Mechanisms and Adaptive Value of Reproductive Synchrony in Colonial Seabirds

Abstract

Advances in the study of the behavioral ecology of colonial birds requires understanding both temporal and spatial dispersion of reproductive activities. Coloniality itself is one aspect of spatial clustering, whereas synchronous breeding represents temporal clustering and is characteristic of many colonial species. Darling (1938) called attention to the importance of reproductive synchrony. His hypotheses, often referred to as the Darling or Fraser Darling effect, linked colony size, social stimulation, reproductive synchrony, and reduced predation into a single behavioral-ecologic-evolutionary framework. Darling hypothesized that birds in larger colonies would experience greater social stimulation which, mediated by neuroendocrine pathways, would accelerate breeding cycles, leading to earlier and more synchronous laying than in small colonies. This would be advantageous in that the time span of hatching would be reduced. Thus more chicks would hatch in shorter time periods. At the peak of hatching many chicks would be vulnerable to predation, but a predator would soon become satiated and could consume a smaller proportion of the overall crop than in a less synchronous situation where hatching was spread out over a longer period of time. Thus factors enhancing synchrony would be favored by natural selection.