Ammospermophilus nelsoniNelson's antelope squirrel

Ge­o­graphic Range

The dis­tri­b­u­tion of Am­mo­sper­mophilus nel­soni is re­stricted to the floor of the south­ern San Joaquin Val­ley, Cal­i­for­nia, the Cuyama and Panoche val­leys in San Luis Obispo County, and the Car­rizo and Elkhorn Plains of the United States. The species is Nearc­tic and en­demic to the above range. (Best, et al., 1990; Tay­lor, 1918)

Habi­tat

Nel­son's an­te­lope squir­rels are found in hot deserts that com­prise the Lower Sono­ran life zone. Lower Sono­ran deserts of North Amer­ica in­clude areas in Texas, New Mex­ico, Ari­zona, Nevada, and Cal­i­for­nia. Nel­son's an­te­lope squir­rels are found in arid grass­lands and shrub lands. They have been recorded in areas where shrub cover ranges from light to medium den­sity and ranges from xe­ro­phytic, al­kali desert scrub and an­nual grass­land re­ceiv­ing less than 15 cm an­nual pre­cip­i­ta­tion, to halo­phytic, al­kali desert scrub and an­nual grass­land re­ceiv­ing 18 to 23 cm of an­nual pre­cip­i­ta­tion. Nel­son's an­te­lope squir­rels pre­fer al­ka­line, loamy soils from 50 to 1100 me­ters el­e­va­tion. Nel­son’s an­te­lope squir­rels de­pend on kan­ga­roo rat bur­rows, so areas they in­habit may be lim­ited to areas with kan­ga­roo rat pop­u­a­tions. (Grinell and Dixon, 1918; Haw­becker, 1953; Mer­riam, 1898; Whitaker, et al., 2008)

  • Range elevation
    50 to 1100 m
    164.04 to 3608.92 ft

Phys­i­cal De­scrip­tion

Nel­son's an­te­lope squir­rels have fusiform bod­ies, small, rounded ears, short legs, and short tails. The dor­sal head and neck and the outer sur­faces of the legs are a dull yel­low­ish-brown or buffy-tan. The tail has thick fringes of hair and the un­der­side is light grey to white. A dis­tinc­tive light-col­ored stripe runs along the side of the body from be­hind the shoul­der to the rump. Males are slightly larger than fe­males, with total length of males rang­ing from 234 to 267 mm (av­er­age 249 mm). Fe­male length ranges from 230 to 256 mm (av­er­age 238 mm). Nel­son's an­te­lope squir­rels have dis­tinct sum­mer and win­ter pelages, with the au­tumn or win­ter pelage being darker than the sum­mer pelage. (Best, et al., 1990; Brown and Williams, 2006; Mer­riam, 1983)

Nel­son's an­te­lope squir­rels can be dis­tin­guished from white-tailed an­te­lope squir­rels by its larger size and grey col­or­ing of the pelage. Nel­son's an­te­lope squir­rels have wider zy­go­matic arches, more in­flated au­di­tory bul­lae, and larger nasal bones. They also have larger upper in­cisors and first upper mo­lars. (Best, et al., 1990; Brown and Williams, 2006; Mer­riam, 1983)

  • Sexual Dimorphism
  • male larger
  • Range mass
    142 to 179 g
    5.00 to 6.31 oz
  • Average mass
    155 g
    5.46 oz
  • Range length
    230 to 267 mm
    9.06 to 10.51 in
  • Average length
    249 mm
    9.80 in
  • Average basal metabolic rate
    0.8 cm3.O2/g/hr

Re­pro­duc­tion

Nel­son's an­te­lope squir­rels have a promis­cu­ous mat­ing sys­tem in which fe­males and males mate with mul­ti­ple part­ners. Not much is known about spe­cific mat­ing be­hav­iors, but an in­ter­est­ing ob­ser­va­tion was made re­gard­ing mate search­ing be­hav­ior. Mates are typ­i­cally found within the home range, but there have been in­stances of fe­males trav­el­ling up to 1 km from their home range in search of a mate. Mate guard­ing and mate de­fense have not been ob­served in Nel­son's an­te­lope squir­rels. ("Five Year Sta­tus Re­port- Am­mo­sper­mophilus nel­soni", 1987; Haw­becker, 1947)

