Hatching asynchrony and feeding rates in yellow warblers: a test of the sexual conflict hypothesis

T. Slagsvold and J. T. Lifjeld have proposed that hatching asynchrony in bird species in which only the female incubates is a strategy used by females to extract more parental investment from their mates. We examined this hypothesis by comparing feeding rates of female and male yellow warblers (Dendroica petechia) tending asynchronously and synchronously hatched broods. Regardless of brood size, feeding rates during the early, middle, and late nestling periods were similar for females tending asynchronously and synchronously hatched broods. Nevertheless, there was a general trend for females tending asynchronous broods to have lower feeding rates, which suggests that females may prefer hatching asynchrony. This is consistent with the sexual conflict hypothesis. Male feeding rates exhibited trends similar to those of females. That is, although the result is not statistically significant, males tending asynchronous broods, regardless of brood size, generally made fewer feeds than males tending synchronously hatched broods. However, males tending asynchronous broods of five did make significantly fewer feeds during the early nestling period than males tending similar-sized synchronous broods. This was also true when the data were combined across brood sizes. This suggests, contrary to the sexual conflict hypothesis, that males, especially those tending larger broods, should favor hatching asynchrony. Consequently, the sexes do not appear to be in conflict as to when incubation should begin, but rather females and males prefer, or at the very least are neutral with respect to, the initiation of incubation prior to clutch completion.