West Mojave Plan FEIR/S - Desert Managers Group

MGS reproduction to occur. Leitner and Leitner (1996) found a clear correlation between falland winter precipitation and the number of juveniles appearing on the same plots in subsequentyears. Following low rainfall, annual herbaceous plants are not readily available, the MGS isunable to attain a minimum amount of body fat (identified by the Leitners as 180 g total bodyweight), and in such years the species forgoes breeding (Recht, pers. comm. in Laabs 1998;Leitner et al. 1995).The Leitners have consistently observed that in years of poor rainfall (i.e., less than 75mm since the MGS entered hibernation), the MGS foregoes reproduction in favor of attainingsufficient body fat to make it through the winter. This is likely a physiological adaptation toensure adult survival, and to avoid birthing young when resources are not sufficient for juvenilesto acquire necessary body fat to hibernate. Gustafson (1993) indicated that the “evolutionarystrategy of suspending reproductive activity and concentrating on gaining weight ensures thesurvival of the species (Leitner and Leitner 1990), as long as droughts are of short duration andsufficiently large areas of habitat exist.”MGS adults are solitary except during breeding, which occurs soon after emergence fromhibernation. Gestation lasts 28-30 days, at which time between 4 and 10 young are born perlitter. Juveniles emerge from natal burrows within four to six weeks, and begin to establish theirown home ranges by about mid-May. Mortality is high during the first year (Leitner and Leitner1996). Females breed in the spring if environmental conditions are appropriate, while males donot normally mate until two years of age (Leitner and Leitner 1996). Laabs (1998) indicated thatsex ratio is consistently female biased, with ratios as high as seven females for each male.3.3.3.2.6 DispersalJuveniles begin making exploratory movements away from the natal burrow by aboutmid-May to early June, and some individuals eventually make long-distance movements (Leitneret al. 1997). Recent radio-telemetry data suggest that females are more likely than males toremain near their natal burrows (Leitner et al. 1997). In 1997, the majority of radio-collaredjuvenile males moved greater than 0.6 miles (1 km.), up to a maximum of 3.9 miles (6.2 km.).Juveniles can apparently traverse steep terrain during dispersal (Leitner, pers. comm. in Laabs1998), and some are known to disperse 3-4 miles from their birthplace (Leitner 1998).The current, 2002 status of the MGS, in terms of numbers of individuals and amount ofoccupied habitat, is difficult to assess due to the limitations of available data. The data that areavailable, the potential associations between MGS historic occurrences and existing habitatcharacteristics, results of recent trapping studies, etc. are compared and discussed in thefollowing sections.3.3.3.3 Winterfat, Spiny Hopsage, and MGS OccurrenceIn the northern portion of its range, the MGS feeds on the leaves (in particular), seeds,and fruits of perennial plants (mostly shrubs) when annual plants are not available. Shrub speciesthat were consumed most often at the Leitner’s Coso study sites were spiny hopsage (Grayiaspinosa), winterfat (Krascheninnikovia lanata) and saltbush (Atriplex sp.) (Leitner and LeitnerChapter 3 3-148