Consequences of La Niña phase of ENSO for the survival and growth of nestling Burrowing Parrots on the Atlantic coast of South America

Abstract

Birds are sensitive to perturbations in climate. Changes in reproductive ecology may reflect changes in food availability caused by environmental conditions. We studied the influence of the La Niña phase of the El Niño Southern Oscillation (ENSO) on breeding success and survival and growth of nestling Burrowing Parrots (Cyanoliseus patagonus) (Aves, Psittaciformes) in Patagonia. During the breeding season 1998–99, a severe drought affected the region as a consequence of a strong La Niña. We compare data from a La Niña event with an average year. Clutch sizes were similar in the two years. In both years, clutch size declined during the season. Our results suggest that environmental conditions are not the primary determinant of clutch size in Burrowing Parrots, and seasonal differences are more likely caused by differences in adult quality. Nestling mortality was higher during La Niña, while the surviving nestlings showed reduced growth. Hatching order had a stronger influence on growth and survival of nestlings during La Niña than during the average year. Last-hatched nestlings always showed reduced growth compared with middle-and first-hatched nestlings, but the difference between nestlings was greater during La Niña.