When climate change affects where birds sing

Recent changes in temperature and precipitation have implications for transmission and excess attenuation of sounds, with important consequences for the choice of vocal display sites by animals. Birds typically sing from within or at the top of the vegetation, and the relative height of such song posts varies consistently among species. I estimated relative height of positions in the vegetation used by singing birds in 1986-1989 and again in 2010 after spring and summer temperatures had increased by 20% and precipitation by 30%, predicting that these changes would increase the height of song post positions. Average song post height increased by 18% or 1.2 m during the study. Because the increase in song post height should depend on relative costs and benefits of such change, I predicted that sexually dichromatic species and species with increasing populations and hence intense intraspecific competition for mates should cause increases in song post height, whereas high predation risk by the sparrowhawk Accipiter nisus should prevent increases in song post height because sparrowhawks preferentially prey on birds high in the vegetation. That was indeed the case. These results suggest that display sites for singing birds can change rapidly, with potential consequences for optimal design of songs, variance in mating success, and predator-prey interactions.