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.

Any viewer of crime dramas might think, though, that there is a better way. Just as DNA traces on an unwashed glass or a carelessly discarded cigarette butt can place a suspect as having been in a particular place, so can DNA shed by a creature as it goes about its business. Ecologists have thought of this, and it certainly works for things like animal droppings. But these, too, must first be detected and collected—and they will identify only the animal that dropped them. What would really speed things up would be a means of sampling an entire habitat at one go.