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A new study by US scientists has revealed that exposure to mercury pollution could be hitting some wild birds' reproductive prospects hard by causing males to pair with other males. The researchers discovered that American white ibises (Eudocimus albus) from south Florida that consumed methylmercury (MeHg), the most toxic and easily absorbed form of mercury found in the environment, were more likely to engage in same-sex pairings - a phenomenon unknown in wild populations of this species with no exposure to the pollutant. The main sources of mercury globally are coal-fired power plants and gold mining though in Florida , mercury was likely to have been released by the burning of medical and municipal waste, reports Nature. The metal is converted into methylmercury by some species of bacteria, usually found in wetlands that also tend to be home to many different bird species. Peter Frederick, an ecologist at the University of Florida , Gainesville , and his colleagues collected 160 white ibis nestlings from breeding colonies in south Florida in 2005, and split them into four groups, each composed of 20 males and 20 females. Once the birds were 90 days old, the researchers began adding methylmercury to their feed. Three of the groups were given low, medium or high doses of mercury based on levels ranging from 0.05-0.3 parts per million recorded in the wild, while the fourth group were given no mercury. Over the next three years, the researchers measured mercury levels in the feathers and blood of the ibises, and observed their mating behaviour. Mismatched mates The team found that the levels of mercury built up in the birds over time, and that exposure resulted in roughly 13-15 percent more nests failing to produce any offspring. A high proportion of these failed nests were found to be male-male pairings. Birds exposed to any mercury displayed courtship behaviour less often than controls and were also less likely to be approached by females when they did. As the level of mercury exposure increased, so did the degree and persistence of homosexual pairing. Males that engaged in homosexual parings were also less likely to switch partners from year to year, which Frederick says ibises tend to do if they have been unsuccessful in mating during their first breeding season. The team's results are published in Proceedings of the Royal Society B today1.

Exposure to mercury pollution causes homosexuality in birds