SPECIES

Golden Eagle Aquila chrysaetos

Todd E. Katzner, Michael N. Kochert, Karen Steenhof, Carol L. McIntyre, Erica H. Craig, and Tricia A. Miller
Version: 2.0 — Published September 17, 2020

Behavior

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Behavior

The behavior of this long-lived species is affected by many factors including age, sex, breeding status, physical condition, geographic location, season, prey availability, and potential or realized disturbance. Much of what we know about behavior comes from studies of nesting Golden Eagles. Less is known about behavior outside the nesting period and of non-territorial individuals during the nesting period. There are likely important, and currently unknown, stage- and age-based differences in behavior. For an ethogram of some behaviors, see Ellis and Schmitt (388).

Locomotion

Walking, Hopping, Climbing, Etc.

From hatching to day 10, nestlings are relatively sedentary, but may crawl around the nest, paddling with their wings and feet (389, 78, 2). As eaglets age, they become more mobile, but still use their wings frequently for balance and support (78). At about 15 to 20 days post-hatching, eaglets begin to stand and walk in the nest (78).

Nestlings frequently walk around and hop in their nests. In the latter part of the nestling period, they often walk out on ledges (CLM) or branches (391). Nestlings hop up and down in their nests while flapping their wings (389, 78, 388). These bouts increase in frequency as they age and approach fledging and may be associated with grabbing at objects in the nest (388; see Behavior: Social and Interspecific Behavior). By age 50 days, nestlings are capable of leaping over each other and horizontally across their nest (78). They also walk backwards to the edge of the nest prior to defecating (389, 78, CLM).

When soliciting food, a nestling may spread, flap, or slap wings or lower its head and rush at an adult in the nest (78, 388). Nestlings close to fledging sometimes act so aggressively towards their parents that the adults appear hesitant to land on the nest (388).

Walks to accomplish a variety of tasks (389). Immediately after fledging they walk or hop to vantage points to gain enough elevation to glide to another location (396, CLM, EHC). When walking, takes great strides that necessitate a rolling motion of the body and a shuffling of the wings to maintain balance (389). Often the head is held a bit down, the body nearly horizontal to the ground. When running, the wings are opened even further and sometimes above the body (389).

Some observers in eastern United States forests have followed Golden Eagle tracks for hundreds of meters down trails, but the reason for these walks is not clear (K. O’Malley, personal communication). Adults walk on the ground or on branches of larger trees while gathering nesting materials or greenery to bring to nests (2, CLM, B. Woodbridge, personal communication). They often walk along hillsides in Denali National Park and Preserve, Alaska, when they are searching for nesting materials or greenery. Eagles also walk along pond, stream, or river edges before drinking or bathing (385, CLM).

When approaching carcasses in wooded or brushy areas, frequently lands in a clearing 10–50 m away from their ultimate destination (TEK, TAM; M. Lanzone, K. O’Malley, B. Woodbridge, personal communication). After landing, they survey the landscape and approach the carcass on foot, with a deliberate pace. In more open habitats, they may land closer to the carcass or even directly on it (EHC; T. Craig, personal communication). When feeding on carrion, they walk or hop over to other eagles, birds, or mammals that are scavenging on the same item and may raise their hackles, rear back, spread their wings and sometimes physically strike other scavengers (CLM, TEK, TAM, EHC; M. Lanzone, personal communication; see Agonistic Behavior: Physical Interactions).

Eagles walk during the “walk and grab” attack mode of hunting (2, see Diet and Foraging: Food Capture and Consumption), and they also run while pursuing prey. Eagles often walk, run, and then bound with both feet while flapping their wings to initiate flight (78, 2). They also walk uphill when their crop is full to gain elevation to facilitate take-off (EHC; T. Craig, personal communication).

Flight

Flight is the most visible behavior exhibited by the Golden Eagle (see 78, 400 for details). Upon their first flight from the nest, juveniles have only rudimentary flying skills. Their initial flights are often characterized by unstable glides with legs dangling, loud and repeated vocalizations, and, ultimately, crash landings (389, 345, CLM, EHC). Eagles generally lack the strength to use sustained powered flight until several days after they fledge. The flight skills of eagles improve quickly within a month of fledging (389, 400, 104, CLM).

Once past the first month out of the nest, the Golden Eagle is an extremely efficient flier (401). They use multiple types of atmospheric updraft to their advantage (389, 246, 297), and they soar and glide for extended periods of time, using very little energy to stay aloft or to travel great distances.

Eagles exhibit a variety of flight behaviors throughout the year including soaring, gliding, flapping, diving or stooping, kiting, and parachuting. They regularly alter their flight behavior in response to variable aerial environments and the purpose of their flight (e.g., traveling, migrating, hunting, transporting prey or nesting materials; 401, 246, 297, 295, 265, 299; see Movement and Migration: Timing and Routes of Migration).

Flight Behavior When Not on Migration

Age, sex, and season all have strong influences on the probability that non-migratory eagles in California will, at any moment, be in flight (402). Subadult birds move more than adults, males consistently move more than females, all birds move more in spring and fall and less in summer and winter. Likewise, the specific physiographic region a bird is using, topography and meteorology influence its probability of being in motion. Flight speed is influenced by a subset of these same parameters (402).

Once in flight, updraft again plays a strong role in the flight altitude the bird uses (403). In particular, topographic roughness, ground elevation and the east-west component of the aspect of the landscape, all linked to thermal updraft, are primary drivers of flight altitude of these birds. Secondary drivers of flight altitude include factors linked to both thermal and orographic updraft such as region, topographic position, steepness of slope and the north-south component of aspect (403).

For details on flight behavior during migration, see Migratory Behavior, below.

Soaring and Gliding Flight

Soars with outstretched wings and tail, with wings often held in a slight dihedral and primary feather tips widely spread and separated (29, 2, 39). Wing position and feather slotting (the spacing between primary feathers) changes with the type of flight behavior. Wings may be held slightly bowed downward when eagles are carrying prey or nesting materials or flying into a head wind (CLM).

Soaring flight is used when hunting, traveling, performing displays, or when flying without any obvious intent (390, 32, 404). Eagles use several types of fast and slow gliding and soaring flights, many of which are punctuated by parachuting and kiting behaviors (248; see Kiting and Parachuting, below). Soaring is the most common type of flight used by breeding males and females in southwestern Idaho (404).

Regularly uses two common types of soaring flight (401, 297). The first, thermal soaring, occurs when eagles take advantage of updrafts created by temperature differentials between the warm ground and cooler air. The ground heats the air, causing it to rise, and creating a column of upward moving air that eagles and other soaring birds can use to subsidize flight. The second type of soaring flight, orographic soaring, occurs when birds use updrafts created when wind is deflected off a hillside. Such soaring is especially common when eagles migrate along the Appalachians, but it also occurs anywhere there are both terrain features and wind (a combination common throughout most of the species’ distribution). Orographic soaring usually occurs at a lower altitude above ground than does thermal soaring (405), because orographic updrafts only extend 200–300 m above the surface of the ground, whereas thermals can extend many thousands of meters in altitude (262).

