Potential Effects of the United States‐Mexico Border Fence on Wildlife

Abstract

Security infrastructure along international boundaries threatens to degrade connectivity for wildlife. To explore potential effects of a fence under construction along the U.S.-Mexico border on wildlife, we assessed movement behavior of two species with different life histories whose regional persistence may depend on transboundary movements. We used radiotelemetry to assess how vegetation and landscape structure affect flight and natal dispersal behaviors of Ferruginous Pygmy-Owls (Glaucidium brasilianum), and satellite telemetry, gene-flow estimates, and least-cost path models to assess movement behavior and interpopulation connectivity of desert bighorn sheep (Ovis canadensis mexicana). Flight height of Pygmy-Owls averaged only 1.4 m (SE 0.1) above ground, and only 23% of flights exceeded 4 m. Juvenile Pygmy-Owls dispersed at slower speeds, changed direction more, and had lower colonization success in landscapes with larger vegetation openings or higher levels of disturbance (p < or = 0.047), which suggests large vegetation gaps coupled with tall fences may limit transboundary movements. Female bighorn sheep crossed valleys up to 4.9 km wide, and microsatellite analyses indicated relatively high levels of gene flow and migration (95% CI for F(ST)=0.010-0.115, Nm = 1.9-24.8, M =10.4-15.4) between populations divided by an 11-km valley. Models of gene flow based on regional topography and movement barriers suggested that nine populations of bighorn sheep in northwestern Sonora are linked by dispersal with those in neighboring Arizona. Disruption of transboundary movement corridors by impermeable fencing would isolate some populations on the Arizona side. Connectivity for other species with similar movement abilities and spatial distributions may be affected by border development, yet mitigation strategies could address needs of wildlife and humans.

Genetic population structure of Peninsular bighorn sheep (Ovis canadensis nelsoni) indicates substantial gene flow across US–Mexico border

“…Natal dispersal of both sexes is consistent with our finding of similar outcomes for AMOVA on both nuclear and mtDNA markers. In fact, our results suggest that ewe dispersal in the Peninsular Ranges may not be as restricted as has been previously inferred from past radio telemetry data (Flesch et al, 2010;Rubin et al, 1998), or mtDNA sequences (Boyce et al, 1999) in the absence of substantive microsatellite data. The GENECLASS2 results also indicated that one ewe may have immigrated from outside the study area (Table 3), though we do not have genotype data for the surrounding populations to confirm this possibility.…”

“…A number of studies have demonstrated the threat a US-Mexico border fence poses to wildlife through habitat loss, subdivision of populations, and severing of migratory corridors (Atwood et al, 2011;Flesch et al, 2010;Lasky et al, 2011). Our results suggest fence completion across PBS habitat would create a dispersal barrier within a metapopulation that is highly connected.…”

A 2018 Horizon Scan of Emerging Issues for Global Conservation and Biological Diversity

“…New political trends are leading to an acceleration of fencing around national boundaries in the USA and Europe. Such fences and associated infrastructure affect the daily movements, migration, and survival of animals ranging from large carnivores to gallinaceous birds [34,35]. Thus, these fences may present a new threat to the viability of wild animal populations.…”

Reptile bycatch in a pest-exclusion fence established for wildlife reintroductions

“…The from domestic to wild populations, excluding exotic predators or competitors, and reducing human-animal conflicts (Hayward & Kerley 2009). However, the fences themselves can negatively impact non-target native wildlife by disrupting natural movement and dispersal processes, increasing mortality via entanglement and exposure, and enforcing inbreeding and isolation (Bode & Wintle 2009;Flesch et al 2010;Hayward & Kerley 2009;Long & Robley 2004). Fences are also costly to build and maintain, with an opportunity cost for other conservation and management priorities (Scofield, Cullen, & Wang 2011).…”