The steppe eagle (Aquila nipalensis) is a large bird of prey. Like all eagles, it belongs to the family Accipitridae. The steppe eagle's well-feathered legs illustrate it to be a member of the subfamily Aquilinae, also known as the "Booted eagles".Helbig, A. J., Kocum, A., Seibold, I., & Braun, M. J. (2005). A multi-gene phylogeny of aquiline eagles (Aves: Accipitriformes) reveals extensive paraphyly at the genus level. Molecular phylogenetics and evolution, 35(1), 147–164. This species was once considered to be closely related to the sedentary tawny eagle (Aquila rapax) 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.
The Steppe eagle is in many ways a peculiar species of eagle. It is a specialized predator of ground squirrels on the breeding ground, also taking other rather small mammals and other prey, doing so more often when ground squirrels are less consistently found.Vazhov, S. V., Bachtin, R. F., Barashkova, A. N., & Smelansky, I. E. (2013). On the Study of the Steppe Eagle in the Altai Kray, Russia. Raptors Conservation, (27). In rather treeless areas of the steppe habitats, these eagles tend to nest on a slight rise, often on or near an outcrop, but may even be found on flat, wide-open ground, in a rather flat nest. They are the only eagle to nest primarily on the ground.Brown, L. & Amadon, D. (1986) Eagles, Hawks and Falcons of the World. The Wellfleet Press. . Usually, one to three eggs are laid and, in successful nests, one to two young eagles fledge.Karyakin, I. V., Kovalenko, A. V., Levin, A. S., & Pazhenkov, A. S. (2011). Eagles of the Aral-Caspian Region, Kazakhstan. Raptors Conservation, (22). The steppe eagle undertakes a massive migration from essentially its entire breeding range, moving en masse past major migration flyways, especially those of the Middle East, Red Sea and the Himalayas. In winter, though less closely studied than during breeding, the steppe eagle is remarkable for its sluggish and almost passive feeding ecology, focusing on insect swarms, landfills, carrion and the semi-altricial young of assorted animals, lacking the bold and predatory demeanor of their cousin species.Steyn, P. (1983). Birds of prey of southern Africa: Their identification and life histories. Croom Helm, Beckenham (UK). 1983.Naoroji, R., & Schmitt, N. J. (2007). Birds of prey of the Indian subcontinent. Om Books International. Although still seen by the thousands at migration sites in larger numbers than other migrating eagles of these areas, the steppe eagle's entire population has declined precipitously.Weiss, N., Haviv, E., Alon, D., Perlman, Y., & Schäckermann, J. (2019). How Fast Does the Steppe Eagle Population Decline? Survey Results from Eilat, Israel. Raptors Conservation, 38. The threats to this species consist of increasing steppe fires and pests around the nests (both probably increased by the warming climate) which can cause a large volume of nest failures. Rivaling these factors, declines are being exacerbated by disturbance and persecution by humans, as well as trampling of nests by livestock. Free-flying steppe eagles are also being killed in alarmingly large numbers, especially in the stronghold nation for breeding of Kazakhstan, by electrocutions on dangerous electricial wires and pylons.Karyakin, I.V. (2018). The status of the steppe eagle in the world: "white spots" in distribution, abundance, ecology and threats. Raptor Research , (S1). Due to these and other reasons, the decline of the species is thought to be considerably more than 50%. Therefore, the species is considered to be endangered by the IUCN. The steppe eagle appears on the flag of Kazakhstan and is the national bird of both Kazakhstan and Egypt.
Taxonomy British naturalist Brian Houghton Hodgson described the steppe eagle in 1833. Aquila is Latin for "eagle" while nipalensis means "from Nepal" based on the location where the type specimen was collected presumably while migrating. Samuel G. Gmelin however, described a species of eagle from Tanais where they were found sitting on ancient mounds or graves of nomads. He called it "Aquila mogilnik," the species name "mogilnik" meaning "burial" in Russian. This was included in the 13th edition of Systema Naturae by his cousin J.F. Gmelin in 1788. The identity of this bird was, however, confused with A. heliaca but research in 2019 suggests that A. mogilnik can reliably be identified and that it would have been a valid senior name for A. nipalensis had it not been declared as a nomen dubium, a doubtful name by Ernst Hartert in 1914. The lack of usage of the name in literature now makes the name nomen oblitum, a valid senior name lost by disuse. The steppe eagle is a member of the booted eagle subfamily within the Accipitridae family. The booted eagle clan are monophyletic and the study of karyotypes has indicated that they likely have few to no close external relations within the overall extant accipitrid family.Li, Q., Lin, J., Li, S., Wang, Y., Li, W., & Zeng, Y. (2000). Studies on the evolution of mitochondrial DNA in 11 species of Accipitridae. Dong wu xue bao.[Acta zoologica Sinica], 46(2), 209–220.De Boer, L. E. M., & Sinoo, R. P. (1984). A karyological study of Accipitridae (Aves: Falconiformes), with karyotypic descriptions of 16 species new to cytology. Genetica, 65(1), 89–107. The booted eagle subfamily all have feathers covering their legs and may be found to some extent on every continent that contains accipitrids. The genus Aquila traditionally comprises large and fairly dark eagles that tend to live in open habitats. However, a significant division was determined to exist between superficially similar eagles such as the golden eagle (Aquila chrysaetos) and its three extant and similar-looking close cousins, as well as three very different smaller and pale-bellied eagles (the Bonelli's, African hawk- and Cassin's hawk-eagles) and the species complex which contains the steppe eagle.Lerner, H. R., & Mindell, D. P. (2005). Phylogeny of eagles, Old World vultures, and other Accipitridae based on nuclear and mitochondrial DNA. Molecular phylogenetics and evolution, 37(2), 327–346. There is a similar genetic disparity with the golden eagle for the steppe eagle as with the spotted eagles which have been deemed distinct enough to form a separate genus, Clanga.Väli, Ü. (2002). Mitochondrial pseudo‐control region in old world eagles (genus Aquila). Molecular Ecology, 11(10), 2189–2194. The steppe eagle genetically clusters closely to the tawny eagle as well as, albeit more distantly, with the eastern (Aquila heliaca) and Spanish imperial eagles (Aquila adalberti).Zhou, C., Tu, H., Chen, Y., Dou, L., Meng, Y., Yang, N., Yu, B. & Wu, Y. (2019). The complete mitochondrial genome of Aquila nipalensis and its phylogenetic position. Mitochondrial DNA Part B, 4(2), 2152–2153. However, the loci evidenced in the Aquila genera have been found to be relatively homogenous, with general studies of isoenzymes showing their genes as about ten times less distanced than certain owl genera.Saag, P., Paaver, T., & Väli, Ü. (2007). Lack of between-and within-species isoenzyme variability in Aquila eagles (Aves: Accipitriformes). Biochemical Systematics and Ecology, 35(11), 774–776.
