Sunday, January 14, 2007

Birds & Galls

I've noticed over the years, that some birds seem to be attracted to the galls commonly found on acacias. On the face of it, these galls seem particularly unlikely to be a food source for small birds. Patently most of them don't have the means to break into them, so why the interest? Well I've looked at many of them, and the only thing I've commonly found, are minute white grubs. These grubs, no more than a couple of millimetres long, are secreted in the crevices, no doubt many other insects find shelter there too. Whether the grubs are the food source I've never been able to ascertain. Neither do I know whether they are in any way associated with the insects that cause the acacias to form galls in the first place. Silvereyes seem to be the main species that seek food on the galls, but photographed here, is a Black-headed Honeyeater. This bird, was one of a family group that took it in turns to search the galls. Has anyone else seen birds on galls, or knows what they are feeding on?

2 comments:

John Tongue said...

Hi Alan,
Though I have a biological science degree, and taught science at high school for a number of years, I certainly don't see myself as an expert. However, I do seem to recall that many 'galls' are produced in response to the tree being invaded by 'gall wasps', or other like insects. Possibly, as the larvae, or juvenites of these insects are leaving the gall, the birds gather for a free 'takeaway'? Just a thought?

Jon Hosford said...

I have seen Eastern Shrike-tit feeding on similar grubs in the galls of young red river gums on the Murray. I have assumed the grubs have hatched from eggs laid by the gall forming insect.