If you're on Washington State's Puget Sound this summer, you may glimpse a boat carrying a stocky Australian cattle dog named Gator. When Gator's body is stiff, his mouth open, ears forward, tail erect, and nose twitching in the wind, you can plausibly conclude one thing: A killer whale has pooped nearby.

Gator is one of 11 scat-detection dogs at the Center for Conservation Biology at the University of Washington, Seattle. Sam Wasser, the center's director, has been studying animals via their droppings for more than 20 years. Some animals are brazen about leaving a pile in the open, while others take pains to hide their waste. To eliminate sampling bias when collecting dung, Wasser began employing detection dogs to track the scat.

Not just any dog can do the job. Detection dogs must be completely, utterly obsessed with their toys. "They're not looking for scat at all," Wasser says. "They want to play with their ball." They'll be given the chance only if they nose in on a sample. According to Wasser, "Gator can do black bear, grizzly bear, lynx, bobcat, puma, maned wolf, wolverine, fisher, killer whale, marijuana, cocaine, heroin, and crack."

Gator's affinity for illicit drugs stems from his career with the Washington Department of Corrections. Dogs' first-class sense of smell means they're frequently called upon to sniff out drugs and explosives. Canines have also been reported to be able to sniff out skin cancer and to identify samples of urine from patients with prostate cancer.

In March, a California-based cancer research organization, the Pine Street Foundation, published results of a study in which dogs identified breast and lung cancer from patients' breath with extreme accuracy (M. McCulloch et al., Integrative Cancer Therapies, 5:1, March 2006). "I think there are always going to be people who say 'dogs can't do that,' but we're constantly being surprised by what nature can do," says Nicholas Broffman, the Foundation's executive director. "We're only just scratching the surface of the power of scent, whether for identifying cancer or whatever else."

For Wasser, that "whatever else" is, at the moment, killer whale feces. Of course, tracking waste at sea presents challenges not faced on land. For other species with buoyant, easy-to-spot waste (right whales, for example, who sport bright orange waste, and on whom Wasser has done some work at Boston's New England Aquarium) those challenges are minimal.

But orca feces is another thing entirely. "Killer whale poop is hard to describe without being disgusting," Wasser warns. "It's bluish-greenish-black and gooey like snot. Sorry." Gator, for his part, remains unfazed. He's spent the summer training on the boat, sniffing out test samples. In August he'll start tracking wild orca scat.

The orca population in the Pacific Northwest has declined some 20% in the last 15 years. Figuring out why, says Wasser, has been a challenge. Some environmentalists have pointed to changes in the availability of Chinook salmon, the whales' primary food source. But orcas suffer plenty of other insults. Pollution in Puget Sound may increase the presence of pathogens, and PCB levels in the tissues of killer whales are an order of magnitude higher than in any other species, Wasser notes. During the summer, whale-watching tour boats pursue the orcas relentlessly. Boats also cause noise pollution, which may have an impact on whales' sonar skills.

Wasser hopes to distinguish the factors that could be harming the whales. By studying their scat, he can retrieve information about diet and nutritional health. He can measure concentrations of cortisol, the stress hormone, and also levels of metabolism-regulating thyroid hormones; when food is scarce, hormone levels drop to slow the whale's metabolic rate. PCBs and other toxins can also interfere with the production of thyroid hormones. By measuring gonadal hormones, Wasser can tell if a female is pregnant and whether her pregnancy is healthy. He can measure immunoglobulin to look at immune function. Wasser also performs DNA analyses to identify individuals and track their health over time. "What makes this so powerful is really the amount of information we can get out of each sample," he says.

Wasser admits that colleagues haven't always taken his work seriously, but they're coming around. Some of his past collaborators have started scat dog programs in other parts of the country, and Conservation International has expressed interest in establishing a program in Brazil. Back at the University of Washington, Wasser is in the process of upgrading his facility to train more dogs. "We're trying to be good conservationists," he says. "If you think you have a good tool for saving a species, you want to get it out there."