West Mojave Plan FEIR/S - Desert Managers Group

suitable habitat. Direct mortality factors also include crushing tortoises along paved andunpaved roads; intentional vandalism, such as shooting tortoises; pet collection; poaching forfood or ceremonial purposes; loss of animals to fire; trampling by cattle; and animals lost tomilitary maneuvers. Not all direct mortality factors are manmade; prolonged drought, wildfirescaused by lightning, and naturally unsuitable geographical features (e.g., playas) are either directmortality factors or natural features that directly affect tortoise densities and distribution (seeSection 3.3.2.5.2, below).Direct mortality factors are often researched in scientific studies, but such studies aretypically limited in scope, for example, to a given cattle allotment or specific motorized raceevent. Such studies should not be dismissed, but they fail to identify either the geographicalextent or severity of mortality factors on a regional scale.To better understand both the distribution and severity of direct mortality factors on aregional scale, data recently collected in the field were used. These included 19 disturbancecategories: Vehicles (Paved Roads, Dirt Roads, Trails, Tracks), Garbage, Shooting (BulletCasings and Shooting Areas), Mining (e.g., test pits, markers), Campsites, Livestock (Sheep andCattle), Wild Horses or Burros, Domestic Dogs, Fence lines and Posts, Utility Lines, DenudedHabitat, Partially Denuded Habitat, Old Buildings, and Military Ordinance. These data represent“observable human disturbances” and in many cases direct mortality factors. They are the basisfor the following discussion.The data have been used to to see where such impacts have occurred and are likely topersist or increase in the absence of proactive management. They allow the identification ofareas where observable human impacts tend to be clustered or, alternatively, are uncommon. Forexample, the data clearly show that in DWMAs the most concentrated areas of cross-countryvehicle tracks are adjacent to BLM open areas (particularly El Mirage and Johnson Valley) anddesert communities (e.g., Silver Lakes). Data show that cattle are not constrained to allotments,as cow dung has been recorded up to several miles outside allotment boundaries. Illegaldumping is most common adjacent to urbanizing areas, as are domestic dogs. These data havebeen used to identify areas where focused management can further assess and remedy problems.Direct mortality factors were recorded during both the 1998-2001 tortoise sign-countsurveys and the 2001-2002 distance sampling surveys. Of 148 tortoises found dead where thesuspected cause of death was given, 76 (51%) were attributed to mammalian predation (coyotes,kit foxes, occasionally feral dogs), 42 (28%) were identified as crushed by off-highway vehicles,13 (9%) due to raven predation, 9 (6%) due to gunshot wounds, and 9 (6%) due to other causes.Urbanization: Urbanization poses serious direct impacts to tortoises, and has resulted inregional extirpations, particularly within the southern and southwestern portion of its range.Historical records and anecdotal evidence indicate that tortoises once occupied all areas fromeastern Antelope Valley, through Lancaster and Palmdale, Pearblossom, Lake Los Angeles,Hesperia, Victorville, Apple Valley, to Lucerne Valley. Current data for these areas show thatChapter 3 3-96