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Belding's ground squirrel

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Belding's ground squirrel
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Sciuridae
Genus: Urocitellus
Species:
U. beldingi
Binomial name
Urocitellus beldingi
(Merriam, 1888)
Distribution of the Belding's ground squirrel
Distribution of the Belding's ground squirrel
Synonyms

Spermophilus beldingi Merriam, 1888

Belding's ground squirrel (Urocitellus beldingi), also called pot gut, sage rat or picket-pin,[2] is a squirrel that lives on mountains in the western United States. In California, it often is found at 6,500 to 11,800 feet (2,000–3,600 m) in meadows between Lake Tahoe and Kings Canyon. This species is not of conservation concern, and its range includes some protected areas.[1]

Physical description

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The Belding's ground squirrel is medium-sized with "a relatively short tail, short limbs, and small ears".[3] It has a gray pelage become more cinnamon at the underside and reddish-brown on the back. Its body length is 230 to 300 millimetres (9.1–11.8 in). The tail is 44 to 76 millimetres (1.7–3.0 in) and is bushy but also flattened. The distal hairs of the tail have three color bands, one black, one white and one red. On average, the ground squirrel weighs 290 grams (0.64 lb). Its feet are covered in little to no hair. Compared to other ground squirrel species, its cheek pouches are moderate in size.

Ecology

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Range and habitat

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Being native to the northwestern United States, the Belding's ground squirrel ranges covers northeastern Oregon and part of Washington, north California, southwestern Idaho, north and central Nevada and northwestern Utah.[4] The ground squirrel prefers to live at higher altitudes, occurring in alpine and subalpine meadows.[5] It is also found in sagebrush flats, brush/grass habitats and cultivated areas.[4] The grounds squirrels are largely restricted to open areas with enough fresh vegetation and water. They do not live in dense forests, tall grasses, rocky slopes or thick shrubbery as they cannot watch for predators. In addition they do not prefer grass that is too short as they cannot hide from predators.[6]

Food and feeding

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Belding's ground squirrels have a largely herbivorous diet. However they will also eat insects, carrion, other vertebrates, and even other conspecifics. They mostly eat flowers and seeds.[4] They also eat nuts, grains, roots, bulbs, mushrooms and green vegetation. Belding's ground squirrels do not keep food in caches. Instead they store fat reserves.[4][7] As such, the ground squirrels eat large quantities of food before hibernation, doubling their body weight.[4] They spend as much as 40% of the summer eating.[7] When eating, the ground squirrel feeds itself with its front paws while standing on its back paws.[7]

Hibernation

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Belding's ground squirrels hibernate at different times, depending on the sex and age of the individual and the altitude of their environment. Adult males go into hibernation between late July and early September when at higher altitudes.[7] Females may follow them in late September, depending on the elevation.[4][6] Juveniles follow their parent into hibernation with juvenile females first going when they are 13 weeks old and males when they are 10 weeks old.[5] They enter when the grasses begin to dry and turn brown, thus avoiding the hot, dry, late-summer famine.[6]

The ground squirrels hibernate in burrow chambers called hibernacula. Males hibernate alone while females tend to hibernate together.[4] The time in which ground squirrel emerge from their hibernation also depends on different factors. At lower elevations, males emerge relatively synchronously in February, while at higher elevations they emerge at the end of April.[4][6] Females emerge later than males, and their emergence is spread over several weeks.[8]

Activity Cycles

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Belding's ground squirrels begin to leave their burrows at sunrise. They are most active in the morning (e.g., feeding, digging, and interacting socially).[6] They warm themselves by stretching out on rocks or on the warm ground.[7] Their activities tend to decrease as the temperature increases. They typically reenter their burrows in mid-afternoon, reemerge in late-afternoon, and submerge for the night at sunset. Juveniles emerge and submerge later than adults.[6]

Demography

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The demography of a free-living population at Tioga Pass was studied using mark-recapture techniques over 11 consecutive field seasons. Results indicated that the 7—8 month hibernation period (October—May) is the most hazardous time, when 66 to 70% of juveniles and 36 to 39% of adults disappear. Males that survived their first winter were recaptured for an additional 1.1 years vs. 1.6 years for females. In general, females live twice as long as males. Few males lived more than 6 years, whereas some females lived more than 11 years; as a result the sex of ratio of the adult population was female—biased, especially among the older population.[9]

Behavior

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Pups

Family relations

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Belding's ground squirrels live in a nepotistic society where most interactions occur between females, their offspring, and collateral kin.[10][5] Females are philopatric, and spend their lives in the area where they were born, whereas males begin dispersing 2 months after weaning and the following spring, and they never return to their natal area.[11][12] Females cooperate to defend territories, protect pups from infanticide, share feeding areas, and give alarm calls when predators approach.[13] Cooperation between females correlates with their degree of relatedness.[14] Ground squirrels recognize their kin by comparing their own odor phenotypes and those of littermates with odors of squirrels they encounter.[15] These phenotypes come in the form of scent from dorsal and anal glands that leave a "pungent" odor in the dust bathing areas.[6] Each animal has its own repertoire of scents that others can use to recognize it. If an individual's odor phenotype matches itself or its littermates closely enough, it is likely a relative. Laboratory tests[15] indicate that females can discriminate between kin and nonkin, and close and distant relatives. Field observations[16][14] indicate that females favor close kin more than distant kin, and behave aggressively toward nonrelatives. Adult males do not display kin recognition, nor nepotistic behaviors.[15]

