. J. Lanzone, J. L. Cooper, D. Brandes, J. A. Tremblay, and J. Lemaître (2015). Use of multiple modes of flight subsidy by a soaring terrestrial bird, the Golden Eagle Aquila chrysaetos, when on migration. Journal of The Royal Society Interface 12: 20150530. Close ). Use of thermals decreases when higher wind speeds break down thermals but create orographic updraft (295 Lanzone, M. J., T. A. Miller, P. Turk, C. Halverson, C. Maisonneuve, J. A. Tremblay, J. Cooper, K. O’Malley, R. P. Brooks, and T. E. Katzner (2012). Flight responses by a migratory soaring raptor to changing meteorological conditions. Biology Letters 8: 710–713. Close ). During spring and autumn migration in northern Canada, tends to avoid flying over high elevation ice fields and snow-covered mountains (247 Eisaguirre, J. M., T. L. Booms, C. P. Barger, C. L. McIntyre, S. B. Lewis, and G. A. Breed (2018). Local meteorological conditions reroute a migration. Proceedings of the Royal Society B 285: 20181779. Close ).

Congruent with their reliance on updraft, the Golden Eagle tends to avoid crossing water that generates little updraft, and large water bodies appear to divert migrating eagles. In eastern North America, Golden Eagles tracked by telemetry appear to get “trapped” on large peninsulas, including the Gaspé Peninsula and the thumb of Michigan. These birds sometimes circle the peninsula many times before retreating or making a long water crossing (TAM). When crossings do occur, they almost always occur near islands.

In eastern North America, the longest water crossing recorded by telemetry was of an adult female crossing 32 km of Lake Superior during November (TAM). Ten individuals crossed 20–26 km of open water in the Gulf of St. Lawrence. These crossings were only in spring and may have been over partially or fully-frozen waterways. Three individuals crossed two times each. Two females, a third-year and a fourth-year, appeared to die crossing 21 and 22 km of open water. Telemetry data suggest they were within 500 m and 1 km of shore when they went into the water (TAM). The cause of death is unknown but could have been caused by exhaustion or interspecific interactions. As an example, observers watched a juvenile Golden Eagle that was attacked and forced into the water by a Bald Eagle as it migrated across Braddock Bay, Lake Ontario, New York (J. Soprano, personal communication).

Migration includes periods of wandering and stopovers (243 Dekker, D. (1985). Hunting behaviour of Golden Eagles, Aquila chrysaetos, migrating in southwestern Alberta. Canadian Field-Naturalist 99: 383–385. Close ), but many individuals migrate with little or no wandering (298 Applegate, R. D., D. D. Berger, W. W. Cochran, and A. J. Raim (1987). Observations of a radio-tagged Golden Eagle terminating fall migration. Journal of Raptor Research 21: 68–70. Close , 186 Brodeur, S., R. Décarie, D. M. Bird, and M. Fuller (1996). Complete migration cycle of Golden Eagles breeding in northern Quebec. Condor 98(2): 293–299. Close , 220 McIntyre, C. L., D. C. Douglas, and M. W. Collopy (2008). Movements of Golden Eagles (Aquila chrysaetos) from interior Alaska during their first year of independence. Auk 125: 214–224. Close , CLM). Adults from eastern Canada migrate more directly to their wintering areas than do younger birds (265 Miller, T. A., R. P. Brooks, M. J. Lanzone, D. Brandes, J. Cooper, J. A. Tremblay, J. Wilhelm, A. Duerr, and T. E. Katzner (2016). Limitations and mechanisms influencing the migratory performance of soaring birds. Ibis 158(1): 116–134. Close ). Some eastern individuals, particularly those migrating through the Midwest to the southeastern United States, stop for long periods of time (> 3 weeks) before proceeding to their final wintering area (TAM). One adult male captured in Pennsylvania and tracked for 4 years spent the first month of each winter in southwestern Virginia and then migrated north to Pennsylvania to spend the rest of the winter.

Eagles tracked by telemetry in eastern North America traveled faster during spring than during fall (265 Miller, T. A., R. P. Brooks, M. J. Lanzone, D. Brandes, J. Cooper, J. A. Tremblay, J. Wilhelm, A. Duerr, and T. E. Katzner (2016). Limitations and mechanisms influencing the migratory performance of soaring birds. Ibis 158(1): 116–134. Close ). Over the entire fall migration, including stopover periods, adults traveled at a rate of 66 km/d ± 8 SE, subadults 63 km/d ± 7 SE, and juveniles 74 km/d ± 28 SE. During spring, adults traveled 110 km/d ± 10 SE, subadults 101 km/d ± 10 SE, and juveniles 102 km/d ± 19 SE. When actively engaged in migration, ignoring periods of stopover, during fall adults traveled 98 km/d ± 7 SE, subadults 95 km/d ± 9 SE, and juveniles 106 km/d ± 19 SE. During spring, adults actively migrated at a rate of 134 km/d ± 7 SE, subadults 130 km/d ± 9 SE, and juveniles 129 k/d ± 11 SE. During fall, adults spent 56 ± 5% of days migrating, subadults 54 ± 3%, and juveniles 57 ± 11%. During spring, adults spent 74 ± 4% of days migrating, subadults 69 ± 4%, and juveniles 66 ± 8%. The maximum distance traveled in one day was 508 km during spring and 412 km during fall (299 Rus, A. I., A. E. Duerr, T. A. Miller, J. R. Belthoff, and T. E. Katzner (2017). Counterintuitive roles of experience and weather on migratory performance. Auk 134: 485–497. Close ).

