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The tawny eagle (Aquila rapax) is a large, long-lived bird of prey. Like all eagles, it belongs to the family Accipitridae. It is estimated that tawny eagles can reach the age of 16 years old.[2]

Tawny eagle
2012-tawny-eagle-0.jpg
From Etosha National Park
Scientific classification edit
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Accipitriformes
Family: Accipitridae
Genus: Aquila
Species:
A. rapax
Binomial name
Aquila rapax
(Temminck, 1828)
AquilaRapaxIUCNver2019 1.png
Range of A. rapax     Resident
Synonyms

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.

TaxonomyEdit

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.[3][4][5] 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.[6]

"Tawny eagle" has been designated the official name by the International Ornithologists' Union (IOC).[7]

DescriptionEdit

 
Close-up showing gape extending only to below the middle of the eye

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).[8][9] 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.

Habitat useEdit

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.[10][11][12][13]

Breeding biologyEdit

NestEdit

In Kgalagadi Transfrontier Park, South Africa, tawny eagles build nests that are positioned in the canopy of large Vachellia erioloba trees.[11] These tend to be the largest and tallest trees averaging 10.9 meters.[11] Nests measure just under 1 m in diameter and 20 cm deep.[10] In Kenya, tawny eagles showed no nesting preference according to tree height or spatial distribution of trees;[14] however, they preferred Euphorbia, Boscia and Euclea tree species.[14] 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).[10] Tawny eagles build new nests yearly and only 2% of nests are reused for breeding purposes the following year.[11]

In the Central Karoo region of South Africa, tawny eagles build their nests in large electric transmission towers.[13] 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.[13] Between 2002 and 2003, 39% of electrical faults recorded on transmission lines were due to large eagle nests.[13] As a result, problem nests were dismantled and rebuilt below the electrical conductors.[13]

Laying datesEdit

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.[11] These laying dates are similar to populations in Zambia, Zimbabwe [12][10] and the Maasai Mara region in Kenya.[14]

Eggs and chick developmentEdit

clutch sizes range from 1 to 3 eggs per nest, but average 1.7 eggs per clutch.[10][12] 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.[10] 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.[10] 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.[10] 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).[10][12]

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.[10] 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.[10] The producer-scrounger theory predicts that vultures rely on eagles for information on carcasses.[15] 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.[15]

The tawny eagle steals food from other raptors in addition to catching its own prey.[2] The Afrikaans name for the tawny eagle is a "Roofarend", meaning the "Robber Eagle".[2] Dietary records from Esigodini indicate that tawny eagles eat a wide variety of prey items and carrion.[10] The diet analysis indicates 36.9% mammals, 51.9% birds, 10% reptiles and 1.2% amphibians.[10] Tawny eagle chicks are unable to survive off carrion alone and thus require freshly caught prey.[2] A similar dietary study conducted in Lochinvar National Park, Zambia found a higher proportion of birds and amphibians (61.4% & 5.5% respectively).[12] The variation in diet between the two study sites is due to differences in habitat and prey availability.[12]

Records show tawny eagles eat birds such as the Wattled Lapwing, helmeted guineafowl and Red-billed Spurfowl.[10][12]

CallEdit

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.[10] In nine years of monitoring tawny eagles in Zimbabwe, the call was not heard once.[10] The reasons for its silence may be due to the flat landscape in which it inhabits.[10]

ThreatsEdit

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.[16][17][18][19]

Further threats to tawny eagles include habitat loss and land-use changes such as intensified cattle grazing and firewood collection.[2] Raptor populations are reliant on seasonal rainfall events which influence the survival of prey populations.[2] 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.[2] Electrocutions and collision risks associated with overhead power lines remain a constant threat to large eagles and vultures.[13] The overarching threat to any raptor population is human population increase which causes competition for habitat and food resources.[20]

ConservationEdit

The tawny eagle is currently listed as Vulnerable on the IUCN list of Threatened species.[1] 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.[21] 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.[20] According to the producer-scrounger foraging theory, vultures are to some extent reliant on tawny eagles to help locate carcasses.[15] Thus, the conservation of eagles outside protected areas is of vital importance to ensure the survival of vultures.[15]

