Tawny eagle

The tawny eagle is considered to appear "inelegant, scruffy-looking" but has a fairly characteristic aquiline silhouette. The species has a fairly long neck and long deep bill with a gape line level with the eye, moderately long wings with fairly pronounced "fingers" and a slightly rounded to almost square-ended and shortish tail, which can be more reminiscent of the tail of a vulture than that of other eagles. The feathering on the legs is extensive and can appear almost baggy-looking. The bill and head are strong and bold, the body well-proportioned and feet are powerful while the countenance is quite fierce-looking. While perching, the tawny eagle tends to sit rather upright, often on stumps, posts, low trees or treetops for long periods of the day or may descend to the ground to walk somewhat unsteadily with a more horizontal posture. The wingtips when perched are roughly even with the tip of the tail. Adults have variably colored eyes, ranging from yellow to pale brown to yellow brown, while those of juveniles are dark brown. Both the cere and feet are yellow at all ages. The tawny eagle is polymorphic with considerable individual variation in plumage, resulting in occasional disparities in plumages that can engender confusion in some. In adulthood, they can vary in coloration from all dark grey-brown to an occasionally streaky (or more plain) foxy-rufous to buffish-yellow. Most adults are usually a general grey-brown or rufous-tawny color, with occasional pale spotting visible at close quarters on the nape and belly, coverts uniformly toned as the body. The nape is consistently dark and uniform despite the feathers often being tipped paler with other feathers in adults, lacking the contrasting paler feathers often seen in other Aquila. Females, in addition to being slightly larger, may tend to be slightly darker and more streaked than the males. The most blackish-brown individuals tend to occur in India. Adults often show relatively little varying colors apart from their somewhat blacker wing and tail feathers, though when freshly molted great wing coverts and secondaries may show small pale tips which may form pale lines along closed wing has tawny upper parts and blackish flight feathers and tail. The head is often similarly tawny in colour as the body but may also sometimes shows darker eyebrows, other thin brown streaks or a darker chin. Meanwhile, the tail is plain or obscurely dark barred (with around 7 subtle bands). The dark morph adult is essentially all dark, dull brown. Some dark morph tawny eagles with wear may show irregular streaking or molting browns and more blackish feathers. Intermediate morph are dark to rufous brown above with the mantle and wing coverts variably streaked or molted lighter rufous as is the head with the crown or crown-sides being paler. The intermediate morph's underside is largely rufous (especially farther south in Africa) with breast and flanks very heavily and broadly streaked dark brown, though at times appears all dark brown contrasting with plain trousers and crissum. Pale morph adult tawny eagles always show a clear contrast between the pale body and wing coverts which bear darker flight feathers and tail. In pale morphs, the underparts are rufous buff to lighty tawny-brown, phasing into somewhat darker lesser and median wing coverts to darker brown to even blackish greater coverts and flight feathers. The head may too be tawny in pale morph tawny eagles but sometimes with thin brown streaks or darker chin. Below pale morph adults are all light rufous to tawny buff or brown, sometimes paler below the belly area. In worn individuals the bodily feathers of pale morph tawny eagles can appear almost whitish. Dark morph juvenile tawny eagles are generally light rufous to rufous brown with creamier lower back to upper tail coverts. Juveniles show thinly pale-tipped dark brown greater coverts and remiges while the tail is barred grey and brown usually with a narrow creamy tip. Dark morph juveniles may fade to pale buff or creamy often before molting into browner plumage. Subsequent stages are not as well-known but it appears dark morph subadults gradually manifest a darker brown or rufous brown color on the mantle, as well as on the head and upper breast while maintaining a buffish rear body (i.e. lower back and rump patch). Generally other morphs are similar but not as well-known and are perhaps individually inconsistent. Many are rufous or sandy after a molt but have mottling later on, the extent of pale feathers indicative perhaps of their ultimate adult morph.