Migratory Connectivity

Migratory connectivity geographically links individuals and populations among life cycle stages (300 Cohen, E. B., J. A. Hostetler, M. T. Hallworth, C. S. Rushing, T. S. Sillett, and P. P. Marra (2018). Quantifying the strength of migratory connectivity. Methods in Ecology and Evolution 9: 513–524. Close ). When migratory connectivity is strong, individuals remain close to each other in all seasons of the year (i.e., individuals that summer in the same area also winter together). When connectivity is weak, individuals that are together in one season are not together in other seasons (i.e., individuals that summer in the same area do not winter together, or, conversely, eagles that winter in the same area do not summer together).

There have been no formal assessments of the strength of migratory connectivity of North American or Eurasian populations. However, it is possible to draw some inference about migratory connectivity from literature describing Golden Eagle migration (301 Domenech, R., T. Pitz, K. Gray, and M. Smith (2015). Estimating natal origins of migratory juvenile Golden Eagles using stable hydrogen isotopes. Journal of Raptor Research 49(3): 308–315. Close , 252 Brown, J. L., B. Bedrosian, D. A. Bell, M. A. Braham, J. Cooper, R. H. Crandall, J. DiDonato, R. Domenech, A. E. Duerr, T. E. Katzner, M. J. Lanzone, D. W. LaPlante, C. L. McIntyre, T. A. Miller, R. K. Murphy, A. Shreading, S. J. Slater, J. P. Smith, B. W. Smith, J. W. Watson, and B. Woodbridge (2017). Patterns of spatial distribution of Golden Eagles across North America: How do they fit into existing landscape-scale mapping systems? Journal of Raptor Research 51: 197–215. Close , 279 Bedrosian, B. E., R. Domenech, A. Shreading, M. M. Hayes, T. L. Booms, and C. R. Barger (2018). Migration corridors of adult Golden Eagles originating in northwestern North America. PLoS ONE 13(11): e0205204. Close ). Twenty-eight eagles hatched and telemetered in Denali National Park and Preserve, Alaska, wintered at latitudes from central Alberta to New Mexico (220 McIntyre, C. L., D. C. Douglas, and M. W. Collopy (2008). Movements of Golden Eagles (Aquila chrysaetos) from interior Alaska during their first year of independence. Auk 125: 214–224. Close ). However, of those birds tracked into the following year, all summered north of the Brooks Range, Alaska. Fifty-two Golden Eagles captured at wintering locations spanning the Appalachian Mountains from New York to Alabama summered in habitats that covered the northern two thirds of Quebec and much of Labrador (144 Miller, T. A., R. P. Brooks, M. J. Lanzone, J. Cooper, K. O’Malley, D. Brandes, A. Duerr, and T. E. Katzner (2017). Summer and winter space use and home range characteristics of Golden Eagles (Aquila chrysaetos) in eastern North America. Condor 119: 697–719. Close ). These trends suggest low levels of migratory connectivity of Golden Eagles within each of these regions. However, when considered at a continental scale, there appear to be moderate levels of connectivity (252 Brown, J. L., B. Bedrosian, D. A. Bell, M. A. Braham, J. Cooper, R. H. Crandall, J. DiDonato, R. Domenech, A. E. Duerr, T. E. Katzner, M. J. Lanzone, D. W. LaPlante, C. L. McIntyre, T. A. Miller, R. K. Murphy, A. Shreading, S. J. Slater, J. P. Smith, B. W. Smith, J. W. Watson, and B. Woodbridge (2017). Patterns of spatial distribution of Golden Eagles across North America: How do they fit into existing landscape-scale mapping systems? Journal of Raptor Research 51: 197–215. Close ). For example, Golden Eagles that summer in northeastern Canada also spend the winter with other eagles from the region in the eastern United States and do not appear to interact with birds that summer in Alaska and northwestern Canada. Furthermore, eagles from central Canada (Manitoba, Ontario) tend to winter farther west than do eagles that summer in northeastern Canada (TAM, unpublished data).

There are few data on proximate cues underpinning Golden Eagle migration. The tendency to migrate is strongest at northern latitudes (262 Kerlinger, P. (1989). Flight Strategies of Migrating Hawks. University of Chicago Press, Chicago, IL, USA. Close ). Departure from northern breeding areas tends to coincide with the first lasting snowfall, freeze-up, decreasing prey abundance, or the presence of north winds (186 Brodeur, S., R. Décarie, D. M. Bird, and M. Fuller (1996). Complete migration cycle of Golden Eagles breeding in northern Quebec. Condor 98(2): 293–299. Close , 269 McIntyre, C. L., and M. W. Collopy (2006). Postfledging dependence period of migratory Golden Eagles (Aquila chrysaetos) in Denali National Park and Preserve, Alaska. Auk 123(3): 877–884. Close ). Poor winter foraging conditions due to low jackrabbit abundance in the Great Basin may stimulate migratory movements among otherwise sedentary eagles (291 Rossman, D. J. (1999). Fall 1998 raptor migration study in the Manzano Mountains of central New Mexico. HawkWatch International, Inc., Salt Lake City, UT, USA. Close ).