Bonnet eagle
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Bonnet eagle ( Spizaetus tyrannus ) |
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| ( Wied , 1820) |
The tyrannical hooded eagle ( Spizaetus tyrannus ), sometimes just a tyrannical eagle , is a large bird of prey from the hawk-like family . It lives in an extensive range in South and Central America, but is considered a rather rare species.
features
Bonnet eagles are relatively large birds, between 64 and 71 cm tall and can weigh more than 1000 g. The rarer subspecies S. t. tyrannus can get a little bigger and heavier. Males tend to be a bit smaller and lighter than their female counterparts, but there is no more extensive sexual dimorphism on the basis of which the sexes can be differentiated. The wings are relatively short and wide, which makes it easier to maneuver within the forest. Their tips are rounded, the hand wings are wide apart. At the base, the wings are slightly narrowed, which, in combination with the posture that is slightly stretched forward in flight, gives them an appearance reminiscent of butterfly wings. Further striking features are the relatively long tail and the feathered legs characteristic of the genus Spizaetus . The short, strong beak is strongly curved. At the back of the head there is an easily recognizable, bushy hood . The plumage shows a black basic color, the contour feathers on the underside as well as the legs are striped black and white. White spots can also be found at the base of the feathers on the back of the head. On the control springs, the black is interrupted by three broad, grayish stripes. A black and white stripe pattern on the underside of the wings can only be seen in flight. The iris of the eye is yellowish to amber, the wax skin is slightly grayish.
Juvenile specimens show a generally brownish color, which is interspersed with white spots and stripes of varying degrees. On the underside, the young birds also have a black pattern, which becomes increasingly dominant towards the sides. Particularly noticeable are a white stripe over the eyes and the completely white throat area.
Confusion with the closely related magnificent hooded eagle ( Spizaetus ornatus ) can occur, since the appearance and especially the flight pattern of the two species are superficially similar. However, a clear distinction is possible on the basis of the rounder wings, the longer control feathers and the generally darker plumage of the tyrannical hooded eagle.
behavior
Tyrannical crested eagles lead a largely solitary way of life outside of the breeding season . They are usually spotted on gliding flights high above their territory, which can last up to ten minutes and are usually undertaken in the morning or early noon. Typical during these flights is frequent and loud shouting, which is presumably intended to be used to demarcate one's own territory. For this a minimum size of about 10 km² is assumed. The species is considered a resident bird that does not take part in the annual bird migration .
nutrition
Boned eagles feed on a purely carnivorous diet, with small to medium-sized mammals making up about 95% of the diet. A number of bat species alone account for around half, including the Jamaican fruit bat and the great fruit vampire . There are also possums , squirrels and young coatis, as well as birds up to the size of a toucan . Reptiles no longer seem to play a role in adult tyrannical hooded eagles, but are apparently very sporadically fed to nestlings. There is also a single description of a young bird that was observed taking in the feces of a raccoon shortly after leaving the nest. According to the researchers, these contained the remains of crustaceans and fish scales. The apparently very variable and opportunistic hunting method of the species is noteworthy. It is known that tyrannical hooded eagles are on the one hand stalking hunters who sometimes wait almost motionless for hours at a waiting room for prey. If it is spotted, the birds rush down with a surprisingly quick movement for their size and strike the prey with their claws stretched out forward. In addition, hooded eagles look for resting places for nocturnal animals during the daytime and plunder them. Apparently this seems to be the preferred hunting method: the observed ratio of nocturnal to diurnal prey is around 70:30, while tyrannical crested eagles are only active during the day.
Reproduction
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Only a single report from February 1989 from the highlands of Guatemala is available for the courtship behavior of the tyrannical hooded eagle . He describes courtship as a complex display during the flight that consists of a series of flight roles and contacts between the partners. Copulation then takes place several times, sometimes several times within a few minutes, but each only lasts a few seconds. The nest is erected on a tree at a height of 23 to 28 m, the structure is often at least partially supported by balls of tendrils . Branches in the shade are preferred to protect eggs and offspring from direct sunlight. In general, the nest is inconspicuous and difficult to make out for the observer. After completion, the female typically lays a single, and in exceptional cases two, eggs. The white eggs, speckled with brown spots, are around 60 × 50 mm in size and weigh around 75 g, their incubation time is around 44 days. The female is solely responsible for the incubation and is provided with food by her partner during this time. However, until the young hatch, the adult male birds only stay in the immediate vicinity of the nest for a short time. After hatching, the nestlings are initially still covered by white down, which is replaced after about 34 days by a first, predominantly black plumage, only in the head area it remains white. The first real feathers appear after about eleven days. In the first week the young tyrant hawk eagle are almost entirely from the mother brooded , but thereafter quickly shows a change in behavior in the female adult bird, which now leaves the nest increasingly frequent and returns after about 40 days only for food delivery. Particularly from this phase of the frequent absence of the parents, there are regular reports of spider monkeys approaching the nest and showing pronounced bullying behavior towards the nestlings. This manifests itself in the destruction of the nest construction or the attempt to throw the young birds out of the nest. These react with threatening gestures and loud calls for the adult birds, which are remarkably passive towards the monkeys. The reasons for the aggressiveness of these monkey species towards tyrannical bonnet eagles are unknown. The nest is abandoned after an average of nine to ten weeks, but the young birds remain dependent on their parents for another year. Successful couples can therefore only raise a brood every other year.
