FLOATER BEHAVIOR AND TERRITORY ACQUISITION IN MALE PURPLE MARTINS

The behaviour of non-territorial male purple martins, Progne subis, was monitored while they were present as 'floaters' in a colony. Most floaters (22 of 24) did not intrude on all territories under observation with equal frequency: a large proportion of their intrusions occurred at only three to five territories. The bias in intrusion frequency on certain territories was not explained by the size of the territory (number of cavities), age of the owner (adult versus subadult male), or the nesting stage of the owner. Males required an average of 8 days (range 2-29 days) to acquire a territory. The behaviour of individual floaters (intrusion rate, frequency of challenge to owner, median duration of intrusions) was not significantly correlated with their tenure in the floating population. Both adult and subadult males acquired territories primarily by gaining control over some of the cavities defended by other males, rather than through eviction or filling vancancies. The behaviour of floaters appears to represent an asymmetric 'war of attrition' where persistence at a territory can pay off even though floaters almost always lose individual fights with owners. © 1991 The Association for the Study of Animal Behaviour.