The Mohave Ground Squirrel

Mohave Ground Squirrel Spermophilus mohavensis

The wild desert tortoise shares its habitat with many other animal and plant species. Like the tortoise, many of these species have been negatively impacted by man’s disturbance and fragmentation of the fragile desert ecosystem. A by-product of the Desert Tortoise Preserve Committee’s desert tortoise habitat acquisition work is that safe harbors are being afforded to many of these other often poorly known species. One of the more significant is the delightful Mohave ground squirrel. There are two articles featured in our newsletter Tortoise Tracks:

 

THE MYSTERIOUS MOHAVE GROUND SQUIRREL

By Phil Leitner

One of the more remarkable denizens of the California desert is a small brown ground squirrel. About 9 inches from nose to tip of tail, the Mohave ground squirrel (Spermophilus mohavensis) is found only in the western Mojave Desert. Their sophisticated desert survival skills allow them to avoid the extremes of the hostile climate. Hard to find and even more difficult to observe and study, these rare and elusive little rodents have baffled biologists over the years. Now, new efforts are underway to discover their habitat requirements and determine their conservation status.

We do know that Mohave ground squirrels are active only in the spring and summer, when they feed eagerly on the leaves and seeds of native shrubs and annual plants. As the desert dries out in June and July, they fatten in preparation for a long period of dormancy. By midsummer they curl up in their underground nests and allow body temperature, heart rate, and metabolism to fall drastically. In this physiological state, they can survive on stored body fat until the winter rains bring a new flush of green vegetation.

Mohave ground squirrels begin to emerge from their burrows in February, when the males may travel up to a mile per day in search of mates. The success of these amorous excursions becomes evident by the end of March, when litters of 6-9 young are born. The babies grow quickly and are weaned by early May. In just a few weeks, they are ready to set off in search of their own patch of desert. Young Mohave ground squirrels disperse in late May and early June. Often they move in next door to their mother’s home range, but some, especially the young males, can move up to four miles before settling down.

In the Mojave Desert, it is not unusual for the winter rains to fail, creating hard times for all desert wildlife. Mohave ground squirrels have their own approach to coping with drought. If the total winter rainfall is under three inches, they simply don’t reproduce. All available forage is converted to body fat and they can enter dormancy as early as April. Better to try again next year than to give birth to young who probably won’t survive and jeopardize your own chances of putting on enough fat to make it through dormancy. As a result, Mohave ground squirrel numbers decline precipitously after a low rainfall year and two successive years of drought can lead to the extinction of local populations. After a couple of good years, dispersing young may recolonize these areas.

The Mohave ground squirrel has long been listed as Threatened under the California Endangered Species Act. In spite of its protected status, little is known of its habitat needs or even where it still occurs. In many areas within its historic range, there are no recent records. This information is essential to the development of a conservation strategy for the species. The Desert Tortoise Preserve Committee is currently taking the lead in a new research effort, with funding from the California Energy Commission. Field studies began this spring in the Desert Tortoise Research Natural Area, the Pilot Knob Grazing Allotment, and the Kramer Hills to locate populations for long-term ecological study. Much more work will be needed to clear up the mysteries surrounding the Mohave ground squirrel and to assure it a secure future in the Mojave Desert ecosystem.

Source: Tortoise Tracks 19:2 Summer 1999

Mohave ground squirrel observations, Spring 2011

Article and photos by Freya Reder

 

The Desert Tortoise Research Natural Area (DTRNA) provides protected habitat not only for the desert tortoise, but for all wildlife and plant species that exist within its boundaries. The Mohave ground squirrel (Xerospermophilus mohavensis) is one such species. The Mohave ground squirrel is a small herbivorous rodent found only in the western Mojave Desert in desert-scrub habitats. Because of habitat loss and fragmentation, the Mohave ground squirrel has long received state protection and has been listed as Threatened under the California Endangered Species Act since 1985. The species is currently under review for federal listing. Like the desert tortoise, the Mohave ground squirrel has a limited period of activity. For adults, this active season usually extends from February through July, with the rest of the year spent in dormancy. For juveniles, this period of activity is extended through August, as additional time is needed for their growth and dispersal from their natal burrows. Past studies have shown that the amount and timing of winter rains affect Mohave ground squirrel reproduction and that in years with significantly low winter rainfall, Mohave ground squirrels will not reproduce in the spring. One of the most exciting discoveries for us at the DTRNA this spring was that it proved to be a reproductive year for the Mohave ground squirrel.

I began the season as the Interpretive Naturalist with equal interests in the desert tortoise and the Mojave ground squirrel, due to their threatened status. Documentation of all species encountered is part of the job of the Naturalist, and so it was with the Mohave ground squirrel. Having had a few fleeting glimpses, I was interested to see and point out a Mohave ground squirrel to a visiting friend. We stopped to observe what turned out to be a lactating female, evident by her dark and swollen nipples. She stood watching us while feeding on unidentifiable seeds in the nearby wash. Making a mental note, I began to look for this female daily when out walking on the trails, and more often than not was rewarded with a sighting of her. This lactating female had several dark patches of skin on her back where hair was missing, making her easily identifiable and leading me to refer to her as “Patches” from then on.

A week later, just after opening the gate to the DTRNA, a couple from Ohio arrived. True wildlife enthusiasts, this couple described themselves as primarily birders who also had a “life list” of mammals throughout the world they intended to see. Today, they had come in search of the Mohave ground squirrel. I pointed our visitors in the direction of Patches’ burrow, telling them I would catch up with them shortly and we would look for ground squirrels and tortoises together. When I joined them a short time later on the Animal Loop, I asked if they had luck and they said yes, they had in fact seen 3 juvenile Mohave ground squirrels! Excited by this news I asked them to show me where they had seen the juveniles. Thirty meters downstream from Patches’ burrow were three juveniles of undetermined sex basking in the morning sun. Later the same day, I was rewarded with a sighting of Patches with the juveniles nearby.

