Breeding near heterospecifics as a defence against brood parasites: can redstarts lower probability of cuckoo parasitism using neighbours?

Breeding habitat choice based on the attraction to other species can be used as a defence strategy. This attraction can provide valuable social information and protection benefits. Increased shared vigilance or cooperative mobbing can come from small birds, while raptors may provide a protective umbrella against brood parasites. The common redstart (Phoenicurus phoenicurus) is part of the migrant bird community and is a regular host for the common cuckoo (Cuculus canorus). We placed redstart nest-boxes near to active nests of great tit (Parus major), and at different distances from active goshawk (Accipiter gentilis) nests. We monitored occupancy rates and followed nest outcomes in terms of brood parasitism and nest predation risk, while following other breeding factors that could be affected (e.g. breeding onset, reproductive investment, and reproductive success). We found that redstarts avoided breeding near to goshawks, but they showed neither attraction nor avoidance to breed next to great tits. Heterospecific neighbours neither reduced brood parasitism risk nor affected overall nesting success in redstarts. Thus, redstarts may not benefit from breeding near heterospecifics. Other front-line strategies may be more important for redstarts to prevent brood parasitism.