Abstract
Individual variation in timing of breeding is a key factor affecting adaptation to environmental change, yet our basic understanding of the causes of such individual variation is incomplete. This study tests several hypotheses for age-related variation in the breeding timing of Lesser Black-backed Gulls, based on a 13 year longitudinal data set that allows to decouple effects of age, previous prospecting behavior, and years of breeding experience on arrival timing at the colony. At the population level, age of first breeding was significantly associated with timing of arrival and survival, i.e. individuals tended to arrive later if they postponed their recruitment, and individuals recruiting at the age of 4 years survived best. However, up to 81% of the temporal variation in arrival dates was explained by within-individual effects. When excluding the pre-recruitment period, the effect of increasing age on advanced arrival was estimated at 11 days, with prior breeding experience accounting for a 7 days advance and postponed breeding for a 4 days delay. Overall, results of this study show that delayed age of first breeding can serve to advance arrival date (days after December 1st) in successive breeding seasons throughout an individual’s lifetime, in large part due to the benefits of learning or experience gained during prospecting. However, prospecting and the associated delay in breeding also bear a survival cost, possibly because prospectors have been forced to delay through competition with breeders. More generally, results of this study set the stage for exploring integrated temporal shifts in phenology, resource allocation and reproductive strategies during individual lifecycles of long-lived migratory species.
Highlights
Individual variation in reproductive performance is an omnipresent feature of the demography of natural populations [1]
In our study population of Larus fuscus, age of an individual has a significant effect on its phenology, with older age classes arriving progressively earlier at the breeding grounds (Figure 1)
After statistical deconstruction of the within- and betweenindividual processes underpinning this pattern, we found support for age-related variation in arrival timing at both the population and individual levels
Summary
Individual variation in reproductive performance is an omnipresent feature of the demography of natural populations [1]. A key life-history trait associated with reproductive performance is the timing of individual appearance on the breeding grounds [12]. A timely arrival on the breeding grounds constitutes an important precondition of successful reproduction, because it affects the length of the period available for breeding and can buffer yearly variation in peak food availability that determines the optimal onset of breeding. Early arrival may improve reproductive success, it may lead to considerable survival costs, e.g. as a result of inclement weather [15]. It is generally believed that the timing of arrival on the breeding grounds has important fitness consequences and is considered to constitute a key fitness parameter, e.g., [16,17]
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