Beach-Foraging Behavior of Northwestern Crows as a Function of Tide Height

Abstract

From 8 February to 8 June 1995, we investigated aspects of the foraging behavior of northwestern crows (Corvus caurinus) in the intertidal zone relative to various tide heights and invertebrate availability along an urban beach in Seattle, Washington. We directly sampled the density and diversity of invertebrates in the upper, middle, and lower littoral zones to assess their distribution. We recorded the number of steps taken and amount of time spent foraging by crows by tidal zone and tide direction. Worms, crabs, and snails were expected to be exposed to predation at lower tide heights, and some species of worms were only found at low tides (<0.36 m). There was no significant difference in the number of bivalves found in relationship to tide height. Among the crows observed, the number of steps and search times were greater during rising than falling tides, but the number of probes was not significantly different be- tween tide directions. In addition, the number of steps between probes and the amount of time between probes decreased during rising tides. The number of crows foraging in the intertidal zone did not appear to be related to tide height. Results of this study suggest that tidal zone and direction influences prey availability and thus certain aspects of the foraging behavior of northwestern crows.