Using GIS to Quantify the Anthropogenic-Induced Raven Threat to Desert Tortoise

Using GIS to Quantify the Anthropogenic-Induced
Raven Threat to Desert Tortoise

(Version 10/4/07) 

Blodwyn M. McIntyre, Thomas E.J. Leuteritz and Mark P. Kumler

ABSTRACT: Common ravens (Corvus corax) are a threat to desert tortoise (Gopherus agassizii) populations in the Mojave Desert. The U.S. Army is expanding its National Training Center (NTC) at Fort Irwin near Barstow California. This will involve the translocation of several hundred tortoises from the expansion area to several new sites outside of the base. In this study we use GIS to quantify the threat ravens pose to desert tortoises in the translocation area prior to initial tortoise release. A survey of ravens within the translocation area allows for a comparison to raven densities at this site in the future. A spline with barriers analysis was used to create a density surface over the translocation area. According to this analysis, raven densities were highest in association with anthropogenic features, linear features, and features with vertical strata. This paper may be the first to actually make a spatially-based connection between highway rest stops and elevated raven densities based on real data.  The study also provides scientists with a baseline for ongoing research into the effectiveness of tortoise translocation.

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