Birds becoming gay because of mercury in their diets.
Researchers in Florida and Sri Lanka studied the effect of the metal in white ibises’ diets to find out why breeding was down.
They found the higher the dose of mercury in the wading birds’ food pellets, the more likely a male bird was to pair with another male.
Dr Peter Frederick from the University of Florida, who led the study, said: “We knew mercury could depress their testosterone levels but we didn’t expect this.
“We’re seeing very large reproductive effects at very low concentrations of mercury so we really need to be paying more attention to this.”
The team fed the birds on food pellets which contained concentrations of mercury equivalent to those in the shrimp and crayfish that make up their wetland diet.
The males with the higher mercury doses performed far fewer courtship displays, so were more likely to be ignored by females.
Wetland habitats, like the Florida Everglades that are home to the birds, are particularly vulnerable to mercury contamination, which can come from burning coal and waste, and run-off from mines.
The report shows wetland birds are particularly badly affected by it.
Gary Heinz, a wildlife researcher from the US Geological Survey, said: “It cannot be broken down, only be moved about and transformed from one chemical form to another.”
“And any effect that might reduce the productivity of a species would likely be harmful in nature.”