Otomys unisulcatus F. Cuvier 1829

408.

Karoo Vlei Rat

Otomys unisulcatus

French: Otomys cafre / German: Karoo-Lamellenzahnratte / Spanish: Rata de laguna de Karoo

Other common names: Bush Vlei Rat, Karoo Bush Rat

Taxonomy. Otomys unisulcatus F. Cuvier, 1829,

type locality not given. Fixed by A. Roberts in 1946 as “Matjiesfontein on the southern edge of the upper Karoo,” Western Cape Province, South Africa.

Some authors have included O. wunisulcatus and O. sloggetti in a separate genus Mpyotomys, but phylogenetic position of these primitive species remains elusive. Monotypic.

Distribution. Occurs throughout the semi-arid Succulent Karoo and Nama Karoo biomes within parts of Northern Cape, Western Cape, and Eastern Cape provinces, South Africa.

Descriptive notes. Head-body 110-205 mm, tail 63-106 mm, ear 20-33 mm, hindfoot 22-32 mm; weight 61-156 g. The Karoo Vlei Ratis large and robust, with large blunt head, short tail, and shaggy fur. Fur is speckled bright tawny brown above and gray below. Tail is short (c.51% of head-body length) and bicolored. Females have four pairs of nipples. Upper incisors have single groove, and lower incisors have two deep grooves. M, has four laminae, and M” has 8-9 laminae. Diploid numberis 2n = 28.

Habitat. Shrublands typically indry river beds and banks and rocky and non-rocky terrain. Near the west coast, Karoo Vlei Rats are associatedwith protected lower lying lees of coastal dunes.

Food and Feeding. Diet includes plant stems and leaves, mostly ofshrubs. Species composition of diets varies geographically, with Acacia karroo (Fabaceae), Atriplex sp. (Amaranthaceae), Lycium austrinum (Solanaceae), Mesembryanthemum sp. (Aizoaceae), and Tribulus sp. (Zygophyllaceae) being important in Eastern Cape; Lycium bushes and Galeria africana, Drosanthemum sp., and Psilocaulon sp. (all three Aizoaceae) being important in southern Karoo; and Ruschia sp. (Aizoaceae), Exomis microphylla (Amaranthaceae), and Zygophyllum flexuosum (Zygophyllaceae) being important in coastal areas of Western Cape.

Breeding. Karoo Vlei Rats seem to be opportunist breeders, responding to rainfall patterns. Breeding occurs year-round in areas that receive summer and winter rainfall, but it occurs in August-September following winter rains in Namaqualand. Gestation is 37 days, and inter-litter interval is 40 days, suggesting postpartum estrus. Litters in captivity have 1-3 young. Young are semi-precocious and nipple-cling until they are six days old.

Activity patterns. The Karoo Vlei Rat is terrestrial, diurnal, and crepuscular. In Eastern Cape, activity peaks during cooler hours in summer and warmer hours in winter. In Western Cape, this species is crepuscular. Activity periods outside last 5-60 minutes, totaling c.3 periods/day.

Movements, Home range and Social organization. Karoo Vlei Rats construct dome-like “lodges” of interwoven sticks around bases of shrubs, connected with nearby lodges and shrubs by radiating runways. Lodges have systems of tunnels leading to nests, latrines, and entrances. There can be underground tunnels underneath lodges. Groups of 2-8 individuals share lodges. Karoo Vlei Rats forage individually or in groups that move up to 50 m from their lodges. They forage in shrubs, climbing up to 1 m. Aggression between group members is low and ritualized, but between individuals of different lodges, higher levels of aggression can lead to fatalities among males. In the Eastern Cape, density of 64 ind/ha was recorded, but in Western Cape, up to 155 lodges/ha were recorded.

Status and Conservation. Classified as Least Concern on The IUCN Red Lust.

Bibliography. Brown (1987), Brown & Willan (1991), Monadjem et al. (2015), Pillay (2001), du Plessis etal. (1991), Roberts (1946), Robinson & Elder (1987), Vermeulen & Nel (1988).