BREEDING SYNCHRONY IN THE LESSER SNOW GOOSE (ANSER CAERULESCENS CAERULESCENS)

Synchronized breeding is characteristic of many colonial species, and has been studied in both temperate and subtropical populations (Smith, 1943; Coulson and White, 1956; Hailman, 1964; Patterson, 1965; Harris, 1966). Breeding synchrony refers to the tendency of individuals to carry out some stage of the reproductive cycle (e.g., courtship, nest establishment, laying, etc.) simultaneously with other members of the colony. The close association between the spatial (coloniality) and temporal (synchrony) clustering of individuals suggests that for some species, the evolution of synchrony should not be considered independent of the evolution of coloniality (Gochfeld, 1980). Synchrony may be adaptive or nonadaptive. Several researchers (e.g., Lack, 1954; Brown, 1967; Nisbet, 1975) have suggested that a selective advantage accrues to those individuals capable of synchronizing their activities with neighboring pairs. This advantage may take the form of reduced predation pressure (Darling, 1938; Kruuk, 1964; Patterson, 1965; and see Robertson, 1973), or an increased efficiency of food localization (Emlen and Demong, 1975). Alternatively, the observed temporal clustering of individuals may result from selection pressures acting on the timing, rather than the synchronization, of reproduction. Populations in unpredictable environments may be highly synchronous simply because of the short time available for the production and rearing of young. In this case, synchronized breeding per se does not confer any selective advantage. Adaptive value can be inferred only if those individuals breeding asynchronously suffer a reduced fitness. Here, stabilizing selection would maintain synchrony in the population through the elimination of genotypes that breed asynchronously. For studies where genetic relationships are known, quantitative genetics provides several simple techniques for investigating the genetical basis of intraspecific variability. "Repeatability" and "heritability" estimates are two such approaches used to partition the total phenotypic. variance of a character into environmental and genetic components (Falconer, 1960). In this paper we consider the genetic and environmental determinants of hatch date variation in a colony of Lesser Snow Geese (Anser caerulescens caerulescens). A female's relative hatch date is the date relative to the colony mean on which her eggs hatch. It is the between-individual variation in relative hatch dates that determines the degree of hatching synchrony at the colony. In this discussion, we assess (1) annual variation in synchrony, (2) the proportion of the within-season variation in hatch date that arises from genetic differences between individuals, and (3) the degree to which hatch date variation, and hence, hatching synchrony, arises from variability in other components of the reproductive strategy. The evolution of hatching synchrony implies that (1) synchronous females have a greater reproductive fitness than asynchronous females, and (2) there is a genetic basis to inter-individual variability in relative hatch dates. Here we consider only the latter question. A discussion of the adaptive value of synchrony will be pre-