Chapter 6: Constraints on acoustic signaling among birds breeding in secondary cavities: The effects of weather, cavity material, and noise on sound propagation

Abstract

Increasing evidence suggests that anthropogenic noise from urbanization affects animal acoustic communication. We investigated whether the begging calls of nestling Eastern Bluebirds (Sialia sialis) varied along a disturbance gradient of ambient noise. Contrary to our prediction and the results of a previous study of nestling Tree Swallows (Tachycineta bicolor), we found that nestling Eastern Bluebirds did not increase the amplitude or structural characteris- tics—including frequency, rate, and duration—of their vocalizations in response to ambient noise. However, we found that prevalent temperature and humidity conditions attenuated begging calls. Specifically, in warmer, more humid weather, vocalizations of nestling Eastern Bluebirds attenuated outside the nest box; this is consistent with research conducted on the propagation of sound in various mediums and temperatures. Finally, our results indicate that increased ambient noise is associated with a decrease in the signal-to-noise ratio of nestling vocalizations. In other words, loud ambient noise likely masks chick begging calls, which suggests that chicks and par- ents may experience communication difficulties in noisy environments. We suggest that future studies explore the effects of ambient noise on parental behavior and aspects of parent-offspring communication and conflict that are related to raising a brood of nestlings.