In flight, the tawny eagle appears as a large raptor with a noticeably protruding head on a long neck, with a deep chest, long and broad wings with a somewhat narrower seven-fingered hand. The trailing edge of the wing is slightly curved outwards, indenting at the junction of primaries and secondaries, whilst the rounded, medium-length tail is usually held spread. The deep beats of the kinked wings can make their flight appear rather heavy and slow but they are quicker and more expansive in wing movements and often less forceful-looking than larger Aquila like steppe eagles and can be very agile when chasing other raptors to rob them. Tawny eagles soar with flat wings or very slightly raised and hands only slightly lower, and may fly similarly in a glide but may too arch when in a fast glide. Adult dark morphs are more or less uniform dark brown above and below, showing indistinctly and slightly paler and greyish primaries on both sides. Above, the main contrast on dark morphs above is paler creamy rump patch while, on the underside, the greyish color is contrasted with blackish tips and a diffused trailing edge along both the wings and tail. Intermediate morph tawny eagles are variably rufous streaked on brown to rufous brown on the back and wing coverts with a similar contrasting pale rump above as dark morphs. Below the intermediate's heavy dark streaks are only subtly different and their coloring can appear almost uniform. The wing quills of intermediate morphs are often greyer with a stronger contrast of the paler inner primaries and blackish wing ends. Pale morph are all pale tawny or buffish on both sides of the wing, which contrasting strongly with demarcated dark brown about the greater coverts, flight feathers and tail and usually the scapulars. The primaries are quite pale on pale morphs with sometimes the hint of a pale carpal comma. Some pale adults have pale bases to all the underprimaries and the quills are sometimes unbarred, but more usually the feathers have dense but narrow dark bars. Dark morph juveniles are light rufous to pale tawny body above which contrasts strongly with dark brown greater coverts, rear scapulars, flight feathers and tail, in turn all highlighting the creamy lower back to tail coverts. Below dark morph juveniles can look similar to pale morph adults apart from trailing whitish edges and often irregular pale diagonals along tips of greater wing coverts, though usually these fade early on. Little is known plumage development but the young eagles moult into brown, becoming patchy with intermediate often showing 1-3 darker bars on wing linings. The underparts of subadults (i.e. around 2 to 3 years or old) are typically two-toned, with darker brown about the breasts, belly and underwings coverts while the remainder of the underbody is creamy light in colour. This two-toned pattern is evinced in subadult tawny eagles both from India and Africa. Adult plumage is obtained between the 4th and 5th years of life.

This is a large bird of prey, though is medium-sized for an eagle and it is one of the smaller species in the genus Aquila. Among currently accepted species in the genus, it is of quite similar size to Bonelli's eagles (Aquila fasciata) (though is notably longer winged), slightly larger than African hawk-eagles (Aquila spilogaster) and much larger than Cassin's hawk-eagles (Aquila africanus). Otherwise, females of the larger species of Aquila are frequently around twice as heavy as an average tawny eagle. As is typical in birds of prey, the female tawny eagle is larger than the male, though relatively modestly so and a difference between the sexes is typically up to 15%. In total length, tawny eagles can measure from 58 to 75 cm (23 to 30 in). A typical length for a tawny eagle is considered about 65 cm (26 in). Wingspans can measure from 157 to 190 cm (5 ft 2 in to 6 ft 3 in). Weight can range in fully grown birds from 1.5 to 3.1 kg (3.3 to 6.8 lb). Average weights were reported in one study as 1.91 kg (4.2 lb) in 5 males and 1.97 kg (4.3 lb) in 5 females. In another study, 10 unsexed adult tawny eagles were found to have weighed 2.5 kg (5.5 lb) on average while, for the same data pool, a sample of 15 had an average wingspan of 182.9 cm (6 ft 0 in). Another small sample of African males, sample size four, averaged 1.85 kg (4.1 lb) while three females averaged 2.28 kg (5.0 lb). The mean mass of the species in one estimate was 2.3 kg (5.1 lb). In all standard measurements combined, the wing chord can vary from 473 to 565 mm (18.6 to 22.2 in), the tail from 242 to 295 mm (9.5 to 11.6 in) and the tarsus from 79 to 92 mm (3.1 to 3.6 in). The culmen length of Kenyan tawny eagles was measured at 33.3 to 42.4 mm (1.31 to 1.67 in), averaging 37.7 mm (1.48 in), while the gape width is 44 mm (1.7 in) on average, ranging from 40.3 to 49.9 mm (1.59 to 1.96 in). The hallux-claw, the enlarged rear talon often used as a killing instrument on accipitrids, can measure from 27 to 37.7 mm (1.06 to 1.48 in), averaging 31.8 mm (1.25 in) in one sample and 32.3 mm (1.27 in) in another. The talon size is not especially large for a booted eagle and is proportionately similar in size to those of steppe eagles and eastern imperial eagles (Aquila heliaca).

The tawny eagle lives in multiple areas where other broadly similar brownish hued and largish raptors often occur. Thus identification is seldom straightforward.