When hunting, often glides low into the wind with their wing tips nearly touching the ground (see Diet and Foraging: Feeding; 317). They also glide in high winds with partially folded wings (388), and between thermals, particularly during migration (297). Glides can be extraordinarily slow (e.g., near stalls) or exceedingly fast (purportedly 190 km/hr; 32). In eastern North America, mean modeled gliding flight speeds during spring migration averaged 17 m/s (65 km/hr; 401).

On migration, the soaring flight of the Golden Eagle is associated with a variety of environmental factors that influence the availability of updraft. At Glacier National Park in Montana, the number of individuals detected during autumn migration increased with increasing air temperature, rising barometric pressure, and decreasing relative humidity (270). In spring at this same site, numbers of birds detected increased with increasing wind speed and rising barometric pressure (270). Likewise, eagles tracked in eastern North America showed a preference for migrating when thermal activity was high (246). This happened during both spring and fall migration, but in spring, migration of pre-adults was more closely tied to increasing thermal activity than was migration of adults.

Flapping Flight

Flapping flight is used regularly but makes up a small proportion of the total flight time of eagles (297). Flapping flight consists of a series of deep wing beats interspersed with shorter sessions of gliding (2). Eagles also may use flapping flight, with an emphasized down stroke, when approaching and chasing off conspecifics (CLM, EHC) and other avian intruders (e.g., White-tailed Eagle Haliaeetus albicilla; 248). Flapping flight is energetically more expensive than soaring or gliding flight (406) and often appears labored (2). Eagles are heavy birds, and the energetic costs during flapping flight can be several times their basal metabolic rate (401). Eagles exhibit behavioral plasticity to minimize this expense by using multiple flight subsidies (see Soaring and Gliding Flight, above). For example, breeding males in central Washington minimize their reliance on powered flight by remaining perched until flight conditions are adequate for soaring (407). They also perch at high elevations near ridge tops where they can attain flight altitude easily. Similarly, wintering eagles in the mountainous areas of east-central Idaho often remain perched until mid-morning, when upslope winds or thermals that facilitate flight are generated (EHC; T. Craig personal communication).

Stoops or Dives

When a Golden Eagle stoops on prey, it holds its wings close to its body and falls headlong towards the ground (390) . Stoops vary in angle and speed from very fast and direct (sometimes vertical), to very slow and indirect (390). They may include a corkscrew dive (390, see Kiting and Parachuting, below). Some stoops include a low-level shallow glide (2). Eagles are said to sometimes attain speeds of 240–320 km/hr in vertical dives (32), although such speeds appear unlikely in most, if not all, situations. Stoops may be accompanied by the loud sound of wind rushing through wing feathers (2, EHC; also see Sounds and Vocal Behavior: Nonvocal Sounds). Eagles often make conspicuous, long dives to nests (248, CLM, EHC), some of which are preceded by undulating flight (248; see Characteristics of Undulating Flight, below).

Characteristics of Undulating Flight

Undulating flight typically starts with an eagle soaring or, upon leaving a perch, tucking its wings close to its body and descending rapidly towards the ground, often in a deep dive (389, 248). As it approaches the ground, the eagle opens its wings and tail and quickly travels upwards, ascending by using its momentum or strong, flapping flight, or both (391, 389, 390, 408, 248, 404, 2, 388). At the apex of the display, the eagle’s flight speed slows, and it begins to tilt back towards the ground, sometimes turning its head to look downward (390, 248, CLM, EHC). It then tucks its wings close to its body and descends rapidly again. A special form of undulating flight is a pendulum flight, in which the eagle performs an aerial back-flip at the apex of the display and then retraces the same path repeatedly, back and forth like a pendulum (248). Territorial individuals can repeat undulating flights for ≥ 20 min (408, CLM). Both sexes perform undulating flights, but males appear to dive more steeply and perhaps faster during undulating flights than do females (CLM).

Undulating flight occurs at many altitudes, ranging from very high above ridges and mountain peaks to very low in valleys or in other areas with relatively restricted views (248, 408, 2, CLM). In western Colorado, low altitude displays (< 100 m above the ground) seem more intense, with undulations more frequent and having smaller amplitudes, than do high altitude displays (408). See Bergo (248) and Harmata (408) for illustrations of the relative amplitudes and frequencies of undulating flight (described as waves by 248) at both high and low altitudes.

The function of undulating flight has been debated (408, 404, 2). On breeding grounds, undulating flights probably are performed as a territorial display (see Behavior: Agonistic Behavior: Undulating flight for territoriality; 408, 404, 388, 409) and as a courtship and pair bonding display (see Behavior: Sexual Behavior: Pair Bond; 390, 248, 29, 410; CLM; B. Woodbridge, D. Wiens, P. Kolar, personal communication). Undulating flight has been observed in winter, again with an unclear function (TAM; M. Lanzone, personal communication).

Kiting and Parachuting

Kiting occurs when an eagle is in flight but maintains a steady position relative to some point on the ground. Eagles often kite into strong winds, holding their wings stiffly but slightly bent and toward their body, with their primary feathers held widely spaced in an upward curve (390, 404, CLM). During kiting, the tail is constantly moving as the eagles use it for steering and stabilization (390).

Parachuting flight occurs when an eagle is in a dive but momentarily slows its descent while looking at something directly below it on the ground (e.g., potential prey or nesting materials). The eagle descends in a dive, then opens its wings and tail to slow its descent, holds still a moment, and then continues its descent as a dive. Eagles often use a series of parachuting events during a descent. Parachuting flight is a slow but uninterrupted stoop, in which an eagle slowly descends using openly spread and slightly elevated wings and tail to slow its descent, with its legs often dangling (2, EHC, CLM).

Roll-over Flight

May roll over when attacked by conspecifics (78), other large raptors, or large corvids (134), when mobbed by other species (CLM, TEK, EHC), or after aerial capture of prey (355). An adult in Montana (presumably female, based on its size) seized a recently fledged (58-day old) Osprey (Pandion haliaetus) in mid-flight (355). A few seconds later, an adult female Osprey (presumably the parent) dove at the flying eagle, forcing the eagle to roll. The eagle quickly righted itself, maintained control of its recently seized prey, and continued flying out of view (355).

Swimming and Wading

Observations of swimming and wading are rare. Two 9.5-wk-old nestlings flew from their nest into the Bruneau River in southwestern Idaho after being flushed from their nest by a biologist. After floating motionless for about 5 min, both nestlings swam to shore using their wings as paddles and taking short breaks every 3.6 to 4.8 m (411). An adult eagle waded into shallow waters along the shore of the South Platte River twice, in an attempt to capture artificial decoy ducks (412).

Self-Maintenance

Preening, Head-Scratching, Stretching, etc.

Nestlings start preening 1–2 days post-hatching. Observations suggest that preening sessions increase in frequency and peak at about 50 days post-hatching, subsequently declining in frequency (78). Preening behavior changes as contour and body feathers emerge (78, 2). Nestlings use a variety of preening methods to oil feathers and rearrange barbs. They may shake and ruffle feathers during preening (78). At about 40 days post-hatching, young eagles begin to scratch their heads (78).

