Weird behaviour of a Malaysian Night Heron

Desmond Wong a.k.a. des95446 encountered a Malaysian Night Heron (Gorsachius melanolophus) in later December 2009. The bird was foraging, picking up some dead leaves then spitting them out. As it went about foraging, it suddenly stopped, raised its crest and lodged its lower mandible against the skin around the neck to widen its gape. It then shook its head left and right.

From the image below, there appears to be an elongated darkish foreign object stuck in the mouth. Was the heron trying hard to dislodge the object from its mouth? The attempt was unsuccessful and the heron continued foraging. Or was it casting a pellet? A dark elongated pellet?

Bird behaviourist John Vickerman has this to say: “…Clearly, there are two issues involved here: (a) regurgitation and (b) why is the lower mandible tucked into the fold of the neck skin?

Regurgitation: As with nearly every bird species, herons do regurgitate pellets of unwanted or indigestible parts of consumed food. Casting of pellets is often accompanied by vigorous head shaking as witnessed by Desmond. In herons, (unlike with most raptors where bony material is nearly always cast via pellets), there are only very few instances where bony material of fish, amphibian or mammalian food have been found. Therefore, herons digestive processes seem to be able to cope very well with bones. However, herons do cast fur from mammals in pellet form.

“Now what is the material that is being attempted to be cast in Desmond’s image? Most bird pellets are, to a varying degree, elongated and oval in shape. It appears to me that this bird is attempting to cast a long and very thin object – rather ‘unoval’ in shape! I am uncertain that this is, in fact, a pellet in the process of being cast by regurgitation. If not, then what is it then? …might a long thin curled-up dead leaf have got stuck towards the back of the throat thus making it difficult to easily shake out with the rest? If that was the case, then it is not unreasonable to expect the bird to embark upon the more drastic, but quite normal, exercise of a regurgitation-type of retching exercise. …My belief is that either the item was discarded in one of the rapid head-shaking movements but out of sight of Desmond, or, with the discomfort at the back of the throat relieved, the item may have been swallowed in which case it could have been a food item that needed repositioning before being comfortably swallowed. I think we shall never know the answer for certain as to what the item was, or whether it was discarded or consumed.

Lower mandible in the fold of the neck skin: In my opinion, this is the most fascinating part of what Desmond witnessed. …In Nature, there are occasions when something quite new is witnessed. One has to believe the evidence of one’s own eyes and new behavioural activities are being documented all the time. Desmond’s could be one such piece of observation documenting a new aspect of the behaviour of this particular and under-researched species as is noted in the book entitled The Herons (JA Kushlan & JA Hancock, Oxford University Press, 2005) that, ‘Much of the basic biology of this species remains to be determined. Information coming out of recent observations hints that this species may be of considerable biological interest. ….This is a species that could reveal new elements of Heron behaviour.’

“I can find no reference to this kind of behaviour in any of the literature I regularly use for reference purposes. …Certainly, Desmond’s evidence of this aspect of the Malaysian Night Heron’s behaviour is too interesting to hide away, especially since it seems there is very little known about many aspects of the biology of this species anyway. It would be a great reward if some researcher somewhere came out of the woodwork having noted similar behaviour, or someone who may wish to use this observation as a stimulus for a research study.”

As a postscript, John has this to add: “…birds can and do impale their bills accidentally in many different ways, and to reject the reasoning behind an observation outright concerning a piece of behaviour just because it hasn’t been recorded before is a very dangerous stance to take with sometimes embarrassing consequences! I learned many years ago that it doesn’t pay to suggest to people that they didn’t see or understand what they claimed to have seen and interpreted – Nature has a nasty habit of coming back and biting you and making you look utterly foolish! However, I do believe very strongly that Desmond’s account of his experience should be more widely circulated if possible, and certainly be archived for future reference. Further corroborative evidence of similar behaviour would be useful – not easy with a species like this which I believe is pretty skulking at best and invisible mostly! It is work like this that earns people their Ph.D.!”

Note: Through the courtesy of KC Tsang, Desmond’s images and observations were circulated in BirdForum. Although there were many responses on this weird behaviour, we have yet to receive any new information. We welcome any new imput.

This post is a cooperative effort between NaturePixels.org and BESG to bring the study of bird behaviour through photography to a wider audience.

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