Vocalizations
The call of the bonnet eagle is described as a series of loud, whistling noises that should sound like wheep - wheep - wheep , followed by a wahee - he sloping towards the end . As a rule, it can only be heard in adult birds when they are in flight; the species tends to be quiet at sleeping or feeding places.
Spread and endangerment
The species inhabits a large, two-part distribution area, the northern part of which extends from the Mexican states of Tamaulipas and Guerrero to the north of Bolivia, Paraguay and Argentina. There is also a smaller area in southeastern Brazil and northeastern Argentina. Mainly lower-lying, flat regions are settled up to an altitude of about 1000 to 1300 m. In Guatemala, however, there have been sightings from altitudes of up to 3000 m. The habitat is mainly moist, evergreen forests, but the observations of various researchers suggest that the species can also cope with more open landscapes. The hooded eagle is considered to be rare to moderately frequent, depending on its location, but the IUCN classifies the species as not endangered as of 2016 (status least concern ). The organization assumes a total population of less than 50,000 specimens, the population trend is generally declining. The ongoing deforestation of the South American forests is considered to be the greatest threat to the survival of the species. In addition, the large, conspicuous birds are regularly shot by farmers who perceive the tyrannical crested eagle as a threat to their chickens. However, it is not certain whether the species actually hunts domestic fowl.
Systematics
The first description of the tyrannical hooded eagle dates back to 1820 and goes back to the German naturalist Maximilian zu Wied-Neuwied , who published it as part of his book Reise nach Brasil from 1815 to 1817 . He originally named the species as Falco tyrannis and initially placed it among the falcons . In addition to the nominated form S. t. tyrannus still the smaller subspecies S. t. serus is considered valid, which, however, inhabits the significantly larger part of the distribution area. So is S. t. tyrannus only known from the southeast of Brazil and the extreme northeast of Argentina, while the entire rest of the distribution area is on S. t. serus is not applicable. The relationships within the genus Spizaetus and the entire subfamily Aquilinae are complex and are still the subject of scientific debate. Among other things, recent molecular genetic studies confirm the monophyly of the Aquilinae, but cast this into doubt for various genera belonging to it - including Spizaetus . Changes in the taxonomic classification of the hooded eagle and its relatives cannot be ruled out in the near future.
- S. t. tyrannus ( Wied , 1820)
- S. t. serus Friedmann , 1950
literature
- David F. Whitacre, Juventino López, Gregorio López: Neotropical Birds of Prey: Biology and Ecology of a Forest Raptor Community . Ed .: David F. Whitacre. Cornell University Press, Ithaka / London 2012, ISBN 978-0-8014-4079-3 , pp. 185-201 .
Web links
- Recordings of vocalizations at xeno-canto.org
Individual evidence
- ↑ a b c d e Steven L. Hilty: Birds of Venezuela . Princeton University Press, Princeton 2002, ISBN 978-0-691-09250-8 , pp. 247 .
- ↑ Whitacre, López & López, pp. 185-186
- ^ Whitacre, López & López, p. 197
- ↑ a b Whitacre, López & López, p. 200
- ↑ a b Whitacre, López & López, p. 187
- ↑ Whitacre, López & López, pp. 186-189
- ↑ Jay P. Vannini: Neotropical raptors and deforestation: Notes on diurnal raptors at Finca El Faro, Quetzaltenango, Guatemala . In: The journal of raptor research . tape 23 , no. 2 , 1989, pp. 27-38 .
- ↑ Whitacre, López & López, pp. 192-193
- ^ Whitacre, López & López, p. 191
- ^ Whitacre, López & López, p. 196
- ↑ Whitacre, López & López, pp. 196-197
- ^ Whitacre, López & López, p. 192
- ↑ Black Hawk-eagle Spizaetus tyrannus. In: iucnredlist.org. BirdLife International, 2016, accessed September 7, 2020 .
- ^ Maximilian zu Wied-Neuwied: Journey to Brazil in the years 1815 to 1817 . The Other Library, 2015, ISBN 978-3-8477-0017-3 , pp. 360 .
- ^ Whitacre, López & López, p. 185
- ^ Lerner et al .: Phylogeny and new taxonomy of the Booted Eagles (Accipitriformes: Aquilinae) . In: Zootaxa . tape 4216 , no. 4 , 2017, p. 301-320 , doi : 10.11646 / zootaxa.4216.4.1 .