The breed­ing sea­son of Nel­son's an­te­lope squir­rels ex­tends from late win­ter to early spring and this species breeds once an­nu­ally. Males achieve re­pro­duc­tive ma­tu­rity ear­lier than fe­males. Brood size varies from 6 to 11 young; with the av­er­age being 9. The av­er­age ges­ta­tion pe­riod is 26 days. Fe­males give birth to off­spring in bur­rows. The young come above ground ap­prox­i­mately on the 30th day after birth. Wean­ing can start or be com­pleted be­fore the young emerge from their bur­row, but this is highly vari­able. Fe­males wean the young by re­fus­ing to nurse and vis­it­ing the bur­row less fre­quently. (Best, et al., 1990; Best, 1999; Mac­don­ald, 2009)

  • Breeding interval
    Nelson's antelope squirrels breed once annually.
  • Breeding season
    Nelson's antelope squirrels breed from late winter to early spring.
  • Range number of offspring
    6 to 11
  • Average number of offspring
    9
  • Range gestation period
    25 to 30 days
  • Average gestation period
    26 days
  • Range weaning age
    30 (high) days
  • Average weaning age
    15 days
  • Range time to independence
    3 to 4 weeks
  • Average age at sexual or reproductive maturity (female)
    377 days
  • Average age at sexual or reproductive maturity (male)
    377 days

Nel­son's an­te­lope squir­rel young are born in an al­tri­cial state. Males do not play a large role in car­ing for the young, as fe­males per­form all ac­tiv­i­ties of nurs­ing and wean­ing. When wean­ing, the fe­male dis­tances her­self from the young and does not re­spond even when young make at­tempts to nurse. The fe­male main­tains con­tact with the young by vis­it­ing them some­times or by just using calls to com­mu­ni­cate. In cap­tiv­ity, at times when for­ag­ing op­por­tu­ni­ties were lim­ited, in­stances of can­ni­bal­ism have been ob­served. (Best, et al., 1990)

  • Parental Investment
  • altricial
  • female parental care
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female

Lifes­pan/Longevity

Nel­son's an­te­lope squir­rels usu­ally live for less than a year in the wild be­cause of high in­fant and young mor­tal­ity rates. They have been doc­u­mented to live for about 4 years in cap­tiv­ity, with the longest cap­tive lifes­pan being 5.7 years. Adult mor­tal­ity rate is 80% and the av­er­age lifes­pan is 8 months. (Best, et al., 1990; Haw­becker, 1975)

  • Range lifespan
    Status: captivity
    5.7 (high) years
  • Average lifespan
    Status: wild
    8 months
  • Average lifespan
    Status: captivity
    4 years

Be­hav­ior

Nel­son's an­te­lope squir­rels live in small fam­ily groups con­sist­ing of 6 to 8 in­di­vid­u­als. Al­though the exact na­ture of their so­cial sys­tem of dom­i­nance is un­known, the closely-re­lated species Am­mo­sper­mophilus leu­cu­rus has ob­served dom­i­nance hi­er­ar­chies. Am­mo­sper­mophilus leu­cu­rus in­di­vid­u­als form lin­ear hi­er­ar­chies that are main­tained by vi­sual and tac­ti­cal cues. Dom­i­nance con­tests re­sult in ag­o­nis­tic be­hav­iors, start­ing with lung­ing and mov­ing to box­ing and fight­ing. ("Five Year Sta­tus Re­port- Am­mo­sper­mophilus nel­soni", 1987; Belk and Smith, 1991; Best, et al., 1990; Best, 1999; Grinell and Dixon, 1918; Haw­becker, 1947; Haw­becker, 1953; Haw­becker, 1975)

