Summary
Tree Swallows (Tachycineta bicolor) show one of the highest levels of extra-pair mating among bird species, yet extra-pair copulations are rarely observed. Despite the suggestion that extra-pair copulations could be taking place away from nest sites, very little is known about movement patterns of individual Tree Swallows during the pre-laying and laying periods. We used radio telemetry to track movement patterns of four female Tree Swallows at dawn and dusk during the pre-laying and laying periods. Our tracking results indicate that individual females differed in their movement patterns: some remained close to their nest site on multiple nights while others were rarely detected near their nest box at night. Despite differences in movement patterns, all four females that we tracked produced extra-pair offspring for which we were unable to identify extra-pair sires, even after sampling the majority of males breeding within our nest-box grids. Despite the small sample size, our results confirmed extensive Tree Swallow movement away from nest-box grids during the pre-laying and laying periods. This highlights the need for future studies of mating behavior away from the nesting site, particularly for species that forage and/or roost in communal areas during their fertile period.
Methodology
Radio telemetry