When perched, free-flying eagles may scratch their head, neck, and upper throat with the talon of the middle toe (78). Jollie (389) described eagles rousing (i.e., shaking) with a quick swishing of feathers. Golden Eagle uses four unique shaking behaviors, each associated with a different context: when they are wet; to dislodge unwanted substances from their feathers; to dislodge unwanted debris from the bill or mouth; and to remove nasal salt secretions from the bill (413, 78). They may shake and fluff to elevate the feathers slightly (78). Eagles also perform wing stretches, yawns, and wing drooping behaviors that may be associated with thermoregulation (78).

Bathing

Captive individuals bathe often (389, 414, 415, 388), but bathing is not frequently observed in the wild. Bathing is reported in the literature by wild eagles in Colorado (389), Nevada (385, 386), southwestern Idaho (T. Craig, personal communication), interior Alaska (CLM), Utah (D. Finlayson, personal communication), and England (398). Wild nestlings have been observed in bathing-like activities in rain (78). Communal bathing of up to 12 individuals has been observed in Arizona and Texas (416, 417).

Bathing and drinking are sometimes associated in the literature. Beecham (418) observed two recently fledged juveniles drinking or bathing at a puddle along a gravel road in southwestern Idaho. May seek out secluded bogs or other water sites that have quick escape routes, presumably because bathing and drinking may make them more vulnerable to predators (389, 385, 170).

Sun-bathing or Dust-bathing

Limited information. Recent trail camera pictures from Utah suggest dust bathing after a water bath (D. Finlayson, personal communication).

Sleeping

Nestlings spend much of their first 4 weeks of life sleeping (78). They often sleep on their belly with their heads resting on the nest.

During the nesting cycle, adult females may sleep on the nest, with their wings bent and head drooped down in front (311, 389), particularly when incubating (KS). Adults sometimes sleep perched on one foot with their head drooped and their bill resting against the throat or upper breast (389) or tucked under their back and scapular feathers (78). During sleep, the lower lids may cover the cornea, and feathers sometimes cover the eyes; see Ellis (78) for details.

Perching and Roosting

Bergo (248) described three types of perching behavior: exposed, where eagles use the highest and most exposed perch that provides optimal view but no shelter; conspicuous, with good views and moderate shelter; and inconspicuous with restricted view and good shelter. Adults and large nestlings may stand on one leg when perched; when this occurs, the other leg is often pulled up and held close to the lower body (78, CLM). Spends long periods of time during the day on prominent perches with good views of the landscape. Soon after fledging, juveniles from tree nests may perch on the ground, but they start perching in trees within 3 weeks of fledging (398). For further details, see Habitat: Perching and Roosting Habitat.

Daily Time Budget

Data on daily time budgets are sparse and known only for nesting eagles. There are few accounts of daily time budgets of non-territorial eagles or of eagles during migration or winter. Most details on the daily time budget come from two studies of nesting birds in southwestern Idaho (404, 419).

In the first study, daily time budgets for males and females differed substantially early in the brood-rearing period, but became more similar after nestlings reached 5 weeks of age (404). When in view, males perched an average of 78% of the daylight hours in which they were observed, females 85% (249, 404). When observed in flight, males flew directly (2% of total time observed), soared (19%), undulated (< 1%), and engaged in other flight behavior (1%); females spent 1%, 14%, < 1%, and 1% of time observed in the same activities (404).

During 692 hours of nest observations over 56 observation days, females spent a significantly greater proportion of the day incubating (87 ± 2%) than did males (14 ± 2%), and only females incubated at night (249). Of the 111 male-initiated changeovers in incubation duties, 17 (15%) involved food transfers to the female at or near the nest (249). Males regularly landed on nests to deliver prey, but were present only 1% of the observation time, and males invested no time brooding or feeding nestlings (249). In contrast, overall daytime nest attendance by females averaged 24 ± 3%, and females spent 11 ± 1% of the observation time brooding or shading young (249). The percentage of daylight hours females brooded or shaded nestlings decreased rapidly as brood rearing progressed, and no nestlings were brooded or shaded after they reached 42 days of age (see Figure 1 in Collopy [249]).

In the second study, also observational, activity budgets in southwestern Idaho changed predictably throughout the four stages of the nesting seasons (i.e., pre-breeding, incubation, early brood-rearing, and late brood-rearing, as defined in 419). During the pre-breeding season, eagles were away from the nest area most of the time and, presumably, out of sight of observers. Activity observed included copulation (< 1% of time when visible) and nest maintenance (1 ± 2% [SD]). During the incubation stage, eagles were more frequently visible and closer to the nest. Most time was spent incubating, perched near the nest, or involved in nest and egg maintenance. During the early brood-rearing stage, adults spent time brooding the young, perched near the nest, feeding young, and performing nest maintenance. In the late brood-rearing stage, birds were less frequently in the area of the nest, but when seen, they were observed feeding young, perching, and performing nest maintenance.

Data from other studies are sparse. During the nesting season, eagles tracked with VHF telemetry in southwestern Idaho hunted from one hour before sunrise to one hour after sunset (306). Using observational data collected from blinds, the daily hunting patterns in north-central Utah were bimodal, with hunting occurring from 08:30–12:00 and from 14:45–18:30 (420).

Time budgets during winter are not well-documented, but most time is likely spent securing food and safe roosting places, or in resting and conserving energy. Time budgets of non-migratory eagles appear to vary in response to preparation for breeding (165). Eagles in east-central Idaho often remain perched early in the morning during winter. In that region, eagles were most frequently observed hunting between mid-morning and late afternoon (EHC, T. Craig, unpublished data). See Movement and Migration: Timing and Routes of Migration for time budgets during spring and autumn migration.

Agonistic Behavior

Physical Interactions

Types of physical interactions between two eagles or between an eagle and another species include direct physical contact, or indirect visual or aural contact. Visual contact, usually via aerial displays such as undulating flights (see Behavior: Locomotion: Flight: Characteristics of Undulating Flight), may reduce physical attacks that put both the attacker and intruder at risk of injury or death (2). Territorial incursions by eagles seeking entry into a breeding population (e.g., non-territorial birds, often called “floaters”; 421) are probably the cause of most aggressive physical interactions between eagles on their breeding grounds (2, CLM) and appear to increase in frequency with density of breeders or floaters (228). In Scotland, aggressive encounters occur most often before egg-laying, and less often during incubation and brood-rearing (2).

Intraspecific Interactions

Physical contact may have important demographic relevance, especially for some age classes of eagles. Estimated proportion of mortality caused by intraspecific fighting in the United States averaged 0.19% for juvenile eagles, 7% for 2 to 3 year-old eagles, and 18% for after-third-year eagles (422). Competition for breeding territories is manifested as intraspecific fighting, both in the air and on the ground (421, CLM).

In a 17-year study in California, 4 tracked adults, including 2 territory holders and 2 non-territory holders, were killed in the nesting season during territorial encounters with other Golden Eagles (see Table 3 in 421). The nesting season deaths of three other birds that did not hold territories also were suspected to be from territorial encounters (421). Talon wounds suggested that a radio-tagged adult female in southwestern Idaho (USGS, unpublished data), an adult male in south-central Montana (423), and one fledgling and two nestlings in central California, all were killed by other eagles (424, G. Hunt, personal communication).