GalleryEdit

ReferencesEdit

  1. ^ a b BirdLife International (2018). "Aquila rapax". IUCN Red List of Threatened Species. Version 2018.2. International Union for Conservation of Nature. Retrieved 17 December 2018.
  2. ^ a b c d e f g Whichmann, M.; Dean, W.; Jeltsch, F. (2004). "Global change challenges the Tawny Eagle (Aquila rapax): Modelling extinction risk with respect to predicted climate and land-use changes". Ostrich. 75 (4): 204–210. doi:10.2989/00306520409485446.
  3. ^ Clark, W. S. (1992). "The taxonomy of Steppe and Tawny Eagles, with criteria for separation of museum specimens and live eagles" (PDF). 112 (3). Bull. B.O.C.: 150–157. Retrieved 2019-07-29. Cite journal requires |journal= (help)
  4. ^ Olson, S. L. (1994). "Cranial osteology of Tawny and Steppe Eagles Aquila rapax and A. nipalensis" (PDF). 114. Bull. B.O.C.: 264–267. Cite journal requires |journal= (help)
  5. ^ Sangster, G.; Knox, A.G.; Helbig, A.J.; Parkin, D.T. (2002). "Taxonomic recommendations for European birds" (PDF). Ibis. 144 (1): 153–159. doi:10.1046/j.0019-1019.2001.00026.x.
  6. ^ Global Raptors
  7. ^ Gill, Frank; Donsker, David, eds. (2019). "New World vultures, Secretarybird, kites, hawks & eagles". World Bird List Version 9.2. International Ornithologists' Union. Retrieved 31 July 2019.
  8. ^ James Ferguson-Lees; Christie; Franklin; Mead; Burton (2001), Raptors of the World, Houghton-Mifflin, ISBN 0-618-12762-3
  9. ^ Tawny eagle (Aquilla rapax), ARKive, 2011, archived from the original on 2018-02-01
  10. ^ a b c d e f g h i j k l m n o p q Steyn, P. (1973). "Observations on the Tawny Eagle". Ostrich. 44 (1): 1–22. doi:10.1080/00306525.1973.9632611.
  11. ^ a b c d e Herholdt, J.; Kemp, A.; Du Plessis, D. (1996). "Aspects of the breeding status and ecology of the bateleur and tawny eagle in the kalahari gemsbok national park, South Africa". Ostrich. 67 (3–4): 126–137. doi:10.1080/00306525.1996.9639697.
  12. ^ a b c d e f g Osborne, T. (1982). "Observations on the Tawny Eagle in Southern Zambia". Ostrich. 53 (2): 107–111. doi:10.1080/00306525.1982.9634734.
  13. ^ a b c d e f Jenkins, A.R.; De Goede, K.H.; Lovelater, S.; Diamond, M. (2013). "Brokering a settlement between eagles and industry: sustainable management of large raptors nesting on power infrastructure" (PDF). Bird Conservation International. 23 (2): 232–246. doi:10.1017/S0959270913000208. Retrieved 2019-07-29.
  14. ^ a b c Kendall, C.J.; Rubenstein, D.L.; Slater, P.L.; Monadjem, A. (2017). "An assessment of tree availability as a possible cause of population declines in scavenging raptors". Journal of Avian Biology. 49 (1): 001–008. doi:10.1111/jav.01497. Retrieved 2019-07-29.
  15. ^ a b c d Ogada, D.L.; Monadjem, A.; McNally, L.; Kane, A.; Jackson, A.L. (2014). "Vultures acquire information on carcass location from scavenging eagles". Proceedings of the Royal Society B: Biological Sciences. 281 (1793): 20141072. doi:10.1098/rspb.2014.1072. PMC 4173674.
  16. ^ "Over 500 Rare Vultures Die After Eating Poisoned Elephants In Botswana". Agence France-Press. NDTV. 2019-06-21. Retrieved 2019-06-28.
  17. ^ Hurworth, Ella (2019-06-24). "More than 500 endangered vultures die after eating poisoned elephant carcasses". CNN. Retrieved 2019-06-28.
  18. ^ Solly, Meilan (2019-06-24). "Poachers' Poison Kills 530 Endangered Vultures in Botswana". Smithsonian. Retrieved 2019-06-28.
  19. ^ Ngounou, Boris (2019-06-27). "BOTSWANA: Over 500 vultures found dead after massive poisoning". Afrik21. Retrieved 2019-06-28.
  20. ^ a b Thiollay, J. (2006). "The decline of raptors in West Africa : long-term assessment and the role of protected areas". IBIS. 148 (2): 240–254. doi:10.1111/j.1474-919X.2006.00531.x.
  21. ^ Underhill, L.; Brooks, M. (2014). "Preliminary summary of changes in bird distributions between the first and second southern African Bird Atlas projects (SABAP AND SABAP2)". Ornithological Observations. 5: 258–293. Retrieved 2019-07-29 – via University of Cape Town Libraries.

External linksEdit