Effects of pesticide spraying on chick growth, behavior, and parental care in 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 behavior and growth of tree swallows (Tachycineta bicolor). In a sprayed apple orchard and two nonsprayed sites in southern Ontario, Canada, in 1996 through 1997, hunger signaling and growth of chicks, feeding activities of adults, and aerial invertebrate abundance were studied before and after insecticide spray events. In the orchard, persistent and significant increases occurred 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 trips by parent birds. These trends did not occur in the control sites. After spray events in the orchard, the trends in feeding sorties of adult birds during chick‐rearing did not coincide with known experimental responses in tree swallows subjected to reduced food resources. However, trends were consistent with those predicted to occur in adult passerines exposed to ChE‐inhibiting insecticides. In contrast, the increased hunger signaling by chicks may reflect chronically low food resources available in the orchard but does not indicate ChE depression. Few differences were found among sites in the size and type of aerial invertebrates caught in traps. Very low densities of invertebrates occurred in the orchard relative to the other locations but the abundance did not vary significantly with insecticide events. Despite changes in avian behaviors associated with insecticide sprays, differences in masses of chicks among sites and after spray events were not related to insecticide use in the orchard. Because first‐year survival of tree swallow chicks is correlated with their mass at fledging, this suggests a need to maintain relatively natural habitats with abundant food resources near sprayed agricultural areas.