Nel­son's an­te­lope squir­rels have a keen sense of ter­ri­tory. When re­moved from their ter­ri­tory and re­leased at a dis­tance, adults are help­less and un­able to nav­i­gate. Fam­ily groups live in ex­ten­sive bur­row sys­tems, which are some­times adapted from kan­ga­roo rat bur­rows. ("Five Year Sta­tus Re­port- Am­mo­sper­mophilus nel­soni", 1987; Belk and Smith, 1991; Best, et al., 1990; Best, 1999; Grinell and Dixon, 1918; Haw­becker, 1947; Haw­becker, 1953; Haw­becker, 1975)

Ther­moreg­u­la­tion plays a key role as these squir­rels do not hi­ber­nate or es­ti­vate. Nel­son's an­te­lope squir­rels for­age ac­tively and are di­ur­nal, usu­ally ap­pear­ing above ground when the tem­per­a­ture is be­tween 10°C and 32°C. Their daily pe­riod of ac­tiv­ity varies sea­son­ally so that most ac­tiv­ity oc­curs within this tem­per­a­ture range. Nel­son's an­te­lope squir­rels are ob­served most fre­quently dur­ing dawn or dusk when it has been ex­tremely hot dur­ing day­time. How­ever, they are ac­tive through­out the day at tem­per­a­tures ex­ceed­ing 42°C in the Elkhorn Plain Eco­log­i­cal Re­serve. They re­treat to bur­rows when tem­per­a­tures are too cold or hot. ("Five Year Sta­tus Re­port- Am­mo­sper­mophilus nel­soni", 1987; Belk and Smith, 1991; Best, et al., 1990; Best, 1999; Grinell and Dixon, 1918; Haw­becker, 1947; Haw­becker, 1953; Haw­becker, 1975)

  • Average territory size
    0.044 km^2

Home Range

Males and fe­males have home ranges of about 4.4 hectares, but they are not evenly dis­trib­uted through­out their range and occur in un­even den­si­ties due to niche pref­er­ences. The max­i­mum ob­served dis­per­sal from the home range was 1,260 m by a male and 900 m by a fe­male. (Best, et al., 1990)

Com­mu­ni­ca­tion and Per­cep­tion

The main senses used by the Nel­son's an­te­lope squir­rels are hear­ing and ol­fac­tion, but the species also re­lies on vi­sion and will scan its en­vi­ron­ment be­fore mak­ing the de­ci­sion to fully exit its bur­row. Ol­fac­tion is used to de­tect dan­ger, to find food and to com­mu­ni­cate. Nel­son's an­te­lope squir­rels also twitch their tails rapidly, in fore and aft move­ments when fright­ened or ex­cited. (Best, et al., 1990; Best, 1999; Bolles, 1988; Tay­lor, 1918)

The Nel­son’s an­te­lope squir­rel gives out alarm calls, which are in­dica­tive of al­tru­is­tic be­hav­ior as it com­pro­mises the safety of the in­di­vid­ual. These calls are in the form of trills that are low-pitched and are char­ac­ter­is­tic of an­te­lope squir­rels that live in closed habi­tats. In fact, the call is ac­com­plished by a con­vul­sive mo­tion of its body rather than by vocal stress. The fe­male uses this call to com­mu­ni­cate with her fam­ily when she is wean­ing. (Best, et al., 1990; Best, 1999; Bolles, 1988; Tay­lor, 1918)

