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Temporal Patterns in Pre-Fledgling Survival and Brood Reduction in an Osprey Colony
John M. Hagan
Vol. 88, No. 2 (May, 1986), pp. 200-205
Published by: Cooper Ornithological Society
Stable URL: http://www.jstor.org/stable/1368916
Page Count: 6
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Temporal patterns in pre-fledgling mortality were examined in a coastal North Carolina Osprey (Pandion haliaetus) colony by checking nests weekly throughout two breeding seasons. Individuals experienced high weekly survival during incubation (>90%), but exhibited a dramatic drop in survival at two to three weeks after hatching. The mortality pattern was identical in both years of study and was characteristic of both early and late nesters. This mortality appeared related to food-stress and occurred when nestlings entered the steep phase of logistic growth. Survival data were also used to test O'Conner's brood reduction model. The model predicted that brood reduction should occur in the population and should be manifested as fratricide, rather than infanticide or suicide. Nestling behavior was in accordance with the prediction of the model in that sibling aggression was common, but parents appeared to feed whichever nestling begged most vigorously. The calculations suggested that this population barely exceeds the threshold for fratricide, an interesting result considering the facultative nature of brood reduction in Ospreys.
The Condor © 1986 Cooper Ornithological Society