Cape ground squirrel
|Cape ground squirrel|
|Cape ground squirrel range|
The name Cape ground squirrel is somewhat misleading as it actually has a much wider area of habitation. This common name may have been arrived at to distinguish it from a tree squirrel (the Eastern Grey Squirrel) found around Cape Town, which was imported from Europe by Cecil John Rhodes.
The Cape ground squirrel has black skin with a coat is made of short stiff hairs without underfur. The fur is cinnamon on the back while the face, underbelly, sides of neck and ventral sides of limbs are white. The sides of its body each have a white stripe that stretches from the shoulders to the thighs. The eyes are fairly large and have white lines around them. The pinnae is small. The tail is flattened on the back and underside and is cover with white hair and 2 black bands at the base. The Cape ground's sexual dimorphism is subtle. Males usually weighing 8-12% more than females, with the former weighing 423–649 grams (0.933–1.431 lb) and the latter weighing 444–600 grams (0.979–1.323 lb). The Cape ground squirrel has a total length of 424–476 millimetres (16.7–18.7 in) for males and 435–446 millimetres (17.1–17.6 in) for females. The dental formula of the ground squirrel is 188.8.131.52. The belly and groin area of the females each have two pairs of mammary glands. The glans penis of the males are large with a prominent baculum. This species is notable for its enlarged testes which are around 20% of the length of the head and body. Molting occurs between August and September and between March and April, once per year.
The Cape ground squirrel lives throughout southern Africa; through Botswana, South Africa and Namibia. Its range covers most of Namibia but is absent from coastal regions and the northwest. Ground squirrels inhabit central and southwestern Kalahari in Botswana. In South Africa, it can be found in central and north-central areas.
Behavior and ecology
Cape ground squirrels live mainly in arid or semiarid areas. They prefer to live in velds and grasslands with hard ground. They can also be found in scrub along pans, on floodplains and in agricultural areas. Ground squirrel are generally active during the day and do not hibernate. They are burrowing animals that dig and live in clusters of burrows averaging around 700 square metres (7,500 sq ft) with 2-100 entrances. Burrow serve to protect the squirrel from extreme temperatures at the surface as well as predators. Nevertheless most of the day is spent feeding at the surface. For thermoregulation, ground squirrels shade their head and back with their bushy tails. Dust bathing is also done. Ground squirrels eat bulbs, fruits, grasses, herbs, insects and shrubs. They do not hoard food so foraging is a daily activity. The Cape ground squirrel usually doesn't have to drink and it gets moisture from the food it eats. A ground squirrel’s daily activities are made of around 70% feeding, 15-20% being vigilant and around 10% socializing. The burrows of Cape ground squirrels are also used by meerkats and yellow mongooses. While Cape ground squirrels and meerkats appear to have a mutual relationships, mongoose and squirrel relations appear to be more commensal. Predators of grounds squirrels include jackals, snakes and monitor lizards. Ground squirrels may be able to scent the differences in the dropping of predators and non-predators. When threatened by predators, like snakes, ground squirrel will engage in mobbing behavior. Multiple squirrels will rush at the predator while using their bushy tails to block it. When the predator strikes back, all the squirrels back off. However, multiple mobbings are generally successful in driving anyway predators.
Cape ground squirrels live in groups of 2-3 adult females and a maximum of nine sub-adults of either sex as well as the females’ dependant offspring. Groups that have more than three females split into smaller groups. Adult males live separately from females and only join when the latter is an estrous. Males groups number up to 19 individuals who are not related and are not agnostic. Within a male group, 4-5 males may form temporary subgroups that change size and members each day. Females groups live in separate burrow clusters. A female group’s home range is ca. 4 hectares (9.9 acres) with core areas of around 0.25 hectares (0.62 acre). Home ranges can overlap however core areas are defended though agonistic behavior. Male group live in home ranges envelop those of several female groups and average 12.1 hectares (30 acres). Within a female group, members use the same feeding and sleeping ranges. No dominance hierarchy exists between them. Male groups, by contrast, have live in ages-based linear hierarchies. Competition between males usually take the form of leaping displays that cause no injuries. In addition, males groups are not territorial like female groups are, and membership are very open. During estrous, a female will be approached, solicited and chased by males trying to mate with her. The most dominant males get the first matings. A female will mate with the same male several times. If a male has not yet mated with a female, he will disrupt the copulations she has with other males. However, mate guarding is rare.
