West Mojave Plan FEIR/S - Desert Managers Group

3.3.3.2.2 Seasonal ActivityThe MGS exhibits a strongly seasonal cycle of activity and torpor (like hibernation),emerging from dormancy as early as January, but more typically in mid-February or March(Leitner and Leitner 1996). Dates of emergence appear to vary geographically. Males typicallyemerge one or two weeks prior to females (Recht, pers. comm.). Once a sufficient amount of fathas been accumulated, individuals enter a period of aestivation and hibernation (Bartholomewand Hudson 1961). Aestivation generally begins sometime between July and September, butmay begin as early as April or May during drought conditions (Leitner, et al., 1995).MGS population dynamics are dependent on the amount of fall and winter precipitation(Leitner and Leitner 1996). The failure to reproduce may result in dramatic population declinesand, if poor conditions persist for several seasons, may become extirpated from a given area.This may be especially true in less optimal habitats. Therefore, entirely suitable habitats can beunoccupied during some years and become reoccupied in others.3.3.3.2.3 Substrate Affinities and Burrow UseThe MGS generally occurs in flat to moderate terrain and is not found in steep terrain.Substrates in occupied habitats have ranged from being very sandy to, less frequently, very rocky(Best 1995, Wessman 1977). For example, of 102 transects surveyed in 1998 (see below) wherethe MGS had been previously detected, 91 (89%) were identified as predominantly sandy and 11(11%) were identified as being rocky. The MGS is considered to be absent, or nearly so, on drylakebeds, lava flows, and steep, rocky slopes (Clark 1993), although juveniles may dispersethrough such areas (Leitner, pers. comm. in Laabs 1998), probably excluding larger playas.Individuals may maintain several residence burrows that are used at night, as well asaccessory burrows that are used for temperature control and predator avoidance (Laabs 1998).Aestivation burrows are dug specifically for use during the summer and winter period ofdormancy (Best 1995), and often occur beneath large shrubs (Leitner et al. 1995).3.3.3.2.4 Home RangesHome ranges of adults vary between seasons and throughout a season, presumably inresponse to quantity and quality of food resources. The Leitners’ studies in the Coso Range haveindicated that there is considerable overlap in the home ranges of individual males and females,though there is no clear evidence that home ranges are defended (Laabs 1998). Juveniles aregregarious, initially staying close to their natal burrows. However, juveniles have demonstratedconsiderable dispersal abilities, having traveled up to four miles from their birthplace in a matterof a few months.3.3.3.2.5 ReproductionThe reproductive success of the MGS is dependent on the amount of fall and winter rains(Laabs 1998) and the new growth of annual forage materials that result. Leitner and Leitner(1992) hypothesized that a standing crop of about 1 gram per square foot may be necessary forChapter 3 3-147