Wildlife can now be detected by sniffing DNA in the air

IN THE PAST, studying ecosystems for signs of change has needed lots of boots on the ground. Plants, being sedentary, can be recorded easily by unleashing an infantry of PhD students eager to make a name for themselves. Taking a census of an area’s animals is, however, a different matter. It frequently involves sitting quietly for hours on end, noting which species walk, flutter or slither by, and what they are up to. Sometimes, the troops assigned to do this see a lot. Sometimes not.