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This section provides a historical account of the trapping of antelope ground squirrels in southwest Idaho in 2017.

Expedition Report: "How to Capture an Antelope Ground Squirrel"


     In late 2016 and early 2017, when Dr. Refinetti was on the faculty of Boise State University (in Idaho), he had the good fortune of befriending Dr. Jim Kenagy, an ecologist from the University of Washington. Dr. Kenagy had extensive previous experience in the study of antelope ground squirrels and other rodent species in deserts of western North America. The two of them set out to search for antelope ground squirrels in southwest Idaho. The procedures were conducted under Idaho Department of Fish and Game Permit No. 160812 and Boise State University Animal Care and Use Committee Protocol No. 006-AC16-013.




     Unlike most rodents, which are active at night, squirrels are generally day-active and are potential candidates as diurnal animal models for biomedical research. The antelope ground squirrel (Ammospermophilus leucurus) is unique among ground squirrels in that it is not a hibernator and remains active on the surface in the field throughout the entire year. With a body mass of about 120 g, it is also intermediate in size between the domestic mouse and the laboratory rat.

     The geographic range of the antelope ground squirrel extends from southwestern Idaho and southeastern Oregon through most of Utah and Nevada, western Colorado, northwestern New Mexico, northern Arizona, southern California, and the full length of the Baja California peninsula. Refinetti and Kenagy surveyed a small part of the northernmost extension of this range in Owyhee County, Idaho, south of the Snake River, in July 2016 to search for likely habitat, with positive confirmation of a considerable amount of undisturbed desert habitat and sightings of the squirrels at and near localities previously recorded in museum databases (vertnet.org).

     In mid December 2016 and early April 2017, they set out Sherman live traps (LFAGTD, H. B. Sherman Traps Inc., Tallahassee, FL) to capture animals for laboratory studies. Thanks to Kenagy's previous experience, they knew that antelope ground squirrels were the only diurnal rodents inhabiting this area, which meant that they did not have to worry about unintentionally trapping other species.

 

     The area of about 200 km2 that they explored (seen in the satellite photograph below) was in the Owyhee Desert, with trapping limited to the vicinity south of Oreana, Idaho (latitude 43°00' N, longitude 116°20' W, altitude 850 m).
 


 

     Much of the Owyhee Desert is public land managed by the U.S. Bureau of Land Management. The soils and vegetation are typical of arid lowland scrub within the Great Basin Desert, with sparsely distributed shrubs, predominantly Great Basin sagebrush (Artemisia tridentata) and greasewood (Sarcobatus vermiculatus). The ground squirrels were strongly associated with the more alkaline soils dominated by greasewood.
 


 

     On the initial survey in July, they sighted antelope ground squirrels in multiple locations within the expected area, generally moving around on the ground but occasionally perched in the top of bushes, as documented in the photograph below (red arrow). They observed a large number of burrow entrances in the habitat. The area is also home to a variety of nocturnal rodent species, including the Great Basin pocket mouse (Perognathus parvus), Ord's kangaroo rat (Dipodomys ordii), Great Basin kangaroo rat (Dipodomys microps), western harvest mouse (Reithrodontomys megalotis), deer mouse (Peromyscus maniculatus), and bushy-tailed woodrat (Neotoma cinerea).
 


 

     As expected in a desert, there is very little precipitation in the summer (8 mm per month). There is a little more precipitation in the winter (22 mm per month), mostly as ice and snow. Low temperatures average −4 °C in the winter and 18 °C in the summer. High temperatures average 4 °C in the winter and 34 °C in the summer.
 


 

     They placed five sets of 50 traps, each set a few kilometers apart. Individual traps were spaced about 6-8 m apart and baited with seeds after sunrise, monitored once or twice during the day, and closed prior to sunset. The locations of two traps are indicated by red arrows in the photograph below.
 


 

     Refinetti and Kenagy deployed 250 traps for two days in December and three days in April. They captured one female and two males in December and four females and five males in April. Upon visual inspection they observed external parasites (fleas and ticks) in December but not in April. Antelope ground squirrels were the only vertebrate animals captured in the traps. By closing the traps at night they avoided the unintentional capture of nocturnal rodents.
 


 

      The animals captured in the field did well in captivity. One to two weeks after capture, all of them had gained weight, increasing on average from 108 g on the day of capture to 132 g two weeks later and stabilizing at a mean body weight of 120 g. The squirrels ate Purina rodent pellets regularly through metal cage tops and drank water from bottles with metal sipping tubes. Carrot slices and grapes offered as supplement were always consumed by the next day.

     At the time of cage changes, the cage was placed in a deep outer container (70 cm deep) to facilitate the transfer because antelope ground squirrels can jump much higher than rats or mice and would otherwise escape from the cage. The animals were scooped from the dirty cage with a 600-ml plastic cup with a screw-on lid and transferred to the clean cage after being weighed.


 

     Four females captured in April were pregnant at the time of capture and gave birth between April 14 and April 19. This seasonal timing is within the range described for a nearby locality in Oregon, corresponding to matings that would have occurred in mid March. The litter sizes of the four litters were 10, 10, 10, and 12, which fall within the range of 6 to 14 previously reported by Dr. Kenagy for a sample of 31 litters in Oregon.

     The pups were born with pink skin color and with the eyes closed (left panel below). By 9 days of age the skin began to show some darker pigmentation. By 13 days the eyelids became conspicuous but remained closed. By 19 days a light, soft body pelage was noticeable. By 24 days body stripes were showing along the flanks (middle panel). After 30 days the eyes were opened, and pups began to venture out of the nest. After 35 days the pups were exploring the cage more extensively and starting to nibble on solid food (right panel). After 40 days all pups moved extensively around the cage and consumed solid food. All pups were successfully separated from their mothers at postnatal day 60, when body mass ranged from 66 to 95 g.
 


For information about other animal species used in the lab, check the Animal Species section of this web site. You may also want to visit the Circadian Rhythms section.


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