Breeding dispersal in black-headed gull: the value of familiarity in a contrasted environment.

1. Some species (e.g. migratory species with high movement ability) are unlikely to experience any physical cost when dispersing, at least at the landscape scale. In these species dispersal is nevertheless behaviourally constrained to avoid non-physical costs such as the loss of familiarity with the breeding environment, and these constraints can be maladaptive in a fast-changing environment. 2. We evaluated such constraints using multievent modelling of a 20-year capture-mark-recapture data set from a multisite population of black-headed gull (Chroicocephalus ridibundus). The population undertakes seasonal migrations that are very large compared with the size of the study area. 3. Distances between colonies appeared as a strong predictor of breeding adults' dispersal rates, confirming behavioural constraints on dispersal. In addition, birds that had recruited outside their colony of birth (natal dispersers) tended to return to their colony of birth later in life (long-term memory effect). 4. An attraction for larger colonies was also visible in breeding adult dispersal patterns. The fact that distance and memory still constrained dispersal although the largest colony provided higher breeding success indicated departures from the ideal-free distribution, probably linked with the lack of information about distant colonies. Moreover, the regional population apparently functioned as a meta-colony where individuals frequently bred in suboptimal-choice locations before being able to recruit in their preferred colony.