Changing Habitat Conditions on Bighorn Sheep Ranges in Colorado

Abstract

Changes in habitat associated with the decline and extinction of 36 populations of Rocky Mountain bighorn sheep (Ovis canadensis canadensis) in Colorado were investigated using a mapping approach. Differences in habitat conditions were compared between: (1) 19 ranges currently occupied by bighorn sheep (in 1982) and 17 ranges no longer supporting sheep herds; (2) presently occupied vs. recently (Ca. 1970) abandoned portions of 3 sheep ranges; and (3) habitat characteristics of the declining Beaver Creek herd in 1962 vs. 1977. Ranges supporting greater numbers of bighorn sheep had more high-visibility habitat, greater area dominated by grass and rock cover, more habitat on and near (.ltoreq. 250 m from) open escape terrain, and greater topographic relief than ranges supporting few or no sheep. Encroachment, over 15 years, of tall, dense shrubland and forest resulted in fragmentation and reduced amounts of high-visiblity habitat on and near open escape terrain on the Beaver Creek range. In the absence of fire or habitat management, vegetation succession has been a major cause of habitat loss for bighorn sheep in Colorado.