Fighting between a resident pair of Golden Eagles and a pair of adult intruders resulted one of the territorial eagles knocking an intruder off the vane of a windmill (408). In another situation, a resident adult eagle grappled on the ground for > 2 hours with an intruding adult, see also ML216843311 . The fighting terminated only when the human observer approached within 2 m of the combatants (408). In Wyoming, 2 of 14 adults that were trapped and relocated ~470 km away, returned after 53-109 days to the vicinity of their former territories and died fighting with the eagles that had replaced them (425). Intraspecific fighting by Golden Eagles has been documented in several parts of Europe (228, 426). In western Norway, females tend to be more involved in aggressive territorial encounters than are males (248).

Physical aerial encounters may include locking talons in mid-air (i.e., talon-grappling; see 388 and Behavior: Locomotion: Flight: Roll-over Flight) . Two cases of talon-grappling in western Montana involved a “rushing attack” from an adult eagle rolling over and presenting its talons to a subadult eagle near an occupied nest (78). In both cases, the adult clasped the subadult’s foot (or feet), and both eagles whirled for a full revolution before releasing (78). Two males in Arizona locked talons and rotated 17 times before striking the ground (427). Two female Golden Eagles, one adult and one subadult, were killed when they crashed into the roof of a residential house in Bludenz, Austria (426). The authors surmised that the two females had engaged in an intensive aerial interaction including talon-locking and that the two eagles could not disengage before hitting the roof. The sound of the eagles crashing into the roof and the damage to the roof resulting from the crash suggested that the eagles smashed into the roof at a very high speed (426).

Golden Eagles have been observed talon-grappling many times during a > 30-year study in Denali National Park and Preserve, Alaska (CLM). The most notable of these occurred during the early nesting season when two adults of unknown sex locked talons about 400 m above the ground and remained locked as they cart-wheeled downward and hit the snow-covered ground. Upon impact, one eagle flew away and the other remained on the ground where it was immediately struck by a previously undetected third adult eagle. The third eagle dove repeatedly at the grounded eagle and then flew off. The grounded eagle hid under a nearby willow shrub for ~40 min before flying away.

Conflicts with conspecifics at carcass feeding sites during winter and migration may involve both display threats and physical contact (428, EHC, TAM, TEK; T. Craig, T. Booms and C. Barger, personal communication). Golden Eagles defending a carcass in eastern North America mantle, gape, flap their wings, and raise feathers on the head and neck (TEK). It has been suggested that sub-adult birds may engage in these behaviors in part to advertise these markings to advertise a willingness to fight for a carcass (36). Fighting that includes strikes with open feet is commonly captured by motion-sensitive trail cameras. Eagles feeding on carcasses in spring in south-central Alaska occasionally lunge at each other with open feet and flared wings. Physical contact during these encounters is rare, but the frequency of fights increases with the number of Golden Eagles feeding on the carcass (T. Booms and C. Barger, personal communication). At carcasses in Norway, females won 5 of 7 aggressive interactions and a younger eagle dominated an older conspecific in 15 of 21 conflicts (428).

For details on vocal interactions between eagles, see Sounds and Vocal Behavior.

Interspecific Interactions

Golden Eagles rarely come near humans even when humans approach or enter a nest (73, 390, 345, MNK, CLM, EHC; T. Craig, personal communication), but they will attack some other mammals that approach their nests. Golden Eagles repeatedly dove at, and hit the back, neck and head of, an adult female grizzly bear (Ursus arctos) and her two cubs of the year when they entered a nest with 10-day old nestlings in Denali National Park and Preserve, Alaska (CLM; see Behavior: Social and Interspecific Behavior: Predation). In Idaho, an eagle was approached by a coyote: the eagle faced the coyote, stood up and spread its wings, causing the coyote to halt abruptly, switch directions, and trot away (EHC). Despite the presence of terrestrial mammalian predators, recently fledged Golden Eagles commonly spend several days on the ground after leaving the nest. That they often survive is likely due to their parent’s defense behaviors (CLM, TEK), and possibly aggressive displays by the young eagles (EHC; see Behavior: Locomotion: Crawling, Walking, Running, Hopping etc.).

Golden Eagles may exhibit aggressive behavior (e.g., diving, undulating flights) towards aircraft, including unmanned aircraft (i.e., drones, TEK). The only Golden Eagle reported in Hawaii was killed when it dove on a helicopter and was struck by the rotating blades (192). Eagles also have been known to attack small fixed-wing aircraft and helicopters, when aircraft approach a displaying pair of eagles at the same or slightly lower level (429 in 430). Golden Eagles in Switzerland recently destroyed a hobbyist’s drone (R. Arrletaz, personal communication). The closely related Wedge-tailed Eagle (Aquila audax) in Tasmania regularly attacks small unmanned aerial vehicles near occupied nests and is known to attack hang gliders and paragliders (TEK; J. Wiersma, personal communication; see also Conservation and Management: Effects of Human Activity: Disturbance at Nest and Roost Sites).

Agonistic encounters with corvids and other raptors are common during the nesting season (404). In Denali National Park and Preserve, Alaska, Golden Eagles aggressively defend occupied nests against potential nestling predators including Gyrfalcon (Falco rusticolus), Great Horned Owl (Bubo virginianus), and Common Raven (Corvus corax) (CLM). Golden Eagles killed, but did not eat, three Great Horned Owls in Utah (J. R. Murphy in 29), adult Ferruginous Hawks in Wyoming (431), and nestling Ferruginous Hawks in the Uintah Basin, Utah (432), possibly in the course of territorial or nest defense (although that explanation seems unlikely in the case of the nestlings). See also Undulating Flights, below.

In a turn of events, Merriam’s Wild Turkey (Meleagris gallopavo merriami) attacked a Golden Eagle that attempted to capture a member of their flock. Three turkeys ran at the eagle, aggressively calling, and flapping their wings. The eagle was apparently startled and quickly left the scene (352).

There is little information on vocal interactions between eagles and other species. However, wild eaglets in the nest may sometimes emit a loud hiss when approached by humans, flighted eagles may make a “chittering” noise when being banded. A captive adult eagle emitted a goose-like honk after being struck several times by a Great Horned Owl (388; for additional details see Sounds and Vocal Behavior).