Alarm calls

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Belding's ground squirrels are preyed on by various mammals (e.g., coyotes, badgers, and weasels) and birds (e.g., red-tailed and rough-legged hawks). Ground squirrels also perceive humans, livestock, and cars as threats.[17] Belding's ground squirrels respond to predators by giving two distinct types of alarm calls.[18] The first, known as the churr call or the trill, is made as a series of 5 or more notes, given rapidly.[19] These calls are given for predators that pose less immediate threats, usually terrestrial predators.[20] Individuals that are close to the alarm caller will respond by standing on their back legs (posting), running on a rock to get a better view of the predator or by returning to their core area.[17]

The second alarm call, known as the whistle, is made as a single high-pitched note.[21] This call is made in response to immediate threats, usually aerial ones.[20] All individuals in hearing range will exhibit evasive behavior such as crouching[20] or fleeing into the nearest shelter.[17] When running from aerial predators, squirrels call while escaping. By contrast, when running from terrestrial predators, escaping squirrels do not call until they make it to safety. In addition, with aerial predators, all squirrels will call while with terrestrial predators, only females with kin will call. The squirrel that first sounds the alarm posts while calling, looking at the predator and will not try to hide.

Reproduction and parenting

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For Belding's ground squirrels mating occurs after hibernation, usually in late May to early June.[9] The ground squirrels mate promiscuously, as both males and females mate with multiple partners.[4] Females are sexually receptive for less than five hours each year.[22] Thus when a female is receptive, the males immediately gather around her.[4] They will fight viciously to gain access, grappling, kicking, scratching, and biting each other. Larger, older, and stronger males are more likely to mate.[9] A single female can mate with as many as five males during her estrous; this increases the chance of pregnancy, and also increases genetic diversity.[4]

Females give birth to one litter a year.[8] Pregnant females will dig nesting burrows and gather grass and grass roots to make nests. Nesting-only territories are established around these burrows. Females protect the burrows against intruding unrelated conspecifics by attacking and chasing them. Defense of the territories lasts until the young are weaned.[4] The gestation period of the ground squirrel lasts 23–31 days and young are born late June to early July in higher elevation regions, while in lower areas such as Central Oregon young are born in March and emerge from their dens en masse about mid-April when the first warm days of spring begin.[4][6] Litter sizes range from 3–8 young. Litter sizes and reproductive values change with female age, being lowest for young (0—1 yr) and old (5—9 yr) female and highest for 2—4 olds.[9]

Females rear young without assistance from males. In their first few weeks of life, pups inhabit their mother's subterranean nest burrow. Pups first emerge from their natal burrows at weaning, when they are about 27 days old (at Tioga Pass, in July and early August).[5] The young remain near the entrance to their natal burrow for several days, and then start to explore more widely. Young males foray farther than females, and males begin dispersing before the end of their first summer. Infanticide is known to occur in Belding's ground squirrels. An intruding squirrel will drag a squealing, squirming juvenile out of the nest burrow, and promptly kill it by biting its head.[23] The killer will also sometimes eat the carcass. Adult females and yearling males are more often the killers.[23] The perpetrators of infanticide do not reside in the same area as the victim. Females never kill their relatives and they will help their kin in protecting their young from infanticide.

Taxonomy

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Belding's ground squirrel was first described by Clinton Hart Merriam in 1888, as Spermophilus beldingi. Three subspecies are now generally recognized:[24]

  • U. b. beldingi (Merriam, 1888)
  • U. b. creber Hall, 1940
  • U. b. oregonus (Merriam, 1898)

