Dispersal and Social Attraction Affect Colony Selection and Dynamics of Lesser Kestrels

Abstract

We studied the mechanisms that regulate colony dynamics in a Spanish population of Lesser Kestrels, using eight years of data from banded individuals in 494 colony-years. Colony growth was positively related to breeding success at the colony the year before. However, individuals of all dispersal statuses, i.e., adult and first-breeding philopatric and immigrant birds, significantly contributed to changes in colony size, indicating an important effect of dispersal on colony dynamics via colony quality. Given that there is strong evidence that Lesser Kestrels base their settlement decisions on conspecifics, we tested whether immigrants used the number of previously settled residents in year t (social or conspecific attraction hypothesis) and/or the breeding performance of conspecifics in year t Ϫ 1 (performance-based attraction hypothesis) to select their breeding colony. Breeding success of colonies varied both in space and time and was autocorrelated from one year to the next. Moreover, lifetime reproductive success of Lesser Kestrels was positively associated with colony size, and individuals can predict final colony size early in the breeding season, so assumptions of both hypotheses were fulfilled. Our results support the social attraction hypothesis, since immigration was positively related to the number of philopatric adults, but not to conspecific breeding success the year before. Given that departure decisions of adults were based on personal information about breeding success and colony size is related to fitness prospects, previously settled individuals provide easy and reliable information about colony quality, and social attraction could be seen as a particular case of public information in Lesser Kestrels. Consistently, absolute numbers of both philopatric adults and immigrants increased with colony size the year before, although immigrants increased only up to a threshold beyond which this trend disappeared. Therefore, immigrants seem to be prevented from settling in the largest colonies, which could explain why all individuals do not concentrate in a few big colonies, but some settle in suboptimal colonies or colonize unoccupied sites. This opposing effect of conspecifics, together with the low levels of temporal autocorrelation in colony quality between time lags Ն2 yr, could promote colony size variability and facultative coloniality in this species.

Possible causes and consequences of philopatry and breeding dispersal in red-backed shrikes Lanius collurio

“…Given the lack of temporal autocorrelation, it may not be surprising that we failed to find support for public information as being important for breeding dispersal decisions, although we acknowledge our study may have been too short to reliably estimate temporal autocorrelation of reproductive success. It is possible that other cues not evaluated here, but suggested conveying public information on habitat quality, such as conspecific density (Stamps 2001;Doligez et al 2004;Serrano et al 2004) or feeding rate (Pärt and Doligez 2003), may influence dispersal behavior of the red-backed shrike.…”

Habitat, human pressure, and social behavior: Partialling out factors affecting large-scale territory extinction in an endangered vulture

“…In spite of its strong connection with population dynamics and animal conservation, behavior has seldom been taken into account in models of extinction and species-habitat relationships (Reed, 1999). The use of conspecifics as cues during the habitat selection process is a widespread strategy that may promote animal aggregations at traditionally occupied sites (Serrano et al, 2004;Sergio and Penteriani, 2005). On the other hand, antagonistic interactions between neighbors may preclude territory establishment, since high intraspecific densities may increase competition for resources (Newton, 1998;Carrete et al, 2006;Serrano and Tella, 2007).…”

Factors influencing subcolony colonization and persistence in a colonial seabird, the common murre Uria aalge

“…This relationship would be expected if either an increase in murres required an increase in nesting locations (a spillover effect) or if the increase in murres provided positive public information (Valone & Templeton 2002), encouraging more conspecifics to settle via social attraction (Serrano et al 2004). Testing specific social attraction hypotheses, such as the influence of differential attendance of individuals (e.g.…”

“…On the other hand, blacklegged kittiwakes Rissa trydactyla evaluate the quality of potential breeding sites by observing the numbers and reproductive success of presumably unrelated birds breeding there (public information, see review in Valone & Templeton 2002) and choose whether or not to settle accordingly (Danchin et al 1998). Similarly, very low density Arctic skua Stercorarius parasiticus colonies attract fewer recruits than do high density, productive colonies (Phillips et al 1998), whereas only colony size, not reproductive success, was found to influence immigration in lesser kestrels Falco naumanni (Serrano et al 2004). However, these mechanisms operate only when a colony is already occupied.…”