Journalist Leila Philip first became interested in beavers when she saw a group of rodents building a pond near her house. Her fascination with what they were doing led her to research and report her new book, Beaverland, which takes a closer look at the animals' impact on North America, from the earliest transatlantic beaver fur trade to today's river restoration efforts. Philip spoke with NPR's Michel Martin about how learning their long history on our continent can highlight beavers' ongoing economic and environmental contributions, especially when it comes to water conservation.