Food Habits

Nel­son’s an­te­lope squir­rels are om­niv­o­rous and ac­tive for­agers. They feed pri­mar­ily on in­sects, green veg­e­ta­tion, and seeds, but will some­times also feed on small ver­te­brates. With re­gards to the lat­ter, the San Joaquin an­te­lope squir­rel con­sumes ro­dents, lizards and mem­bers of its own species as car­rion. Their diet pref­er­ences are largely de­pen­dent on the amount of moist veg­e­ta­tion avail­able. With re­spect to green ma­te­r­ial, red-stemmed fi­la­ree (Erodium ci­cu­tar­ium) and the red brome (Bro­mus rubens) are pre­ferred. Other food sources in­clude the ephedra, a species of clover and lo­coweed. When moist food be­comes very scarce turpine weed is eaten. A pref­er­ence for a par­tic­u­lar type of in­sect has not been doc­u­mented. The San Joaquin squir­rel eats seeds only when eas­ily ob­tain­able green ma­te­r­ial and in­sects are not avail­able. (Haw­becker, 1947; Mac­don­ald, 2009)

Nel­son’s an­te­lope squir­rel as­sumes a dis­tinc­tive pos­ture while feed­ing. It squats on its rear limbs with the tail cocked be­hind the back and holds its food in the forepaws. Its en­larged in­cisors and abra­sive cheek teeth help in break­ing down food. (Haw­becker, 1947; Mac­don­ald, 2009)

The Nel­son’s ground squir­rel does not live near a source of water and so water does not con­sti­tute a great part of its diet. It can be in­ferred that its prin­ci­pal source of mois­ture is from the veg­e­ta­tion eaten. Al­though it ac­cepts large amounts of water in lab­o­ra­tory con­di­tions, it can sur­vive for seven months in the shade, with­out water. (Haw­becker, 1947; Mac­don­ald, 2009)

  • Animal Foods
  • reptiles
  • carrion
  • insects
  • Plant Foods
  • leaves
  • seeds, grains, and nuts

Pre­da­tion

Nel­son's an­te­lope squir­rels em­ploy a va­ri­ety of tech­niques to guard against preda­tors. The com­plex bur­row sys­tems serve as pro­tec­tion against preda­tors. When emerg­ing from a bur­row, they ex­er­cise ex­treme cau­tion and do not exit quickly. They rely on ol­fac­tion and use this ca­pa­bil­ity while for­ag­ing and flee­ing dan­ger. They use char­ac­ter­is­tic alarm calls to com­mu­ni­cate dan­ger and may also rely on the warn­ing calls of birds like horned larks and white-crowned spar­rows for de­tec­tion of preda­tors. Nel­son's an­te­lope squir­rels use their sur­round­ings while evad­ing preda­tors. They use shrubs and bur­rows of kan­ga­roo rats as sites of refuge. Their buffy or tan pelage make them dif­fi­cult to see in their arid habi­tats. When for­ag­ing, these squir­rels move close to the ground in a very dis­tinc­tive man­ner, by a se­ries of short, rapid jumps. Amer­i­can bad­gers are the most im­por­tant preda­tors of these squir­rels. They dig into the bur­rows to prey on young and adults. They are also eaten by coy­otes (Canis la­trans) and (kit foxes Vulpes macro­tis). ("Five Year Sta­tus Re­port- Am­mo­sper­mophilus nel­soni", 1987; Best, et al., 1990; Brown and Williams, 2006)

  • Anti-predator Adaptations
  • cryptic

Ecosys­tem Roles

Nel­son's an­te­lope squir­rels are preyed upon by mid-sized preda­tors, and serve as host to var­ius en­dopar­a­sites and ec­topar­a­sites. They are hosts to ces­todes (Hy­menopelis citelli), ne­ma­todess (Spirura in­fundibu­li­formis and Physa­loptera spini­cauda), and also acan­tho­cepha­lans (Monil­i­formes du­bius). The ec­topar­a­sites they are host to in­clude fleas (Siphonaptera) and ticks (Ixodes). Nel­son's an­te­lope squir­rels have a sym­biotric re­la­tion­ship with kan­ga­roo rats Dipodomys de­serti, tak­ing refuge in their bur­rows. They fur­ther im­pact their habi­tat by con­tin­u­ing to bur­row. Be­cause they are seed col­lec­tors, they also dis­perse seeds in their en­vi­ron­ment. (Best, et al., 1990)

