Black bear population and connectivity in the Sky Islands of Mexico and the United States

The Sky Island region is a mountainous region surrounded by grasslands, deserts and intermountain valleys, located between Mexico and the United States. However, different land management and human impact can have an effect on its wildlife populations. Currently, the border wall poses an immediate threat to the survival of black bears (Ursus americanus), considered an endangered species in Mexico. Our aim was to determine the conservation status of black bears in the Sierra San Luis as affected by the border fence. We determined population size through camera traps and radio-telemetry, and modeled population occupancy using PRESENCE. We documented a bear population with more than 500 individuals. Surveys along the border failed to detect bears crossing it, but we identified linkages between the two countries, which shall be important for future landscape planning. Increased vehicular traffic, migration, and drug traffic have a negative effect on bear populations, exacerbated by an increase in anthropogenic activities resulting from the construction and maintenance of the border wall. We recommend modifications to the structure of the border wall, and to increase wildlife monitoring by the United States authorities in order to reduce the potential impacts that this structure has on black bears and other wildlife populations.