Responses of Desert Bighorn Sheep to Removal of Water Sources

Abstract

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, movement rates, and distance to water catchments during winter and autumn. There were 10 desert bighorn sheep mortalities in the treatment range and 8 in the control range; 7 mortalities in each mountain range were during pretreatment. Twelve of the 18 total mortalities occurred during summer. Survival rate was lower during pretreatment than posttreatment in both mountain ranges. We did not document increased mortality or a change in lamb:female or yearling:female ratios after removal of water catchments. Home‐range area and movement rates declined with incre...

Spatial distributions and resource selection by mule deer in an arid environment: Responses to provision of water

“…The importance of water in patterns of resource selection by desert ungulates is often postulated, but selection has been difficult to detect (Krausman and Etchberger, 1995;Marshal et al, 2006;Cain et al, 2008). We identified strong selection for sources of permanent water by mule deer, while simultaneously accounting for variation in availability of water among individuals resulting from placement of their UDs on the landscape as well as other important aspects of habitat in this ecosystem.…”

Global positioning system and associated technologies in animal behaviour and ecological research

“…Although these positions are often less accurate (hundreds of metres to kilometres), they provide a backup to GPS positioning (Collecte Localisation Satellites 2008b). Argos is used as a data transfer system for animal-borne GPS (Yasuda & Nobuaki 2005;Meyburg et al 2007;Cain et al 2008;Mandel et al 2008).…”

Habitat use by a desert ungulate: Predicting effects of water availability on mountain sheep

“…Even ''long term'' manipulative experiments have not provided unequivocal results that will assist land managers in making informed decisions about the contributions of wildlife water developments to conservation programs. For example, Cain et al (2008) experimentally removed water sources from mountain sheep habitat, but were unable to fully assess the impacts of that action on life history parameters of those specialized ungulates. Indeed, the very attributes of arid climates (low, but highly variable precipitation [Noy-Meir, 1973;Schwinning and Sala, 2004]) that likely make water availability an important factor influencing the distribution of desert ungulates precluded Cain et al (2008) from drawing firm conclusions about the importance of that resource in their study area.…”

“…For example, Cain et al (2008) experimentally removed water sources from mountain sheep habitat, but were unable to fully assess the impacts of that action on life history parameters of those specialized ungulates. Indeed, the very attributes of arid climates (low, but highly variable precipitation [Noy-Meir, 1973;Schwinning and Sala, 2004]) that likely make water availability an important factor influencing the distribution of desert ungulates precluded Cain et al (2008) from drawing firm conclusions about the importance of that resource in their study area. Our modeling exercise, however, allowed us to ''manipulate'' the availability of water in seven mountain ranges, and to make predictions about the influences of those manipulations on habitat quality for mountain sheep.…”

“…Small populations are subject to increased probabilities of extirpation (Berger, 1999;Lande, 1988;Wehausen, 1999), but the persistence of those populations has important implications for metapopulation structure (Bleich et al, 1990Epps et al, 2007;Schwartz et al, 1986) and the overall conservation of these specialized, desert-adapted ruminants. Provision of water sources remains controversial (Bleich, 2005;Krausman et al, 2006), and manipulative experiments (Cain et al, 2008) have produced only equivocal results, largely a result of the vagaries characteristic of arid climates. Nonetheless, those concerned with the conservation of mountain sheep must decide how to maintain population size, habitats, and connectivity (Longshore et al, 2009), factors that are critically important to the persistence of that taxon (Bleich, 2006).…”