The old-fashioned way to survey an area's fauna is to watch and wait, to trek and listen, and to examine tracks and scat. But in the era of cheap, rapid DNA sequencing, there's potentially an easier method: just sequence some soil and see what shows up. Animals urinate, defecate and shed skin flakes and hair, leaving traces of their DNA in the ground.

Eske Willerslev of the University of Copenhagen and his team trialled the method in areas where the species were a known quantity: zoos, safari parks and an ostrich farm. They found that dirt-DNA analysis could identify almost all of the animals living in each area, and that the amount of DNA of each species correlated well with its biomass. Taking multiple samples from different areas improved the method's accuracy.

Mol. Ecol. 10.1111/j.1365-294x.2011.05261.x (2011)