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



The breeding period extends for a year, from courtship to juvenile dispersal. Clutch size is one egg. Usually a single chick is raised every year, although in the long-term pair productivity is about 0.5 chicks per year. When conditions are appropriate, eagles try to breed yearly. For example, nine consecutive breeding attempts have been recorded in nine years in a nest in Argentina, with seven successful and two unsuccessful breeding attempts (JMG et al., unpublished data). Thus, an adult pair may be seen copulating or even incubating while the last juvenile is still in the breeding territory, although most often it is chased away by the parents before egg-laying (SK and TRF, unpublished data).

Based on available data, the courtship period extends for two to three months ( Kohn et al. unpublished data, TRF unpublished data), the incubation period extends for 51 d (Grande et al., unpublished data), chick-rearing has a duration of about 3.5 months, and the post-fledging period extends for about 4–5 months (37, 40, TRF, unpublished data).


Breeding phenology varies throughout its range and even between years for the same pair. Climatic factors (mainly precipitation rates) and not latitude are primarily related to the phenological variation in the species (JG, unpublished data), and, as with many tropical species, the incubation and brood rearing periods usually occur during the dry season (14, 40, 41, 37).


Generally, nest building is February–March, incubation March–May, hatching in May, and chick-rearing May–August (52).


In a nest located in the western Andes in Nariño, incubation began in May, at the end of the wet season (52). In Huila, in the central Andes, a nest was built between February and March, with chick rearing between May and late July (14). A nest located in Farallones de Cachalá y Medina, Cundinamarca on 14 March contained a 6-week-old chick (40), which allows the courtship period to be estimated between October and December, incubation from mid-December to late January, chick rearing from late January to early May, and the post-fledging period between mid-May to September.


Phenology at 15 nesting sites found during 2019 in Baños de Agua Santa (central Andes) was as follows: Courtship began in early May; incubation started from early or late May to early or mid-July; chick rearing took place from early or mid-July to early or mid-October; the post-fledging period extended through mid-March (Rivas-Fuenzalida et al., unpublished data). However, great variability in the same nests were detected between years; in 2020, incubation took place between early November and mid-December (Kohn et al., unpublished data). In two nests found in 2019 near Baeza (northeast Andes), incubation occurred between late August to early October with chick rearing from early October to late December; the post-fledging period was from late December to late April (Rivas-Fuenzalida et al., unpublished data). In a nest found in the inter-Andean valley of Pichincha in 2018 (northern Andes), courtship took place between April and August; incubation occurred from mid-August to late September; the fledging period was between late September and early October; the post-fledging period extended from early October to early February. In two nests located near Pimampiro, an inter-Andean valley (northern Andes), both pairs ended the post-fledging period in early to mid-July (Rivas-Fuenzalida et al., unpublished data).


The nesting period occurs during the dry season, and juveniles become independent toward the end of the wet season. Data from 14 nests in the central Andes (Rivas-Fuenzalida et al., unpublished data) indicated the following phenology: the courtship period was between early February to early or mid-June; incubation occurred between early or mid-June to mid or late July, but in some cases as early as mid-March; chick-rearing occurred from late July or early August to late October; the fledging period occurred from early August to early November; and the post-fledging period extended from mid-August to late March or early April. A nest located on Manu road had a recently fledged juvenile in the nest in early October (T. Ludwick, eBird).


Incubation was recorded in May for a single nest (14), which matches with the phenology of a nest in northwestern Argentina (37).


For eight years, egg laying occurred from late April to early September without a clear peak in the period, but it always occurred during the coldest and driest months of the year (37). Nestlings hatched between the third week of June to the last week of October; fledging occurred at 3.5–4 months of age, from early October to mid-February, such that fledging and dispersal mostly coincided with the rainy season.

Nest Site

Black-and-chestnut Eagle uses steep, forest-covered sites at elevations ranging from 1,300 to 2,900 m where they usually select tall emergent trees (taller than surrounding canopy) to build their nests, which can be surrounded both by old-growth or secondary forest; nests are often placed 16–35 m above the ground (14, 52, 37, 41, TRF, unpublished data).


In Peru, 15 nest sites were located at elevations ranging from 1,300–2,330 m (mean of 1,821.3 m), and were relatively close to permanent water courses (mean distance of 381.3 m), open areas (mean distance of 286 m), and human activity (mean distance of 822 m). The slope at nest sites averaged 36.2°, and they had no particular cardinal orientation (Rivas-Fuenzalida et al., unpublished data). Nine nests have been observed in Argentina, all within the montane cloud forest in the Yungas, at elevations between 1,350–1,940 m. Similar to the nests reported in Peru, Argentinean nest were a short distance from water courses (20–480 m), open areas (30–920 m), human activity (30–1,300 m) and on steep slopes (37, TRF, JMG and SZ, unpublished data).

