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El Niño-Southern Oscillation Effects on Provisioning and Growth in Red-Tailed Tropicbirds

E. A. Schreiber
Colonial Waterbirds
Vol. 17, No. 2 (1994), pp. 105-119
Published by: Waterbird Society
DOI: 10.2307/1521289
Stable URL: http://www.jstor.org/stable/1521289
Page Count: 15
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El Niño-Southern Oscillation Effects on Provisioning and Growth in Red-Tailed Tropicbirds
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Abstract

Patterns of provisioning and growth in Red-tailed Tropicbird chicks (Phaëthon rubricauda) were studied on Christmas Island and Johnston Atoll, central Pacific Ocean. Spatial and temporal variation in these patterns were examined in relation to the occurrence of El Niño-Southern Oscillation (ENSO) events. Among ENSO years, provisioning rates differed and in some ENSO years chicks were fed fewer and smaller meals resulting in lower chick masses. Rate of wing growth did not correlate with reduced chick mass on Johnston Atoll, but it did on Christmas Is. where the effects of ENSO events were more severe. During an ENSO event in 1991, the amount of food received daily was higher on Johnston Atoll than on Christmas Is., but chicks on Christmas Is. gained more per gram fed. Chicks did not undergo long periods of fasting even during an ENSO, a postulated cause of slow growth and fat deposition in seabird chicks. Mean number of feeds day-1 was 0.9 on Christmas Is. and 1.3 on Johnston Atoll. Fledging success ranged from ca. 76% of eggs laid on Christmas Is. to ca. 87% on Johnston atoll. Results of this study do not support the hypothesis that the slow growth of seabird young and attendant life history characteristics are a consequence of energy limitations on adults due to feeding on a distant and variable food source.

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