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Behavioral Ecology Vol. 13 No. 2: 274279 Clutch size variation in the Nazca booby: a

Summary: Behavioral Ecology Vol. 13 No. 2: 274279
Clutch size variation in the Nazca booby: a
test of the egg quality hypothesis
L. D. Clifford and D. J. Anderson
Department of Biology, Box 7325 Reynolda Station, Wake Forest University, Winston-Salem, NC
27109, USA
In obligately siblicidal bird species, aggressive behavior by a dominant chick results in a fixed brood size of one, yet these species
usually show clutch size variation between individuals. Simmons proposed that variation in clutch size in obligately siblicidal
species is related to a trade-off between egg quality and egg quantity: some individuals produce a single highly hatchable egg,
while others produce two small, lower quality eggs. We tested the egg quality hypothesis as an explanation for observed clutch
size variation in the Nazca booby (Sula granti), an obligately siblicidal seabird. We tested the assumption that egg volume is
positively correlated with hatchability and the prediction that eggs from one-egg clutches are larger than eggs from two-egg
clutches. We did not find a positive relationship between egg volume and hatchability in this species. Eggs from two-egg clutches
were either equivalent in volume or larger than eggs from one-egg clutches. Thus, the egg quality hypothesis was rejected as
an explanation for clutch size variation in the Nazca booby. Instead, two-egg clutches appear to be favored because of the
insurance value of the second-laid egg, while one-egg clutches result from food limitation. Key words: clutch size variation, egg
quality hypothesis, Nazca booby, obligate siblicide, Sula granti. [Behav Ecol 13:274279 (2002)]
Obligately siblicidal birds present a particularly interesting
case of clutch size variation because, despite a fixed
brood size of one, some individuals produce multiple-egg


Source: Anderson, David J. - Department of Biology, Wake Forest University


Collections: Environmental Sciences and Ecology