Head to Head

Abstract

Turner et al. (2004) developed a habitat selection model for a population of desert bighorn sheep (Ovis canadensis) in the Peninsular Ranges of southern California that is listed as a threatened and endangered population by the state of California and the federal government, respectively. We are concerned that the recent publication of an article by Turner et al. (2004) could be detrimental to the management and recovery of bighorn sheep in the Peninsular Ranges because it lends credibility to a flawed analysis of bighorn sheep habitatuse patterns. The model attempts to extrapolate conclusions from a limited subset of bighorn sheep data that is not representative of the study area and was not gathered in a manner conducive to the analysis methods used by the authors. The authors classified habitat pixels as “active” or “inactive” based on the presence-absence of bighorn sheep observations without considering monitoring intensity. Turner et al. (2004) also failed to consider the implications of basing their model almost entirely on a bighorn sheep subpopulation known to have atypical habitat selection patterns. This subpopulation in the northwestern Santa Rosa Mountains frequently used food and water sources within hillside urban areas. Because the Turner et al. (2004) model was developed using data primarily from this atypical subpopulation, the model has low external validity and is unlikely to accurately predict habitat selection by other bighorn sheep subpopulations in the Peninsular Ranges. Furthermore, with the NW sub-population used in model development now excluded from urban areas, the Turner et al. (2004) model is unlikely to accurately predict habitat selection patterns of even this sub-population. We suggest the Turner et al. (2004) model is at best only applicable to this subpopulation between the years 1994–1998.