Communicative Interactions

Undulating Flights

Undulating flights during the nesting season are, at least in part, a territorial display (408, 248, 409, CLM; see Behavior: Locomotion: Flight: Characteristics of Undulating Flight). Eagles from adjacent territories sometimes perform undulating flights simultaneously (404, 410, CLM). Undulating flights in southwestern Idaho occur near the territory boundary or within view of a neighboring territorial eagle, rather than near the occupied nest (n = 388; 404, 176). In one study in Scotland, undulating flight was performed with equal frequency in all parts of the eagle’s territory (409). In contrast, in western Colorado, the intensity of undulating flights is greater the closer an intruder is to the resident pair’s nest or hunting areas. Most (73%) undulating flights recorded there occur at low altitude when an intruder is detected within the resident pair’s home range (408). In that study, the intruding eagle left the home range soon after the undulating flight began, and the territorial pair stopped undulating when the intruder departed. In central California, adults appear to use undulating flight to advertise their nesting and foraging areas to neighboring pairs and to non-territorial birds (D. Wiens, personal communication). In some cases, these Golden Eagles undulate directly over or near apparent intruders. An adult near Healy, Alaska, repeated long, deep, and steep undulating flights in mid-April for over 2 minutes directly above 3 adult and 1 subadult Golden Eagles who were feeding on a caribou (Rangifer tarandus) carcass within what appeared to be the displaying bird’s territory. The displaying eagle came within 10 m of the eagles feeding on the carcass several times when at the lowest point in the undulating flight (CLM; S. B. Lewis, personal communication).

In areas of central California and interior Alaska that have high densities of breeding pairs, undulating flight by a territory holder or pair may trigger undulating behavior by neighboring pairs or individuals (CLM; B. Woodbridge, P. Kolar, personal communication). Undulating flights in Scotland are thought to be a response to stimuli such as the presence of intruding eagles, the presence of a mate, and interactions with the mate such as copulation and prey delivery (2). Territory holders also have been observed to undulate when migrating eagles fly through their territories (281). Adults establishing nesting territories in Norway undulate more often than do established territory holders (248). In contrast, recently established pairs in southwestern Idaho perform undulating flights less frequently than do pairs that have held territories for longer periods (176).

The presence of other avian predators within a territory may induce resident eagles to undulate or exhibit other territorial behavior. In northern Colorado, a resident male eagle performed an undulating flight and then chased Ferruginous Hawks (408). May also undulate in response to human intruders who venture too close to an occupied nest (408).

Undulating flights by young, presumably non-territorial individuals, also have been reported (408, 400). In the month of April, Harmata (408) observed a young Golden Eagle undulating above the territory it likely had fledged from in the prior season, in response to an intruding adult conspecific and in the presence of its parents who were perched nearby. The young bird performed undulating flight interspersed with aggressive stoops for 12 min, after which the intruding adult took off and slowly flew away (408). Bahat (400) observed two birds, a female and male that were approximately 26 - 33 days post-fledging, undulating near their natal nest without the evident presence of an intruder but in the presence of one of their parents. That study also reports that a juvenile male Golden Eagle performed an undulating flight 55 days after fledging, in response to two adult Egyptian Vultures (Neophron percnopterus) that flew near its natal nest.

Undulating flights by migratory individuals are sometimes observed during winter (TAM). These behaviors may also be associated with defense of non-breeding territories or of food resources.

Other Displays

Golden Eagle also may perch conspicuously, presumably to exhibit territoriality (248). Territorial eagles may spend long periods of the day perched on prominent outcrops or ridgelines in their territories during the nesting season (248, 404, CLM). The presence of nests, including both occupied and alternative nests, also may serve territorial and display functions (2, 433), as does nest decoration with green sprigs or branches of vegetation (434)

Territorial Behavior

Territoriality is the practice of maintaining a territory. Home range is the space an animal uses (for details on home range, see Demography and Populations: Population Spatial Metrics). Territory defense is accomplished by displays such as undulating flight, high soaring flight, occasional chases, display of talons, and conspicuous perching (408, 248, 404, 176, 2, 410, CLM, MNK). These non-contact behaviors likely reduce fighting that can be lethal to one or both parties (2). When non-contact displays are not effective, territory holders may fight with conspecific intruders (435, 248, 2, 388, CLM).

Older individuals seem to tolerate younger, non-breeding eagles in their territories at many times of the year (410). Eagles have been observed to ignore apparent food-begging by subadults within their territories during the non-breeding season (410). In southwestern Idaho and California, non-local adult and pre-adults can regularly be captured outside of the nesting season in nesting territories occupied by a territorial pair (176; P. Bloom, personal communication).

Territorial defense by eagles in the conterminous United States and southern Canada probably begins far earlier in the season than was once assumed. For example, eagle home ranges in the Mojave Desert were smallest during October, about three months before egg-laying, suggesting that was when eagles were most concerned about defending the borders of their territories (165). Some territorial eagles remain on and defend their nesting territories year-round (404, 436, 176, 407, 437, 421, 410, 438), although defense is almost certainly strongest during the nesting season. Residents may undulate outside the nesting season, in response to a neighboring territorial pair. However, ranging behavior of at least some of these eagles changes outside of the nesting season (176, 407, 165; see Demography and Populations: Population Spatial Metrics), suggesting that territorial defense is less intense during this period (248). Likewise, in Idaho, aggression was rarely observed between territory holders and intruders within and outside of the nesting season (176).

Long-distant migratory territorial eagles leave their breeding range in autumn and return in spring and thus only occupy and defend their nesting territories for a portion of the year. In some parts of Alaska, some individuals may overwinter at or near the latitude of their nesting territory, but there is no information available on whether these eagles remain on and defend their territory (CLM). In Denali National Park and Preserve, Alaska, few, if any eagles remain on territory year-round and territorial behaviors, courtship, and nest building activities usually start soon after individuals arrive on nesting territories (CLM).

Seasonal Variation in Territoriality

Aggressive attacks on non-territorial eagles by territorial eagles during the nesting season are common in some areas (435, 248, 2). The reactions of territorial eagles to non-territorial birds vary by season and situation. Residents in Norway chased four of eight intruding subadults from territories and undulated in response to at least two other intruders (248). Similar behavior occurs on the breeding grounds in Denali National Park and Preserve, Alaska (CLM). In contrast, territorial adults often react passively to non-territorial subadults near nests during the nesting season in Scotland, southwestern Idaho, North Dakota, and central California (439, 199, 323, 410; M. Collopy, personal communication). Territory holders also appear to tolerate conspecifics within their territories in the relatively rare instances of group hunting (see Diet and Foraging: Food Capture and Consumption).

Sexual Behavior

Mating System and Operational Sex Ratio

Usually monogamous, but two males were observed to copulate with one female in central California, and the trio successfully raised young (G. Hunt, personal communication). Trios also are observed occasionally in the Mojave Desert of California and Nevada (165; D. Driscoll, personal communication). Watson (2) described several documented cases of 3 eagles occupying the same territory including two cases in Scotland (440), one in Norway (248), and one in Swedish Lapland (441 in 2).

Male:female sex ratios for annual cohorts of fledglings in southwestern Idaho ranged from 0.60:1 to 5:1 (442), with males outnumbering females in 10 of 14 years of that study. A consistent male bias characterized all age groups over 4 years in a population in central California (421). Male:female ratios for fledgling eagles in those years were 18:13, 13:9, 16:9, and 21:8, with an average of 64% males. Sex ratios in nests with 1 vs > 1 fledglings were similar (61% vs 62% males, respectively). Free-ranging, non-territorial eagles captured for radio-tagging in the same study area were 62% males (76:47 individuals). By age class, the male:female ratio for free-flying birds was 12:6 for non-territorial adults, 27:17 for subadults, and 3:4 for free-ranging juveniles (209). Wintering eagles captured in east-central Idaho from 1990–1997 were 60% male (male:female ratio of 174:116 individuals). Male:female ratios by age class were 103:62 for preadults and 71:54 for adults (443).

