Monday, October 02, 2023
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Wallace's Hawk-eagle (Nisaetus nanus)

What a magnificent find on the banks of the Kinabatangan!

As Chin Hock and I we were cruising up the Kinabatangan, we spotted this conspicuous clump of branches stacked rather untidily in the fork of a tree. 

We had found a raptor’s nest perched 20 metres up from the river. 

We tied the boat to the trees on the bank to get a more stable platform from which we could get a few nice shots.  After ten minutes the strain on the  neck was getting unbearable from the stress of peering up at 80 degrees. 

But this pair of hawk-eagles were quite calm and generous with their poses, even exchanging places at the nest, as if taking turns for a photoshoot. 

The Wallace’s Hawk-eagle, presumably named after that most famous English naturalist, is an uncommon resident in Peninsular Malaysia and Borneo, and apparently absent from North and West Sabah. 

As there are other look-alike raptors that mimic this hawk-eagle, we needed to find the distinguishing feature on their tarsus or feet to ensure this is indeed the Wallace's and not the imposters.

Two suspects of this mimicry 'crime' are the Oriental Honey Buzzard and the Jerdon's Baza. The hawk-eagle is considered the model and the other two the mimics. In this interesting behavior called Batesian mimicry, a smaller, less numerous species like the Jerdon's Baza would mimic the Wallace's Hawk-eagle to protect itself from attacks from larger eagles or other Wallace's. The rare resident race of Oriental Honey Buzzard also mimics the Wallace's Hawk-eagle, although it is similar in size - so I'm not sure why it does that. I guess they have issues?!

Anyway, the key to distinguishing the Wallace's from the other two mimic birds is in the feet or tarsus - the Wallace's is feathered all the way to the base of the toes (i.e. the ankles), while the other two would-be's do not have feathers on their tarsus.

This was the tree with the nest

Some other close ups of the Wallace's Hawk-eagle