Effects of pesticide spraying on chick growth, behavior, and parental carein tree swallows (Tachycineta bicolor) nesting in an apple orchard in Ontario, Canada

The objective of this study was to investigate the consequences of the use of cholinesterase (ChE)-inhibiting insecticides in an apple orchard on beha vior and growth of free swallows (Tachycineta bicolor). In a sprayed apple orchard and two nonsprayed sites in southern Ontario, Canada, in 1996 throu gh 1997, hunger signaling and growth of chicks, feeding activities of adult s, and aerial invertebrate abundance were studied before and after insectic ide spray events. In the orchard, persistent and significant increases occu rred in hunger signaling by tree swallow chicks after organophosphorus (OP) insecticide spray events in both years and, after a second OP insecticide spray in 1996, significant decreases occurred in the number of feeding trip s by parent birds. These trends did not occur in the control sites. After s pray events in the orchard, the trends in feeding sorties of adult birds du ring chick-rearing did not coincide with known experimental responses in tr ee swallows subjected to reduced food resources. However, trends were consi stent with those predicted to occur in adult passerines exposed to ChE-inhi biting insecticides. In contrast, the increased hunger signaling by chicks may reflect chronically low food resources available in the orchard but doe s not indicate ChE depression. Few differences were found among sites in th e size and type of aerial invertebrates caught in traps. Very low densities of invertebrates occurred in the orchard relative to the other locations b ut the abundance did not vary significantly with insecticide events. Despit e changes in avian behaviors associated with insecticide sprays, difference s in masses of chicks among sites and after spray events were not related t o insecticide use in the orchard. Because first-year survival of tree swall ow chicks is correlated with their mass at fledging, this suggests a need t o maintain relatively natural habitats with abundant food resources near sp rayed agricultural areas.