Oh the noise!

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Science  09 Sep 2011:
Vol. 333, Issue 6048, pp. 1360
DOI: 10.1126/science.333.6048.1360-a

Cities and highways are noisy. Such anthropogenic noise causes substantial interference with the acoustic communication of many species. Most urban noise is low in frequency, and birds that live in noisy areas have been shown to alter the frequency of their songs, shifting from low to high frequencies in order to be heard above the din. This may seem like a reasonable solution to the problem; however, Halfwerk et al. show that singing higher-frequency songs has fitness costs. They recorded the songs of pairs of great tits (Parus major) in a Dutch forest and found that low-frequency song is related to female fertility and that the mates of low-frequency–singing males are less likely to stray. In fact, males with higher-frequency songs were less likely to be the sole father of their mate's offspring. When they experimentally exposed the birds to sound similar in frequency to urban noise, males shifted to singing high-frequency songs. This shift allowed them to be heard, but also placed them at frequencies less preferred by females. These results suggest that species facing noisy conditions are faced with a trade-off: Sing high and be heard or demonstrate your quality by singing low and be drowned out by ambient noise. Such a trade-off demonstrates the divergent selection pressures of anthropogenic environmental changes.

Proc. Natl. Acad. Sci. U.S.A. 108, 10.1073/pnas.1109091108 (2011).

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