One of the central missions of the Recovery Program is to track changes in population size. Radio collars placed on bighorn sheep throughout the range have been immensely helpful in this effort, allowing researchers to find bighorn in the wild, obtain information on lambing status and habitat use, and investigate mortalities. In 2011 about 100 bighorn sheep in eight herd units carried functional radio collars. Each radio collar costs several thousand dollars, a price certainly proportional to their great worth. The Sierra Nevada Bighorn Sheep Foundation has purchased a number of collars for the use of DFW’s Recovery Program, and has also help to fund the helicopters used to capture sheep for collaring.