This deer was chomping on apples when it became startled — perhaps by the camera flash, or maybe by the photo-bombing flying squirrel behind it. (Hailey and Logan Lehrer)

Some of the most basic questions in wildlife research for a long time were 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 gotten a lot more accessible, thanks in large part to digital photography. Researchers can now place in remote places cameras with big memory cards and motion sensors. Known as “camera traps,” they snap photos when animals walk by, and they’ve revolutionized the study of wildlife.

For years, Roland Kays, a biologist at North Carolina State University, e-mailed 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 centerpiece of Kays’s 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 centuries, some of which ended up in the pages of National Geographic.

Shiras’s 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. As Animalia wrote recently, their images led Georgia-based scientists to conclude that wild animals are spread throughout at least 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,” he said.

A tiger emerges from cooling off in mud at Manas National Park in India. (WWF-India)

Camera trap images confirmed that the giant sable antelope of Angola had survived that country’s long civil war. “That’s the most basic thing: Something is there, they’re still around,” Kays said.

A female giant sable antelope passes close to the camera as her herd mates kneel to eat clay from a salt lick in Cangandala National Park, Angola. (Pedro Vaz Pinto)

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’d get lots of pictures of coyotes, and probably one photo of a cat.”

Rock Creek Park sits in the middle of residential areas of Washington, D.C., where lots of cats reside. But a camera trap survey of the park turned up only this one photo of a cat — and 126 of coyotes. (eMammal)

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

A coyote carries a domestic cat it has caught to a highway underpass in Southern California. (Kevin Crooks)

Here are a few more photos from Kays’s book:

Long-tailed macaques are a common species in Southeast Asia, where they mostly feed on fruit, but also on insects, lizards and handouts from tourists. (Benoit Goossens)

A young giant anteater rides on its mother in the Brazilian Pantanal. Females carry their young for six to nine months, or until they are about half her size. (LFB Oliveira, GS Hofmann & IP Coelho)

A cow elephant and its calf cross a swollen river in Gabon. (Xavier Hubert-Brierre)

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