The steppe eagle has historically been considered conspecific with the tawny eagle, even until as recently as 1991.Stresemann, E., & Amadon, D. (1979). Order Falconiformes. Check-list of birds of the world, 1, 271–425.Amadon, D. (1982). The genera of booted eagles: Aquila and relatives. Journal of the Yamashina Institute for Ornithology, 14(2–3), 108–121.Howard, R., & Moore, A. (1991). A complete checklist of the birds of the world (No. Ed. 2). Academic Press Ltd. The latter species resides year-round in the African and Asian areas, often used seasonally as wintering grounds by the steppe eagle. The species were ultimately separated on the grounds of the differences in morphology, disparate coloring, distinct life histories, and behaviours.Clark, W. S. (2005). Steppe Eagle Aquila nipalensis is monotypic. Bull. BOC, 125(2). Testing of genetic materials has reinforced the species distinction of the steppe and tawny eagles. Genetically, the steppe eagle is thought to be basal to related species such as the tawny and imperial eagles.White, C. M., Olson, P. D., & Kiff, L. F. (1994). Family Falconidae (hawks and eagles). Handbook of the birds of the world, 2: 52–214. A fossil species, Aquila nipaloides, has been found in Italy, Corsica, Sardinia and France and was hypothesized to most closely related to the steppe eagle based on osteology of the ramus (although did evidence some differences in leg morphology).Louchart, A., Bedetti, C., & Pavia, M. (2005). A new species of eagle (Aves: Accipitridae) close to the Steppe Eagle, from Pleistocene of Corsica and Sardinia, France and Italy. Despite being even more strongly distinctive from the steppe eagle than the tawny eagle, the eastern imperial eagle has been seen to hybridize with the steppe eagles in the wild, once in Turkey and at least three times in Kazakhstan. Each hybrid with imperial eagles has been known to involve pairs of subadult or juvenile eagles and all known hybrid pairings were between male steppe eagles (or apparent steppe-imperial hybrids themselves) mated to female imperial eagles. Some of these hybrid pairs also produced seemingly healthy young with roughly intermediate characteristics.Karyakin, I., Kovalenko, A., & Zinevich, L. (2016). The first case of successful breeding of offspring by a mixed pair of steppe eagle and imperial eagle in Western Kazakhstan and registration of probable hybrids between the steppe eagle and burial eagle in Russia and Kazakhstan. Raptor Research , (32).Szilvia, J. (2015). A parlagi sas (Aquila heliaca) és a pusztai sas (Aquila nipalensis) hibridizációjának molekuláris vizsgálata (Doctoral dissertation).
The Steppe eagle has been generally considered to contain two subspecies. One was the nominate subspecies, A. n. nipalensis, which breeds in the eastern portions of the range (perhaps from the East Kazakhstan Region to all points east) while the western breeding population, found in most of Kazakhstan and European Russia, was considered as the subspecies, A. n. orientalis. The separation of the two subspecies was largely based on size, with the eastern population being larger and much heavier than the western eagles. The more eastern birds tend to be a shade darker and a have a more extensive nape patch, as well as having a more conspicuously deep gape-line. However, both western and Russian researchers have since made a convincing advocacy that the steppe eagle is actually a monotypical species. It was found that both previously claimed subspecies appear to broadly overlap in the breeding range and become indistinguishable at the Kazakh-Russian meeting point. The primary differences, i.e. in size and mildly in color, can be explained as clinal variations due to the environment. The breeding populations of the eastern and western eagles are insufficiently allopatric and too extensively engage in introgression to be properly regarded as full subspecies.Karyakin, I., Zinevich, L., Schepetov, D., & Sorokina, S. (2016). The population structure of the range of the steppe eagle and preliminary data on the genetic diversity of its populations and the status of subspecies. Feathered predators and their protection, (32). Erroneously, a checklist once included the former subspecies of A. n. orientalis as being part of the subspecies of tawny eagle from Asia, A. r. vindhiana, an error that was later corrected.Sibley, C. G., & Monroe Jr, B. L. (1993). A world checklist of birds. Ann Arbor, MI: Edwards Brothers Inc.
Description