2022-0211 A Day On The Beach

Territorial Sanderling on Limantour Spit

Compared to the preceding photograph, the posture of this bird is even more hunchbacked. The wing is drooping even more. Sometimes the posture is so extreme that the wing is almost dragging on the beach. This happens when two territorial neighbors get close right near their shared boundary.

Part of my PhD dissertation (fieldwork at the Bodega Marine Lab) analyzed data on food density and the numbers of intruding Sanderling feeding in different sectors of the beach. The analysis indicated that territory size was mostly determined by the number of intruders... the more there were the more difficult it became to defend a large territory. And that intruder density was probably due to food availability: more intruders attempted to get into the best feeding sites. Our data rejected a long-standing competing hypothesis: that territory size was adjusted to food density so that a bird defended larger territories where there was less food. The reasoning behind this hypothesis was that a bird would choose to defend a territory big enough to secure a food supply.

Here's the reference:
Myers, J.P., P.G. Connors and F.A. Pitelka. 1979 Territory size in wintering sanderlings: the effects of prey abundance and intruder pressure. Auk 96:551-561


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SanderlingLimantour Spit