Before European colonization of North America, the use of animals for food and clothing seemed to have been in balance with wildlife populations, but once native people could trade pelts for cloth, blankets, iron goods, and guns, the harvest of fur-bearing animals increased rapidly and soon wiped out local populations. Beaver was the most important animal in the fur trade, valued for the soft under-hairs shaved from pelts and felted for hats and other uses. William Clark wrote in 1806 that the Yellowstone River and other Missouri branches penetrating the Rocky Mountains abounded in fine beaver and otter, and in 1833 Prince Maximilian recorded that fur-bearing animals along the Missouri had decreased to an extraordinary degree in just a few years and that the business would soon no longer be significant there, listing about 25,000 beaver hides, about 40,000 to 50,000 bison hides, about 1,000 to 100,000 muskrats, and 20,000 to 30,000 deer taken in the course of one year. Many beaver populations were wiped out by the mid-1800s, but in the past 75 years beavers have repopulated most of their former habitats. Beavers mate for life and live in colonies of one or two family groups, usually including adult pairs, kits, and yearlings, and the deep water behind a maintained dam provides storage for winter food.