Responses of Desert Bighorn Sheep to Removal of Water Sources

• Published in: Wildlife monographs 2008-09, Vol.171 (1), p.1-32
• Main Authors: Cain, James W, Krausman, Paul R, Morgart, John R, Jansen, Brian D, Pepper, Martin P
• Format: Article
• Language: English
• Subjects: Animal populations; Animal, plant and microbial ecology; Anthropogenic factors; Applied ecology; Arid zones; Arizona; bighorn sheep; Biological and medical sciences; Birds; Catchments; Climatic conditions; Conservation, protection and management of environment and wildlife; Deserts; Diet; Drought; Dry season; Forage; foraging; Fundamental and applied biological sciences. Psychology; General aspects; Habitats; home range; Limiting factors; Moisture content; Mortality; Mountain ranges; Ovis canadensis; Ovis canadensis mexicana; Parks, reserves, wildlife conservation. Endangered species: population survey and restocking; Pretreatment; Productivity; recruitment; s; Sheep; Sonoran Desert; Studies; Summer; Survival; Trajectory control; Ungulates; Vegetation cover; water catchment; Watersheds; Wildlife management; Wildlife refuges; Winter
• ISSN: 0084-0173; 1938-5455
• DOI: 10.2193/2007-209

In arid regions of the southwestern United States, water is often considered a primary factor limiting distribution and productivity of desert ungulates, including desert bighorn sheep (Ovis canadensis mexicana). Thus, wildlife management agencies and sportsmen's organizations have invested substantial time and resources in the construction and maintenance of water catchments. Although the availability of freestanding water sources is believed to influence many aspects of the ecology of desert bighorn sheep, the efficacy of these water sources has been questioned and has not been examined experimentally. We used a before-after–control-impact study design to determine if removal of water catchments changed diet, characteristics of foraging areas used by female desert bighorn sheep, home-range size, movement rates, distance to catchments, adult mortality, productivity, or juvenile recruitment in 2 mountain ranges on the Cabeza Prieta National Wildlife Refuge, Arizona, USA. During pretreatment (2002–2003), we ensured that water catchments were available to desert bighorn sheep in both mountain ranges; during posttreatment (2004–2005), we drained all water catchments in the treatment range. We measured diet composition, characteristics of foraging areas, 50% and 95% kernel home ranges, movement rates, and distance to water catchments seasonally from 2002 to 2005. We also estimated adult survival, lamb:female, and yearling:female ratios from 2002 to 2005. We predicted that removal of water catchments would result in 1) increased use of foraging areas with more vegetation cover, more thermal cover, and higher succulent abundance; 2) increased consumption of cacti and other succulents; 3) an increase in home-range size, movement rates, and distance to nearest catchment; and 4) a decrease in adult survival, productivity, and juvenile recruitment. Removal of water catchments in the treatment range did not result in predicted changes in diet, foraging area selection, home-range size, movement rates, mortality, productivity, or recruitment. Female desert bighorn sheep did use areas with more thermal cover during the summer after removal of water catchments, but other characteristics of foraging areas used by bighorn sheep and their diet did not change appreciably with removal of water catchments. We did not document changes in home-range area, movement rates, or distance sheep were from water during hotter months; we only documented changes in home-range area, moveme