Effects of exotic Lonicera and Rhamnus on songbird nest predation

Habitat fragmentation and disturbance exacerbate the invasion of exotic plant species that, in turn, may attract nesting songbirds by providing a branch structure suitable for nest sites. We document that American Robin (Turdus migratorius) nests in two exotic plants, Lonicera maakii and Rhamnus cathartica, experienced higher predation than nests built in comparable native shrubs (Crataegus, Viburnum) and native tree species. This was due to a combination of lower nest height, the absence of sharp thorns on the exotic species, and perhaps a branch architecture that facilitated predator movement among the exotic species. In a more subtle interaction, nesting Wood Thrushes (Hylocichla mustelina) experienced apparent competition with robins for nest sites in Lonicera, and this interaction was further aggravated by an increased selectivity for Lonicera by nesting robins, possibly due to their early leaf flush and expansion. By documenting increased nest predation in songbirds nesting in exotic shrubs, our results suggest that restoring native plant communities may benefit the surrounding avian community.