Abstract

The South American Tern Sterna hirundinacea Lesson, 1831 occurs in the Atlantic Ocean, from Tierra del Fuego (Argentina) to Bahia (Brazil) and in the Pacific Ocean all around the southern part of the continent, up the Peruvian coast. Daily observations were conducted from April to November in 2003, 2005 and 2006 to gather information on the reproductive biology of the South American Tern in the Cardos Island (SC, Brazil). Although, adults arrived earlier in 2005 and 2006, their breeding chronology followed the same pattern in all three years, with well-characterized reproductive stages. In 2006, the average time of copulation was about three minutes and the number of inseminations (sexual intercourses) stayed constant throughout the day. The period of egg-laying and total number of nests was higher in 2005 (2417 nests), than in 2003 (2124) and 2006 (1852). The smallest average egg sizes (length, width, weight) occurred at the end of egg-laying in 2003, while the largest occurred in the beginning of 2006. Eggs hatched earlier in 2005 and 2006 compared to 2003, with the earliest hatching at the end of May.

Key words: Behavior ecology, seabird breeding, Sterna hirundinacea.