http://www.ncbi.nlm.nih.gov/pubmed/22673657

Am Nat. 2012 Jul;180(1):142-5. Epub 2012 May 23.

Birds and anthropogenic noise: singing higher may matter.

Slabbekoorn H, Yang XJ, Halfwerk W.

Source

Behavioral Biology, Institute of Biology, Leiden University, P.O. Box 9516, 2300 RA, Leiden, The Netherlands.

Abstract

Abstract In a recent theoretical study, Nemeth and Brumm explored the effect of amplitude and frequency variation in birdsongs on signal transmission in forested and noisy urban environments. They argued that "increased song pitch might not be an adaptation" but "an epiphenomenon of urbanization." Here we address the validity of comparing the communication benefits of changes in amplitude and frequency to question the adaptive significance of "urban songs." We believe that their calculations actually confirm considerable high-frequency benefits under noisy urban conditions, between and within species. Hence, we conclude that noise-dependent frequency shifts in urban birds can be adaptive.