Aspects of the breeding biology of the Neotropic Cormorant Phalacrocorax olivaceus at Golfo San Jorge, Argentina

QUINTANA, F; YORIO, P.; GARCÍA BORBOROGLU, P

MARINE ORNITHOLOGY

African Seabird Group

Año: 2002 vol. 30 p. 25 - 29

1018-3337

We studied the breeding biology of Neotropic Cormorants Phalacrocorax olivaceus at Golfo San Jorge, Argentina, during 1999. A total of 104 nest platforms with signs of occupation was counted, at 66 (63.5%) of which eggs were laid. Nests were built on top of medium to large bushes located up to 50 m inland. Average height of nests was 0.53±0.13 m. Nest platforms were built of sticks and twigs, and occasionally lined with grass, sea-weed, feathers, shells, and seabird bones or carcasses. First eggs were found on 15 November. Egg laying continued for more than six weeks until the last week of December. Median date of laying was 2 December. Clutch size varied from one to five eggs, with a mean clutch size of 3.51±0.69 and modal clutch size of three eggs. Mean volume for all eggs was 35.9±3.2 cm3. Egg volume was similar within eggs of a clutch. The length of the incubation period was estimated at 26.6±2.2 days. Of the 178 eggs laid, 54 (28.7%) were lost. Number of eggs hatched per nest averaged 2.6±1.2. Median hatching date of a-eggs was 20 December. Mean number of chicks alive per nests at 10 days of age was 2.1±1.1.