Acorn Woodpecker Predation on Cliff Swallow Nests

Unlike many other woodpeckers that feed on woodboring insects and larvae, Acorn Woodpeckers (Melanerpes formicivorus ) feed primarily on acorns, insects caught by flycatching, and sap. Acorn Woodpeckers are known to eat eggs that have been removed from two-female communal nests. The authors report here on an instance when nest predation by Acorn Woodpeckers may have harmed a colony of Cliff Swallows (Hirundo pyrrhonota ) nesting in the Stanford Quadrangle at Stanford University, Stanford, California. They observed eight Acorn Woodpecker visits to this colony during the week of 28 May through 3 June 1985, between 08:00 and 09:00. Though attempts at predation sometimes failed when mobbing Cliff Swallows induced the Acorn Woodpecker to flee, in four (50%) of these visits the woodpecker succeeded in stealing an egg from a nest.