Within a short period of time, I began to observe several adult Mohave ground squirrels. Soon, I spotted another lactating female near the latrine in the Interpretive Center (IC). This female also had dark, swollen nipples but lacked the dark patches of skin on her back. A few weeks later, another separate litter of four juveniles emerged, this time on the entrance road into the DTRNA. Simultaneou sly, a litter of antelope squirrels emerged in the same area, on the same day, often appearing to use the same burrows. I took advantage of their proximity to the road to capture some brilliant footage on my camera of the juveniles, two while they were being bitten by red ants. One of these juveniles I captured on film encountering this tiny but formidable foe for the first time face to face. Additionally I observed them feeding on the seeds of checker fiddleneck (Amsinckia tessellata) seeds and red-stemmed filaree (Erodium cicutarium), and the forbs of rose and white wild buckwheat (Eriogonum gracillimum); one individual sampled the dried flower of a goldfield (Lasthenia californica).

A third lactating female was observed while on “morning rounds” with visitors. I wanted to inspect a tortoise burrow in a nearby mineral assessment mound. When first approaching the mound I had seen and pointed out a Mohave ground squirrel to the visitors. Through binoculars I observed while it stood in alarm and then disappeared into the mouth of tortoise burrow. Upon closer inspection of the tortoise burrow and its fresh tortoise tracks, the ground squirrel’s head appeared a few meters away in the mound. She glanced at me, chirped twice in alarm, and disappeared into the same hole. Only in the photographs did I later see that the squirrel was a lactating female.

In preparation for the long period of dormancy during fall and winter, the Mohave ground squirrel must acquire bulk mass in the form of fat reserves in order to survive. It is common and necessary for them to triple in body weight and mass during this time. Adult females take longer to acquire bulk mass due to their reproduction; therefore, the male’s state of enormity becomes evident well before that of the females or juveniles. One male in particular appeared to put on bulk mass well before the others and I began to seek him out daily.

This adult male’s burrow was situated in the same mineral assessment mound previously mentioned, the female now presumably displaced or had simply moved house. He was what I refer to as “user friendly” in his tolerance and seeming disinterest in my presence on foot, providing I approached cautiously. It was not unusual to spend 15 or 20 minutes, sometimes longer observing and photographing him as he would forage and sometimes cache the seeds of thistle sage (Salvia carduacea) and dried fiddleneck. Of equal interest to him were Fremont pincushion (Chaenactis fremontii) and creosote (Larrea tridentata) flowers. This male began acquiring bulk mass earlier than any of the other adult males I observed and by this time seemed quite stationary; I observed him foraging no further than a meter or so from one of his burrow entrances.

Excited further by these field observations, I reported my findings to Dr. Kristin Berry who then shared this information with the rest of the Desert Tortoise Preserve Committee (DTPC). Given that it was clearly a good year for Mohave ground squirrel reproduction in the DTRNA, the DTPC determined that it would be advantageous to survey the surrounding expansion areas for the presence of Mohave ground squirrels. I undertook their request with relish and over the course of the next three weeks undertook the task of surveying these expansion areas by vehicle and on foot. Recording the geographic locations, date, times, approximate temperature, behavior, forage species, and the presence or absence of white-tailed antelope squirrels, and using photographic documentation whenever possible, I covered areas of frequent sightings regularly by vehicle and expanded into new, unexplored areas daily.

During the hours of field observation, the Mohave ground squirrels foraged heavily on dry fiddleneck seeds and filaree seeds, both dry and green. Additionally they were seen foraging on flowers of creosote bush, Anderson’s thorn bush (Lycium andersonii), desert calico (Loeseliastrum sp.), and what appeared to be miniature woolly star (Eriastrum diffusum), and the seeds of little gold poppy (Eschscholzia minutiflora), thistle sage, and Fremont pincushion. At the end of the three weeks and approximately 75 hours of surveying, we had recorded 69 observations of Mohave ground squirrels in and around the DTRNA. Based on geographic locations and timing of observations and the physical features of the animals, we estimate at least 32 individuals were sighted, including 19 adults (7 females, 3 males, and 9 of undetermined sex) and 14 juveniles (3 females, 1 male, and 9 of undetermined sex). The DTRNA is indeed an important area not only for the preservation of the desert tortoise, but also that of the Mohave ground squirrel. The DTPC hopes to continue studying this species and its habitat needs in and around the Natural Area.

I would like to give special thanks to Denise LaBerteaux from her assistance in sex determination and identification. Dr. Berry and the other DTPC board members deserve special thanks as well for their prompt response and for launching this field survey. Lastly, I would like to thank Mary Kotschwar for her unyielding support, encouragement and assistance throughout this study and the season.

 

References

Bartholomew, G.A. and J.W. Hudson. 1960. Aestivation in the Mohave ground squirrel Citellus mohavensis. Bulletin of the Museum of Comparative Zoology 124:193–208.

Best, T. L. 1995. Spermophilus mohavensis. American Society of Mammalogists, Mammalian Species Number 509:1–7.

California Department of Fish and Game. 2011. State & Federally Listed Endangered & Threatened Animals of California. Accessed September 9, 2011.

Harris, J.H. and P. Leitner. 2004. Home range and use of space in Mohave ground squirrels (Spermophilus mohavensis). Journal of Mammalogy 85: 517–523.

Harris, J. H., and P. Leitner. 2005 Long-distance movements of juvenile Mohave ground squirrels, Spermophilus mohavensis. Southwestern Naturalist 50: 188-196

 

Source: Tortoise Tracks 31:3 Fall 2011

 

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