SINGING SEASIDE: PACIFIC WRENS (TROGLODYTES PACIFICUS) CHANGE THEIR SONGS IN THE PRESENCE OF NATURAL AND ANTHROPOGENIC NOISE

摘要

Noise pollution poses a significant obstacle to vocal communication. Songbirds rely on acoustic signals for mate choice and territory defense, and masking of these signals can have negative fitness consequences. Prior investigations reveal that birds mitigate the negative effects of acoustic masking by increasing their signal amplitude or by singing with higher minimum frequencies. In this study, we evaluate the responses of male Pacific Wrens (Troglodytes pacificus) to natural ambient noise (ocean surf) and anthropogenic noise (highway traffic) in Pacific Rim National Park Reserve, B.C., Canada. Pacific Wrens, known for their complex songs, are specialists of old-growth forest. We hypothesized that Pacific Wrens would compensate for the effects of ambient noise in their environments through modifications to their songs that enhanced their transmission properties. Recognizing that longer, higher frequency, and more complex signals propagate better in noisy environments, we predicted that Pacific Wrens would increase the length of their songs, the length of the syllables within their songs, the number of syllables per song, and the minimum frequency of their songs. Recordings of 52 territorial Pacific Wrens showed that proximity to highway traffic noise had a significant effect on song duration but no significant effect on any of the other measured variables. Pacific Wrens that were recorded near the shoreline, however, sang songs with longer syllables, and higher intra-individual variation in song duration. Number of syllables, syllable minimum frequency, and song duration did not vary with distance from the shoreline. We conclude that natural and anthropogenic noise sources influence the singing behavior of Pacific Wrens.