Effect of El Niño-Southern Oscillation Conditions on Nestling Growth Rate in the Dark-Rumped Petrel

During a 5-year study of the Dark-romped Petrel (Pterodroma phaeopygia) in the Galapagos Islands we found that chick growth rate was lower and that fledging was later during the El Niner-Southern Oscillation (ENSO) of 1982-1983 than in other years. ENSO chicks attained lower peak mass at a later age than non-ENSO chicks. However, after the prefledging mass recession, chicks of all years fledged at similar size and mass. The longer nestling period and slower chick growth of ENSO chicks probably reflect a decrease in the energy available for growth due to lower ocean productivity and reduced food resources during the ENSO. It is likely that the flexible fledging period allows petrels to raise chicks successfully even during periods of food scarcity.