In the mid-1980s, mammalogist Katherine Ralls conducted fieldwork with the University of Minnesota on the California sea otter. For the first time ever radio transmitters were surgically implanted in sea otters to collect biological data. The information offered new insight into sea otter movements, foraging, 24-hour activity patterns and reproductive and survival rates.

Ralls has also done extensive fieldwork on California's endangered San Joaquin kit fox. She's published around 20 kit fox papers that look at population dynamics, interactions between kit foxes and coyotes, and survey methods. She recently published a paper on kit foxes living in Bakersfield, California who are surviving and thriving on a diet of human junk food.

In this podcast Ralls tells the story of the first sea otter the research team caught and surgically implanted a radio transmitter into. They named the otter "Jack" and he proved to be a very willing study subject. She also discusses her work on the urban kit foxes living in Bakersfield.

• Smithsonian National Zoo: Katherine Ralls biography | Sea otter research | Kit fox research