SPECIES

Black-and-chestnut Eagle Spizaetus isidori Scientific name definitions

Tomás Rivas-Fuenzalida, Juan M. Grande, Sebastián Kohn, Felix Hernán Vargas, and Santiago Zuluaga Castañeda
Version: 2.0 — Published November 23, 2022

Behavior

Locomotion

Walking, Hopping, Climbing, etc

Occasionally walks on the ground. Adults and juveniles can be seen climbing and hopping between tree branches to find better vantage points (TRF, JMG, SK, FHV, SZC, unpublished data).

Flight

Wing beats are slower than those of other species in the genus Spizaetus. Flight is distinguished by U-shaped (dihedral) positioning of the wings, with the wing tips exaggeratedly guided upwards while soaring, less so while gliding. During courtship or aggressive territorial encounters, the eagles can perform acrobatic maneuvers at high speed, flying up and down in a coordinated fashion and occasionally interlocking talons and holding on to each other as they fall towards the ground (TRF, JMG, SK, FHV, SZC, unpublished data).

Self-Maintenance

Preening, Head-Scratching, Stretching, Bathing

Preens mainly in early morning and afternoon, but also when perched at other times. The eagle preens in a typical manner, similar to other birds, using the uropygial gland to waterproof the plumage. To perform this maneuver, it brings its bill towards the gland while lifting and opening its tail a little, to coat the bill in oil and then spread it throughout its plumage. It uses its claws to scratch its head, neck, and throat. It stretches like other birds, with a leg or wing extended downward and dorsolaterally, one at a time. Bathing has not been observed, but is assumed to be similar to other raptors (TRF, JMG, SK, FHV, SZC, unpublished data).

Sleeping and Roosting

Roosts on dry or leafy branches, utility poles, trees, sometimes on the ground or on rocks, usually singly, but sometimes in pairs, especially near the nest. Sleeps in a typical bird sleeping position, usually standing on one leg with head tucked back between tertials (TRF, JMG, SK, FHV, SZC, unpublished data).

Agonistic Behavior

Territorial Behavior

Little studied. Slow gliding over the crest of elevated mountains probably allows eagles to mark their territory and prevent intruders from entering it. However, when an intruder does enter a territory, both birds fly high and display their claws, chase each other, and perform acrobatic flights with steep dives, similar to courtship flights and with the aim of showing occupation of the territory. Adults also expel their own young of the previous season or other juveniles from their territory through grazing attacks and even claw hooking (TRF, unpublished data). As in other birds of prey, adults usually show greater aggression towards individuals of the same sex (TRF, unpublished data).

Sexual Behavior

Courtship, Copulation, and Pair Bond

Monogamous. As the breeding period extend for about a year, pair bonds usually are maintained throughout the year. During the entire breeding period, the adult pair communicates by vocalizing around the nest site. During courtship, both members of the pair soar over the nesting area with their legs hanging downwards. The male follows the female from above, trying to catch her in the middle of the air, while the female turns around, holding her claws upwards, facing those of the male. Sometimes this results in aerial cartwheeling (27, TRF, unpublished data). After a few flights, the female swoops down to the top of a large tree (sometimes the nest tree), followed by the male. They immediately copulate, perched on a large horizontal branch or directly on the nest, and frequently then begin to carry branches to the nest (TRF, unpublished data).

Social and Interspecific Behavior

Degree of Sociality

In Peru two immature individuals have been seen flying and moving together between the edges of occupied nesting territories (TRF, unpublished data). Pair bond usually are mantained throught the year (TRF, JMG, SK, FHV, SZC, unpublished data).

Nonpredatory Interspecific Interactions

Black-and-chestnut Eagle is known to prey upon other raptors, including hawks, falcons, and caracaras (48, 37, 49, SK et al. unpublished data, TRF unpublished data). Likely because of this, they are often chased by other smaller raptors while soaring, such as Orange-breasted Falcon (Falco deiroleucus), Peregrine Falcon (Falco peregrinus), White-tailed Hawk (Geranoaetus albicaudatus), Black-and-white Hawk-Eagle (Spizaetus melanoleucus), Short-tailed Hawk (Buteo brachyurus), Barred Hawk (Morphnarchus princeps), Red-throated Caracara (Ibycter americanus), and Crested Caracara (Caracara plancus).

The species is not usually aggressive towards other raptor species itself, unless they get too close to their nesting site during the breeding season (27; TRF, unpublished data). In Ecuador and Argentina, the species did not show any aggression towards a Solitary Eagle (Buteogallus solitarius) when it flew near its nesting sites (TRF, unpublished data). In Argentina, three different eagles were seen attacking adult Andean Condor (Vultur gryphus) that flew near their breeding site (TRF and SZ, unpublished data). Also in Argentina, a female covered the chick and cried loudly in an aggressive position in response to flyover Andean Condor, Black-chested Buzzard-Eagle (Geranoaetus melanoleucus), and Turkey Vulture (Cathartes aura). In Ecuador, a juvenile eagle was seen attacking Turkey Vulture, apparently as a game or training to hunt (TRF, unpublished data). In Peru, Turkey Vulture was also attacked near the eagles´ nesting site (27). Juveniles have also been observed "attacking" people (for example, while on ziplines in the canopy, riding a motorcycle in Ecuador, and while walking on a mountain trail in Peru) but without making physical contact, possibly as a game to develop hunting skills. Adults have also shown aggressive behavior towards humans on some occasions during the breeding season, or when people have attempted to climb the nesting tree during the day (TRF, JMG, SK, FHV, SZC, unpublished data).

Predation

No predators are known for this eagle. Terrestrial predators such as canids, felids, or mustelids could presumably prey on fallen chicks or injured/diseased adults on the ground, but this has not been documented. A tayra (Eira barbara) was recorded exploring a nest of the species outside the breeding season in Argentina (JMG, unpublished data), so this large carnivore could pose a threat to young and adult eagles at the nest.

Recommended Citation

Rivas-Fuenzalida, T., J. M. Grande, S. Kohn, F. H. Vargas, and S. Zuluaga Castañeda (2022). Black-and-chestnut Eagle (Spizaetus isidori), version 2.0. In Birds of the World (S. M. Billerman, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.baceag2.02