Intrapopulation Variation in Hatching Synchrony in House Wrens: Test of the Individual-Optimization Hypothesis

Intrapopulation variation in hatching synchrony has been documented in several avian species, although little attention has been paid to this phenomenon. We experimentally reversed some synchronously and asynchronously hatched broods to test an individual-optimization hypothesis to explain variation in hatching synchrony in a population of House Wrens (Troglodytes aedon) in central Illinois. Contrary to expectation, the number and quality (as measured by mass) of fledglings produced in reversed broods was the same as that for unmanipulated broods, as were recapture rates of juveniles and offspring recruitment to subsequent breeding populations. Thus, the results do not support the individual-optimization hypothesis as an explanation of intrapopulation variation in brood hatching intervals in this House Wren population. In this and other studies we have not been able to detect any advantage associated with producing either synchronous or asynchronous broods. Although other adaptive hypotheses to explain such variation remain to be tested, we suggest that variation in hatching intervals may indicate that female control of hatching pattern is imprecise and may be unrelated to fitness in this House Wren population.