  • Ecosystem Impact
  • disperses seeds
  • creates habitat
Mu­tu­al­ist Species
Com­men­sal/Par­a­sitic Species
  • ces­todes (Hy­menopelis citelli)
  • ne­ma­todes (Spirura in­fundibu­li­formis)
  • ne­ma­todes (Physa­loptera spini­cauda)
  • acan­tho­cepha­lans (Monil­i­formes du­bius)
  • fleas (Siphonaptera)
  • ticks (Ixodes)

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

Nel­son’s an­te­lope squir­rels do not gen­er­ally live close to human set­tle­ments. They may con­tribute to con­trol­ling in­sect pop­u­la­tions by eat­ing them and they may help to dis­perse the seeds they gather and store. (Belk and Smith, 1991; Haw­becker, 1947)

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

In lab­o­ra­tory con­di­tions, Nel­son's an­te­lope squir­rels have been pos­i­tive for west­ern equine en­cephalomyelitis, St. Louis en­cephali­tis, Powas­san virus, and Modoc virus. How­ever, there is no doc­u­mented in­stance their role in spread­ing dis­ease to hu­mans or do­mes­tic an­i­mals. (Best, et al., 1990)

Con­ser­va­tion Sta­tus

Nel­son’s, or San Joaquin, an­te­lope squir­rels are clas­si­fied as en­dan­gered on the IUCN Red List. Ac­cord­ing to the Cal­i­for­nia De­part­ment of Fish and Game, the biggest threat to Nel­son’s an­te­lope squir­rels is habi­tat de­struc­tion due to crop cul­ti­va­tion and ur­ban­iza­tion. Ex­ces­sive graz­ing by live­stock af­fects these squir­rels and also causes soil ero­sion. Uses of ro­den­ti­cides and in­sec­ti­cides, which de­stroy prey pop­u­la­tions, neg­a­tively im­pact Nel­son’s an­te­lope squir­rels. The En­dan­gered Species Re­cov­ery Pro­gram (2006) of Cal­i­for­nia has sug­gested a list of con­ser­va­tion mea­sures that stress the im­por­tance of land use prac­tices and man­age­ment strate­gies. A de­tailed con­ser­va­tion pro­gram for San Joaquin an­te­lope squir­rels in­cludes de­ter­min­ing habi­tat man­age­ment, pro­tect­ing ad­di­tional habi­tat in sur­round­ing areas of the squir­rel’s range, habi­tat en­hance­ment in areas like Kern County, and rein­tro­duc­tion to pro­tected areas, such as Pix­ley Na­tional Wildlife Refuge. ("Five Year Sta­tus Re­port- Am­mo­sper­mophilus nel­soni", 1987; Best, et al., 1990; Brown and Williams, 2006; Grinell and Dixon, 1918; Whitaker, et al., 2008)

Other Com­ments

The genus Am­mo­sper­mophilus has a rich fos­sil record. Its di­ver­gence can be dated to the Miocene as post-Pleis­tocene fos­sils re­sem­bling Nel­son’s an­te­lope squir­rels have been found near Kern County, Cal­i­for­nia. They are thought to have in­vaded the area over the passes of south­ern Sierra Nevada and Tehachapi moun­tains. Due to the change in the mois­ture lev­els to less arid con­di­tions in the cor­ri­dor be­tween Mo­jave Desert and San Joaquin val­ley, Nel­son’s an­te­lope squir­rels be­came re­stricted to the San Joaquin val­ley. (Best, et al., 1990; Haw­becker, 1953)

Con­trib­u­tors

Divya Bal­aji (au­thor), Yale Uni­ver­sity, Eric Sar­gis (ed­i­tor), Yale Uni­ver­sity, Rachel Raci­cot (ed­i­tor), Yale Uni­ver­sity, Tanya Dewey (ed­i­tor), Uni­ver­sity of Michi­gan-Ann Arbor, Cather­ine Kent (ed­i­tor), Spe­cial Pro­jects.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

carrion

flesh of dead animals.