References

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  1. ^ a b Cassola, F. (2016). "Urocitellus beldingi". IUCN Red List of Threatened Species. 2016: e.T42464A22264836. doi:10.2305/IUCN.UK.2016-3.RLTS.T42464A22264836.en. Retrieved 11 November 2021.
  2. ^ "Animal Life in the Yosemite (Mammals)". National Park Service. Archived from the original on 2009-02-26. Retrieved 2009-09-03.
  3. ^ Stephen H Jenkins, Bruce Eshelman. 1984. Spermophilus beldingi. Mammalian Species. 221:1–8
  4. ^ a b c d e f g h i j k l m Sherman, P. W. a. M. L. M. (1979). "Four Months of The Ground Squirrel." Natural History 88: 50–57.
  5. ^ a b c d Holekamp, K.E. (December 1986). "Proximal causes of natal dispersal in Belding's ground squirrels". Ecological Monographs. 56 (4): 365–391. doi:10.2307/1942552. JSTOR 1942552.
  6. ^ a b c d e f g h Turner, L. W. (1972). Autecology of the Belding ground squirrel in Oregon. Department of Biological Sciences. Tuscan, University of Arizona
  7. ^ a b c d e Loehr, K.A.; Risser, A.C. (August 1979). "Daily and seasonal activity patterns of the Belding ground squirrel in the Sierra Nevada". Journal of Mammalogy. 58 (3): 445–448. doi:10.2307/1379353. JSTOR 1379353.
  8. ^ a b Morton, M.L.; Gallup, J.S. (December 1975). "Reproductive cycle of the Belding ground squirrel (Spermophilus beldingi): seasonal and age differences". Great Basin Naturalist. 35 (4): 427–433. JSTOR 41711496.
  9. ^ a b c d Sherman, P.W.; Morton, M.L. (October 1984). "Demography of Belding's ground squirrels". Ecology. 65 (5): 1617–1628. Bibcode:1984Ecol...65.1617S. doi:10.2307/1939140. JSTOR 1939140.
  10. ^ Sherman, Paul W. (September 1977). "Nepotism and the evolution of alarm calls". Science. 197 (4310): 1246-1253. doi:10.1126/science.197.4310.1246.
  11. ^ Holekamp, Kay E. (November 1984). "Natal dispersal in Belding's ground squirrel (Spermophilus beldingi)". Behavioral Ecology and Sociobiology. 16 (1): 21-30. doi:10.1007/BF00293100.
  12. ^ Holekamp, Kay E.; Sherman, Paul W. (June 1989). "Why male ground squirrels disperse: A multilevel analysis explains why only males leave home". American Scientist. 77 (3): 232-239. JSTOR 27855724.
  13. ^ Sherman, Paul W. (1981). "Chapter 19: Reproductive competition and infanticide in Belding's ground squirrels and other organisms". In Alexander, Richard D.; Tinkle, Donald W. (eds.). Natural Selection and Social Behavior: Recent Research and New Theory. Chiron Press. pp. 311–331. ISBN 978-0913462089.
  14. ^ a b Sherman, P.W. (July 1981). "Kinship, demography, and Belding's ground squirrel nepotism". Behavioral Ecology and Sociobiology. 8 (4): 251–259. doi:10.1007/BF00299523. S2CID 7935876.
  15. ^ a b c Holmes, Warren G.; Sherman, Paul W. (August 1982). "The ontogeny of kin recognition in two species of ground squirrels". American Zoologist. 22 (3): 491–517. doi:10.1093/icb/22.3.491.
  16. ^ Sherman, Paul W. (June 1980). "Chapter 20: The limits of ground squirrel nepotism". In Barlow, George W.; Silverberg, James; Livingstone, Frank B. (eds.). Sociobiology:Beyond Nature/Nurture?. Westview Press. pp. 505–544. ISBN 978-0891583721.
  17. ^ a b c Turner, L.W. (November 1973). "Vocal and escape response of Spermophilus beldingi to predators". Journal of Mammalogy. 54 (4): 990–993. doi:10.2307/1379099. JSTOR 1379099.
  18. ^ Leger, Daniel W.; Berney-Key, Susan D.; Sherman, Paul W. (August 1984). "Vocalizations of Belding's ground squirrels (Spermophilus beldingi)". Animal Behaviour. 32 (3): 753-764. doi:10.1016/S0003-3472(84)80151-7.
  19. ^ Robinson, S.R. (August 1980). "Anti-predator behavior and predator recognition in Belding's ground squirrels". Animal Behaviour. 38 (3): 840–852. doi:10.1016/S0003-3472(80)80144-8. S2CID 53159426.
  20. ^ a b c Mateo, J.M. (September 1996). "The development of alarm-call response behavior in free-living juvenile Belding's ground squirrels". Animal Behaviour. 52 (3): 489–505. doi:10.1006/anbe.1996.0192. S2CID 53193203.
  21. ^ Sherman, Paul W. (October 1985). "Alarm calls of Belding's ground squirrels to aerial predators: nepotism or self-preservation?". Behavioral Ecology and Sociobiology. 17 (4): 313-323. doi:10.1007/BF00293209.
  22. ^ Hanken, J.; Sherman, P.W. (April 1981). "Multiple paternity in Belding's ground squirrel litters". Science. 212 (4492): 351–353. Bibcode:1981Sci...212..351H. doi:10.1126/science.7209536. PMID 7209536.
  23. ^ a b Sherman, P. W., Reproductive Competition and Infanticide in Belding's Ground Squirrels and Other Animals. Natural Selection and Social Behavior. R.D.A.A.D.W. Tinkle. New York and Concord, Chiron Press: 311–331.
  24. ^ Wilson, D. E.; Reeder, D. M., eds. (2005). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. ISBN 978-0-8018-8221-0. OCLC 62265494.
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