The Influence of Conspecific and Heterospecific Neighbours on Avian Reproductive Success

We investigated the influence of conspecific and heterospecific neighbours on the reproductive success of mountain bluebirds (Sialia currucoides) and tree swallows (Tachycineta bicolor) over eight breeding seasons. The abundance of heterospecific neighbours was negatively associated with reproductive success in mountain bluebirds but positively associated with reproductive success in tree swallows during the early nesting period (i.e., hatching rate). For bluebirds, conspecific and heterospecific neighbour abundance was associated with higher reproductive success (i.e., fledging rate) during the later stages of the nesting period; the same was true for conspecific abundance for tree swallows. These findings could be explained by either positive behavioural interactions (e.g., shared defence) or by habitat quality. We found contrasting effects of nearest neighbour distance. For both mountain bluebirds and tree swallows, having a tree swallow neighbour in close proximity was positively associated with reproductive success during the early nesting period, while having a mountain bluebird neighbour in close proximity was negatively associated with reproductive success during the late nesting period for mountain bluebirds. Together, these results indicate that the effects of conspecific and heterospecific neighbours on reproductive success are species-specific and vary depending on the phase of reproduction.