The reproductive activity of swifts is affected by seasonal fluc tuations of aerial insects which are largely unpredictable, depending day by day on climatic conditions. In this work we investigated whether the parental food provisioning is influenced by hourly fluc tuations of insect abundance or if adults maintain a constant feeding rate. We found during each day that the amount of food delivered to nestlings was not related to hourly insect availability. We also verified that daily insect abundance is related to daily minimum and maximum temperature (38% of variability explained) and is unrelatedtorainfall. Finally we compared, during different reproductive seasons, the aerial insect abundance and the biomass (eggs and nestlings) produced by adult swifts. Insect abundance was constantly high from June to September and did not precisely match the main period of biomass production (first clutch), which reached a maximum in July.