A nest found in Farallones de Gachalá y Medina, Cundinamarca (Cololmbia) was located at 2,038 m within a 309 ha forest remnant surrounded by pastures. This forest patch was connected by three thin forest corridors (each approximately 75 m in width and 1,000 m in length) to a larger patch of contiguous dense natural forest approximately 52,287 ha in size. Within a 0.5 ha buffer surrounding the nest tree, tree density was 947 trees/ha and trees had a mean diameter at breast height (dbh) of 0.51 m ± 0.67 (SE). Canopy cover was 53%, slope inclination was 368, and the slope faced south-southeast (41). Another nest located in Fomeque, Cundinamarca, was situated on the edge of a forested corridor connected to a larger patch of continuous dense natural forest and was at 2,561 m. Within the 0.5-ha buffer surrounding the nest tree, tree density was 78 trees/ha, and trees had a mean dbh of 0.62 m ± 0.25 m (SE). (41). In Ecuador, a nest located in Intag Valley, Imbabura, was in a secondary forest remnant, connected to a larger mature forest by ravine forest corridors. The nest tree was at 2,241 m. Within a 0.5 ha buffer surrounding the nest tree, tree density was 2,568 trees/ha, and trees had a mean dbh of 0.29 m ± 0.14 m (SE) (41). A nest in Bolivia was reported on a montane slope covered by dense forest at 2,340 m (14).

Site Characteristics

In Peru, 15 nests were positioned at the top (28–40 m) of tall emergent trees (height 25–37 m, dbh of 0.53–1.52 m) of nine genera: Eriotheca, Ceiba, Brosimum, Juglans, Pachira, Ficus, Erythrina, Cedrela, and Ocotea (Rivas-Fuenzalida et al., unpublished data). In Colombia, a nest studied in Farallones de Gachalá y Medina, Cundinamarca was in a 48 m tall emergent fig (Ficus sp.), and having a dbh of 3.06 m; the nest was located 43 m above the ground, in a fork of a secondary and two tertiary branches, where the angle of the main branch supporting the nest was 55°. Another nest studied at Fomeque was in a 22 m tall emergent tree (species unknown) that had a dbh of 0.76 m; the nest was located 16 m above the ground, in a fork of one primary and two secondary branches, where the angle of the main branch supporting the nest was 105° (41). In Ecuador, a nest found in Intag Valley was in a 35 m tall emergent cecropia (Cecropia telealba) with a dbh of 0.66 m; the nest was located approximately 30 m above the ground, in a fork of one primary and five secondary branches, where the angle of the main branch supporting the nest was 90° (41). In Argentina, one nest was located 22 m above the ground in the fork of secondary branches in a walnut tree (Juglans australis); two additional nests were 25 m above the ground in a cedar (Cedrela sp.) and 30 m above the ground in a tipa (Tipuana tipu), respectively (37).


Structure and Composition

Nests are large circular or oval structures made of large, dry branches, while the inner cup is lined with sprigs of green leaves (37). Nests are located at the top or in the center crown of large emerging trees, from which eagles have unobscured views of their territory.


In Peru, nest platforms were ca. 1–1.5 m in diameter and had a depth of 50–80 cm (Rivas-Fuenzalida et al., unpublished data). Two nests in Colombia measured 1.1 m x 1.3 m in diameter and 0.6 m in depth, and 0.9 x 1.4 m in diameter and 0.52 m in depth, respectively (41). One nest in Ecuador was about 1.2 m x 1.5 m in diameter and 1 m in depth (41). In Argentina, one nest was 1.5 x 1.2 m when it was first measured, but later measured 2 x 1.8 m after 7 years (37).

Maintenance and Reuse of Nests

Relatively little information, but one nest in Argentina was expanded over a 7-year period, probably by the same pair (37).



A single egg was described as spheroidal in shape (14).


One egg recorded as 51 x 33.58 mm (14).

Color and Surface Texture

In Colombia, one egg was described as white with a wash of chocolate-brown spots (14). A review of photographs of eggs from Argentina, Peru, and Ecuador showed most were white with no or very few tiny pale brown spots, though one in Ecuador was chocolate-brown in color (n = 11) (SK, TRF, JMG, unpublished data).

Clutch Size

All recorded clutches have been of one egg (14, 37, SK, TRF, SZ, JMG, unpublished data).


