Diet Selection by Yearling Northwestern Crows (Corvus caurinus) Feeding on Littleneck Clams (Venerupis japonica)

Abstract

Abstract Yearling and adult Northwestern Crows (Corvus caurinus) used similar methods in searching for buried Japanese littleneck clams (Venerupis japonica) and therefore encountered similar proportions of different-size clams. The mean size of clams eaten by yearling birds was significantly smaller than the mean of those eaten by adults despite the similar proportions encountered. The estimated lower limit of the diet (the smallest clams eaten by the average bird) was 25.5 mm for yearlings and 29.0 mm for adults. Yearlings took more time to find and handle clams and required more drops to break them open than did adults. Consequently, yearlings achieved only one-third the rate of net energy intake of adults feeding from the same food source. However, the extended diet consumed by the yearlings yielded close to the maximum possible rate of energy intake, within the limits imposed by their inefficiency.