One source that can especially engender potential confusion in its wintering range is the formerly conspecific steppe eagle. The steppe is larger with a shorter neck, relatively longer and narrower wings, a more massive beak, particularly via the exceptional depth of the gape (although in flight can appear smaller headed due its less protruding neck) and has a longer and rounder tail. Furthermore, steppe eagles tends to have much bolder and widely spaced barring on the wings than tawny eagles and more distinct dark trailing wing edges and paler throats.

Beyond steppe eagles, comparisons to various other groups of sympatric booted eagles may be made. Compared to the spotted eagles, the tawny eagle's tail is longer, the bill more prominent, the wings usually less squared-off in flight, the neck longer and the overall look rangier, despite these species being of often similar size. In contrast to the imperial eagles, the wings of the tawny eagle are broader and have less even trailing edges, the bill is slightly less prominent, and the wings are more likely to be held slightly upwards, while the body size is smaller. When compared to the golden eagle species complex, of which only the golden and the Verreaux's eagle (Aquila verreauxii) are usually relevant (although three dissimilar and sympatric pale-bellied eagles, of a size with tawny eagles or smaller, are found as part of this evolutionary chain), the tawny eagle is considerably smaller, its wings do not taper as much nor are they as likely to be held in a strong dihedral, and proportionately, the bill is notably longer and the tail is rather shorter. Greater spotted eagles (Clanga clanga), like the steppe eagle a Palearctic breeding eagle who often winters in the resident range of tawny eagles, is fairly similar, but that species has a relatively shorter and broader tail, less baggy feathers on the legs and usually a rather darker and more uniform adult plumage. The fulvescens form of the greater spotted eagle must be distinguished from the pale forms of the tawny eagle by its underwing pattern, often with completely blackish underwing coverts and usually plain looking dark remiges over the entire primaries with more distinct pale carpal arcs. The likewise migratory lesser spotted eagle (Clanga pomarina) is smaller than the tawny eagle and more compact with a distinct white U above the tail. The residential African Wahlberg's eagle (Hieraeetus wahlbergi) can have a similar uniform plumage as in tawny eagles but always has greyer flight feathers and is much smaller than tawny eagles with relatively longer and more rectangular wings and a longer, narrower and straighter-tipped tail. The eastern imperial eagle in juvenile plumage can appear similar to the pale and intermediate morph tawny eagles, but the imperial eagle is usually visibly larger, with slenderer, longer wings, a longer, broader tail as well as having dark brown streaking on the chest, mantle and wing coverts and bearing more distinct pale trailing edges and wing bars.

Dark-morph tawny eagles in India may be distinguished from similarly sized black eagles (Ictinaetus malaiensis) by the latter being slenderer and having longer, darker and more paddle-shaped wings with a narrower base and a much longer, narrower and distinctly barred tail. More dissimilar eagles such as Circaetinae, i.e. brown snake eagles (Circaetus cinereus), black-breasted snake eagles (Circaetus pectoralis) and juvenile bateleurs (Terathopius ecaudatus), are sometimes mentioned as a potential source of confusion but are usually rather distinct (all larger headed, rather smaller billed, shorter tailed and bare legged with often less uniform coloring) even in their most similar hues.

Tawny eagles are generally silent in most of their range. However, unlike steppe eagles, which are almost always silent away from their breeding grounds, they are said to occasionally vocalize in any season. They are also more vocal when not breeding than the spotted eagles. The usual call is a harsh, hollow-sounding, loud bark, variously transcribed as kowk-kowk, kau-kau, kiok-kiok or ki-ark. The call is fairly high-pitched (slightly less deep than the steppe eagle's when the latter is breeding) but is still deeper voiced than spotted eagles. In Kruger National Park it is said the call is loud and far-travelling. Male tawny eagles are the most frequent vocalizers in the species, particularly during sky-dances, but also in other contexts. These include but are not limited to food arguments, disturbances during nesting and males attracting females for food passes. In nine years of monitoring tawny eagles in Zimbabwe, however, the call was not heard once. Its silence there may be due to the flat landscape. Other call recorded include a harsh grating k eke ke... in aerial courtship displays and a throaty kra in kleptoparastic pursuits. A kra-kra call may emitted at times to warn intruders. The female may also emit an occasional mewing, high shreep-shreep at the nest as well as a rare raucous scream (possible food-begging and alarm calls, respectively). The young chick tawny eagle chips initially but once its feathers emerge, it tends to beg with a loud call, i.e. we-yik, wee-yik.