Egg Size and the Egg Predatory Behaviour of Crows

Montevecchi, William A. (1976) Egg Size and the Egg Predatory Behaviour of Crows. Behaviour, 57 (3-4). pp. 307-320. ISSN 0005-7959

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Abstract

Patterns of corvid predation on different sized white eggs were studied in a series of field experiments. Different sized eggs were set out singly and in simulated nests containing clutches of same sized and different sized eggs. The eggs were set out in meadows where they were subjected to intense predation by crows. The most common predation method of the crows was to fly off with eggs and to cache (bury) or eat them at a distance from the site of predation. The larger eggs were more frequently pecked open at the egg site and were less effectively picked up and carried off by the crows. Apparently as a result of the ease of grasping smaller eggs, these eggs were much more vulnerable to predation than were larger eggs. These results combined with field observations and previous findings indicate that Corvus predators may exert differential pressures on different sized eggs both within and among clutches, intra- or interspecifically. These patterns of crow predation analyzed in terms of the gulls' parental investment among the different eggs within a three egg clutch suggest that smaller third eggs may have been (and continue to be) selected in the evolution of a balanced predator-prey system between crow predators and ground nesting gulls. Cooperative aspects of corvid group hunting patterns are also discussed.

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