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Ground Squirrels

Marie Kubiak

1.1 Introduction

Ground squirrels make up the subfamily of Xerinae, within the Sciuridae (squirrel) family and include a variety of well-known species such as the groundhog and marmot. The species within this subfamily that are more commonly kept as pets, and are covered in this chapter, are prairie dogs, Richardson's ground squirrels and Siberian chipmunks. Biological parameters for these species are included in Table 1.1.

1.2 Husbandry

1.2.1 Siberian Chipmunks

Siberian chipmunks (Tamias sibiricus) are squirrel-like rodents originating primarily from Northern Asia. Although common in the pet trade in Europe in the late twentieth and early twenty-first century, in 2015 this species was added to EU Invasive Alien Species (IAS) Regulation (1143/2014), resulting in a ban within the European Union on importation, keeping, breeding, transport, trade, and accidental or intentional release of this species, though an exemption is made for animals to be transported for veterinary care. As such this species can only be kept by existing owners for their natural lifespan, or under licence for medical, research, or conservation purposes. At present these restrictions remain in place for the United Kingdom. Pet Siberian chipmunk numbers are declining as animals reach the end of their life and no new animals are able to be acquired or bred. Other species of chipmunks may be legally kept but are extremely rare as pets. The Pallas squirrel (Callosciurus erythraeus) and Fox squirrel (Sciurus niger), both rarely kept as pets, have also been listed as invasive species and are subject to the same restrictions.

Chipmunks are terrestrial though have good climbing capabilities and will use the full height of enclosures. They are inquisitive and highly active so enclosures should be secure - such as large aviaries with narrow spaced mesh. Nest boxes should be provided (at least one per animal) with hay substrate and branches, tunnels, hides and wheels provided for enrichment and to encourage activity. Chipmunks will chew plastics, wood, wires and other materials and this should be taken into account when planning enclosure construction, and when toys or décor are added. They are omnivores and can be fed a rodent pellet diet but this should be supplemented with seeds, vegetables, insects, and hay. Food may be stored in substrate or nest boxes so it is important to check and clean enclosures thoroughly on at least a weekly basis to prevent spoilage. Fresh water should always be available and water bottles are generally accepted well. Free range access within a house is not advisable due to potential for escape, injury, or damage inflicted to household possessions. In winter wild chipmunks do not exhibit true hibernation but have fluctuating torpor, with several days of dormancy followed by a period of normothermia, activity, and feeding. In torpor their body temperature drops to around 5?°C and heart rate slows to 4?beats/min. In captivity there is no drive for torpor as temperatures tend to remain stable through seasons and food is abundant. There is no evidence that absence of torpor has any negative impact.

1.2.2 Prairie Dogs

Prairie dogs (Cynomys spp.) are large, North American members of the squirrel family and have five recognised species. Of these only the black-tailed prairie dog (Cynomys ludovicianus) is encountered with any frequency as a pet in the UK. Well-socialised individuals can make good pets but even the tamest prairie dog can become aggressive during their breeding season.

Captive animals require deep substrate to form their burrows as well as a large overground area for activity, sufficient to enable a group of animals to be kept together. Enclosure size requirements have been detailed as 2?×?2?×?2.5?ft (L?×?W?×?H) per animal (Pilny and Hess 2004) but this should be regarded as an absolute minimum and 4?×?4×?2.5?ft would be considered more suitable as a minimum to allow animals to display normal behaviour. An area of deep substrate should be provided to allow creation of burrows and can be hay, shredded paper, or soil. Artificial burrows and shelters such as drain pipes or wooden boxes can be provided for hide and sleeping areas. Cage bars should be no further than 1?inch apart to prevent escape. An elevated observation shelf should be provided as prairie dogs are inquisitive and will often climb to investigate activity in the surrounding area (Pilny and Hess 2004). Plastic should be avoided as it is likely to be chewed. Chosen toilet areas will be well defined allowing easy daily cleaning of urine and faeces and a litter tray can be placed in the chosen site. A warm room or supplemental heating is necessary to provide temperatures of 20-22?°C as prairie dogs may enter torpor at cooler temperatures (Johnson-Delaney 2006). Torpor is not obligatory in prairie dogs but is a facultative response to temperature drop and lack of available food and water. Although body temperatures reduce, they remain significantly higher than ambient environmental temperature at approximately 19?°C even in deep torpor bouts. These deep torpor bouts are interspersed with periods of activity and normothermia when environmental conditions improve (Lehmer et al. 2001). As torpor is facultative there is no need to replicate the conditions in captivity and to date no adverse effects have been reported with absence of torpor in prairie dogs.

Table 1.1 Biological parameters (for animals not undergoing torpor).

Body weight Lifespan Body temperature (°C) Respiratory rate (/min) Heart rate (/min) Sexual maturity Gestation Siberian Chipmunk (Tamias sibiricus) 50-150?g 5-10?years 37-38 70-80 250-350 8-14?months 30-31?days Black tailed-prairie dog (Cynomys ludovicianus) 0.7-2?kg 7-10?years 35.3-39 40-60 200-318 2?yrs 30-35?days Richardson's Ground Squirrel (Urocitellus richardsonii) 0.4-0.6?kg 4?years 37.5-39.5 40-100 245-275 11?months 23?days

Prairie dogs are hindgut fermenters and require a high fibre intake to maintain intestinal health. Where a normal appetite is present, provision of a variety of grasses, hay, flowers, herbs, fresh vegetables and leaves and occasional invertebrates is appropriate (Orcutt 2005). Pelleted diets designed for rabbits or rodents can be convenient food source for owners but should make up no more than 10% of the diet, with high fibre material making up the majority of food provided. Seeds and grains can be offered in small quantities as treats or to increase body condition but can lead to obesity or disruption to normal intestinal function if fed in excess.

1.2.3 Ground Squirrels

Ground squirrel species are uncommon as companion animals though Richardson's Ground squirrels (Urocitellus richardsonii) (RGS) are occasionally kept. This species is native to the grasslands of the Northern United States of America and Southern Canada and do cross over territory with prairie dogs. In the wild, female familial groups exist with solitary males only being tolerated during breeding. In captivity they can be maintained in social single-sex colonies or mixed sex colonies with males being neutered. Though destructive and with a tendency to bite defensively, RGS tend to make good companion animals with regular handling and interaction.

Captive animals have similar requirements to prairie dogs, though as a smaller species enclosures can be less extensive, with 3?×?2?×?1.5?ft advised per animal. Cage bars should be no more than 0.75?inch apart. The observation shelf should not be placed more than 18 inches above the ground as RGS are not good climbers. Ambient temperatures of 18-25?°C are advisable but they are adapted to cooler temperatures and will not enter torpor unless temperatures drop to below 7?°C (Michener 1983). In the wild RGS are obligate hibernators and will spend up to nine months of the year in true torpor, with body temperature dropping to close to environmental temperature as heart and respiratory rates slow dramatically (Michener and Koeppl 1985). Brief periods of around 12?hours of warming to normal body temperature occur during this torpor (Michener and Koeppl 1985). In captivity temperatures are stable and food is readily available and torpor rarely occurs. These less harsh conditions aid overall longevity but the lack of torpor and high metabolic rate all year round may be associated with higher rates of neoplasia seen in RGS in captivity.

RGS are omnivorous with their dietary requirements intermediate between prairie dogs and...