In a recent experiment in captive white ibises, many of the males exposed to the metal chose other males as mates.

These "male-male pairs did everything that a heterosexual pair would do," said study leader Peter Frederick, a wildlife ecologist at the University of Florida in Gainesville.

"They built their nest, copulated together, stayed together on a nest for a month, even though there were no eggs—they did the whole nine yards."

(Related: "Homosexual Activity Among Animals Stirs Debate.")

Wild white ibises—among the most common birds in Florida's Everglades—are exposed daily to mercury through their diets of crustaceans and other small invertebrates.

The prey animals take up