How nest site characteristics influence breeding success in Red-legged Cormorants Phalacrocorax gaimardi

ANA MILLONES ; ESTEBAN FRERE

ACTA ORNITHOLOGICA

MUSEUM & INST ZOOLOGY

Lugar: Warszawa, POLAND; Año: 2018 vol. 52 p. 239 - 244

0001-6454

For seabirds, nest site features are an important factor that determines reproductive success. During threebreeding seasons (2010?12), we visited two coastal cliff colonies of Red-legged Cormorants Phalacrocorax gaimardi in theRía Deseado, Argentina, and studied how nest site characteristics influenced their breeding success. We measured sixphysical characteristics at 46 nest sites, and we counted the number of fledglings produced each year from each nest(breeding success). We also related nest site temperature and wind exposure with nest site orientation. Breeding successwas higher at nest sites with a broad base (greater capacity for holding young) and at nests that were less exposedto winds greater than 25 knots (46.25 km/h), which were sites with a north orientation. The lowest breeding success wasobserved in nest sites that were exposed to the strongest winds (i.e., sites with a south orientation). Strong winds oftenblow eggs and chicks away from the nests and increase opportunistic predation by gulls Larus sp. No significant relationshipwas found between nest site orientation and nest site temperature. Breeding success decreased with the distanceto the nearest nest, which agrees with the idea that higher density of reproductive individuals reduces effectivenessof predators. Nest cover, distance from the top of the cliff, and distance from the tide line had no effect on breedingsuccess at this study scale. Our results suggested that nest site characteristics that were related to protection againstadverse weather conditions (e.g., strong winds) and avian predation, in combination with a suitable nest space, determinedthe breeding success of Red-legged Cormorants.