Applies techniques he developed for evaluating sea otter health to river otters in Indiana. Has found that old growth forests in the United States contain up to 50 percent more songbird species and 50 percent more individual birds than do similar second-growth sites. Has tracked neotropical bird populations in Great Smoky Mountain National Park and thrush populations in the Midwest. Uses DNA fingerprinting to determine the rates and consequences of inbreeding in the field and to measure genetic variation in small populations. Also studies social interactions such as dominance hierarchies, territoriality, mating systems and submissive behavior.
Current studies focus on the bannertailed kangaroo rat in Arizona.
Other current projects include investigations of diving behavior in Arctic ringed seals, the causes of population decline in kangaroo rats, the role of vocalizations as reproductive isolating mechanisms in African forest monkeys, and the effects of habitat acoustics on primate vocalizations. Students also are currently investigating dispersal and its relationship to behavior and population structure in Yellowstone red foxes and white-footed mice.