Breeding biology of Royal and Cayenne terns at a mixed-species colony in Patagonia

QUINTANA, F.; YORIO, P.

WILSON BULLETIN

Año: 1997 vol. 109 p. 650 - 662

0043-5643

eurygnatha) at Punta Leon, Patagonia, during 1989-93. In all years, both speciesbred in a single colony with their nests intermingled. Colony size varied between 1,150 and1,830 pairs. Colony formation occurred during the first or second week of October. Nestingdensities were relatively high (9.8 to 1 1.1 nests/m*). Both species started to lay eggs duringthe second and third week of October in all years. During 1993, clutch size for Royal andCayenne terns was 1.3 2 0.5 and 1.1 + 0.3, respectively. The length of the incubationperiod was 25.7 2 0.9 and 29.1 + 3 days for Royal and Cayenne terns, respectively. During1993, hatching snccess was 0.72 f 0.34 and 0.68 2 0.42 chicks per nest for Royal andCayenne terns, respectively. Egg losses (45.3%) were mainly from predation. First-hatchedchicks were observed during mid November. Chick survival to 10 days of age was 90%and 66.7% for Royal and Cayenne terns, respectively. At approximately 20 days of age,some tern chicks started to abandon the colony to form creches at the beach. Royal andCayenne terns generally fed out of sight from the colony and preyed upon the same species,including Odontestes spp., Stromateubsr asiliensis, Engraulis anchoita, and Sprattus fueguensis.