Tuesday, 6 October 2009

Bent-billed Curlew

I watched a curlew feeding on the tidal flats at Budle Bay at the weekend. When the bird withdrew its bill, I thought I had a new species for a moment .......

..until the protruding worm wriggled before being swallowed.

After the bird poked its bill into the mud, I watched as it moved its head from side to side and front to back. It was clearly 'feeling' for food and therefore must have some sort of sensitivity in the bill tip. In fact, if it is able to detect a soft-bodied worm, it must be very sensitive indeed.
Reading around to find out more about the design of the bill, I discovered that it is full of sensory organs located in small pits in the bill structure (as are other waders such as snipe for example). This prompted me to go and root about in the garage for a curlew skull that I collected from a dead bird and cleaned up some years ago.

If you look closely at the tip of the bill (and note that this is the underlying bone structure without the bill sheath that overlies this), you can see lots of small holes - presumably the location of these sensory structures.
The common perception of a bird's beak as hard, dead material probably derives from the painful experience of a budgie peck. In reality, the bill of the curlew is a delicate and complex structure.

Later, the bird wandered off into the distance and beyond my compact camera range. As I followed it in the telescope it found a small crab, picked it up by one leg and shook it vigorously. The leg broke off - as it is designed to do (there is a line of weakness designed-in as a predator escape mechanism). The curlew discarded the leg and picked up the crab again by another and did the same. Although I couldn't be sure, it looked like all were similarly treated until the hapless, and by now, legless, decapod was swallowed. A neat trick, but was that learned or inherited behaviour? Somebody somewhere must know....

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