West Mojave Plan FEIR/S - Desert Managers Group

Male tortoises may be more active during the fall, when their testosterone and viablesperm levels are higher than during the spring. Dr. Kristin Berry (pers. comm.) has shown thatmale sperm counts and viability are both relatively higher in the fall than in the spring of a givenyear. Data collected between 1998 and 2001, which were mostly restricted to the summer andfall periods (i.e., July through October), show that twice as many males were encountered ineach of the three survey years as compared to females. Over the three-year period where gendercould be determined, a total of 73 males and 35 females (2:1 ratio) were found, representing 26%and 13%, respectively, of the animals found (WMP data).This was not observed during distance sampling, where surveys were performed in thespring. In 2001 and 2002, 87 males (40% of all animals where gender could be determined) and69 (32%) females (1:1.26 ratio) were observed. Gender could not be determined for 60 tortoises,including 32 sexually immature animals. This probably indicates that males were somewhatmore detectable than females in the summer and fall months when males are actively courtingand mating with female tortoises, which is supported by numerous field observations.Tortoises may be active throughout the year. Dr. David Morafka has shown that juveniletortoises regularly emerge from burrows throughout the winter when conditions are favorable.Tortoises have recently been observed aboveground in early November west of California City(LaRue, pers. obs. 2002) and in late November at the DTNA (Michael Connor, pers. comm.2001). Several were observed in early January 2003 in the Fremont Valley (Bob Parker, per.comm. 2003). Those animals may have opportunistically taken advantage of rain that fell inNovember and the early production of annual plants in January. Tortoises regularly emergethroughout the year at Edwards in response to several days of unseasonably warm temperature(Mark Hagan, pers. comm. 2003). These anecdotal accounts may represent a small fraction ofadult animals in the population, and most animals may remain in their burrows through thewinter.Freilich et al. (2002) and Duda et al. (1999) have shown that tortoises are relatively moreactive in wetter years when compared to drier years. This observation is supported by distancesampling data collected in the Fremont-Kramer and Superior-Cronese DWMAs during thesprings of 2001 (relatively wet year) and 2002 (“driest year in recorded history”). In the 2001,wet year, a total of 104 tortoises was encountered, including 29 (28%) in burrows and 75 (72%)in the open; in 2002, the dry year, of 112 tortoises observed, 57 (51%) were observed in burrowsand 55 (49%) in the open. This indicates that about a quarter of the observed tortoises were inburrows in the wetter year, compared to about half of those observed in the dry yearFood resources for desert tortoises are dependent on the availability and nutritionalquality of annual and perennial vegetation, which is greatly influenced by climatic factors, suchas the timing and amount of rainfall, temperatures, and wind (Beatley 1969, 1974, Congdon1989, Karasov 1989, Polis 1991 in Avery 1998). In the Mojave Desert, these climatic factors aretypically highly variable; this variability can limit the desert tortoise’s food resources.Desert tortoises will eat many species of plants. However, at any time, most of their dietoften consists of a few species (Nagy and Medica 1986, Jennings 1993 in Avery 1998).Additionally, their preferences can change during the course of a season (Avery 1998) and overChapter 3 3-74