waders and their estuarine food supplies - Vlaams Instituut voor de ...

the burrow depths and on the fraction of worms being
actively feeding.
Prey si/e selection hy waders
The pre; si/c selection of a bird may be predicted, assuming
that birds piobe lo a certain depth and do this
ai random, as shown for Oystercatcher (Ch. 8) and
Knot (Ch. 12). Comparison of the si/e frequency distribution
of the prey taken with those of the size classes
on offer, reveals that birds ignore the small size
classes. These small prey are unprofitable, i.e. the intake
rate during handling the prey is below the average
intake rate during handling and searching combined.
By ignoring these prey, ihe birds enhance their intake
rate.
INTRODUCTION
Ignoring prey to maximize intake rate
An experiment was set up to test w bether an Oystercatcher
feeding on bivalves buried at different depths
maximized its intake rate (Ch. 7). Shallow prev could
be handled very fast and were thus highly profitable, ln
conliasl. it tOOk much time to eal pre) fioin giealei
depths. The prediction was that the decision to include
these prey in the diet, or to ignore them, would depend
on the intake rate. It was found that the bird, conforming
the prediclion. took all prey within reach of the bill
at low prey densities, but only prey from the upper few
cm when the prey occurred at high densities. However,
the bird was able to eat more prey than the model predicted
for the high prey densities. The explanation w as
that the bird selectively took only the prey thai could
The observation lowers on ihe lidal Hals were strong enough lo resist winds with hurricane force and storm tides, but Ihe force of drifting ice
was ioo much. Hence we had io rebuilt the towers alter everv severe w inter.
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