Steppe Eagle

The steppe eagle is a large, bulky and robust-looking eagle. It is mainly dark brown in colour with a longish but very thick neck and a relatively small head that nonetheless features a strong bill and long gape-line. It appears long-winged and has a longish and rather rounded tail and markedly well-feathered (almost with disheveled looking feathers) legs. Steppe eagles tend to perch somewhat upright and usually do so in the open, often utilizing isolated trees, posts, rocks or other suitable low lookouts such as mounds or straw-piles. The species often is seen on the ground where may stand for long periods of the day and walk with horizontal posture and with wingtips just exceed the tail-tip. Steppe eagles, like tawny eagles, can fairly tame and approachable, unlike many of the other Aquila eagles. The adult is a somewhat variable brown with darker centers to the greater coverts. More pronouncedly in the eastern part of the range, adults have normally prominent pale rufous to dull orange-yellow to yellow-brown patches on the nape and hindcrown. Any other paler areas (such as the feather tips of the back and uppertail coverts) are obscured on perched adults. The massive gape-line runs to level with the rear of eye (further emphasized by dark border against paler chin) and is longer than in any other Aquila eagles including tawny eagles. Combined with their deep-set eyes, it lends steppe eagles an altogether rather fierce facial expression. Steppe eagle juveniles are almost invariably paler than adults, with some ranging overall from umber-brown to tawny-buff but then some are darker and more deeply brown. Juveniles tend to be brown to grey-brown on the upperparts but for generally rufous-buff nape patch (more so on eastern population). The juveniles bear conspicuously and broadly white-tipped black about the greater coverts, wings and tail and a bold but narrow cream band on the brown medians. The juvenile steppe eagle's white uppertail coverts is generally concealed when perched; the underparts are usually the same as the upperparts but may be somewhat paler tawny-buff hue. Upon their 2nd year, the plumage is still much as the 1st year appearance but show the pale tips to secondaries, median coverts and tail as often well-worn and narrower; by the start of 2nd winter the, tips of retained juvenile flight-feathers and coverts are heavily abraded and very thin. By the end of 2nd winter, often the immatures look very worn and have nearly lost pale tips altogether and from 3rd year onward manifest a variable mix of old and new feathers. Generally, immatures are often rather scruffy in appearance until adult-like plumage attained at year five, after which the feathers generally appear more compact. Adults have brown to hazel eyes, while juveniles have distinctly dark brown eyes; the cere and feet are yellow at all ages. In flight, the steppe eagle appears as a large, impressive and visibly heavy raptor with a well-projecting large head and bill and rather broad neck and long, broad wings. They evidence proportionately long arms, especially in the larger eastern birds. The wings tend to be held almost parallel-edged and square-ended with 7 very elongated emarginations. Often juveniles can tend to appear somewhat narrower winged. The broad body of the species often looks suspended underneath and the tail appears rounded or even wedge-shaped, measuring about 3/4 of the length of wing-base. The wingspan is about 2.6 times greater than the total body length. On the upperwings, steppe eagles show a pale greyish primary patch that is often quite large and obvious (especially on non-adults), often being pale at the base on the greater primary coverts but on adults (especially dark birds) much less marked. On the underwing, a very small carpal crescent may be present but can vary from invisible to slightly more marked. The flight feathers are greyish and all have 7–8 well-spaced blackish bars (albeit less conspicuously than on spotted eagles), while the fingers are plain blackish. Adults are basically all fairly uniform dark brown (wings can be negligibly greyer or rarely yellowish brown). Adults may evidence in flight some whitish patches on back and tail coverts that are varying from insignificant to fairly prominent. Adult eagles that do show a dark-barred greyish primary patch usually have that confined to a wedge-shape on inner primaries though can sometimes be rather more prominent. Below adults show dark-barred grey flight feathers and tail with the broad blackish trail edges and wing ends being rather distinctive; the wing linings are often slightly paler to darker than remiges and often with an obscure remnant of broken paler central band. Juveniles are quite distinctive in flight if seen in reasonable view. Above, juveniles are pale greyish-brown to yellow-brown about the body and forewing-coverts, have a broad whitish U above the tail. They possess broad white tips to the blackish greater coverts, flights feathers and tail creating obvious