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Open Access Publications from the University of California

Evaluating Wildlife Corridor Linkages: Do Freeway Underpasses Connect the Peninsular and Transverse Mountain Ranges?

  • Author(s): Murphy, Michelle L.
  • Advisor(s): Allen, Michael F.
  • et al.

Habitat connectivity is a key component for the persistence of populations, for maintaining genetic diversity, and for weathering environmental extremes and climate shifts. Desert environments are stressful largely because of extreme swings in precipitation and temperature, and thus maintaining connectivity becomes a critical conservation strategy to ensure mobile species can track temporal and spatial shifts in habitat suitability. These linkages are especially critical in light of expected distributional shifts due to climate change. Expansion of urbanization and energy resource development, as well as the transportation and energy infrastructure required to support those changes, are fragmenting desert environments at an increasing rate. Highway underpasses and culverts are often identified in conservation planning as wildlife corridors, providing connections between previously contiguous suitable habitats, but do they facilitate or impede wildlife movement? I assessed wildlife use of seven pre-existing interstate freeway and state highway underpass structures to determine whether they are utilized as corridors for wildlife movement. The underpasses occur between southern California's Peninsular and Transverse Mountain Ranges, a key linkage between Baja California's biotic province and that of the Sierra Nevada. I utilized non-invasive monitoring methods, including camera traps, track-plates, and track beds, over 13 months to capture wildlife presence, determine rates of underpass usage, identify spatial and temporal wildlife use patterns, and to assess some factors that may constrain wildlife use. My results indicated a negative association between native carnivore presence and human activity within and near the underpass structures. Bobcats exhibited a strong negative relationship with motorized vehicles while coyotes displayed a weak negative relationship with humans on foot. Underpass dimensions influenced the rate of wildlife use, with small- and medium-bodied species preferring long, narrow structures whereas bobcats preferred structures that were wide, short, and open. Future strategies for maintaining or enhancing landscape connectivity in desert systems should provide a range of underpass structures to support use by many animals, and develop underpasses that discourage human use.

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