Courtship

Courtship displays include territorial displays, mutual soaring and gliding, mutual aerial displays, carrying materials to nests, vocalizing, chasing, long periods of perching close together, foot touching, flying along cliffs, and nest building (345, 105, 408, 2). Mock attack and evasive behaviors by pairs of adults may serve as courtship behavior (248). Courtship displays observed from late January through mid-February in Butte Valley in northern California include low-level "slow chasing" flights wherein both adults flew back and forth along a hillslope, calling and then landing together on a prominent snag, a rock, or the ground (B. Woodbridge, personal communication).

Carrying, dropping, and recapturing airborne inanimate objects such as rocks, sticks, and prey remains also may function as courtship display (390, 2; but see Behavior: Social and Interspecific Behavior: Play). Use of objects, along with aerial maneuvers, may give potential mates the opportunity to gauge skills that parallel those used in catching prey (2). Courtship behavior in the Butte Valley of northern California also included eagles picking up a stick or clump of grass, carrying it while flying and vocalizing, but not placing the material on a nest (B. Woodbridge, personal communication).

Territorial eagles may perform brief and lower altitude undulating flights, apparently as intra-pair communication. When this occurs, the male undulates very briefly just before perching next to a female or when returning to a nest (248, 410; P. Kolar, personal communication). Depending on the circumstances, undulating flight may function as a courtship display (CLM; D. Wiens, P. Kolar, personal communication). Copulation often immediately follows bouts of undulating flight during the early nesting season in these areas. In contrast, undulating flights in northern Colorado were not observed in association with copulation (408). In central California, undulating flights and other courtship behaviors are observed throughout the nesting season, but the frequency with which they are seen peaks before eggs are laid (438; D. Wiens, personal communication).

Copulation

Copulation occurs most frequently before egg-laying, but also may occur year-round and probably functions to maintain pair bonds (390, 418, 78, 399, 408, 444, 2). Eagles in Montana copulated several times per day from the beginning of March until 55 days after completion of the clutch (399). In Denali National Park and Preserve, Alaska, copulation events are detected throughout the nesting season (CLM).

Copulation often occurs on a conspicuous perch (248, CLM) . In northern California, copulation has been observed on prominent juniper or ponderosa pine snags and rock outcrops, and occasionally on old hay bales and power poles (B. Woodbridge, personal communication). In Denali National Park and Preserve, copulation has been observed on ridge tops and prominent mountain peaks (CLM).

Prior to copulation, the female leans forward, points her bill down, droops her wings laterally (possibly to balance), and often deflects her tail slightly to one side (389, 78). The male then lands on or hops onto the female’s back from flight (78, 2). The female slowly raises her tail as the male lowers his tail over hers, both birds flap wings, the male slowly wags his tail and then leans back as copulation is completed (389). Copulation events are usually quick, lasting from 10 to 20 s (2), and eagles may vocalize during copulation (389, 394, 78). Eagles may copulate several times within an hour (389, CLM).

In southern Idaho, Beecham (418) made five observations of a male bringing fresh material into the nest and then flying with its mate to a nearby spot and copulating. Copulation events in Colorado and Montana were occasionally followed by preening, mutual preening and beak rubbing, and shaking (389, 78). Copulation also may be followed by mutual soaring, rolling and foot touching, racing along cliffs, extended periods of perching close together, and undulating flight (408, 2, CLM). In other settings, copulation is occasionally accompanied by food transfer (78) and sometimes followed by undulating flight (390, CLM; P. Kolar, personal communication).

Pair Bond

Pair bonds appear to be maintained by vocalizations, copulation events, nest building, perching together for extended periods of time, and undulating flights (408, 248, 2). Pair bonds may be maintained year-round in the conterminous United States (see Behavior: Agonistic Behavior: Territoriality).

Territorial pairs in resident populations may stay together for the entire year, but recent telemetry studies indicate that some residents may leave their nesting territories temporarily (165, MNK). Long-term pair bonds might not be as strong in migratory populations because bonds need to be re-established annually when potential breeders (including previous territory holders and individuals who have not held territories) return to the breeding grounds (2).

Recent observations of putative male-female pairs at baited camera trap stations in winter suggest that some pairs of migratory eagles may overwinter together or form pair bonds on wintering grounds (TAM, EHC; M. Lanzone, personal communication). A pair of migratory eagles (presumably the same birds each winter) has been seen together on wintering grounds in the southern Appalachians in four consecutive years. The pair vocalize and perform undulating flights near carcass trapping stations (TAM; M. Lanzone, personal communication). A pair of eagles captured in Kentucky during winter, spent the summer on the same home range in Manitoba (TAM; M. Lanzone, A. Berry, personal communication). A similar observation of a telemetered pair occurred in Scandinavia, where the pair maintained a home range in Sweden and winter range together in Finland (445). However, data from 3 pairs of radio-tagged migratory Golden Eagles in Alaska provided no evidence that they maintained a pair bond year-round (J. Eisaguirre, T. Booms, unpublished data).

Data on mate fidelity are scarce. Dixon (311) and Jollie (389) suggested that the Golden Eagle does not mate for life. Observations of tagged birds suggest that some pairs stay together for ≥ 2 yr. Four mated pairs occupied the same nesting territories over two years in southwestern Idaho (249), and another mated pair stayed together for ≥ 3 seasons (176, MNK). Three mated pairs of migratory eagles stayed together for two nesting seasons in Alaska (J. Eisaguirre and T. Booms, unpublished data). Conversely, following an unsuccessful nesting season in southwestern Idaho, an adult female left her mate from the previous year to nest successfully with a male from another territory (176).

Inbreeding

Data are incomplete, but there is some evidence for reduced heterozygosity and thus inbreeding within Golden Eagle populations (86).

Extra-Pair Mating Behavior/Paternity

No information from North America. Circumstantial evidence indicates that an extra-pair copulation occurred at a nest in Scotland (440). Extra-pair paternity is rare or nonexistent in a population of the closely related Imperial Eagle (Aquila heliaca; 259).

Brood Parasitism of Conspecifics

Not known to occur.

Social and Interspecific Behavior

Degree of Sociality

The degree of sociality varies by season and breeding status. Two to five individuals may feed simultaneously on the same carcass in winter (446, 180, B. Woodbridge, personal communication, TEK, EHC, CLM), but spacing is maintained, sometimes by aggressive displays (EHC; T. Craig, personal communication). Up to 6 eagles, mainly adults, fed simultaneously on a moose carcass at spring capture sites in southwestern Alaska (T. Booms and C. Barger, personal communication). Up to 13 Golden Eagles have been observed on wolf-killed carcasses in the Greater Yellowstone Ecosystem during winter (241). Two adult and two young Golden Eagles flushed off a freshly killed 3 to 4 month-old male coyote pup near Medicine Hat, Alberta, Canada in early August (447). Eagles also gather communally at carcasses in Norway in winter, but they can be aggressive and sometimes do not tolerate another eagle close by (428).

