Intercolony movements and prospecting behaviour in the colonial lesser kestrel

The exploratory activity of individuals aimed at collecting information about potential future breeding sites is known as prospecting. We studied prospecting behaviour in the colonial lesser kestrel, Falco naumanni, using detailed information from radiomarked individuals, whose breeding attempts we terminated at the chick stage, and intensive videotape recording of nests. Half of the radiomarked individuals actively prospected nests in both their own and foreign colonies and they visited colonies up to 7400 m away from their own breeding colony. The presence and number of prospectors arriving at a given nest were influenced by parameters at both the colony and the nest scale. Prospector visits per nest increased with colony productivity and decreased with colony size. The latter does not necessarily mean that prospectors avoid large colonies but rather may be consequence of a dilution effect in colonies where more potential nests can be prospected. The number of prospectors attracted per nest was positively associated with colony connectivity, indicating that both high spatial colony isolation and a small number of breeding pairs in nearby colonies reduced the arrival of prospectors at a given nest. Finally, prospector visits per nest increased and then decreased with parental feeding rates, indicating this parental activity can attract prospectors up to a certain threshold at which nest owners visit their nests frequently enough to keep prospectors away. Overall, this study suggests that prospecting is the mechanism of acquiring public information that could ultimately determine breeding dispersal decisions and the growth and dynamics observed in breeding aggregations.