whitish bars on the wings and trailing edges as well as a large and prominent whitish patch covering much of the inner primaries (causing barring to stand out more so and offsetting plain black wing end). On its underside, the juvenile is mid-brown to brownish-yellow with a paler throat and creamy crissum. Below, the creamy central wing band is even broader than above, while the greater coverts all white with some dark centres on primaries (rare extreme pale individuals appear to have almost uniform paler colour on the entire wing lining and lesser and medians buffish-white to pale sandy, often whitish pale primary-wedges). Despite reports that some juvenile 1st years have subtle or no central wing bands, these are believed to be cases where these feathers exist but are obscured by long median coverts. At the end of the first year, the young steppe eagle tends to have pale tips to wings, tail and upperwing coverts become rather abraded; thereafter the development young evidence much variation due to individual differences. Usually, by the end of 2nd winter, the wing looks even more worn and uneven in pattern, with any newly acquired narrowly white-tipped quills clearly longer than old worn juvenile ones that have lost their pale tips. From the 3rd winter on, the pale parts clearly reduced, flight feathers and tail often appear quite ragged and by the 4th year start to more resemble adults. From the end of the 3rd year to when they obtain adult plumage, the eagles tend to have adult-like broad blackish trailing edges and tail often coupled with dark-barred grey base to black fingers and traces of the pale band along greater underwing-coverts. Maturity is obtained between the 4th and 5th years, not at 6–7 years as previously reported despite some presumed five-year-old eagles still have flecks of pale on the wing coverts and the throat and more subtle nape patches than they will ultimately manifest.

Steppe eagles appeared to have evolved the strategy of migrating from their breeding grounds, due in large part to the temporary seasonal availability of their main prey, ground squirrels. They probably migrate in greater numbers than any other eagle in the world and can appear to be frequent enough at migration sites that they may mask less numerous migrating eagles that are mistakenly missed in their ranks. The migratory behaviour of this species is arguably amongst the best-studied aspect of its entire biology. Autumn migration often begins around October on fairly broad fronts, and may peak around late October. It usually ends in late November to December but steppe eagles frequently travel somewhat nomadically while not breeding and so individuals may not reach their winter terminus point until about January. Spring migration usually commences in February, peaking early from late February to March, with likely all gone from Africa by the end of the latter month, then continuing in a diminishing trickle into April and May. In passage at Suez, the steppe eagle is one of the earlier migrating raptors on average alongside the long-legged buzzard (Buteo rufinus), averaging about a month sooner in passage than the common buzzard (Buteo buteo) (the most common migrant there) and slightly sooner than the lesser spotted eagle, as well as much sooner than some other raptors there. On average, the wintering period in Africa is relatively brief, at a mean of about up to about 4 months (down to about 2), while adult steppe eagles spend up to 7 months (max of around 5 months for a young eagle) on their breeding grounds. In autumn records from Africa, younger eagles migrate the earliest and adults the latest. Radio-tagging studies confirmed, much as in the lesser spotted eagle, that in spring juveniles migrated later, wandering about more so and came back to the summering grounds much later. One young steppe eagle that was banded in passage in the United Arab Emirates wintered initially in Yemen before returning for the summer to Kazakhstan, then migrating to eastern Africa the following winter, showing that they can change their migratory habits over time. Many studies corroborate that steppe eagles generally migrate lesser distances as they age. Peak movements around the Red Sea show as many as 76,000 steppe eagles moving over Bab-el-Mandeb in the fall of 1987, with up to 65,000 (in 1981) in Suez and up to 75,000 in Eilat, Israel in the year 1985. Once migrating steppe eagles enter Africa in autumn, no mass migrations have been recorded anywhere for the species in the continent. Although not large, some semi-significant spring movements were detected in Egypt, despite none being recorded in the fall. In autumn, steppe eagles usually pass over Bab-el-Mandeb in the north of Red Sea while in spring they predominantly cross to the south of the Red Sea around Suez. The mean number of steppe eagles that annually pass over Eilat in spring are estimated at 28,032 with a mean peak day of 10 March, making them roughly the fourth most common migrating raptor in spring