UF study: Mercury causes birds to turn homosexual
The head researcher says the study has no relevance to human sexuality.
Published: Wednesday, December 1, 2010 at 12:02 p.m.
Last Modified: Wednesday, December 1, 2010 at 12:02 p.m.
A University of Florida researcher has found that mercury consumption can cause white ibises to exhibit homosexual behavior.
Researchers had previously observed that mercury, which is emitted by coal-fired power plants and cement kilns, can affect the reproduction of wading birds. A five-year study led by UF wildlife ecology and conservation professor Peter Frederick found that mercury increased the tendency of male ibises to nest with other males.
"It really seems to change the sexual preference of the birds," Frederick said. "That really hasn't been shown before."
The study was published online Wednesday in the biological research journal Proceedings of the Royal Society B. UF researchers built a 13,000-square-foot netted aviary in Gainesville for the research. They split 160 white ibises into four groups, feeding varying levels of mercury to three of them and no mercury to the fourth.
About 55 percent of male ibises fed a high-mercury diet were nesting with other males in one year of the study. The degree of homosexual pairing for all three dosed groups increased with their mercury exposure. Male ibises given mercury showed lower rates of performing courtship rituals and high-mercury females produced 35 percent fewer fledglings than females in the control group.
While Frederick said the research has implications for other types of birds, he said that the findings are unlikely to apply to human sexuality, which is more complex.
"This has zero relevance for humans," he said.
But he said the research adds to a growing body of evidence that chronic exposure to even low mercury levels can affect wildlife. Researchers observed in the 1990s that wading bird populations in the Everglades had fallen. After pollution-scrubbing equipment was added to trash incinerators and mercury removed from the batteries, the population rebounded.
Mercury sources in North Florida include Gainesville Regional Utilities' Deerhaven coal-fired power plant and the Suwannee American Cement plant in Branford near the Ichetucknee River. Frederick said mercury from emissions can be converted into its more toxic form of methylmercury in shallow, warm wetlands with high turnover.
Studies have shown that mercury emissions tends to fall out within 125 miles or the source, he said, so regulatory efforts should focus on sources near those kind of wetlands.
"There's actually a really good argument to be made for local solutions to local problems," he said.
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