Large, big-headed, rather slim rat. Upper parts rather grizzled-black and yellow. Flanks paler. Coat coarse. Dark stripe down center of back may be distinct running from top of the head to the base of the tail. Underside whitish to grayish. Hairs on rump longer and more or less tinged yellow to orange. Feet buffish orange to blackish above. Head large, rather pointed. Whiskers sparse and short. Ears small and rounded, tinged orange. The tail is about 80% of body length, slender, blackish above, pale below. Fur dense, concealing tail rings. No terminal tuft.

The species is mostly a sub-Saharan species although it occurs in the Arabian Peninsula, where it may have been introduced by man, and has been recorded across the Sahara, but it is mostly extinct there. This species is widespread in savannas in Africa, found from Senegal across the Sahel to Sudan and Ethiopia, from here it ranges southwards to Uganda and central Kenya. Its presence in central Tanzania and Zambia is uncertain. The species is found along the Nile Valley where its distribution is restricted to a narrow strip of flooded plain. It has additionally been recorded from at least three isolated Saharan mountain ranges. In Ethiopia it is not found above 1,600 m asl.

The range of African grass rats, Arvicanthis niloticus, is traditionally held to extend along the Nile river valley and across most of sub-Saharan Africa, with the exception of the southern and southwestern regions of the continent. However, much debate over the number and range of species within the genus Arvicanthis has yet to be resolved, and the range of A. niloticus may be much more restricted. From genetic analysis, Ducroz, Volobouev, and Granjon (1998) claim this species occurs only in Egypt and northern West Africa, but Musser and Carleton (1993) argue that A. niloticus also inhabits regions including and surrounding Ethiopia.

Biogeographic Regions: ethiopian (Native )

61 records. Latest in 2008 (El-Mansouria canal).

Narrow (Nile, oases of Western Desert). AOO=197.4 km². EOO=221394.6 km². 7 locations.

Narrow (Northeastern Africa from Egypt and Sudan south to Kenya and Tanzania west to Uganda, Nigeria, and Senegal. Also southwestern Arabia)

Rosevear (1969) described African grass rats as “medium-sized rats with stoutish bodies.” Adults of this species range in head and body length from 106 mm to 204 mm with an average of about 130 mm. Tail lengths range from 85% to 90% of the head and body length and average around 100 mm. Average mass of A. niloticus is 118 g, with a range of 50 g to 183 g. Males are slightly larger than females with reported average masses of 120 g to 123 g for males and 92 to 114 g for females.

Arvicanthis niloticus has a roundish head with large, round ears that are covered with short, fine fur. Incisors are not grooved; the snout is rather short, and the tail is covered in small, barely visible hairs. The hindfoot is well-developed, and the inner three hind toes are longer than the outer two. In contrast, the forefoot is smaller with a relatively short, though usable, thumb.

Variation in the coat color of this species has been reported; however, ambiguity in the boundaries of this species may have resulted in the misidentification of another species of the genus Arvicanthis as a color variant of A. niloticus. According to Rosevear (1969), the dorsal fur of these rats consists mostly of ringed hairs, which are dark black or brown at the base, lighter yellow, reddish-brown, or buff in the middle, and black at the tip. Short underfur, gutter hairs, and all-black guard hairs are also present and, combined with the ringed hairs, produce a "salt and pepper" effect. The ventral coat is shorter and lighter in appearance.

Range mass: 50 to 183 g.

Average mass: 118 g.

Range length: 106 to 204 mm.

Average length: 130 mm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: male larger

Length 159-202 mm, tail 125-173 mm, weight 102-201 gm.

Type for Arvicanthis niloticus
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Mammals
Sex/Stage: Male;
Preparation: Skin; Skull
Collector(s): J. Loring
Year Collected: 1910
Locality: Rhino Camp, Lado Enclave, Uganda, