Oriental Pied Hornbills moulting rectrices

posted in: Feathers-maintenance, Hornbills | 0

“The pair of Oriental Pied Hornbills (Anthracoceros albirostris) that was prospecting for a nesting cavity at Pasir Ris Park in January 2011 seemed to be unsuccessful. We crossed path again, on 25 Feb 2011. Apparently, they had a guest and were still not nesting after slightly more than one month.

“The female was first spotted on a stump at a height of just 2 metres. She was fairly accommodating and allowed me to approach near. I noticed that the central long black tail feathers that were part of her rectrices, on the top part of her tail, were missing (above left). The rectrices must be in moult with the two distinct black tail feathers discarded. Only the white feathers that were normally hidden under the two central black feathers were present. Thus exposed, I discovered that the white rectrices that were usually hidden were not completely white. The upper part of these feathers was in black. A close-up image of her tail revealed two new pin feathers had begun to grow out from her tail, replacing the discarded black feathers on top of the remaining rectrices (above right). The tube-like sheaths with new emerging vanes were clearly visible.

“As I moved closer, I saw the male perching on another tree a short distance away (above left). Then, another female was seen, perching on the same tree, but on a different branch, not far from the male. The central long black tail feathers of the male were similarly missing in moult. The second female was the odd one out as she still had her central black rectrices in place (above right).

“The three hornbills did not remain there for long. One after another, all of them disappeared into the dense undergrowth. Being large birds, it was remarkable to see them squeezing through the gaps in between the stems and foliage before disappearing into the dense vegetation.

“In the field, I was not sure which was the original partner of the male. After reviewing and comparing with previously captured images of the pair, I was able to determine that the male’s original mate was the first female. The clues could be found in the unique markings on her bill. The images of the pair taken on 4 Feb 2011 showed both birds still with their black rectrices intact (above).

“With their rectrices moulting at the same time for this pair of hornbills, I cannot help but wonder whether birds are capable of controlling the timing of their moulting. Could this pair share a bond so closely that they decided to moult together? Or was it merely coincidence?”

Kwong Wai Chong
23rd March 2011

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