Causes and consequences of fine-scale breeding dispersal in a female-philopatric species

Abstract

The potentially confounded effects of factors affecting breeding dispersal have rarely been simultaneously examined. The consequences of breeding dispersal are even less studied, presenting a paradox: breeding dispersal seldom seems to improve breeding success, despite its presumed adaptiveness. We studied the causes and consequences of breeding dispersal in female-philopatric eiders (Somateria mollissima) in relation to the spatiotemporal predictability of nest success. Previous nest fate, breeding experience, and breeding density simultaneously affected breeding dispersal. Dispersal distances were longer among inexperienced breeders and after failed breeding. Individual dispersal distances decreased with increasing nest-site-specific breeding density, whereas island-specific nesting success peaked at intermediate densities. The fate of neighbouring nests ('public information') did not influence dispersal. Breeding dispersal was unrelated to subsequent hatching success, controlling for individual quality (body condition, breeding experience, previous nest fate), while it delayed hatch date, which is likely to impair reproductive success. This delay may result from the loss of acquired information of local breeding conditions, prolonging nest prospecting and establishment, also helping explain why breeding dispersal did not increase at high breeding densities, despite a potential reduction in nesting success. In long-lived species, however, dispersal-induced reductions in reproductive output in one season could be offset by improved parental survival prospects. Careful nest prospecting may be profitable, because overall nest success had a strong island-specific component but showed weak temporal variation, and successive individual nest fates were predictable between years. Once a safe nest site is found, females may breed at the same place successfully for many years.

Context‐dependent stress responses and their connections to fitness in a landscape of fear

“…Annually and spatially variable predation pressure was quantified by island‐specific predation pressure, which was calculated as the number of predated nests divided by the total number of nesting attempts (including predated nests and nests in which the ducklings had already hatched) on each island in the years 2009–2011 (cf. Öst et al ., ). Nest surveys were carried out and nest fates recorded only during our first visit to each part of the islands (Öst et al ., ) because additional visits may induce nest predation and abandonment (Bolduc & Guillemette, ) and hence bias our estimates.…”

“…Thirdly, individual variation in body reserves is pronounced during incubation because of substantial differences in energy reserves at incubation onset and weight loss during incubation (Hanssen, Engebretsen & Erikstad, ; Öst et al ., 2008 a ), which females cannot compensate for due to complete breeding anorexia (Parker & Holm, ). Finally, there is significant predation pressure on nesting females (Ekroos et al ., ; Iles et al ., ), the level of which shows large annual (Jaatinen, Öst & Lehikonen, ) and spatial (Öst et al ., ) variation, giving rise to temporally and spatially variable trade‐offs between reproduction and survival.…”

Relative Importance of Social Status and Physiological Need in Determining Leadership in a Social Forager

“…We calculated the number of years since the bird was first ringed and used this as a minimum estimate of years of maternal experience [23], [28]. This is a reasonably accurate age indicator because more than half of the females are trapped annually [29], the fidelity to specific breeding islands is very high [30], and annual trapping effort has been similar since 1996.…”

“…FID is a repeatable measure of boldness towards predators [26], despite considerable annual variation in predation risk [30]. FIDs of captured females were measured while re-visiting nests for marking ducklings in conjunction with another study.…”

The early birds and the rest: do first nesters represent the entire colony?

“…This finding indicates that eiders respond to the crowding (increased nest density) in the colony. Common eider's decisions to initiate nesting will partially depend on density and the choices of other females in the colony, either as a result of observing the actions or nest success of others (''public information'') or that females are attracted to the high nest densities, perhaps seeing the crowding as a sign of safety (Danchin et al 1998;Valone 2007;Ö st et al 2011). Such individuals could be reluctant to nest early and wait to initiate their own nests until they see sufficient conspecifics on their nests.…”