there (and they often pass in intermingled flocks with other soaring raptors, but not those with powered flight). In Eilat, steppe eagles constitute 6.4% of all raptors seen, nearly all of the Aquila eagles seen and, among those that could be aged, an estimated 60–70% of the steppes seen were thought to be adults. More unusually, the steppe eagle may be the only raptor to also use Israel as a common migratory flight path in autumn as well as spring, with even commoner migrating raptors such as common buzzards and European honey buzzards (Pernis apivorus) being rare there in the fall. In Nepal over 2.5 weeks starting in 20 October, nearly 7852 steppe eagles were tallied, making up more than 80% of the recorded migrating raptors, with peak times of movement being between 10:00 AM and 4:00 PM, especially between noon and 2:00 PM. Over 3 years of study in Nepal, 21,447 steppe eagles were recorded (as many as 1102 within a day and a mean of about 15.2 an hour) at the counting sites. Strong evidence of east-to-west migratory movements, rather than south or northbound, has been made in the Kathmandu Valley. It was indicated based on the directional studies that especially juveniles from the eastern part of the breeding may be more frequently migrate westbound to reach wintering areas such as the Middle East and Africa. On the contrary, juveniles and subadults during the wintering season seem to considerably outnumber adults in the Indian subcontinent so many do head due south. Of 3381 ageable steppe eagles in passage in Nepal, 56% were juveniles or immature, 44% were adults; of 7852 eagles, 58% migrated in groups of 1–5, 30% in 5–20 groups and 12% in larger flocks. In Himachal Pradesh of India, about 11,000 steppe eagles were recorded in autumn migration in 2001 and about 40% less were counted the next spring. This study indicated different migratory paths being used in the seasons, presumably following the winds predominant direction around the terrain, with the westerly autumn migration mostly in the western Himalayas and the easterly spring migration more so in the east of Nepal. Staging areas are not well-delineated in India but appear to concentrate around feeding sites such as landfills. A single female that was radio-tagged in Mongolia was recorded to travel southwest and stop in southeastern Tibet, which is also the southernmost part of the species breeding range. The data from this female indicated that not all steppe eagles move to warmer climates and, based on that she remained stationary until her return to Mongolia, that she was not nomadic as many eagles of the species are. During return spring migration, the steppe eagles in passage in Nepal will reportedly amass into groups of approximately 5 to 20 eagles at only about 20 to 70 m (66 to 230 ft) above the terrain before rising up to cross between the snow-covered peaks. 16 radio-tagged eagles that returned in their first spring migration to their Kazakh summering grounds were recorded to winter as first-year juveniles either, in roughly equal measure, in the Arabian Peninsula or southern Africa, and covered straight-line distances, ranging from 3,489 to 9,738 km (2,168 to 6,051 mi), although individually could meander up to 20,644 km (12,828 mi) for one eagle migrating from wintering grounds Botswana. Of the 16 returning Kazakhstan eagles, spring migration lasted an average of 40 days, ranging individually from 38 to 54 days and covered a mean of 355 km (221 mi) each day. The migration path generally led the eagles around almost every direction of the Red Sea, many also passing over Israel and some wrapping around the Caspian Sea. A different radio-tagging study of 19 juveniles (about 57% of which survived) from Russian or Kazakh sites found that autumn movements in the 1st year migration averaged 4,222 km (2,623 mi) and confirmed not only that they freely changed wintering sites anywhere from India to southern Africa but they never returned, surviving or not, to their natal site in the 1st year, instead return to wandering widely across the northern steppe. The 1st migration averaged 52 days and were much briefer for females than for males, with the discrepancies more pronounced for eagles originating from the Altai Mountains. 15 birds tracked in this study were found to have migrated most frequently to winter in south Pakistan (right along the borderlands to India) or in eastern Turkmenistan. Spring migration began on a mean date of 25 March for the 15 young eagles and lasted about 26 days on average, covering a mean of 3,925 km (2,439 mi), with females initiating migration on average 18 days later than males and migrating more briefly, more quickly and more often with fewer stops than males. 9 eagles which were tracked successfully in their first spring passage in this study wandering widely mostly in natural steppe hunting for squirrels and 8 of these tracked to their 2nd autumn migration took about 1.5 times shorter on their 2nd autumn passage and migrated about 17% less far on average.