Variation in avian vocalizations during the non-breeding season in response to traffic noise

Low-frequency traffic noise that leads to acoustic masking of vocalizations may cause birds to alter the frequencies or other components of their vocalizations in order to be heard by conspecifics and others. Altering parts of a vocalization may result in poorer vocal performance or the message contained in the vocalization being received incorrectly. During the winters of 2011-2012 and 2012-2013, we recorded and measured the 'chick-a-dee' call of Black-capped Chickadees (Poecile atricapillus) and the 'po-ta-to-chip' call of American Goldfinches (Spinus tristis) to determine whether components of the calls produced in areas of high traffic noise and low traffic noise differed in any way. We found that both chickadee and goldfinch calls had higher minimum frequencies in areas with high traffic-noise than in low traffic-noise areas. The maximum frequencies showed no differences in either species' calls. This suggests that chickadees and goldfinches alter the part of their calls that are acoustically masked by traffic noise in effort to better transmit the vocalization. These differences suggest that increasing anthropogenic noise may influence avian communication and that noise management should be included in conservation planning.