The study is part of Caldwell's research on how mercury is transferred up the food chain, affecting the reservoirs' ecosytems. Although scientists have known about mercury levels at Caballo and Elephant Butte since the 1970s, they still aren't sure where the metal is coming from. The mercury concentration increases up through the food chain and eventually reaches humans. At high concentrations, mercury can cause nerve tissue damage and birth defects. According to the New Mexico Fish Consumption Advisory, mercury levels are high enough that pregnant and nursing women should avoid consuming fish-eating fish like walleye and bass caught in Caballo and Elephant Butte.
Some levels are so high that men are advised to eat no more than one fish a year.
The advisory is published by New Mexico's health, environment, and game and fish departments. In their study, the researchers collected cormorant eggs to analyze the mercury levels the eggs received from mother birds. After the chicks hatched, the researchers took blood and feather samples to find out if mercury levels increased during the early stages of the birds' lives when they grow fast and eat a lot. But the researchers also found that the birds can excrete the mercury. It's a good way to get rid of it.