EASTERN BLUEBIRDS PREFER BOXES CONTAINING OLD NESTS

Eastern Bluebirds (Sialia sialis) chose boxes containing old nests in 38 of 41 instances in which these boxes were paired with empty ones. O ther species nesting in bluebird boxes chose boxes containing old nest s in four of five instances. This result conflicts with the prevailing opinion that cavity-nesting birds avoid boxes that contain old nests and, presumably, high parasite loads. It is suggested that bluebirds p refer re-working old nest material to building a completely new nest, and/or that choice of boxes with old nests actually enhances parasite control because old nests harbor wasp (Nasonia vitripennis) larvae tha t parasitize blood-sucking blowflies (Protocalliphora sialis).