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

Abstract

Summary1. The role of individual experience vs. the use of conspecific cues on breeding 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 individual 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 identify the relative contribution of each explanatory variable while controlling 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 experience (i.e. the number of years a bird bred in a particular colony) was the only factor influencing breeding dispersal. Birds showed higher site fidelity the greater their experience in a colony, which could be related to benefits derived of increased local familiarity. A second GLMM showed that, before birds acquired experience in a particular colony, individual nest failure due to predation and proximity to other colonies increased the probability of dispersal, dispersal being also higher in colonies with poor conspecific breeding success. Furthermore, solitary nesting birds were more prone to disperse and dispersal probability decreased the larger the colony of origin, according to fitness expectations associated with colony size. 4. A GLMM explaining dispersal distances retained two variables -birds dispersed farther the lower the breeding density in the surroundings, and the larger the distance to the nearest colony. Dispersing birds tended to settle 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 experience in a particular colony at the time of taking a dispersal decision. However, inexperienced birds also partially cue on the size and breeding success of their own colonies ( but not on the size or breeding performance of other colonies), and birds moved larger distances when dispersing from areas of low populational density. These results support some degree of conspecific attraction.

Possible causes and consequences of philopatry and breeding dispersal in red-backed shrikes Lanius collurio

“…Other factors potentially related to the social constraints hypothesis, such as individual quality and age, were not assessed. The importance of individual quality (other than age) for breeding dispersal has generally received little attention, whereas age-related effects on breeding dispersal were found in some studies (Pärt and Gustafsson 1989;Payne and Payne 1993;Daniels and Walters 2000;Newton 2001;Blakesley et al 2006), but not in others (Forero et al 1999;Serrano et al 2001;Hoover 2003;Sedgwick 2004). …”

Habitat- and density-dependent demography of a colonial raptor in Mediterranean agro-ecosystems

“…Further benefits of living in large colonies include the reduced risk of predation for adults and their offspring and the reduction of individual investment in vigilance . Moreover, colony size regulates the dispersal of lesser kestrels, which use the number of conspecifics as a cue to colony quality and tend to move to large colonies (Serrano et al, 2001;Serrano and Tella, 2003). Earlier studies found colony size to be positively associated with reproductive success in this species (Serrano and Tella, 2007), and nestling survival was higher in large colonies (Serrano et al, 2001), due to the interaction between nest distance and breeder abundance (Di Maggio et al, 2013).…”

“…The low breeding dispersal is congruent with findings in other populations (cf. Serrano et al, 2001 in which 71.6% of breeding lesser kestrels were recruited into the same colony or settled in colonies within their previous foraging habitats). Moreover, no cases of adult emigration to neighboring populations were detected during the study period, in spite of specific monitoring of the colonies outside the Gela Plain.…”

The Migration of the Lesser Kestrel Falco naumanni in Eastern Europe - A Ringing Recovery and Direct Observation Approach

“…Juveniles that dispersed did so on long distances, while adults showed much higher fidelity on their breeding grounds. There is evidence that the probability of dispersal decreases with age (Serrano et al 2001, Calabuig et al 2008 while such long distance dispersal movements exist but could be underestimated (Prugnolle et al 2003). A reason for that could be that estimating philopatry rates from ringing recovery data has its drawbacks since ringing intensity varies with locations and longdistance dispersal movements of individuals could be difficult to detect.…”