When perceiving something at a threat, ground squirrels will emit a whistle-like call as an alarm call. The alarm call comes in two forms; the short by shrill "bi-jo" which signal serious danger, and a medium-pitched "bi-joo" sound with is used for lesser dangers. During agonistic encounters, squirrels emit deep growls as signs of aggression. Juvenile squirrels make play calls, nest-chirpings, and protest squeaks.
Cape ground squirrel mate and reproduce year-round but mating occurs mostly in dry winter months. Since females copulate with multiple males, the males' large testes are useful for sperm competition. After copulation, males will masturbate which could serve to keep the genitals clean and reduce the risk of sexually transmitted infections. In groups, only one females at a time enters estrous which lasts around three hours. Gestation lasts around 48 days or 42–49 days. Lactation begins not long before the pups are born. A lactating female isolates herself in a separate burrow to care for their young but she returns to her group after weaning or if her litter is lost for some reason. There are 1-3 pups in a litter. They are born altricial, hairless and blind. The pups stay in the burrows for their first 45 days. By 35 days, the eyes are open. Seven days after emerging from the burrows, the pups can eat solid food. Lactation ends at around 52 days. Males reach sexual maturity at eight months while female mature at 10 months. The former leave their natal groups while the latter remain.
The Cape ground squirrels populations does not seem to be threatened overall. In some areas, it is persecuted as an agricultural pest. In addition, humans have used poisonous grass to control ground squirrel due to crop damage and rabies. It inhabits protected areas, such as Kgalagadi Transfrontier Park in Botswana and South Africa and Etosha National Park in Namibia.
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- Griffin, M. & Coetzee, N. (2008). Xerus inauris. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 8 January 2009.
- Skurski, D., J. Waterman. 2005. "Xerus inauris", Mammalian Species 781:1-4.
- Skinner J. D., R. H. N. Smithers. 1990. The mammals of southern African subregion, University of Pretoria.
- Lynch C. D. 1983. "The mammals of the Orange Free State", Memoirs van die Nasionale Museum 18:58-60.
- Zumpt I. F. 1970. "The ground squirrel", African Wild Life 24:115-121.
- Herzig-Straschil, B. 1978. "On the biology of Xerus inauris (Zimmermann, 1780) (Rodentia, Sciuridae)", Zeitschrift für Säugetierkunde 43:262–278.
- Herzig-Straschil B. 1979. "Xerus inauris (Rodentia, sciuridae)-an inhabitant of arid regions of southern Africa", Folia Zoologica 28:119-124.
- Smithers R. H. N. 1971. The mammals of Botswana, Salisbury, Rhodesia, Museum Memoirs No. 4.
- Waterman, J. M. 1995. "The social organization of the Cape ground squirrel (Xerus inauris; Rodentia: Sciuridae)". Ethology 101:130–147.
- Bennett, A. F., R. B. Huey, H. John-Alder, and K. E. Nagy. 1984. "The parasol tail and thermoregulatory behavior of the Cape ground squirrel (Xerus inauris)", Physiological Zoology 57:57–62.
- Waterman, J., J. Roth. 2007. "Interspecific associations of Cape ground squirrels with two mongoose species: benefit or cost?". Behavioral Ecology and Sociobiology, 61(11):1675-1683.
- Belton, L., N. Ball, J. Waterman, P. Bateman. 2007. "Do Cape ground squirrels (Xerus inauris) discriminate between olfactory cues in the faeces of predators versus non-predators?", African Zoology, 42(1): 135-138.
- Waterman, J. M. 1997. "Why do male Cape ground squirrels live in groups?" Animal Behaviour 53:809–817.
- Waterman, J. M. 2002. "Delayed maturity, group fission and the limits of group size in female Cape ground squirrels (Sciuridae: Xerus inauris)", Journal of Zoology 256:113–120.
- Waterman, J. M. 1998. "Mating tactics of male Cape ground squirrels, Xerus inauris: consequences of year-round breeding", Animal Behaviour 56:459–466.
- Waterman, J. M. 1996. "Reproductive biology of a tropical, non-hibernating ground squirrel". Journal of Mammology 77:134–146.
- Waterman JM, 2010. "The Adaptive Function of Masturbation in a Promiscuous African Ground Squirrel". PLoS ONE 5(9): e13060. doi:10.1371/journal.pone.0013060