EXTRA-PAIR MATING EFFORT OF MALE HOODED WARBLERS, WILSONIA-CITRINA

Few researchers have been able to quantify the time or effort expended by male birds in seeking extra-pair copulations with neighbouring fem ales, In this study, we radio-tracked male hooded warblers, to determi ne the frequency and duration of intrusions onto neighbouring territor ies. Extra-pair fertilizations are common in hooded warblers, with 35% of females producing extra-pair young. Males intruded onto territorie s where females were nest building more often than expected by chance and approached females during most intrusions (78%), suggesting that t hese intrusions were extra-pair copulation attempts. Almost all intrus ions (96%) were to adjacent territories, and males made an average +/- se of 0.4 +/- 0.2 forays/h and spent 4.7 +/- 2.6% of their time off-t erritory. Males were involved in fights or chases with the resident ma le in 21% of intrusions, but were apparently undetected during most in trusions. Males with high intrusion effort onto neighbouring territori es had the lowest rate of intrusions onto their own territory by other radio-tracked males, Males varied extensively in their intrusion effo rt, but this was not significantly correlated with male body mass, age or song rare. The percentage of time spent intruding onto other terri tories was small (0-8%), so males probably do not face strong trade-of fs between making extra-pair copulation forays and other activities li ke mate guarding and feeding offspring. (C) 1998 The Association for t he Study of Animal Behaviour.