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If you sully the environment, the birds will know—and they’ll give you up, too. U.S. Geological Survey scientists use common species like tree swallows to detect toxins. The birds eat insects that hatch in lake or stream sediment; pollutants in those ecosystems then show up in their eggs and chicks. At one site, this method showed toxic chemicals persisting seven years after cleanup began. Homing pigeons, meanwhile, have been similarly tasked with checking air quality here and abroad. And black-footed albatross feathers have revealed increases in Pacific Ocean mercury levels. A bird in the hand, it seems, can reveal contamination in the bush.

This story originally ran as “Trash Detector”in the March-April 2013 issue of Լ����Ƶ magazine.