Desert bighorn sheep (Ovis canadensis nelsoni) persist in the southern California deserts as a metapopulation in habitat fragmented by three major interstate freeways. Since the 1960s, these barriers to movement have led to reductions in bighorn genetic diversity of up to 15% (Epps et al. 2005). Small herds of a few tens to several hundred individuals occupy mountain habitat patches, isolated by intervening valleys, where local extinctions and recolonizations of marginal habitat are frequent. Connectivity between these habitat patches occurs as gene flow, primarily through the movement of rams, and demographic connectivity, which involves both sexes and is required for recolonization (Creech et al. 2014). Following an outbreak of respiratory disease in 2013, individuals were captured and fitted with telemetry and global positioning satellite collars that soon revealed the interstate highways were not absolute barriers (Dekelaita 2020). Crossings were rare but contributed to a detectable increase in genetic diversity (Epps et al. 2018). Proposals to construct a high-speed train within the Interstate 15 corridor that connects the metropolitan areas of Los Angeles and Las Vegas would alleviate traffic congestion and provide an efficient transportation alternative. Concrete barriers to separate the train from vehicular traffic, and fences to keep pedestrians and animals off the tracks, however, would eliminate the infrequent bighorn movements across the highway and complete the isolation of metapopulation fragments. Wildlife habitat connectivity is a concern that unifies people across the political spectrum. Thirty nongovernmental organizations, with purposes ranging from hunter advocacy to National Park advocacy, signed a letter to California Department of Transportation supporting the restoration of wildlife corridors across Interstate 15 via construction of wildlife overpasses. This transportation project provides a unique opportunity to not only alleviate traffic congestion but to restore habitat connectivity and contribute to sustainable wildlife populations.
Vegetation management within transportation corridors (e.g., for pollinators)