Hatching asynchrony and reproductive success in the blackbird

Abstract

A GENERAL problem of parental investment is that resources required to nourish offspring may be unpredictable at the time fertilization occurs1-5. Lack1 suggested that the best strategy for altricial birds faced with such unpredictability might be to lay an optimistic clutch size and to begin incubation before laying is complete. This causes the eggs to hatch asynchronously, which may allow the brood to be reduced to the optimum size by the quick elimination of the youngest nestling if food is scarce. If females hatched their eggs synchronously, food shortage could lead to poor growth of the whole brood if the nestlings are then equally competitive. Lack predicted that synchronous and asynchronous broods would consequently be equally productive in times of plenty, but asynchronous broods would be better when food is scarce1,3. By manipulating both food availability and brood hierarchies, and following offspring survival after fledging, I show that in blackbirds (Turdus merula) asynchronous broods are more productive when food is scarce, but not when food is abundant. Show more