Barbets and cavity excavating
Posted by BESG on 9 November 08, Sunday
Contributed by Dr Eric Tan
Barbets are primary cavity nesters, or most of them are. They thus nest in freshly excavated cavities that they dig from rotting tree trunks and branches. This is one of a few groups of birds that are able to excavate their own cavities. Such capability is rather surprising, considering the large, usually sharply pointed bill that do not appear to be adapted for such an activity.
For roosting, some species excavate their own cavities. Others use cavities abandoned by other birds. Some even take over cavities being excavated or actively evict nesting or roosting occupants.
When actively excavating a cavity, as in the case of the Green-eared Barbet (Megalaima faiostrica) above, the tail of the bird is appressing to the bark, just like woodpeckers when probing tree trunks for insects. The entrance is usually just large enough to fit the body of the bird. This gives it an advantage when defending its cavity from intruders.
When excavating, wood chips are usually carried away, so as not to make the nest location conspicuous to predators. Red-faced Barbet (Lybius rubrifacies) has been known to even swallow the chips and regurgitate them away from the nest. Nest excavation can take from a few days to 30 days or more. Both sexes, as far as is known, help in the excavation.
Usually, barbets do not reuse the nesting cavity after the chicks have fledged, thus providing cavities for use by non-excavating cavity nesters like parrots, kingfishers, owls, etc.
Image by Dr Eric Tan.
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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Categories: Barbet, To'can, H'guide, Nesting
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