Pollutants cause birds to sing tainted love songs

By Ewen Callaway Traces of a chemical once used by power plants leave birds looking fit, but singing another tune altogether. Wild chickadees exposed to permitted levels of polychlorinated biphenyls (PCBs) can’t keep a tune as well as other birds. Because females go for males with the best songs, PCB-exposed birds might lose out on mates, says Sara DeLeon, an ecologist at Cornell University in Ithaca, New York, who presented her research at a recent conference at the university. “The birds are living, not dying, but [PCBs] are affecting some part of their life cycle,” she says. Researchers have long known that some chemicals, such DDT, can throw off a bird’s song, but none have determined whether exposure to trace amounts in the wild can influence songs and mating. DeLeon and her team examined chickadees living along New York’s Hudson River, not far from a General Electric power plant that used PCB insulators from 1907 until the 1970s, dumping some 500,000 kilograms of the toxic chemical into the river. The US government ordered GE to clean the PCB-contaminated waters, one of the country’s largest waste cleanups. Yet traces remain in many sites on the river, but below government safety levels, DeLeon says. Although numerous songbirds live along the Hudson, DeLeon’s team focused on black-capped chickadees, small birds with a two-note song. The best singers mix up the notes they sing, but the ratio between the two notes tends to stay the same. PCB-exposed birds, on the other hand, sing all over the register. Birds that attempted to sing several different “remixes” of the two-note song belted out songs with the notes too far apart. While birds that sing just one tune tend to blur the two notes together. DeLoen’s team made the discovery after analysing the songs with a computer program. The difference is only apparent to her when she can see the song as a visual spectrogram, she says. The poorer vocal performances could arise because PCBs stunt growth and development in a part of the brain important for song, says Tim DeVoogd, a neuroscientist also from Cornell. “One of things they can do is mess up hormone receptors in the brain, and you need hormone receptors to develop correctly– to be either male-like or female-like,” he says. “The birds might look like they are just fine, but they either can’t produce a song or can’t find a mate.” Yet not all chemicals make for shoddy songs. Earlier this year, a team of UK researchers discovered that oestrogen-mimicking compounds, such as bisphenol A, endow starlings with more complex songs that females prefer over chemical-free songs. “It was kind of scary because their immune system was shot to hell,” DeLeon says of the starlings. “The females were preferring males that were singing better, but [the song] wasn’t an honest signal of quality.” This could steadily dilute the starling gene pool, a worrying prospect that could threaten some populations. Yet even female choice against chemically tainted birds, as is the case with the Hudson River chickadees, can threaten local birds if males don’t seem a good mating prospect and females move elsewhere in search of untainted love,
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