Lifetime fitness correlates of natal dispersal distance in a colonial bird

Authors


Correspondence author. E-mail: serrano@ebd.csic.es

Summary

1. Obtaining empirical evidence of the consequences of dispersal distance on fitness is challenging in wild animals because long-term, unbiased data on reproduction, survival and movement are notoriously difficult to obtain.

2. Lifetime fitness correlates of natal dispersal distance were studied in an isolated population of the facultatively colonial lesser kestrel Falco naumanni (Fleischer) monitored during 8 years at north-eastern Spain, where most birds (83%) dispersed from their natal colony to settle at distances ranging from 112 m to 136·5 km.

3. Neither annual breeding success nor age at recruitment was affected by natal dispersal distance. However, a capture–mark–recapture analysis revealed that survival during the year following recruitment decreased exponentially with dispersal distance, with differences of up to 15% between philopatrics and long-distance dispersers. In subsequent years, it remained similar irrespective of the natal dispersal distance moved. These results did not seem to be biased by long-distance dispersers settling differentially in the periphery of the population (which could emigrate permanently and be considered dead in future occasions) or within-individual consistency in successive dispersal distances, so our results appear to reflect genuine survival differences between dispersal tactics.

4. Average lifetime fledgling production, average lifetime recruitment success and rate-sensitive individual fitness (λind) also decreased with the distance from the natal to the first-breeding colony, indicating that dispersal decisions early in life affecting immediate survival prospects may translate into long-term fitness costs.

5. Both survival and lifetime fitness models including continuous dispersal distances significantly improved the characterization of the effect on fitness compared with models considering dispersal as a discrete process (i.e. dispersal vs. philopatry at a colony level).

6. Long-distance dispersers were more likely to establish new colonies regardless of whether they recruited in the centre or the periphery of the population, revealing their important role in the colonization of unoccupied patches. Individuals experienced a higher probability of mortality in small and newly funded colonies, so lifetime fitness costs of dispersal seem to be explained by recruitment in sites where average quality is low because of high uncertainty in survival prospects.

Ancillary