Evaluating wildlife corridor linkages: Do freeway underpasses connect the Peninsular and Transverse mountain ranges?

Background/Question/Methods

Expansion of urbanization and alternative energy resource development, along with the transportation and energy transmission infrastructure required to support those changes in land use, are fragmenting desert environments at an increasing rate. Habitat connectivity is a key component for successful conservation strategies, especially so in light of expected distributional shifts due to climate change. Highway underpasses and culverts may function as wildlife corridors, providing connections between previously contiguous suitable habitats, but do they facilitate or impede wildlife movement? In this analysis six pre-existing interstate freeway and state highway underpass structures and the surrounding habitat matrix are being evaluated for one year to determine whether they support connectivity between southern California’s Peninsular and Transverse Mountain Ranges, a key linkage between Baja California’s biotic province and that of the Sierra Nevada . Camera traps, track-plates and track bed methods are utilized to capture wildlife presence, determine relative frequency of underpass usage, and to elucidate spatial and temporal wildlife movement patterns. 

Results/Conclusions

Results to date suggest a negative association between wildlife presence and human activity within and near the underpass structures, with species such as bobcat utilizing underpasses having little to no human activity. Relative frequency of wildlife occurrences is also disproportionate between the north and south side of all I-10 underpass openings, with more wildlife approaching underpass structures from the south and humans from the north. This may be due to the characteristics of the habitat matrix on either side, with the north side being more fragmented and closer to human habitation. Underpasses placed with minimal human use are more utilized than those with frequent human activity, and should be part of large-scale conservation planning. Results of this study will be used as pilot data for planning and implementing a more expansive study to identify generalized principles for effective corridor design in arid environments.