chemical

uses smells or other chemicals to communicate

crepuscular

active at dawn and dusk

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

folivore

an animal that mainly eats leaves.

fossorial

Referring to a burrowing life-style or behavior, specialized for digging or burrowing.

granivore

an animal that mainly eats seeds

herbivore

An animal that eats mainly plants or parts of plants.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

scavenger

an animal that mainly eats dead animals

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

Ref­er­ences

Cal­i­for­nia De­part­ment of Fish and Game. Five Year Sta­tus Re­port- Am­mo­sper­mophilus nel­soni. EW87. Tur­lock: Calif. Dep. of Fish and Game, Nongame Bird and Mam­mal Sec. rep. 1987.

Belk, M., D. Smith. 1991. Am­mo­sper­mophilus leu­cu­rus. Mam­malian Species, 368: 1-8.

Best, T. 1999. Am­mo­sper­mophilus nel­soni. Pp. 407-408 in D Wil­son, S Ruff, eds. Smith­son­ian Book of North Amer­i­can Mam­mals, Vol. 1999, 1999 Edi­tion. British Co­lum­bia: UBC press.

Best, T., A. Titus, C. Lewis, K. Cae­sar. 1990. Am­mo­sper­mophilus nel­soni. Mam­malian Species, 367: 1-7.

Bolles, K. 1988. The Evo­lu­tion and vari­a­tion of an­tipreda­tor vo­cal­iza­tions of an­te­lope squir­rels. Zeitschrift für Säugetierkunde, 53: 129-147.

Brown, N., D. Williams. 2006. "En­dan­gered Species Re­cov­ery Pro­gram" (On-line). San Joaquin an­te­lope squir­rel Am­mo­sper­mophilus nel­soni. Ac­cessed April 30, 2012 at http://​esrp.​csustan.​edu/​speciesprofiles/​profile.​php?​sp=amne.

Cypher, B. 2001. Spa­ciotem­po­ral Vari­a­tion in Ro­dent Abun­dance in the San Joaquin Val­ley. The South­west­ern Nat­u­ral­ist, 46/1: 66-75.

Grinell, J. 1933. Re­view of the Re­cent mam­mal fauna of Cal­i­for­nia. Berke­ley, Cal­i­for­nia: Uni­ver­sity of Cal­i­for­nia.

Grinell, J., J. Dixon. 1918. Nat­ural His­tory of the Ground Squir­rels of Cal­i­for­nia. Sacra­mento, Cal­i­for­nia: Cal­i­for­nia State Print­ing Of­fice.

Haw­becker, A. 1975. The Bi­ol­ogy of Some Desert Dwelling Ground Squir­rels. The Hague, Nether­lands: Dr. Junk, b.v.

Haw­becker, A. 1953. En­vi­ron­ment of the Nel­son An­te­lope Ground Squir­rel. Jour­nal of Mam­mal­ogy, 34/3: 324-334.

Haw­becker, A. 1947. Food and Mois­ture Re­quire­ments of the Nel­sons An­te­lope Ground Squir­rel. Jour­nal of Mam­mal­ogy, 28/2: 115-125.

Haw­becker, A. 1958. Sur­vival and Home Range in the Nel­son’s an­te­lope squir­rel. Jour­nal of Mam­mal­ogy, 39: 207-215.

Heller, C., J. Hen­der­son. 1976. Hy­po­thal­a­mic Ther­mosen­si­tiv­ity and Reg­u­la­tion of Heat Stor­age Be­hav­ior in a Day-ac­tive Desert Ro­dent Am­mo­sper­mophilus nel­soni. Jour­nal of Com­par­a­tive Phys­i­ol­ogy, 108: 255-270.

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