Cornell Lab of Ornithology reports a study that shows low levels of PCBs (polychlorinated biphenyls) are changing Black-capped Chickadeess and Song Sparrows bird songs. Birds were observed that had consumed insects that were contaminated with the PCBs. It is believed that the PCBs mimic hormones and interfere with development in the part of the bird’s brain that governs song and song structure.
The changes in song were tied to specific PCBs. There are 209 variations, 41 of which were tested. The greatest variation in song was among birds in areas with higher levels of certain types of PCBs. It was found that Song Sparrows at the most polluted sites, birds were singing trills, with more high-quality strings of notes compared to the songs of sparrows in non-contaminated sites.