Incubation Period

The incubation period was 51 d in two consecutive years at a nest in northwest Argentina (Grande et al., unpublished data).

Parental Behavior

Almost all incubation is done by the female, including all nocturnal incubation. The male only incubates for very short periods of time when the female leaves the nest to feed (Grande et al., unpublished data).


Information needed.

Young Birds

Condition at Hatching

At hatching, chicks are covered in white down with a black mask between the eyes and the beak.

Growth and Development

Molt into Juvenile Plumage

Primaries start to appear at 30 d, with scapulars at 35 d, which become very noticeable at 40 d when the first wing coverts also begin to appear on the upper part of the wrist. At 45 d, the dorsal area begins to be covered with feathers, although in lower density than in the upper part of the wings. At 48 d, the shafts of the rectrices are observed, together with the first supracaudal feathers. At 50 d, the dorsal neck and crown feathers begin to grow. At 60 d, the remiges are of considerable length, the rectrices are also more noticeable, both the neck and the crown are largely feathered, and the chest and tarsi feathers are becoming more noticeable. By day 70, the young bird is almost fully feathered, although with many remnants of down scattered throughout the body, especially on the abdomen and legs. There are very noticeable brownish feather patches on the flanks and legs. At 80 d, two dark bands are clearly visible on the tail, the crown crest is highly developed, and the remiges almost reach their final length. At 90 d, the sides of the neck and tarsi are darker and very few patches of down remain. Both the remiges and rectrices have reached their full length (Grande et al., unpublished data).


During the first 10 days of life, the young bird spends most of its time lying in the nest or sleeping. At 12–15 d, the chick can moves around the nest on its own to either escape the heat or warm themself. At 30 d, it wanders over a large part of the nest, walking with difficulty, and making small flaps. At 40 d, it becomes more active and spends more time standing and looking around the nest and preening. At 45 d, it begins to play with objects inside the nest, trying to "hunt" them, and attempt to eat on its own. At 50 d, it eats several times by itself and runs around the nest more frequently. At 60 d, it will leave the nest and explore a large part of the nest tree, climbing up the branches and taking small flights of up to 5 m. It spends most of the day alone and pecks lichens, mosses, and epiphytes from the branches of the nest tree, dropping them to the forest floor. The young bird flies out of the nest tree at around 13 weeks (TRF, unpublished data).

Parental Care

There is marked task separation between the sexes. Almost all parental care and nest maintenance are carried out by the female: she contributes more to repairing and lining the nest, performs most of the diurnal incubation (only alternating with the male for very short time periods for feeding) and all the nocturnal incubation, and broods the chick.


The female is responsible for brooding the chick, and broods the chick regularly until about 45 days of age. After 45 d, brooding time is adjusted based on temperature, probably until the chick is able to thermoregulate on its own, at which point the female no longer broods the chick. The female stays near the nest at almost all times until the chick is at least around 100 days old, rarely venturing farther than 200 m from the nest. She emits alarm calls when other raptors get very close to the nest (e.g., Plumbeous Kite (Ictinia plumbea), Andean Condor (Vultur gryphus), Turkey Vulture (Cathartes aura), and Black-chested Buzzard-Eagle (Geranoaetus melanoleucus)). She also directly attacks and physically strikes researchers when they climb the nest tree, suggesting that she may behave similarly toward terrestrial predators that climb trees.


The male provides most of the food for the female and the nestling through most of the breeding period (53, TRF, SZ, JMG, unpublished data).

Cooperative Breeding

Not reported.

Brood Parasitism by Other Species

Not reported.

Fledgling Stage

Departure from the Nest

The young eagle leaves the nest at 13 weeks, but still uses the nest to feed for at least 4 more weeks (37, 40, Rivas-Fuenzalida et al., unpublished data).

Association with Parents or Other Young

Young are dependent on adults until at least 28 weeks of age (40). During the fledging period, the young eagle spends most of the time perched (58%), followed by feeding (19%). During the post‐fledging period, it spends more time flying (40%), although the time spent perched is also important (38%) (40).

Immature Stage

Little studied. Juveniles begin to disperse when they are between 8 and 15 months old (40, SZ and JMG, unpublished data). During their natal dispersal, they wander across large areas, reaching distances of up to 60 km from the nest. While they usually settle in different areas far from their natal territory, some tracked juveniles visited their natal nest again before establishing their own territory (54). An immature eagle tracked for up to four years established its own territory when it was around three years old (SZ, unpublished data). In northwestern Argentina, a pair formed of three-year-old individuals was observed copulating and building a nest (TRF, unpublished data).

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