|From Etosha National Park|
|Range of A. rapax Resident|
Aquila rapax rapax
It breeds in most of Africa, both north and south of the Sahara Desert, and across tropical southwestern Asia to India. It is a resident breeder which lays one to three eggs in a stick nest in a tree, crag, or on the ground. Throughout its range, it favours open dry habitats such as semideserts, deserts steppes, or savannah plains.
Dutch naturalist Coenraad Jacob Temminck described the tawny eagle in 1828.
It was once considered to be closely related to the migratory steppe eagle, Aquila nipalensis, and the two forms have previously been treated as conspecific. They were split based on pronounced differences in morphology and anatomy. Two molecular studies, each based on a very small number of genes, indicate that the species are distinct, but disagree over how closely related they are.
This is a large eagle, although it is one of the smaller species in the genus Aquila. It is 60–75 cm (24–30 in) in length and has a wingspan of 159–190 cm (63–75 in). Weight can range from 1.6 to 3 kg (3.5 to 6.6 lb). It has tawny upper parts and blackish flight feathers and tail. The lower back is very pale. This species is smaller and paler than the steppe eagle, and it does not share that species' pale throat. Immature birds show less contrast than adults, but both show a range of variation in plumage colour.
Tawny eagles occur in a wide variety of habitats in Africa and western India. Habitats in Southern Africa include semi-desert (Namibia and Botswana), arid Savanna's and Grasslands in South Africa, Miombo woodlands in Zimbabwe.
In Kgalagadi Transfrontier Park, South Africa, tawny eagles build nests that are positioned in the canopy of large Vachellia erioloba trees. These tend to be the largest and tallest trees averaging 10.9 meters. Nests measure just under 1 m in diameter and 20 cm deep. In Kenya, tawny eagles showed no nesting preference according to tree height or spatial distribution of trees; however, they preferred Euphorbia, Boscia and Euclea tree species. In Kruger National Park, tawny eagles have been recorded using nests of other species of raptor such as white-backed vulture (Gyps africanus) and white-headed vulture (Trigonoceps occipitalis). Tawny eagles build new nests yearly and only 2% of nests are reused for breeding purposes the following year.
In the Central Karoo region of South Africa, tawny eagles build their nests in large electric transmission towers. Populations of large eagles like the martial eagle (Polemaetus bellicosus) and verreaux's eagle (Aquila verreauxii) have been recorded breeding on these power pylons since the 1970s. Between 2002 and 2003, 39% of electrical faults recorded on transmission lines were due to large eagle nests. As a result, problem nests were dismantled and rebuilt below the electrical conductors.
Of 26 tawny eagle nests monitored between 1988 - 1996 in the Kgalagadi Transfrontier Park, 84.6% of the laying dates occurred between May and June. These laying dates are similar to populations in Zambia, Zimbabwe  and the Maasai Mara region in Kenya.
Eggs and chick developmentEdit
clutch sizes range from 1 to 3 eggs per nest, but average 1.7 eggs per clutch. Eggs are incubated by the female for 40–44 days before hatching. Only one chick invariably survives after hatching. This is due to siblicide, where the older chick fatally wounds the younger chick in the first few days of life. The male may occasionally incubate the eggs. For the first 10 days, the adult female observes the chick very closely, relying on food provisioned by the male. After two weeks, the chick is left alone for 2.5 hours each day, whilst the adults forage. By week 7, the chick has only a small amount of down feathers remaining and weighs 2150 grams. The chick is fully grown and capable of fledging the nest after 11–12 weeks. Breeding success, recorded as young per pair per year (ypy), was lower in Namibia and Tsavo East National Park than in Zimbabwe (0.4, 0.5 and 0.78 ypy respectively).
Foraging and foodEdit
Although the tawny eagle does hunt for food, it also relies on carrion as a food source. They have been recorded feeding on carcasses as large as African elephants and as small as vervet monkeys. They are frequently recorded on roadsides where roadkill provides a steady food source. Tawny eagles have often been recorded feeding with vultures, bateleur, steppe eagle, hyaena and jackal. At large carcasses, there is a hierarchical social structure based on the size of the scavenger. The Eagles remain on the periphery of the vulture feeding frenzy and wait for pieces of flesh to appear. Often they will be able to pick up small scraps but will wait until the carcass is finished and few vultures remain to feed. Tawny eagles are dominant over bateleur at carcasses. The producer-scrounger theory predicts that vultures rely on eagles for information on carcasses. Due to their smaller size, eagles are able to begin foraging earlier in the morning and are thus more likely to locate a carcass first.
The tawny eagle steals food from other raptors in addition to catching its own prey. The Afrikaans name for the tawny eagle is a "Roofarend", meaning the "Robber Eagle". Dietary records from Esigodini indicate that tawny eagles eat a wide variety of prey items and carrion. The diet analysis indicates 36.9% mammals, 51.9% birds, 10% reptiles and 1.2% amphibians. Tawny eagle chicks are unable to survive off carrion alone and thus require freshly caught prey. A similar dietary study conducted in Lochinvar National Park, Zambia found a higher proportion of birds and amphibians (61.4% & 5.5% respectively). The variation in diet between the two study sites is due to differences in habitat and prey availability.
Tawny eagles are generally silent in most of their range. However, in Kruger National Park it is said to make a Kow-Kow noise which is loud and far travelling. In nine years of monitoring tawny eagles in Zimbabwe, the call was not heard once. The reasons for its silence may be due to the flat landscape in which it inhabits.
Tawny eagles face a number of threats that affect their breeding behaviour, foraging success and ultimately the survival of individual birds. The most recent and devastating threat to survival occurred on the 20th of June 2019. The carcasses of 468 white-backed vultures, 17 white-headed vultures, 28 hooded vultures, 14 lappet-faced vultures and 10 cape vultures were found alongside 2 tawny eagles. A total of 537 vultures and 2 eagles were found poisoned in northern Botswana. It is suspected that they died after eating the carcasses of 3 elephants that were laced with poison by poachers. Carcasses are poisoned to ensure that scavengers are unable to aid rangers in the effort to locate poached wildlife. By circling above dead animals, large raptors act as an early detection system for anti-poaching rangers.
Further threats to tawny eagles include habitat loss and land-use changes such as intensified cattle grazing and firewood collection. Raptor populations are reliant on seasonal rainfall events which influence the survival of prey populations. Climate change is alternating rainfall patterns in the arid regions of Southern Africa and impacting on prey populations. There is a clear correlation between rainfall events and breeding success of tawny eagles. Electrocutions and collision risks associated with overhead power lines remain a constant threat to large eagles and vultures. The overarching threat to any raptor population is human population increase which causes competition for habitat and food resources.
The tawny eagle is currently listed as Vulnerable on the IUCN list of Threatened species. There was a clear decrease in tawny eagle sightings between SABAP and SABAP2 in Southern Africa, occurring in only 323 of 1440 quarter degree grid cells. Roadside counts conducted in Mali, Niger and Burkina Faso show that although the majority of raptor species are in drastic population decline, only the tawny eagle and snake eagles are surviving outside of protected areas. According to the producer-scrounger foraging theory, vultures are to some extent reliant on tawny eagles to help locate carcasses. Thus, the conservation of eagles outside protected areas is of vital importance to ensure the survival of vultures.
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|Wikimedia Commons has media related to Aquila rapax.|
- Tawny eagle - Species text in The Atlas of Southern African Birds
- Tawny eagle at Animal Diversity Web