Ecological Implications of Bird Predators on the Larch Casebearer in Wisconsin1

Abstract

Birds are important predators of Coleophora laricella (Hubner) in Wisconsin. Population decline of the larch casebearer in the winter, probably attributable to birds, was 23.5%, of which 30–40% was calculated to consist of nonparasitized larvae. Spring predation by birds, between April and June, causes a significant loss in prey population, although many of the larvae eaten are parasitized. Apparently the birds involved do not discriminate between parasitized and nonparasitized larvae. Feeding activity in the spring was 3 times that recorded in the fall, under laboratory conditions, and probably reflected the –specific feeding image— developed by the birds for the larger and more active spring larvae. The Magnolia, Dendroica magnolia (Wilson); and Yellow Warblers, D. petechia (L.); the Ruby-crowned Kinglet, Regulus calendula (L.), and the Black-capped Chickadee, Parus atricapillus L., exhibited the most frequent feeding response to the larch casebearer. No instances of –clipped-off— cases were observed III any of the laboratory feeding trials or in the field. All birds swallowed both case and larva completely except for the Black-capped Chickadee which, in the spring only, removed the case from the tree, extracted the larva, and then dropped the case to the ground.