Peninsular bighorn sheep (Ovis canadensis nelsoni) face multiple threats across their range, including loss of population connectivity due to roads, increasing renewable energy development, and expansion of the U.S.-Mexico border fence. While a substantial amount of research on Peninsular bighorn sheep has been conducted in the U.S., very little information is available on the populations in Baja California, Mexico. In 2012, we initiated a bi-national project to study the population status, genetic population structure, and connectivity of Peninsular bighorn sheep in northern Baja California. We used non-invasive fecal sample collection to obtain genetic samples for analysis. Samples were collected in three different mountain ranges in northern Baja: the Sierra Juarez, Sierra San Pedro Martir, and Sierra de Los Cucapah. Through performing a series of validation tests, we were able to demonstrate that reliable genotypes from fecal DNA can be obtained from field-collected samples for population genetic studies. In 2013, we also captured and GPS-collared 10 bighorn sheep (5 rams and 5 ewes) in the Sierra Juarez and monitored their movements. In addition, camera traps and ground surveys were used to document use of the U.S.-Mexico border region.
Our data showed several genetically distinct populations within our study area: one north of highway MEX-2 extending into the U.S.; one south of MEX-2 extending into the Sierra San Pedro Martir; and potentially a newly discovered one in the Sierra de Los Cucapah, although our sample size was limited. GPS telemetry data revealed that ewes tended to maintain consistent movement patterns and home ranges throughout the year in the Sierra Juarez. Conversely, rams had much larger home ranges than ewes and significantly increased their movements during July through December. Home range size for rams was also considerably larger than previously reported for Peninsular bighorn sheep. While we documented use of the U.S.-Mexico border region with multiple crossings across the international border, we did not observe any crossings of highway MEX-2. Three of the GPS-collared rams spent time near the highway, but did not cross. Connectivity between populations in the Sierra Juarez and Sierra San Pedro Martir appears high, but becomes limited near the U.S.-Mexico border across highway MEX-2, based on both movement and genetic data. However, more data are needed to further understand the effects of this highway on ram and ewe movements, population viability, and disease transmission.