Effects of nest-box density on the behavior of tree swallows during nest building

In territorial species, increased density is often linked to an increase in aggressive interactions, which may result in trade‐offs between competitive behavior and nest construction. We examined the impact of nesting in areas of high‐density versus low‐density nest boxes on conspecific interactions and nest‐building effort in a population of Tree Swallows (Tachycineta bicolor). We also examined whether expected differences in behavior related to variation in nest quality and reproductive success in high‐density and low‐density areas. No differences in either nest‐building behavior or reproductive success were observed between areas of high‐density and low‐density boxes, but there was a tendency of more frequent behavioral interactions at high density. Similarly, there was a significant difference between pairs defending single nest boxes and those defending multiple nest boxes in the number of interactions with conspecifics. These results suggest that although there may be more competition with conspecifics for Tree Swallows nesting at high density, this does not appear to affect either nest quality or reproductive success.