Compensating for diminishing natural water: Predicting the impacts of water development on summer habitat of desert bighorn sheep

Artificial water sources have been used for decades to enhance and restore wildlife habitat but the benefits of their use have been subject to debate. During the past century, the number of natural springs in Joshua Tree National Park, California, USA, has declined. In response to concerns about the viability of the bighorn sheep (Ovis canadensis nelsoni) population, a number of water developments were constructed throughout the park. We modeled potential historical and present-day summer habitat of female bighorn sheep to evaluate the effectiveness of the artificial and remaining natural water sources in maintaining habitat and to determine how loss of artificial sources might affect future habitat availability. Prior to 1950, 583.5 km2 of summer habitat was potentially available. Presently, only 170.6 km2 of habitat is available around natural water sources and 153.5 km2 is available around guzzlers. When all perennial water sources are included in the habitat model (minus overlap), 302.3 km2 of summer habitat is potentially available. This represents only 51.7% of summer habitat available prior to 1950. Without artificial water developments, 47.7% of present-day summer habitat would be lost, which raises important management questions regarding the debate about what is natural or artificial within otherwise protected areas.