These dogs, which sniff out the scents of various invasive species, are chosen from shelters when they're about a year old. The group screens some 1,000 pups to find each of the 30-or-so conservation heroes—and half drop out during training, according to Pete Coppolillo, the director of the program. He's looking for energetic canines who are focused on their toys, which motivates them to get their work done. "They are excited to do their jobs—they love it," says Coppolillo. "Most of our dogs have to be told when to stop working."