Vol. 44, No. 5
David M. Larson
Traffic noise may mute interspecific reactions to Tufted Titmouse alarm calls. Photograph by John Flannery (CC BY-SA 2.0).
I’ve been thinking a lot about noise lately. Early this summer I had to relocate one of my Breeding Bird Survey points to reduce the incessant noise from a propane station. The compressor made it nearly impossible for me to hear any bird sounds. Another survey point is too close to the traffic of Interstate 95. Those observations lead me to think about how birds react to anthropogenic noise. Recent studies have shown that noise affects animal distribution, behavior, and reproductive success (Francis and Barber 2013).
A study published recently (Grade and Sieving 2016) tested the effects of highway noise on interspecific communication in songbirds. Specifically, the researchers tested the extent to which highway noise affects the response of Northern Cardinals to playback of Tufted Titmouse alarm calls. They played the titmouse high-seet alarm calls at varying distances from two busy highways (3200–3600 vehicles per day) in north central Florida. Their hypothesis was that the typical anti-predator responses of the cardinals (freezing) would decrease with increased ambient noise levels. Indeed, they found that at background noise levels above 50 decibels (dB)—for comparison, 50 dB is as loud as a moderate rainfall, per the American Speech-Language-Hearing Association—none of the cardinals responded to playback of alarm calls, but at lower noise levels, almost 80 percent of the cardinals responded to the same alarm calls. Clearly, the response of the cardinals was blunted by higher ambient noise levels. What this project did not address was whether the noise masked the sound of the alarm calls so the cardinals could not hear them or whether the noise distracted the cardinals so that they did not respond normally.