[1][3] Individuals show a wide range of variation in plumage from pale to dark, varying with moult and age giving rise to the name "changeable".

[6][7] The changeable hawk-eagle was formally described in 1788 by the German naturalist Johann Friedrich Gmelin in his revised and expanded edition of Carl Linnaeus's Systema Naturae.

[8] Gmelin's description was based on the "crested Indian falcon" or the Falco Indicus cirratus that had been first described in 1676 by the English naturalists Francis Willughby and John Ray from a live bird kept in the Royal Aviary in St James's Park, London.

[17] Gamauf et al. (2005) analyzed mtDNA cytochrome b and control region sequence data of a considerable number of specimens of the crested hawk-eagle and some relatives.

In the continental population, genetic diversity is considerable, and the evolutionary pattern of the two studied genes did not agree, and neither did the origin of specimens show clear structures.

[17] Gamauf et al. (2005) therefore suggest the island taxa which are obviously at higher risk of extinction are, for conservation considered evolutionary significant units regardless of their systematic status.

This case also demonstrates that a too-rigid interpretation of cladistics and the desire for monophyletic taxa, as well as universal application of single-species concept to all birds will undermine correct understanding of evolutionary relationships.

It would even not be inconceivable to find mainland lineages to group closely with the western island taxa, if little genetic drift had occurred in the initial population.

[17] N. c. limnaeetus appears for all that can be said with reasonable certainty basal pool of lineages in the crestless group that, despite not being monophyletic, should be considered a valid taxon as long as gene flow is possible through its range.

As is the head, the underparts are variable with juveniles in much of India and in Sri Lanka showing thin brown streaks on chest or small spots on breast, with obscure tawny barring on thigh, legs and crissum.

The species tends to fly with a fast agile flight, showing powerful shallow beats interspersed with glides on flat or bowed wings with their carpals well forward (above level of bill) and primaries swept back.

Meanwhile, in both juvenile and adult dark morph, the blackish-brown colour of the body extends to the hand but the base of their tail, their primaries and, less so, their secondaries are a much paler, contrasting grey with streaking similar to other changeable hawk-eagles.

The shrill ringing and loud call of the changeable hawk-eagle is various described in pattern of yeep-yip-yip-yip, rising kwip-kwip-kwip-kwee-ah and penetrating klee-leeuw (for birds from the Sunda islands).

From western birds from India and Sri Lanka, the call is a slightly different ki-ki-ki-ki-ki-ki-ki-keee, beginning short, rising in crescendo and ending in long, drawn-out scream.

In northern India and Malaysia, the calls of this species have variously been compared to those of the Eurasian curlew (Numenius arquatus) and the crested serpent eagle (Spilornis cheela).

Like most tropical raptors, the changeable hawk-eagle is largely residential, but stragglers from peninsular India have roamed to northeastern Burma and southeastern Thailand and some records in the Lesser Sunda Islands (Bali, Palau and Lombok) may be from vagrants from Java.

[1][3][5][33] The species may live in savannah woodland, cultivation with trees, timbered watercourses, tea plantations, forest villages and even suburban edge.

Their physical form and flight style is typical of forest-dwelling raptors in general and is often compared to the features of true hawks or Accipiters in particular larger species such as goshawks.

[41][42] Therefore, what is known of changeable hawk-eagles dietary biology is largely drawn together based on reliable eye-witness and anecdotal accounts, photographic evidence and wide-ranging bird census surveys, rather than direct, extensive study.

On the other hand, Brown & Amadon (1986) description of this species as "not a very rapacious bird" is not entirely justified as extremely large prey relative to the hawk-eagle's size may also be readily taken.

One study in Gujarat showed several rather small prey species largely being taken such as the Indian chameleon (Chamaeleo zeylanicus), Oriental garden lizard (Calotes versicolor), other lizards, common myna (Acridotheres tristis), red-vented bulbul (Pycnonotus cafer), other birds (including unidentified parakeets and gamebirds), Indian bush rat (Golunda ellioti) and a palm squirrel.

[5][46][47] In Mudumalai National Park, only three prey types were specified to genera which consisted of black-hooded oriole (Orolus xanthornus), common bronzeback snake (Dendrelaphis tristis) and an unidentified giant squirrel.

[5][43][53][54] Even more impressive accounts and photos show that changeable hawk-eagle can hunt and kill adult mammals with formidable defenses such as felids and primates, although it cannot be ruled out that they will usually attack infirm or injured specimens rather than healthy ones.

[43][58][59][60][61][62] While their predator-prey relationship is even more nebulous, the peculiar, smaller but toxic nocturnal primates known as slow lorises are known to fall prey as well to changeable hawk-eagles.

During the display, the shoot up vertically and nose-diving or stooping, if the rival hawk-eagle continues to engage the defending individual, they will fly at each other at "lightening speed" doing a complete loop-the-loop turn in air.

[3][30] In the equatorial Greater Sunda islands, eggs have been recorded in 8 different months at any time from December to October with peak activity falling usually between February and August.

The eaglet may be preening, standing more and wing flapping by 4 to 5 weeks old, and may also be encouraged to eat at by its mother, however consuming a single food item may take up to 6 hours at this point.

This trend, holding steady in population or even increasing while other hawk-eagle species have declined, has been reported in the Indian subcontinent, Malaysia, Java and the Philippines as well as elsewhere in southeast Asia.

[36] However, their adaptability can be overstated and this species requires tall trees (though secondary growth forest is acceptable), appropriate habitat composition and ample prey populations to flourish.

[3][5] A more secondary concern, but potentially depleting populations in India at least, is that it will not infrequently hunt chickens (especially during breeding when such easy prey is hard to resist), which has in turn resulted in changeable hawk-eagles being locally persecuted.