The effect of call similarity on call discrimination by Tree Swallow (Tachycineta bicolor) nestlings in the presence of noise

Abstract

As the extent of noise expands with urbanization, so does the extent of its impacts on wildlife. The impact of noise is particularly strong when it comes to the disruption of avian communication. Birds rely heavily on acoustic communication. They are especially vulnerable during the nestling stage of their lives because of their heavy reliance on parental care for survival. It is assumed that in noisy environments call recognition becomes difficult and thus would make already difficult distinctions (i.e., similar calls) more difficult, however this assumption is yet to be tested. My study attempts to answer the question: How does call similarity impact the call discrimination of nestling Tree Swallows (Tachycineta bicolor) in the presence of noise? A study in 2016 investigated the impacts of noise on call recognition by raising half of the nests in noise while the other half were used as a control group. Both groups were then administered two sets of playback tests, one under noisy conditions and one under quiet conditions. During each test, a parental call was played as well as the call of an unfamiliar adult and the nestlings’ responses were recorded. Using data collected in 2016 my study calculated the spectrogram correlation and Euclidean distance of 37 call pairings (one parent call and one unfamiliar adult). The impact of rearing treatment (quiet vs. noise), playback condition (quiet vs. noise) and call similarity measures were then compared to the nestling response data using a mixed linear model. Neither call similarity nor noise had a significant impact on the nestlings’ call discrimination, suggesting that even when calls are similar and conditions noisy, nestlings can access the call elements necessary for recognition. While this study found no impact of noise on call recognition, noise cannot be ignored especially given its other, more detrimental impacts (e.g., cochlea damage). Further research into the exact mechanism used by nestlings and the impacts of inconsistent noise (e.g., noise which occurs at fluctuating amplitudes) is needed to better understand how nestlings discriminate between similar calls in noisy environments.