420.

Nairobi Grass Rat

Arvicanthis nairobae

French: Rat-roussard de Nairobi / German: Nairobi-Grasratte / Spanish: Rata de hierba de Nairobi

Other common names: East African Arvicanthis

Taxonomy. Arvicanthis nairobae J. A. Allen, 1909,

Nairobi, Kenya.

Arvicanthis nairobae is easily confused with A. mniloticus, making the geographical boundaries of the species unclear. Diagnosis is best based on chromosomal complement, that of nairobae having 2n = 62, FN = 78. Monotypic.

Distribution. On basis of chromosomally determined specimens, Nairobi Grass Rat occurs in narrow band from C & W Kenya

to N Tanzania; it may be present also in S Ethiopia.

Descriptive notes. Head—body 118-167 mm, tail 94-129 mm, ear 15-19 mm, hindfoot 22-30 mm; weight 51-135 g. The Nairobi Grass Rat is medium-sized; fur dorsally quite coarse and grizzled chestnut brown, and ventrally tan and softer-textured. Ears are small and covered with short brown hairs. Tail is relatively short (¢.73% of head—body length), darker above than below, and coarsely scaled with small bristles. Limbs are relatively short, with four digits on forefoot (first digit is absent; fifth digit is highly reduced but still bears a claw) and five digits on hindfoot.

Habitat. Somali-Masai grasslands and savannas, especially where there is woody cover combined with long grasses; e.g. dead trees and man-made bomas (livestock enclosures comprising woody Acacia fence).

Food and Feeding. The Nairobi Grass Ratis herbivorous. Dietmostly consists of grass, with other plants; some arthropods also eaten.

Breeding. Reproduction is seasonal. Average litter size (number of embryos) 5-5 (range 2-12).

Activity patterns. Nairobi Grass Rats are diurnal and terrestrial.

Movements, Home range and Social organization. The Nairobi Grass Rat is very social, living in large colonies. Densities may reach 100-200 ind/ha.

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

Bibliography. Castiglia et al. (2006), Happold (2013a), Monadjem et al. (2015), Neal (1981).