Changeable Hawk-Eagle: A lesson in IDing a bird

The Changeable Hawk-Eagle is known in Malay as Helang Hindek which translates to foot leverage eagle.  The Malay name refers to this eagle's habit of sitting upright “at the outer end of a branch” [i.e., the lever arm] “…a bird of prey that wants a clear view of its surroundings.”  The quotations are both from sealang.net/malay/dictionary.htm; search for hindek.  

Is this a Foot-leverage Eagle?

The English name ‘hawk-eagle’ also refers to this bird’s hunting style.  It is an eagle that hunts in dense or open forest in the manner of a goshawk.  The ‘changeable’ part of the English name is potentially misleading.  It does not mean a single bird can change its appearance in the manner of a bian lian or Chinese opera face changer (Chinese Face Changing-theatrebeijing.com).  Instead, ‘changeable’ refers to the extreme variability of this hawk-eagle which ranges across 13 million square km, from India to Philippines.  Although I have seen this species previously (in India) I did not initially recognise it when I saw the Malaysian subspecies.

This hawk-eagle is ‘changeable’ because

  •        Firstly, it exists in three distinct colour morphs: pale, dark (melanistic) and intermediate forms.  Melanism is quite widespread in the animal kingdom.  For example, melanistic leopards or black panthers are well known; melanism has been noted in ten other cat species.  Peppered moths, lizards, vipers, and squirrels are some of the other animals exhibiting melanism.  Amongst the birds, about 20% of the world’s hawks and eagles have documented colour morphs.  Generally the pale form is generally more common; if instead the dark form predominates, then the lighter morph birds are termed leucistic.
  •         Secondly, the crest of these eagles can range anywhere from non-existent to 14 cm long.  

Does this bird possess a crest?

Whilst I knew of the different colour morphs, I was unaware or had forgotten the difference in crest lengths.  Hence, when I turned to an old guidebook, I was doubtful.  Was my bird a juvenile honey-buzzard or an adult changeable hawk-eagle?  I decided to do some online research.  From Wikipedia I learned (or re-learned) that the crestless form of this hawk-eagle exists and “is found through the Himalayan foothills … to much of southeast Asia including the Malay Peninsula[emphasis added].”  Furthermore, the Wikipedia article stated “the honey buzzard generally looks much more solidly orange-buffy as a base colour rather than whitish below.” (wiki/Changeable_hawk-eagle).  My tentative ID began to swing from honey-buzzard to hawk-eagle. 

Finally, I compared my bird to online photographs of the changeable hawk-eagle.  My two sources were Birding in Malaysia  with 10 photographs and the Oriental Bird Club Image Database with 433! Possibly, just possibly, too much of a good thing?  You be the judge.  Birding in Malaysia’s first photograph (by Ooi Beng Yean shot in Chemor, Perak on 18th August, 2002) looked remarkably like my bird. I decided I had seen an adult pale-morph short-crested Changeable Hawk-eagle.  I should admit to much admiration (and a little envy) of the remarkable first photograph in the Oriental Bird Club Image Database. It is by Shyam Ghate shot in Tadoba National Park, India on 3rd May, 2015.  I still have much to learn about bird identification and nature photography.  Ars longa, vita brevis.

  

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