SEASONAL AND ANNUAL VARIATION IN BROOD ATTENDANCE, PREY TYPE DELIVERED TO CHICKS, AND FORAGING PATTERNS OF MALE COMMON TERNS (STERNA-HIRUNDO)

The study took place over 2 years (1990 and 1991) on a concrete breakw ater located 1 km offshore on Lake Erie near Port Colborne, Ontario. T en male Common Tems (Sterna hirundo) in 1990 and 12 in 1991 were radio -tracked by boat or car during the chick-rearing stage. Concurrent beh avioural observations of the radio-tagged birds and 23 additional cont rol birds documented the time each sex spent away from or at the nest. The frequency and prey species/size composition of feeds to chicks we re recorded. Individuals that carried transmitters had predictable for aging patterns. In peak- (clutch initiation in early May) and late-nes ting males (clutch initiation in late June) intra-individual variabili ty was low. Late-nesting males exhibited greater interindividual varia bility than peak-nesting males. Adults recaptured in 1991 exhibited si milar foraging patterns to those they expressed in 1990. There were di urnal, seasonal, and interannual variations in prey delivered to chick s. We suggest that these were due to the temperature tolerances of the prey, rainbow smelt (Osmerus mordax) and emerald shiner (Notropis ath erinoides), that controlled their vertical distribution in the water c olumn, and to the presence of large schools of larval fish during the late nesting season.