Natal dispersal does not entail survival costs but is linked to breeding dispersal in a migratory shorebird, the southern dunlin <em>Calidris alpina schinzii</em>

Abstract

<div lang="en" class="abs"><p class="abs_header">Abstract</p><p>The costs and benefits of dispersal are often assessed by comparing fitness between dispersing and non-dispersing individuals. Importantly, individuals that disperse between their natal and first breeding site may subsequently be more likely to disperse between breeding sites compared to those that remained philopatric to their natal site. Such within-individual consistency in dispersal behaviour can bias local survival estimation, and thus the survival comparison between dispersing and non-dispersing individuals, if breeding dispersal leads to permanent emigration from the study area. We examined whether adult survival correlates with natal dispersal in a migratory shorebird, the southern dunlin <em>Calidris alpina schinzii</em>, in two isolated patchy populations where permanent emigration is expected to be extremely rare. To assess whether local adult survival could be biased by non-random breeding dispersal, we analysed between-patch breeding dispersal probability and quantified within-individual consistency in dispersal. Among females, natal dispersers were more likely to disperse again as adults compared to non-dispersers, while no difference was observed in males which were always highly site faithful. Yet, adult survival did not differ between natal dispersing and non-dispersing individuals in either sex. Breeding dispersal probability was higher in failed compared to successful breeders. Breeding dispersal often resulted in dispersal back to the natal patch, i.e. delayed natal philopatry. Our results suggest no survival costs of dispersal after first reproduction. Despite individual consistency, survival estimates of dispersing individuals were not biased because nearly all available breeding habitat was covered. We show that consistency in dispersal can occur even in site faithful species like the southern dunlin. Studies of the effects of dispersal on survival should therefore account for within-individual consistency in dispersal if not all available breeding habitat is monitored in open populations. In particular, delayed natal philopatry may lead to biased local survival estimates for immigrants when compared with philopatric individuals.</p></div>