When the birds go unheard: highway noise disrupts information transfer between bird species.

Highway infrastructure and accompanying vehicle noise is associated with decreased wildlife populations in adjacent habitats. Noise masking of animal communication is an oft-cited potential mechanism underlying species loss in sound-polluted habitats. This study documents the disruption of between-species information transfer by anthropogenic noise. Titmice and chickadees broadcast specific calls to alert kin of predator threats, and sympatric vertebrates eavesdrop on these alarm calls to avoid predators. We tested if tufted titmouse alarm call eavesdropping by northern cardinals is disrupted by road noise. We broadcast recorded alarm calls to cardinals in natural areas near and far from highways. Cardinals reliably produced predator avoidance responses in quiet trials, but all birds in noisy areas failed to respond, demonstrating that highway noise is loud enough to disrupt this type of survival-related information via masking or cognitive distraction. Birds in family Paridae are abundant, highly social and vocal residents of woodlands across the Holarctic whose alarm calls are used by many species to mediate predation risks. Our work suggests that communication network disruption is likely to be widespread, and could help explain the pattern of reduced biodiversity near roadways.