MEEHAN, T.D.; LEASE, H.M.*; WOLF, B.O.; Univ. of New Mexico; Univ. of New Mexico; Univ. of New Mexico: Negative Indirect Effects of Insectivores (Cliff Swallows) on the Fruit Set of an Insect-Pollinated Herb (Sweet Clover)

Though an abundance of research has focused on direct interactions between birds and plants, relatively few studies have reported on indirect interactions. We conducted a study along the Middle Rio Grande in New Mexico to determine if avian aerial insectivores had a negative, indirect impact on insect-pollinated plants through predation of insect pollinators. We found a significant negative relationship between proximity of sweet clover (Melilotus officinalis) to cliff swallow (Hirundo pyrrhonota) breeding colonies and sweet clover fruit set. The apparent effect of cliff swallows was strongest within 200 m of breeding colonies (approximately 50% reduction in fruit set) and decreased nonlinearly to a distance of approximately 400 m. We also found considerable taxonomic overlap, at the order and family level, between the insects visiting sweet clover and those eaten by cliff swallows. We discuss how sustained, indirect effects of colonial insectivores could have interesting implications for the evolution of plant phenology and morphology and lead to patterns in pollination mode and plant community structure.