Hornbills in Nameri

I was reminded of Nameri and the Pakke Tiger Reserve since we began to discuss a trip to Tawang. One of my best memories from Nameri comes from February 3, 2009. Walking by the banks of the Jia Bhoroloi river just before sunset, we were transfixed by the sight of a huge flock of hornbills coming in to roost for the night. The beating of their enormous wings is a bass sound that you will not forget once you hear it. We stood in silence listening to the flock approach and settle on to trees. Every tree along the river that we could see had hornbills roosting on them. Here is a photo I took that evening: twenty-five hornbills in one tree.

At that time we had put them down as Oriental pied hornbills. But now looking at the photo I think they are all Wreathed Hornbills (Rhyticeros undulatus): the neck of the male is white in front, except for a yellow band just below the bill, and the back has some red; the chest is black, and there is no casque on the bill. Male Oriental Pied Hornbills (Anthracoceros albirostris) would have had a white chest, black neck, and the males would have a casque on the bill.

Interestingly, all the birds on this tree are male. My photos do show some trees which have both sexes. But this raises another question. A little reading shows that there are usually equal numbers of males and females in a population. During the breeding season (March to July) the female seals herself into a nest, in a hole in a tree, using her saliva and droppings. As a result, during the breeding season one sees more males than females. This photo was taken in early February, which is not the breeding season, so one should have seen equal numbers of the sexes. In trees with two sexes, the males and females sit paired up. Maybe I should have photographed several more trees to check whether there are also segregated roosts of males and females. I’m sure some scientist knows the answer to this question.

Note added

In the Wreathed hornbill, the juveniles all look like
males, and the females do not start changing their
coloration till after the 1st year. In the non-breeding
season, one sees these large flocks of young birds
which all look like males.

Aparajita Datta (Nature Conservation Foundation)

Asking a scientist does work surprisingly often. I sent a link to this blog and photo to a leading expert on hornbills, and received the reply alongside. So there are no gangs of juvenile males and females, the sex ratio is even, and my photo just includes many juveniles of both sexes, some adult females, and, possibly, the same number of adult males. I’d missed the adult females, until the expert pointed them out to me.