Experimental Designs for Tortoise Pacing Diversion Structures and Tortoise Guards Along Highway Barriers

Abstract. In a study to reduce Mojave Desert Tortoise (Gopherus agassizii) mortality along roadways, we tested the feasibility of structures that discourage tortoises from 1) walking or “pacing” along barriers or 2) crossing areas where gates or openings occur. The diversion designs we tested (one straight and one curved structure, each 7.6 m long) deflected tortoises away from fences at nearly the same rate as tortoises who continued walking along barriers despite the diversion (36.8% vs. 35.7%). No “tortoise guard” structures that we tested, similar to cattle guard structures, were 100% effective at preventing tortoises from crossing the opening. We identified essential characteristics of an effective “tortoise guard” such as minimum gap sizes in the structure and a construction design that allowed a tortoise to climb out of a trench under the structure.