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Is Reproduction By Tree Swallows (Tachycineta Bicolor) Cost-Free?, Michael T. Murphy

Biology Faculty Publications and Presentations

We manipulated brood sizes of Tree Swallows (Tachycineta bicolor) in 1996 and 1997 to test for the existence of intra- and intergenerational costs of reproduction. Modal clutch size was six eggs, but experimental brood sizes ranged from two to nine young. Nestling starvation was higher in 1996 (and dependent on brood size) than in 1997, but in both years enlargement of brood size resulted in increased productivity. Nestling mass near fledging was negatively correlated with brood size, but tarsus length and wing chord were not. Food deliveries by parents increased steadily between broods of two to six young but then …