The Responses of Redshank (Tringa totanus (L.)) to Spatial Variations in the Density of their Prey

Abstract

Present evidence suggests that a predator's response to increases in the density of its prey is an accelerated rate of feeding up to an asymptotic level where further increases in prey density result in no further change in feeding rate (Holling 1965). Hence when predators respond to local variations in prey density by aggregating in areas where the prey density is greatest, they are probably showing a preference for those localities where their feeding is most efficient (Hassell 1966). Very often the measurements necessary to demonstrate these responses in feeding efficiency and density are difficult to make under field conditions. On estuaries, however, the numbers and feeding rate of some birds are relatively easy to measure and the density of their prey often easy to assess. Preliminary studies on the Ythan estuary in Aberdeenshire (Goss-Custard 1966) revealed that these aspects of predation could be conveniently studied in the redshank (Tringa totanus (L.)), a wading bird which feeds on several species of small invertebrates. The aims of the present study, then, were to test the hypothesis that both the density of redshank and their feeding efficiency were positively correlated with prey density.