The Steppe eagle (Aquila nipalensis) is a large and impressive raptor. Its well-feathered legs illustrate it to be a member of the subfamily Aquilinae, also known as the "booted eagles". The Steppe eagle is in many ways a peculiar species of eagle. It is a specialized predator of ground squirrels on the breeding ground and is the only eagle to nest primarily on the ground. These raptors undertake a massive migration and are also remarkable for their sluggish and almost passive feeding ecology, lacking the bold and predatory demeanor of their cousin species. Although still seen by the thousands at migration sites in larger numbers than other migrating eagles of these areas, Steppe eagles’ entire population has declined precipitously.
The Steppe eagle is a large, bulky, and robust-looking eagle. It is mainly dark brown in color 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. 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. The massive gape line runs to level with the rear of the eye (further emphasized by a dark border against the paler chin). 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 generally rufous-buff nape patch (more so on the 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's white uppertail coverts are generally concealed when perched; the underparts are usually the same as the upperparts but may be somewhat paler tawny-buff hue. 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 is 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.
Steppe eagles breed only in four large nations: Russia, Kazakhstan, Mongolia, and China. They are entirely migratory, wintering in the east and, to a lesser extent, southern Africa. The steppe eagle's wintering range also extends into the Middle East. They occur broadly in the season in several central and southern parts of the Arabian Peninsula as well as regularly in eastern Iraq and western Iran with odd ones north to Turkey and Georgia. Other countries where Steppe eagles spend winter include Yemen, Azerbaijan, and Syria as well as, albeit rarely doing so, the United Arab Emirates, Lebanon, and Kuwait. Steppe eagles prefer to breed in open dry country, within the steppe in both upland and lowland areas. They usually avoid agricultural land, however, they can nest near roads. They also occur when breeding in flat plains, arid grassland, semi-desert, and even desert edge. Wintering Steppe eagles often inhabit human-modified areas in order to access easy foods. These include landfills and livestock carcass dumps. More natural habitats tend to be various wetlands or other waterways where they are available. In winter, mostly savanna and grasslands are used, also sometimes dry woodland, mountain slopes, old fields, and orchards.
Steppe eagles generally spend time singly or in pairs. However, they may also be seen in the company of conspecifics throughout the year. They also often flock during migration and aggregate in occasionally ample numbers during non-breeding times, usually at fruitful feeding sites, sometimes briefly cooperating with one another especially to klepoparasitize other birds of prey. Steppe eagles fly with slow, deep, and stiff-looking wing beats, holding wings fully extend on upstrokes. Whilst soaring, their wings are held flattish or slightly flexed but sometimes with their hands lowered. They often fly with the head dropped with hands arched in a glide or often arms straight out and hands drooped. Steppe eagles usually perch upright in the open, often utilizing isolated trees, posts, rocks, or other suitable low lookouts such as mounds or straw-piles. They are also often 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. Breeding Steppe eagles mainly hunt in a low soaring or gliding flight, at a maximum of 200 m (660 ft), diving or making short, accelerated stoops onto their prey. Usually, they tend to capture their prey on the ground. They also may hunt in any season on the ground, moving with a shambling gait as necessary, and may give chase on foot to both vertebrate and insect prey. Steppe eagles can often ambush prey by standing in wait next to burrows, suddenly pouncing quickly onto the quarry upon its emergence. During the breeding season Steppe eagles often hunt in pairs while, in winter and migration, they often share by up to the dozens abundant food sources. Steppe eagles also frequently rob other raptors of their catches, approaching from any angle and pursuing closely until the victim is forced to land or drop its food. Steppe eagles are not very vocal especially when not breeding. Their main call is a raspy bark. In aerial displays, a loud whistle has been recorded. Other calls include low and croaking notes aside from a high shriek when startled.
Steppe eagles are carnivores and prey mainly on small-sized mammals, with some birds (such as queleas) and reptiles and (mostly in winter) frequently insects (such as termites and locusts) and carrion. Despite their opportunistic nature, Steppe eagles are somewhat specialized predators of particular mammals such as ground squirrels while breeding and, during non-breeding times, feed on various foods including insect swarms, semi-altricial young of assorted animals, landfills, and carrion. On the breeding grounds, they also prey on voles, pikas, zokors, and sometimes marmots, hares, gerbils, and hedgehogs.
Steppe eagles are monogamous and form long-lasting pair bonds. Their breeding season lasts from late March or early April to roughly late August, although several steppe eagles can remain on their breeding grounds until at least October. The nest is a large stick platform, varying greater in size based on available materials. Most nests are around 70-100 cm (28-39 in) in diameter and around 20-50 cm (7.9-19.7 in) deep. It is lined with twigs and much clutter. The nest is usually placed in an exposed site among stones, often on a hummock or sometimes low bushes and a spot on the ground which is usually raised slightly above the mean layout of the environment. The female lays 1-3 eggs and the incubation lasts around 45 days. Hatching is often sometime in May but can continue to early June. Eaglets are covered in white down when they hatch. They fledge relatively quickly at somewhere between 55 and 65 days, due probably to the vulnerability of the nest sites.
The major threats to the Steppe eagle include habitat loss, persecution, wildfires, predation (and trampling by cattle) of chicks, and electrocutions and wire collisions, especially the latter causes. Furthermore, the genetic diversity of this species may be rapidly declining as well. The diagnosed causes of decline in Xinjiang, Tibet, and Qinghai were found mostly to be poaching, poisoning from rodent control programs, poisoning also targeted towards predators, illegal trade, food shortages, and wire collisions but perhaps most of all habitat destruction, often with their former homes destroyed to make way for roadworks, tourism, and mine exploration, with more destruction from overharvest of trees and plants and overgrazing by livestock, and accidents are frequent. Poisoning is thought to be quite prevalent in the Altais, as well as powerline electrocutions. Persecution through shooting likely continues to be of determent to Steppe eagles migrating or wintering in the countries of Georgia, Armenia, Iraq, and Jordan and, in Iraq, along with many raptors end up being offered at local markets. In Saudi Arabia, the turnover to more intensive farming activity has depleted to available habitat usable for Steppe eagles.
According to IUCN Red List, the total population size of the Steppe eagle is below 37,000 pairs. Currently, this species is classified as Endangered (EN) on the IUCN Red List, and its numbers today are decreasing.