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A highway's road-effect zone for desert tortoises (Gopherus agassizii)

January 1, 2006

Roads and highways can affect populations of animals directly (e.g. due to road mortality) and indirectly (e.g. due to fragmentation of habitat and proliferation of non-native or predatory species). We investigated the effect of roads on threatened desert tortoise (Gopherus agassizii) populations in the Mojave Desert, California, and attempted to determine the width of the road-effect zone by counting tortoise signs along transects at 0, 400, 800, and 1600 m from the edge of a highway. Mean sign count was 0.2/km at 0 m, 4.2/km at 400 m, 5.7/km at 800 m, and 5.4/km at 1600 m from the highway edge. The differences between all pairs of distances, except 800 and 1600 m, were statistically significant, suggesting that tortoise populations in our study area are depressed in a zone extending at least 400 m from roadways. We speculate that the major cause for this depression zone is road mortality.

Citation Information

Publication Year 2006
Title A highway's road-effect zone for desert tortoises (Gopherus agassizii)
DOI 10.1016/j.jaridenv.2005.06.020
Authors W.I. Boarman, M. Sazaki
Publication Type Article
Publication Subtype Journal Article
Series Title Journal of Arid Environments
Series Number
Index ID 70030367
Record Source USGS Publications Warehouse
USGS Organization