Oriental Pied Hornbill – possible co-operative breeding

“I have intentionally left out details on the location and dates for this observation as these birds are still breeding and I want to avoid them being disturbed by too many observers/photographers.

“I was watching birds when I came across a pair of Oriental Pied Hornbills (Anthracoceros albirostris convexus) who, at first, appeared to be displaying some courtship behaviour. I was taken aback when the adult female regurgitated a prey, a large insect (top), and then proceeded to fly over to a nearby nesting hole and possibly feed another bird or birds inside (above).

“I did not approach the nest to look as was concerned with disturbing the nesting and am uncertain as to whether any adult female and/or young were in the nest. The adult male then did the same action (above). I am trying to understand this behaviour and there are a number of possibilities:

“1. Was this co-operative breeding?
Co-operative breeding is known to occur in some species of Hornbills. Kinnaird ‎& O’Brien (2007) provide a list of hornbills known to practice co-operative breeding. For my region only the Bushy-crested Hornbill (Anorrhinus galeritus) and the White-crowned Hornbill (Berenicornis comatus) have been documented to practice co-operative breeding. It has yet to be described in Oriental Pied Hornbills. It is possible that what I observed was co-operative breeding as Oriental Pied Hornbills are fairly social and I have often seen them in flocks or feeding together.

“2. Has the young not fledged?
A second possibility is that this adult female has recently left the nesting hole and a young (or more) had not yet fledged for some reason? The sealing on the nest was partially broken. It is possible that young are due to fledge and the adult female has left first? Or that the young cannot fledge due to injury or disease.

3. Is this some form of courtship behaviour?
A third option was that this is a courtship behaviour; some ritual that encourages mating or showing a desire to start another round of nesting? I did see the male allopreening the female briefly and making soft calls. So could the regurgitation of feeds and visit to nesting hole be a courtship behaviour that cements a bond between the pair?

“Having watched birds for more than 40 years I am certain that we are just scratching the surface of our understanding and knowledge of bird behaviour.

“Appreciate any opinions or ideas from experience or literature.”

References:
1. Margaret F. Kinnaird, ‎Timothy G. O’Brien. The Ecology and Conservation of Asian Hornbills: Farmers of the Forest. University of Chicago Press, 2007.
2. Ng Bee Choo. Hornbills-Thailand: Status and distribution of hornbills in Thailand. Oriental Bird Club Bulletin 28, November 1998. LINK
(Brown, Bushy-crested and White-crowned Hornbills employ a co-operative breeding strategy. This means they have nest helpers, usually yearlings of the same family, to assist with the feeding of the female and the chicks.)
3. Alan Kemp. The Hornbills: Bucerotiformes (Bird Families of the World). Oxford University Press, USA, 1995.
4. Kemp, A.C. & Boesman, P. (2017). Oriental Pied Hornbill (Anthracoceros albirostris). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/55904 on 22 April 2017).

Dato’ Dr Amar-Singh HSS
Ipoh, Perak, Malaysia
2017

Location: Malaysia