Aguja

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Aguja
Portrait of an agujas of the subspecies Geranoaetus melanoleucus australis

Portrait of an agujas of the subspecies Geranoaetus melanoleucus australis

Systematics
Class : Birds (aves)
Order : Birds of prey (Accipitriformes)
Family : Hawk species (Accipitridae)
Subfamily : Buzzard-like (buteoninae)
Genre : Geranoaetus
Type : Aguja
Scientific name
Geranoaetus melanoleucus
( Vieillot , 1819)
Aguja in Ecuador
Aguja in flight
Agujas in their youthful dress look typically brown like a buzzard

The Aguja ( Geranoaetus melanoleucus , also Blue Buzzard , Kordillerenadler or the Aguja, from Portuguese águia = Eagle) is a bird of prey from the subfamily of the buzzard-like (Buteoninae). It occurs along the Andes and in other, climatically more moderate parts of South America . It inhabits open and semi-open landscapes of all kinds and populates mountain regions up to heights of at least 3000 meters. The prey consists mainly of small and medium-sized mammals, but also birds and insects. He builds his eyrie on cliffs, in tall trees or cacti.

description

Agujas reach about the size of a greater spotted eagle with a body length of 60–76 cm and a wingspan of 149 to 184 cm . Males weigh around 1700 g, females 2300 g. They are among the largest and most powerfully built buzzards. The beak is relatively large and high, but not eagle-like. The iris is brown, the wax skin pale yellow as are the featherless legs. The wings are long and wide and have very wide margins at the base, the tail is short and wedge-shaped to rounded. Females are significantly larger and heavier than males.

In adult birds the head and upper side are bluish slate gray to blackish or dark soot brown. The upper breast is also colored and clearly distinguishes itself from the white underside. The longer, more pointed feathers have fine white tips on the chest, neck and upper back, and the arm wings are banded. Cheeks and throat are somewhat lightened; Shoulder plumage, small and medium arm covers are ash gray with fine dark banding and black shaft lines. The control feathers are blackish with a fine white border. The underside is white up to the under tail-coverts and including the leg fletching and, depending on the subspecies, unmarked or finely banded dark.

Young birds appear brownish like buzzards. They are blackish brown on top with cinnamon-colored to whitish dots on the head and upper back, light stripes above the eyes and beige to reddish light brown, dark dotted or spotted throat and chest. Back, shoulder plumage and upper wing coverts are lined with beige to reddish light brown. The lower abdomen and under wing-coverts are more or less densely banded dark up to a monochrome dark brown. The control feathers are cloudy gray-brown with blackish banding. It takes several years for immature birds to become fully colored. Until then there are several transitional dresses.

distribution

Distribution area of ​​the agujas

The aguja is native to the climatically more moderate regions of the Neotropic . Its patchy distribution extends on the one hand along the Andes. In Venezuela the species occurs in the Cordillera de Mérida , in Colombia mainly in the Cordillera Oriental , but also in the Cordillera Occidental from Cauca southwards. The distribution then extends over Ecuador and Peru , where the species also inhabits the coastal hill country, over Bolivia , Chile and Argentina to Tierra del Fuego . The area also extends from the east and south-east of Bolivia via Paraguay and the south and east of Brazil. There, in the regions near the Atlantic, it extends at least to Bahia , if not even to Piauí and Paraíba . It extends south through Uruguay and into eastern Argentina.

Geographic variation

Two subspecies are recognized, of which the nominate form , which is widespread to the east, is on average larger and on the underside pure white, the form G. m , which occurs in the Andes . australis, however, finely banded with dark transverse bands. In the latter subspecies, a clinical (gradual) increase in size towards the south and increasingly stronger banding from 25 ° N can be observed. The northern part of the population was therefore sometimes called G. m. meridensis delineated.

  • G. m. australis Swann , 1922 - from northwestern Venezuela along the Andes south to Tierra del Fuego
  • G. m. melanoleucus ( Vieillot , 1819) - eastern and southern Brazil to Paraguay, Argentina and Uruguay

There may be a rare, dark morph that is sooty black with gray leg fletching. However, this is only known from one copy.

