Conspecific reproductive success affects age of recruitment in a great cormorant, Phalacrocorax carbo sinensis , colony

Abstract

Few studies have addressed the proximate factors a¡ecting the age at which individuals of long-lived bird species are recruited into the breeding population. We use capture^recapture analysis of resightings of 16 birth cohorts of colour-ringed great cormorants, Phalacrocorax carbo sinensis, in a Danish colony to assess the evidence for two hypotheses: conspeci¢c attraction (earlier recruitment when the colony is large) and conspeci¢c reproductive success (earlier recruitment following years of high breeding success). For both males and females, conspeci¢c reproductive success was the most important covariate explaining the interannual variation in age of recruitment; colony size was also important for females. These covariates explained nearly 60% of the year-to-year variation for both sexes. The age of recruitment increased for cohorts born after 1990, and this increase was correlated with a decline in breeding success in the colony; we interpret this as an indirect and delayed density-dependent e¡ect. Females were recruited earlier than males (mean age of recruitment for cohorts born before 1990: 2.98 years versus 3.53 years); the most plausible reason for this is a skewed sex ratio in favour of males in the adult population. Recruitment of males may thus, to some extent, be constrained by the availability of females. This study provides the ¢rst evidence that conspeci¢c reproductive success can a¡ect the age at which individual birds start to breed.

Long- and short-term influence of environment on recruitment in a species with highly delayed maturity

“…The breeding success of the colony, defined as the number of young fledged per breeding pair, can be viewed as an index of the average seasonal parental investment, which may influence the quality of the fledglings produced and consequently immature survival. The breeding success of the colony was also considered as major information about the quality of the colony, as it is known to affect settlement and the decision to start breeding in some colonial seabirds (Danchin et al 1998;Frederiksen and Bregnballe 2001). The breeding success is dependent on the environment and it is known to be correlated to SSTA in this population (Nevoux et al 2007).…”

Experimental evidence of a link between breeding conditions and the decision to breed or to help in a colonial cooperative bird

“…Reducing the risks associated with breeding activity might be particularly important for young individuals for two reasons: they probably incur disproportionately high costs of breeding through reduced survival, as suggested in two recent studies (Tavecchia et al 2001;Orell & Belda 2002), and they may experience comparatively lower reproductive output (Green 2001;Magrath 2001). Thus, long-lived cooperative (or non-cooperative) species should be particularly reluctant to breed in suboptimal habitats or under suboptimal conditions, as indicated by several correlative studies (Emlen 1990;Koenig et al 1992;Komdeur et al 1995;Frederiksen & Bregnballe 2001;Ekman et al 2001). This hypothesis is supported by our results in sociable weavers: in a species with no spatial constraints on breeding, when the overall costs of reproduction were reduced by the provision of an easily obtainable food supplement, we were able to lower their age at first independent breeding and to increase the proportion of individuals breeding in any given season.…”

Gathering public information for habitat selection: prospecting birds cue on parental activity

“…spatial aggregation of individuals (see Danchin & Wagner 1997;Wagner et al 2000;Clobert et al 2001)), but also on life-history traits (e.g. age at first breeding (Boulinier & Danchin 1997;Frederiksen & Bregnballe 2001)) and sexual selection (e.g. female mate choice in 'hidden leks' (Danchin & Wagner 1997;Wagner et al 2000)).…”