Some of the most basic questions in wildlife research were, for a long time, surprisingly hard to answer. Where do wild animals live, if they still live at all? How many are there? What do they eat?

In the past 15 years, the answers have become a lot more accessible, thanks in large part to digital photography. Researchers can now place cameras with big memory cards and motion sensors in remote places. Known as "camera traps," they snap photos when animals walk by, and they've revolutionised the study of wildlife.

For years, Roland Kays, a biologist at North Carolina State University, emailed fellow scientists for their camera trap images and saved them on his computer in a file of what he called "greatest hits". His collection grew to more than 600 images from 150 researchers in 52 countries. Now they're the centrepiece of Kays' new book, Candid Creatures, which chronicles the use - and discoveries - of camera traps.

Things have come a long way since American photographer George Shiras first used camera traps to take photos of deer and other wildlife in the late 19th and early 20th century, some of which ended up in the pages of National Geographic. But Shiras' remote-controlled cameras were bulky and heavy, took only one photo at a time, and their flash was created by an explosion of magnesium powder, Kays said in an interview. Things got better when film came along, he said, but "you were limited to 36 pictures, and then you'd run out of film".


Today's digital cameras can store hundreds of images, and they stand up to heat, rain, animal nibbles and invasive insects. Their images led Georgia-based scientists to conclude that wild animals are spread throughout at least one half of the Chernobyl Exclusion Zone. Kays said they also helped him discover in Panama that the seeds buried by small rodents called agoutis were frequently stolen by other rodents, then stolen back by agoutis.

"A picture tells a thousand words," said Kays, who shared some of the images from the book. "Maybe a picture is worth a thousand data points, in this case."

Camera trap images have also helped tiger researchers, who can tell individual animals apart by their different stripe patterns, know more about the big cats' small population and how much prey they need to survive, Kays said. "That's been critical to tiger conservation."

Using camera traps, Kays and colleagues concluded that feral cats are rare in 32 protected areas from South Carolina to Maryland. "That's probably because there's so many coyotes," Kays said.

"We definitely get predators with prey in their mouths, and I think that's pretty cool," Kays said.