About Morphnus guianensis (Daudin, 1800)
This species, the crested eagle (Morphnus guianensis), is a large but slender eagle. It measures 71 to 89 cm (28 to 35 in) long and has a wingspan of 138 to 176 cm (4 ft 6 in to 5 ft 9 in). A small number of crested eagles have been weighed, ranging from 1.2 to 3 kg (2.6 to 6.6 lb). The average weight of crested eagles in Tikal, Guatemala was reported to be only 1.75 kg (3.9 lb), with a recorded male weight of 1.27 kg (2.8 lb), and a small number of females weighing between 1.85 to 1.98 kg (4.1 to 4.4 lb). Standard measurements show females are about 14% larger on average than males. The crested eagle has a large head, an appearance enhanced by the often extended feather crest that gives the species its name. It has bare legs, with a large tarsus length of 10.3 to 11.2 cm (4.1 to 4.4 in). The tail is fairly long, measuring 34 to 43 cm (13 to 17 in) in length; this long tail partially explains the considerably low weights recorded for an eagle of this size. The wings are quite short relative to the eagle's size, but are broad and rounded. Forest-dwelling raptors often have a relatively small wingspan to allow movement within dense, twisted forest environments. The wing chord measures 42.5–48.5 cm (16.7–19.1 in). The plumage of the crested eagle is somewhat variable. The head, back and chest of most adults are light brownish-gray, with a white throat, a dark spot on the crest, and a small dark mask across the eyes. There are also various dark morphs, where the plumage is sooty-gray or blackish in some cases. Distinctive juvenile crested eagles are white on the head and chest, with marbled-gray coloration on the back and wings. They change to a sandy-gray color in their second year of life. Dark morph juveniles are similar but are dark brownish-gray from an early age. In flight, crested eagles are all pale on the underside except for grayish coloration on the chest. This species often overlaps in range with the more common harpy eagle, which is likely its close relative and somewhat similar in appearance. There is evidence of an unusual interspecific relationship in Panama, where an adult crested eagle fed a juvenile harpy eagle while the adult harpy eagles were away. During these interactions, the crested eagle brought new nesting material to the nest and occasionally brought food to the juvenile harpy eagle.
The crested eagle has a sparse distribution across an extensive range that extends from northern Guatemala through Belize, Honduras, Nicaragua, Costa Rica, Panama, the subtropical Andes of Colombia, northeastern Venezuela, Guyana, Suriname, French Guiana, Brazil (where it has suffered heavily from habitat destruction, and is now found practically only in the Amazonian basin), and east Andean Ecuador, southeastern Peru, Paraguay and eastern Bolivia to northern Argentina. The crested eagle inhabits humid lowland forests, mostly old-growth tropical rainforests. It can also range into gallery strips and forest ravines. Across most of its range, the species is sighted from sea level up to 600 m (2,000 ft). However, in Andean countries, it appears to be a local resident in foothill forests up to 1,000 m (3,300 ft) elevation, or even 1,600 m (5,200 ft). It may show some preference for living near water, including coasts or rivers.
The crested eagle appears to be a still-hunter, as it has been observed perched for long periods of time while visually scanning the surrounding forest. The crested eagle may avoid direct competition with the harpy eagle by generally taking smaller prey. Even so, the crested eagle is a powerful avian predator in its own right, and most studies indicate it is primarily a predator of small mammals. Small monkeys are often represented in its diet, such as capuchin monkeys, tamarins, and woolly monkeys. Data from the Atlantic Forest of Brazil shows that crested eagles focus on small-to-mid-sized monkeys: either adults of small monkeys like squirrel monkeys and tamarins, or small and young specimens of larger species like white-faced sakis and red-faced spider monkeys. Attacked monkeys are usually estimated to weigh from 0.3 to 3 kg (0.66 to 6.61 lb). Other mammalian prey may include many types of arboreal rodents, as well as opossums, sloths and kinkajous. Further studies indicate that compared to other forest raptors, the crested eagle is specialized to hunt small to mid-sized monkeys, and prefers to attack the young of even smaller monkey species such as tamarins. In Tikal, the primary prey appeared to be opossums, from tiny mouse opossums to mid-sized Didelphis species. The largely nocturnal prey taken by crested eagles indicates a thorough searching hunting technique, which overlaps with that of the black hawk-eagle in the region, but not with that of the ornate hawk-eagle there. Despite being smaller, ornate hawk-eagles tend to take larger prey, are more opportunistic, and have a stronger preference for hunting birds. Findings on primary prey in the Brazilian Amazon rainforest were almost the same: crested eagles prefer small opossums and nocturnal animals, which make up about 70% of the diet, and approximately 69% of the diet is mammalian, followed by reptiles and birds. Various studies have also noted that snakes (both arboreal and terrestrial varieties, with several instances of predation on boas reported) and other reptiles (mainly lizards including iguanas) are common in its prey base, but the relative frequency of different types of prey varies greatly between individuals, and reptiles appear to be secondary to mammals. It will also hunt tree frogs. Birds may make up a larger portion of the crested eagle's diet than they do for harpy eagles. Birds such as jays, trumpeters and guans have been observed being preyed upon at fruiting trees, and male cocks-of-the-rock have been preyed upon while displaying noticeably at their leks. However, dietary studies indicate birds are even less significant in the diet than reptiles. Incidents of crested eagles inspecting harpy eagle nests have been reported, and remarkably, an incident of a crested eagle killing a post-fledging young harpy eagle has been reported. The crested eagle is almost always observed singly or in pairs, and is solitary like most raptors. The breeding season starts from March–April (the borderline between the dry season and the wet season in the neotropics). Nests are typically built in the main fork of a large, emergent forest tree. The nest is often very large but has a relatively shallow cup, and is usually concealed near the canopy in greenery. The typical clutch size appears to be two, but only one eaglet has ever been recorded hatching from a crested eagle nest. The eggs are dull white ovals. One recorded egg of this species measured 64 mm × 50.7 mm (2.52 in × 2.00 in) and weighed 90.5 g (3.19 oz). Growth rates appear to be typical for a forest eagle: initial wing quills emerge at about 21 days, primary feathers emerge from their sheaths at about 4 weeks, and fledging occurs at about 100 to 110 days. Female crested eagles are reported to be diligent about sitting on and feeding chicks, and also shield chicks from harsh sun or rain, while the male primarily delivers food, announcing his presence with a loud call. Even after fledging, the young crested eagle is still fully reliant on its parents, and evidence indicates it may take from 16 up to perhaps 30 months before the eagle becomes fully independent. This means crested eagles can typically breed only every other year, which is typical for tropical, especially forest-dwelling, eagles.