Habitat

The aguja populates light dry forests , tree savannas with pseudo-beech trees, transitional habitats between dry forest and pampas ("Espinal"), savannas and pastureland, as well as partly semi-desert scrubland such as Monte . It is particularly common in rocky mountain landscapes with gorges and adjacent grasslands, but rarely rises to the Páramo . In Peru, it predominantly populates the relatively dry habitats in valleys and on the western slopes of the Andes, while it is mostly rare on the more humid, east-facing slopes. The altitude distribution usually extends from up to 3500 m above sea level, but in Colombia only begins at 1600 m, in Chile only extends up to 2200 m and in Venezuela sometimes above 4500 m. Sometimes the species can also be found in higher altitudes.

nutrition

The aguja feeds on smaller mammals , birds and their nestlings, snakes and lizards, carrion, insects and other invertebrates . Mammals make up at least 80% of the prey. These mainly include bush rats , guinea pigs , skunks , Andean jackals and viscachas as well as the brown hares and wild rabbits introduced in parts of South America . The weight of the prey is up to 2 or 3 kg. In a Chilean study, wild rabbits accounted for 44% of the prey in terms of numbers and even 82% in terms of weight; in northern Argentina, brown hares provided most of the food. In the case of birds, the prey spectrum ranges from the owl rabbit to the Chilean partridge to the penelope chickens . In Brazil, 81% of city ​​pigeons were found to be prey in one nest .

The aguja hunts mainly out of flight - either circling or in longer gliding flights, hanging in the wind or occasionally shaking - and descends on its prey in a dive. It is also rather seldom to be seen hunting from high seat. The main activity falls in the morning and afternoon; only in winter do the birds spend most of the day in flight. The species can often be seen hunting in pairs and exploits the thermals on mountain ridges facing north and west. It appears that insects are sometimes hunted on foot, and sometimes the rust potter's nests, which are formed from dried mud, are broken open to prey on the nestlings. Agujas have been observed chasing collar swifts and catching swarming leaf cutter ants of the Atta genus from the air. They also hunted Chimangokarakara's remains of prey.

Reproduction

The breeding season of the agujas is between February and August in Venezuela and between September and April in Ecuador. However, with birds flying out between April and mid-July in southern Colombia, the species may breed on the equator all year round. In Peru it breeds between May and October, in central Argentina and Chile, however, between September and January and further south between October and February and thus during the summer months there.

The massive nest made of twigs measures around 85 cm in diameter and can grow to 100 to 160 cm over the years. It usually stands on ledges or ledges in steep rocks, but sometimes also in tree tops, on electricity pylons, on saguaros or other large cacti, lower bushes or even on the ground. It is usually re-used over a number of years, but often rebuilt at another location after a while, so that it is not uncommon for several nests to be found within a radius of 150 m around a long-term breeding site. Courtship flights and copulations usually take place over a period of two weeks.

The clutch consists of two, more rarely one or three eggs, which are incubated between 37 and 40 days. The downy boys are white. In Brazil, the nestling period was 56 days, in central Chile around 59 days. The boys only become independent after about 10 months.

The breeding success in northern Argentina was 1.1 youngsters flown out per breeding attempt and 1.8 for successful broods. 63% of them were successful.

Duration

Not much is known about the total stock, as there is also uncertainty about the exact distribution. However, the species is generally common and has a very large range, so five-digit population numbers are likely. The IUCN therefore regards the species as harmless. Locally, as in Alagoas (Brazil), deforestation and the creation of secondary habitats can lead to an expansion of the distribution, but also, as in southern Argentina, to local declines. There, strychnine was often used by sheep farmers to combat predators, but this has decreased in recent years in favor of other, more selective control methods. Elsewhere, such as around Santiago de Chile , increasing settlement and the associated destruction of habitats can have a negative impact.

literature

Individual evidence

  1. ^ "Aguja" in Duden , accessed on January 23, 2015
  2. ↑ a b c d e f g h i j Ferguson-Lees / Christie (2001), p. 642, see literature
  3. ↑ a b Ferguson-Lees / Christie (2001), p. 641, see literature
  4. ↑ Bierregaard et al. (2014), Habitat section , HBW alive, see literature
  5. ↑ Thomas S. Schulenberg, Douglas F. Stotz, Daniel F. Lane, John P. O'Neill, Theodore A. Parker: Birds of Peru (Revised and Updated Edition), Princeton University Press 2010, ISBN 978-1-4008- 3449-5
  6. ↑ a b c d Bierregaard et al. (2014), section Food and feeding , HBW alive, see literature
  7. ↑ a b c d Bierregaard et al. (2014), section Breeding , HBW alive, see literature
  8. ↑ Bierregaard et al. (2014), Section Status and Conservation , HBW alive, see literature

Web links

Commons : Geranoaetus melanoleucus  - Collection of images, videos and audio files