Feeding Grounds, Daily Foraging Activities, and Movements of Common Terns in Southern Brazil, Determined by Radio-telemetry

Fourteen Common Terns (Sterna hirundo) were radio-tagged on their wintering grounds at Lagoa do Peixe, Rio Grande do Sul state, southern Brazil. Aerial radio-tracking was made along 850 km from northern Rio Grande do Sul state to Montevideo, Uruguay. During 23.6 h of tracking in February 2003, we recorded 100 locations of 12 radio-tagged terns. Birds were located within a range of 165 km from the tagging area, and most locations were at sea (74 at sea vs. 26 roosting on the beach), due to frequent movement of the birds when feeding and most tracking during feeding periods. Each bird was located 4-14 times (mean = 8.3 locations/bird). Common Terns fed predominantly between 15-20 m isobaths (56% of at sea locations), and 10-15 m isobaths (32%), which corresponded to a maximum of 8 km offshore. Minimum distance traveled in five days of intensive tracking was 46 km, and maximum distance was 167 km. Daily movement was 19 km on average (minimum 6 km d-1, maximum 49 km d-1). Nine out of 12 birds were found at sea in both early morning and late afternoon periods. Eight out of 12 birds were recorded feeding at sea in consecutive periods of the day (morning and afternoon), indicating two feeding trips a day.