Juveniles and subadults and, on rare occasions, adult Golden Eagles may roost together (448, 410). Large numbers of Golden Eagles roosted on power poles on the Idaho National Engineering Laboratory in southeastern Idaho in years when jackrabbit densities were high. On a cold night in early February 1982, over 124 Golden Eagles roosted along a stretch of 85 power poles, with a density of ~5.6 eagles/km and with up to seven on a single power pole (448). These individuals perched within 0.25 m of each other (EHC, T. Craig personal communication).

During winter, pre-adult eagles in Utah often associate with each other (305) and sometimes with Bald Eagles (305, EHC; T. Craig, personal communication). Both species may feed together on the same carcass in south-central Alaska (T. Booms and C. Barger, personal communication), and at camera trapping stations in eastern North America (TEK). The size of a carcass may influence the tolerance of eagles for each other, as smaller carcasses reduce the space between birds and may result in more aggressive interactions. In eastcentral Idaho, Bald Eagles often waited on nearby perches when a Golden Eagle was on a deer carcass and did not feed until the Golden Eagle left (EHC; T. Craig, personal communication).

Eagles occasionally bathe in groups (416, 417) or congregate at bogs for drinking and bathing (385). Kettles of up to 30 individuals have been observed during migration (281).

Social behavior of fledglings and adults is generally non-aggressive before independence (249). During the post-fledgling dependence period, fledgling siblings frequently exhibit non-aggressive social behavior (396). For example, siblings may follow each other, fly, perch, and allopreen. There are few reports of aggression between adults and their offspring. However, in Israel, fledglings sometimes make mock attacks on their parents, and adults sometimes engage in mock attacks against recently fledged offspring (400).

Social behavior and interactions of nestlings often are related to both food solicitation and aggressive or apparently exploratory behaviors (78, 388). Nestlings soliciting food have been observed to lower their head and face an adult while vocalizing (see Sounds and Vocal Behavior: Vocalizations). Nestlings preen and may bite their siblings or adults. The former behavior may help establish a pair bond.

Play

It is difficult to interpret play by eagles. Both adults and young carry sticks, drop them, and then retrieve them while in flight (449, 450, 29). O’Toole et al. (396) observed three different sibling pairs catching and plucking prey together. Adults on breeding grounds sometimes repeatedly carry moss, a clod of dirt, or dead prey to a great height, drop it, then dive after and catch it (390, 451). These behaviors were originally interpreted as play, but they also could be courtship (2).

In southwestern Idaho, Koch (452) observed a juvenile Golden Eagle drop a rock near the location where he subsequently flushed two Dusky Grouse (Dendragapus obscurus). He provided three possible explanations for this behavior including a purposeful intent of dropping a rock to affect the grouse, a deliberate drop of the rock with no specific intent to affect the grouse, and a purely random event. In Spain, a pre-adult Golden Eagle dove with another eagle, then landed, grabbed small stones, flew to a height of 40 m, and slowly released the rocks, all for no apparent reason (453). Nestlings frequently grab at objects in the nest and sometimes at nestmates and parents. These interactions do not appear aggressive but have been interpreted as play (388; see Behavior: Social and Interspecific Behavior: Degree of Sociality).

Golden Eagles sometimes dive at mammals including elk (Cervus elaphus; 322), mule deer (Odocoileus hemionus) and white-tailed deer (O. virginianus; TEK, J. Toynbee, personal communication), caribou (CLM), Dall sheep (Ovis dalli) (CLM; K. Whitten, personal communication), red fox, coyote, wolf, and grizzly bear (454, 455, 456, 457, CLM). The intent of these dives on mammals is not always as evident, but some have been interpreted as play. Murie (455) observed an eagle dive about a dozen times at an adult wolf standing near its den. The eagle barely avoided hitting the wolf, which jumped into the air each time and snapped at the eagle. The eagle always turned upward just before contact with the wolf (455). Hock (457) describes a physical encounter between a subadult Golden Eagle and a red fox that he interpreted as play. The eagle stooped and knocked a fox backward into a shallow pond. The eagle then perched nearby, and the fox came at it at a dead run. At the last possible moment, the eagle took off directly over the fox’s head. Hock (457) suggests that this was not an act of predation by the eagle because there was an abundance of other prey available, including thousands of waterfowl and ample ptarmigan and ground squirrels. Similar observations of the two species were interpreted as predation by Dixon (454) and Rausch (456).

Nonpredatory Interspecific Interactions

Mobbing and Harassment

Many species of birds harass or mob Golden Eagle. In southwestern Idaho, Prairie Falcon (Falco mexicanus) respond aggressively, with vocalizations and chases, towards Golden Eagles that intrude into their nesting territories (345, 458). In the same area, Collopy and Edwards (404) reported non-predatory agonistic interactions with Black-billed Magpie (Pica hudsonia), Common Raven (Corvus corax), American Kestrel (Falco sparverius), Prairie Falcon, Northern Harrier (Circus hudsonicus), and other Golden Eagles. In Denali National Park and Preserve, Alaska, often harassed by Northern Harrier, Short-eared Owl (Asio flammeus), Common Raven, Black-billed Magpie, Gyrfalcon, and Merlin (Falco columbarius) (CLM). Likewise, in the Canadian arctic, nesting Rough-legged Hawk (Buteo lagopus), Peregrine Falcon (Falco peregrinus), Gyrfalcon (Falco rusticolus), and Common Raven may pursue and engage with Golden Eagles (134). Occasionally larger falcons (e.g., Prairie Falcon, Peregrine Falcon, and Gyrfalcon) drive eagles to the ground (459, MNK). This can result in injury or death to the eagle (460, CLM). In one instance, a mated pair of adult Peregrine Falcons attacked and apparently killed an adult Golden Eagle that intruded into their territory in Zion National Park, Utah (460).

Aerial encounters between territorial Golden Eagles and Gyrfalcons can be common during the nesting season, particularly near occupied nests of either species (461, CLM; T. Johnson, personal communication). These encounters can include adults and fledglings of both species, as well as attacks on nestlings or non-territorial subadults. Aerial battles among territorial Gyrfalcons and Golden Eagles often include direct physical contact, vocalizations, and spectacular aerial maneuvering by both species (CLM; T. Johnson, personal communication). In one case, four recently fledged Gyrfalcons and their parents repeatedly dove on a non-territorial subadult Golden Eagle as it flew through their territory in Denali National Park and Preserve, Alaska (CLM). When a Gyrfalcon approached, the eagle often dropped its head to avoid being struck by the falcons. The attacks continued until the eagle flew out of their territory. Similar interactions between the two species were reported in the northern Yukon Territory by Platt (459), including one where an aggressive male Gyrfalcon caused a Golden Eagle nest to fail.

Black-billed Magpies frequently harass and sometimes steal prey from Golden Eagle. Magpies have been seen pulling tail and wing feathers of Golden Eagle feeding on carcasses in Alaska and Idaho, with another magpie grabbing food when the eagle responds to the first (CLM, EHC; T. Booms and C. Barger, personal communication). In another instance in Alaska, two magpies swooped at the head of an adult Golden Eagle that was feeding on an Arctic ground squirrel it had just killed (454). The attack was repeated with increased intensity until the eagle struck back at the magpies. When the eagle did this, it released the dead squirrel, and a third magpie approached on the ground and carried off the squirrel.

