Factors affecting breeding dispersal in the facultatively colonial lesser kestrel: individual experience vs. conspecific cues

1. The role of individual experience vs, the use of conspecific cues on bre eding dispersal decisions have seldom been determined in colonial birds. We studied causes of breeding dispersal in the lesser kestrel (Falco naumanni ), a species that breeds in colonies of variable size as well as solitarily . During a 6-year study in Spain, we gathered information on 486 subsequent breeding attempts and on 26 explanatory variables which evaluated individu al experience, conspecific cues in terms of breeding performance and colony size, and different ecological and populational characteristics. 2. Two decisions were separately analysed: whether or not to disperse, and how far to move. Generalized Linear Mixed Models (GLMMs) allowed us to iden tify the relative contribution of each explanatory variable while controlli ng for the non-independence of individual dispersal decisions across years. 3. Females seemed to disperse more often than males (34% vs. 19%), and both sexes apparently dispersed less with age. However, a GLMM showed that expe rience (i.e. the number of years a bird bred in a particular colony) was th e only factor influencing breeding dispersal. Birds showed higher site fide lity the greater their experience in a colony, which could be related to be nefits derived of increased local familiarity. A second GLMM showed that, b efore birds acquired experience in a particular colony, individual nest fai lure due to predation and proximity to other colonies increased the probabi lity of dispersal, dispersal being also higher in colonies with poor conspe cific breeding success. Furthermore, solitary nesting birds were more prone to disperse and dispersal probability decreased the larger the colony of o rigin, according to fitness expectations associated with colony size. 4. A GLMM explaining dispersal distances retained two variables - birds dis persed farther the lower the breeding density in the surroundings, and the larger the distance to the nearest colony. Dispersing birds tended to settl e within their previous foraging areas (median dispersal distance = 1.6 km) , being constrained by the availability of nearby colonies. 5. Lesser kestrels mainly cue on their own breeding performance and experie nce in a particular colony at the time of taking a dispersal decision. Howe ver, inexperienced birds also partially cue on the size and breeding succes s of their own colonies (but not on the size or breeding performance of oth er colonies), and birds moved larger distances when dispersing from areas o f low populational density. These results support some degree of conspecifi c attraction.