Petition to list the Mohave Ground Squirrel - Defenders of Wildlife

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Petition to list the Mohave ground squirrel Page 22 of 49 Transportation An extensive network of roads and highways lies within the range of the Mohave ground squirrel and they are known to be run over by vehicles (Gustafson 1993). Paved routes themselves render habitat completely unusable by the Mohave ground squirrel for burrowing or forage production. Extensive vehicular routes may also pose a behavioral barrier to some movement, thus further fragmenting otherwise quality Mohave ground squirrel habitat. Although radio-collared Mohave ground squirrels have readily traversed 4-lane divided highways, these crossing are made at considerable mortality risk (Leitner, personal communication). A 1998 survey reported in the Western Mojave Desert Off-Road Vehicle Designation Project Environmental Assessment and Draft CDCA Plan Amendment (“WEMO Route Designation”) described the number and types of human disturbances along 310 transects throughout the range of the Mohave ground squirrel. Thirty-seven percent of these transects were bisected by roads. Currently, camping is allowed up to 91.5 m (300 feet) from existing roads on all BLM lands. Additionally, there is evidence of disturbance to vegetation along roadsides up to 400 m out. Thus, the impact zone reaches beyond the roadbed itself. In our GIS threats analysis, we buffered the major highways within the range of the Mohave ground squirrel (SR 14, SR 58, and US 395) by 400 m from the center line to account for the road impact zone. This is based on the minimum level of road effects determined for the desert tortoise in the Mojave Desert (Hoff and Marlow 2002) and consultation with experts in the field (Mohave Ground Squirrel Technical Advisory Group). In fact, Hoff and Marlow (2002) found road impacts to desert tortoises more than 4,000 m from the highest traffic level road that they studied. Therefore, our 400 m estimate is highly conservative. The results of our analysis show that this calculated threat of highways affects over 66,000 ha (163,000 acres) of Mohave ground squirrel habitat, equal to 3.3% of the species range. iii. Habitat Degradation Off-highway vehicle (OHV) use, grazing by sheep and cattle, drought, habitat fragmentation, domestic animal predation, and rodenticides all degrade the quality of Mohave ground squirrel habitat. Off-highway vehicle use Bury et al. (1977) studied the effects of off-highway vehicles on terrestrial vertebrates in the Western Mojave Desert at four sites south of Barstow. Direct effects include running over individual animals, collapsing their burrows, and breaking shrubs which provide cover. LaRue (WEMO Route Designation, p. 30) crushed a juvenile male Mohave ground squirrel on a dirt road as it attempted to cross in front of his truck near Water Valley. Direct mortality by OHVs is likely to affect male juvenile Mohave ground squirrel disproportionately because they are more likely to travel longer distances during natal dispersal than adults or female juveniles. Indirect effects, deemed more significant, include disturbance of soils and destruction of shrubs, both of which combine to reduce the number of spring annuals. Bury et al. (1977) concluded that off-highway vehicles detrimentally affect wildlife and Creosote Bush Scrub habitat in the Mojave Desert. Brooks (1999a, 2000
Petition to list the Mohave ground squirrel Page 23 of 49 from WEMO Route designation) found roads serve as dispersal corridors for non-native species and that non-native species are more common along roadsides. The displacement of native species on which Mohave ground squirrel persistence depends greatly reduces the habitat quality surrounding both paved and dirt roads and routes. The WEMO Route Designation report of the 1998 vegetation studies indicates that 47% of the 310 transects studied were bisected by some type of OHV track. Within the Mohave ground squirrel range, there exist four authorized off-highway areas operated by the BLM (Jawbone Canyon, Dove Springs, El Mirage, and Spangler Hills), constituting over 417 square kilometers (161 mi 2 ). The WEMO Route Designation reports the number of square miles of trials and tracks in the Spangler, El Mirage, Jawbone/Dove, and California City/Rands OHV access areas. Cumulatively these areas contain 710 km 2 (274 mi 2 ) affected by above average trails, and 840 km 2 (324 mi 2 ) impacted by tracks. If El Mirage is subtracted, because it falls in the portion of the range that is apparently unoccupied, this leaves an impact area of 661 km 2 (255 mi 2 ) for above average trails and 790 km 2 (305 mi 2 ) for tracks. In addition to the direct impacts, the indirect impacts, including those of habitat fragmentation, render this habitat severely degraded for Mohave ground squirrels. It appears that Mohave ground squirrels may occur and disperse through some open areas, but not others. The reasons for this are unknown. However, it is important to note that, while there is some evidence that Mohave ground squirrels are known to occur and/or move through Dove Springs Open Area, the same is not true for Spangler Hills (P. Leitner, unpublished data). It would appear that this is related to the location of Mohave ground squirrel core populations and the limits of dispersal, especially as these factors relate to rainfall patterns and habitat availability. The WEMO Route Designation states that data support a “spill-over” effect from open areas, with higher incidences of vehicle impacts in adjacent areas than non-adjacent areas. The document specifically admits that “areas adjacent to Jawbone and Spangler Hills [,] remain susceptible to open area-related impacts” (p. 32). The document goes on to say that vehicle impacts may also be prevalent in areas not adjacent to open areas. Within the proposed Mohave ground squirrel Conservation Area, this includes “lands within the Rand Mountains, west of Silver Lakes, within Kramer Hills, north of Hinkley, and southwest of Fort Irwin.” East and northeast of Fremont Peak, Fremont Valley, Iron Mountains north of Silver Lakes, Superior Valley (one 10.4 km 2 region), and southeast of Harper Lake are also mentioned as areas with possible vehicular impacts. In our GIS analysis, we buffered the authorized ORV use network by three meters, based on the minimum tortoise depression zone along highways edges for the desert tortoise (Boarman 2002; Nicholson 1978, Berry and Turner 1987, LaRue 1993, Boarman and Sazaki 1996, von Seckendorff Hoff and Marlow 1997, cf. Baepler et al. 1994). This is the best available estimate for road impacts to wildlife within the range of the Mohave ground squirrel. It should be noted, however, that Mohave ground squirrels have been observed to cross unpaved roads readily and high speed paved highways as well (P. Leitner, personal communication). Our results indicate that nearly 3,000 ha (7,300 acres) of additional Mohave ground squirrel habitat are impacted by legal ORV use. This figure, amounting to
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Petition to list the Mohave Ground Squirrel - Defenders of Wildlife

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