Many other species also may attack eagles. In Spain, two adult Egyptian Vultures attacked an adult Golden Eagle that flew about 10 m above their flying fledgling (462). Eagles in flight may ignore attacks from smaller raptor and non-raptor species, or they may roll and extend their talons toward a chasing individual (463, 2, MNK, CLM, EHC). This interaction usually is not fatal, but it can sometimes end in injury or death of the attacking species (e.g., Carrion Crow, Corvus corone; 464). Bald Eagle sometimes attacks Golden Eagle; see Movement and Migration: Migratory Behavior: Flight Behavior During Migration and also Competitive Interactions, below.

Non-aggressive Interactions

Golden Eagle often ignores smaller avian and mammalian species, including some that are taken as prey, that visit or live near their occupied nests. House Finch (Haemorhous mexicanus) have nested in crevices on the underside of an occupied nest in southern California (Sumner 1929). Cliff Swallow (Petrochelidon pyrrhonota), European Starling (Sturnus vulgaris), and Western Kingbird (Tyrannus verticalis) are recorded breeding near occupied eagle nests in southwestern Idaho (Hickman 1967). The kingbirds hunted insects around the eagle nest. Similar observations have been reported in Denali National Park and Preserve, Alaska (CLM). There, Say’s Phoebe (Sayornis saya) occasionally nest near, and forage in, occupied Golden Eagle nests. A juvenile Northern Shrike (Lanius borealis) visited an occupied eagle nest with one nearly-fledged nestling, but only when the parent eagles were not at the nest. Collared pika (Ochotona collaris) colonies are often on talus slopes below occupied Golden Eagle nests, and at least one Arctic ground squirrel colony was directly behind an occupied Golden Eagle nest on a small hillside. Finally, Dall sheep, including ewes with young lambs, often rest, sleep and forage on talus slopes and cliffs ≤ 15 m from occupied Golden Eagle nests.

Competitive Interactions

Some interspecific interactions with other eagle species and larger mammalian carnivores may be related to competition for food. Golden Eagle is dominant over White-tailed Eagle (Haliaeetus albicilla) at carcasses in Norway (428), but the two species do not appear to compete for food in Scotland (465). At moose carcasses during late spring in south-central Alaska, adult Bald Eagle is usually subordinate to a Golden Eagle of any age, but subadult female Bald Eagle was dominant over any age class of Golden Eagle (T. Booms and C. Barger, personal communication). In nearly 1,600 hours of observation at these moose carcasses, there was only one observation of an adult Golden Eagle physically attacking a Bald Eagle (an adult male). Finally, Golden Eagle has been observed to fend off coyotes from carcasses on which the eagles were feeding (325).

Large distances between occupied nests of eagles and of Rough-legged Hawk, Gyrfalcon, Peregrine Falcon, and Common Raven suggest interspecific competition for nest sites or space (134). In the east-central Italian Alps and pre-Alps, Peregrine Falcons avoid nesting near occupied Golden Eagle nests (466). In contrast, Peregrine Falcons and Gyrfalcons in Alaska often use nests originally built by Golden Eagles, and often within 2 km of occupied eagle nests and territories (CLM, EHC). Saker Falcon (Falco cherrug) may use nests of Golden Eagles and other eagle species in central Asia (TEK). In the same area, Golden Eagle and White-tailed Eagle use nests originally built by the other species (TEK). It is possible that non-migratory populations have different levels of tolerance than migratory populations.

Some species of avian scavengers (e.g., Red-tailed Hawk (Buteo jamaicensis), Red-shouldered Hawk (Buteo lineatus), Turkey Vulture (Cathartes aura), Common Raven, American Crow) may avoid feeding on carcasses if Golden Eagles are present (Blazquez et al. 2009, 180, CLM, TAM, M. Lanzone personal communication). The same appears true for mammalian scavengers. During early April in Denali National Park and Preserve, Alaska, a lone wolf sat within 100 m of a partial moose carcass but only visited it when Golden Eagles were not present (CLM).

Kleptoparasitism

Territorial Golden Eagles in the Mojave Desert, Nevada tolerate Common Ravens landing on occupied nests (467). Digital trail cameras documented ravens on Golden Eagle nests in 23 occupied eagle territories, including two nests occupied by eagles. Ravens visited one of the occupied eagle nests 23 times over 20 days, with visit lengths ranging from 1 to 29 min (mean 3 min). During visits, ravens fed on prey items delivered by the adult eagles and on a ~3-week-old eaglet that had died in the nest. They also pecked and harassed the remaining living nestling. Ravens fed on 30% of the prey items delivered to the nest by adult eagles. Only a single raven was detected on the nest at one time, and ravens were not observed on the nest when adult eagles were visible in images. Kleptoparasitism by ravens became less frequent as the nestling developed and stopped when it reached seven weeks of age. After the eaglet fledged, ravens continued to visit the empty nest throughout the remainder of the summer and early autumn. The authors of this report suggested that these observations suggest that some Golden Eagle nestlings could be killed by Common Raven.

Predation

The only record of egg predation of a Golden Eagle in North America occurred near Atlin, British Columbia, Canada when a Common Raven removed an egg from a nest (468). Predation on eagle nestlings is thought to be rare, but Eurasian Eagle-Owl (Bubo bubo), Great Horned Owl, and Common Raven are known to kill nestlings of other large eagle species (TEK).

A female grizzly bear (Ursus arctos) and her two spring cubs walked into an occupied Golden Eagle nest and ate both 10-day old nestlings (L. and D. Keeler, personal communication). The nest was < 10 m above the ground on an easily accessible ledge on a small cliff. The bear may have been attracted to the nest by the odor of fresh and rotting prey remains in the nest (CLM).

The wolverine (Gulo gulo) occasionally preys on nestlings in southwestern Alaska (174), and a wolverine caught and killed an adult Golden Eagle that had been incubating on its nest in northern Sweden (469). Tracks in the snow suggested that the wolverine walked to a shelf immediately below the nest before it killed the eagle. It is not known if the eagle was caught while incubating, or while defending the nest (469).

Other mammalian predators also kill eagles. Evidence from tracks in snow in Idaho suggested that an adult female eagle fed on an elk (Cervus canadensis) carcass, then walked uphill in the snow and was killed by gray wolves (Canis lupus) (T. Craig, J. McFarland, personal communication). Likewise, a telemetered Golden Eagle in New Mexico was killed near the carcass of an ungulate that had been killed by a large cat, probably a mountain lion (Puma concolor). The proximity of the two suggested to observers that the eagle and the ungulate were both killed by the same animal (D. Stahlecker and R. Murphy, personal communication).

Recommended Citation

Katzner, T. E., M. N. Kochert, K. Steenhof, C. L. McIntyre, E. H. Craig, and T. A. Miller (2020). Golden Eagle (Aquila chrysaetos), version 2.0. In Birds of the World (P. G. Rodewald and B. K. Keeney, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.goleag.02