Does breeding density and forest fragmentation constrain extra-pair matings and nesting success in hooded warblers (Wilsonia citrina)

Songbirds actively pursue a mixed reproductive strategy of sharing parental care responsibilities with one social mate while seeking extra-pair copulations with additional non-mates. However, the effect of breeding density on extra-pair paternity remains unclear. Hooded warblers (Wilsonia citrina) are socially monogamous songbirds that breeds throughout eastern North America, with extra-pair fertilization frequencies of 40%. I studied the effects of breeding density on extra-pair fertilization behaviour, and whether forest fragmentation causes reduced extra-pair fertilizations or nesting success for birds in small fragments.;I tested the breeding density hypothesis using DNA fingerprinting and behavioural data. Contrary to prediction, extra-pair fertilizations were common in fragments of high (35%) and low (43%) breeding density. Low density extra-territorial forays were made by males and females, and females appeared to advertise their fertility to extra-pair males by giving conspicuous chip vocalizations at an average rate of 13.27 chips/min during their fertile period.;To evaluate the ecological consequences of fragmentation, I tested the habitat fragmentation hypothesis. Nest predation was not statistically different for large, medium and small forest tracts. Similarly, fledging success (no. young fledged/brood) was comparable for large, medium and small fragments. Male paring success averaged over 90% for all sites. Small fragments were inhabited by a significantly greater proportion of young males than the large forest tract.;This study demonstrates the active pursuit of extra-pair fertilization by male and female hooded warblers precludes the effect of breeding density over the range of interterritory distance examined. Evidence indicates that older males outcompete younger males for territories in contiguous forest tracts. New threshold models of breeding density effects and forest fragmentation are proposed in a re-evaluation of how breeding density and forest fragmentation may constrain extra-pair mating success and nesting success in songbirds. (Abstract shortened by UMI.)...