Feeding Rates of Warblers in Spring

摘要: -Populations of migrant warblers were correlated with populations lepidopterous larvae in spring a heavily forested area southern Illinois. The birds appeared to feed entirely on these larvae, mostly taken from oaks. Estimates gross calorie intake indicated positive energy balance for an larval biomass 0.70 g per m3, and negative 0.02 m3. Warblers chose either the smaller size classes (under 15 mm) or species (especially leafrollers) out proportion their availability, but birds' was dependent upon irruption geometrids. Lepidopterous constituted 7598% available foliage invertebrates, other groups insufficient alone support populations. Larvae about 80% water, ingested 1.2-1.7 times own weight day order attain caloric 14.8-19.0 kcal bird-day. food resources 7.2 kcal/day, behavior consistent goal conservation. Among problems faced by migrants after flight is that finding adequate supplies continue migration, particularly as landing may be completely unknown birds. In Illinois only measurements forest habitat have been those Twomey (1945) Calef (1953) who found four eight more elmmaple at peak migration May than present June. We wondered how accommodated large numbers migrants, much required arboreal migrants. Kendeigh's (1979) study invertebrates three east-central areas showed seasonal population patterns various invertebrates. There close similarity between timing emergence bird this region. Stimulated papers question respond we began, 1979, concurrent studies potential (1) where tracts extensive, (2) restricted. Our primary consider availability warblers. interest not influence insect populations, reverse. case, it important know rates predation. When opportunity arose 1981 consumption forest-edge two widely divergent levels, interrupted our principal make observations reported her .