Colony foundation in the lesser kestrel: patterns and consequences of the occupation of empty habitat patches

Understanding the process of colonization of new habitat patches is critical to clarify the proximate mechanisms involved in the distribution of a species and particularly in the formation of breeding aggregations. We studied the process of colony foundation in a long-term monitored population of lesser kestrels, Falco naumanni. For this purpose, we first analysed which habitat/demographic features influence the occupation of empty habitat patches experimentally supplied with nestboxes. Second, we studied the individual characteristics of founders and the reproductive consequences of occupation of new breeding patches in comparison with individuals settled in already established colonies. We found that the probability of occupation of experimental breeding patches increased with the relative cover of cereal crops. Regardless of sex, founders and individuals that settled in pre-existing colonies did not differ in body condition or age. However, there was a higher proportion of unringed kestrels in new than in pre-existing colonies, suggesting that founders are mostly immigrants from distant populations. Founders and nonfounders had similar breeding success, but the former had a lower parasitic burden of feather lice, indicating that occupying new breeding patches could reduce parasite pressure and/or transmission. Our results suggest habitat characteristics influence settlement decisions in the absence of pre-existing social cues, but do not support the idea that founders are suboptimal individuals unable to gain access to previously established colonies.