Consuming high doses of the chemical mercury makes some birds appear to turn gay, scientists say.
It is known that mercury reduces breeding rates in white ibises but scientists in Florida and Sri Lanka were surprised to discover that the higher the dose given to male birds, the more likely they were to try to mate with another male.
Researchers gave birds food pellets containing mercury and found that males which received higher doses were more likely to find male partners and shun mating displays to attract females.
Mercury pollution appears to affect wetland birds the most. It can come from burning coal and waste, plus run-off from mines.
It is thought to mimic hormones in the body, leading to changes in behaviour.
Dr Peter Frederick of the University of Florida, who led the study, told the BBC: ‘We knew mercury could depress their testosterone levels, but we didn’t expect this.’
He added that the next step would be to look at the behaviour of mercury-contaminated animals in the wild.