Morphological and genetic techniques for distinguishing captive vs. wild stock are often insufficient. We found differences in carbon isotope values from Canis latrans (Coyote) and Canis lupus (Wolf) eating wild vs. domestic diets. Wild canids in the Northeast have lower δ¹³C values because they eat prey that mainly feed on C₃ plants. However, canids eating typical domestic diets have more positive δ¹³C values (≈ 6‰) because of the Zea mays (Corn; a C₄ plant) fed to domestic stock and used in dog foods. We applied this technique to hair and bone samples from eight Wolves in the northeastern USA, where no natural Wolf populations are known. Three Wolves had strongly negative δ¹³C values, typical of a wild-food diet, while the other five Wolves had more positive values typical of captive animals. As expected, we found no significant difference in ι;¹⁵N isotope values between captive and wild animals. This new evidence suggests that, while some Wolves are escaping from captivity, at least three animals have apparently dispersed into the area. This finding adds new urgency to the preparation of conservation plans for the potential natural recovery of this endangered species in the region.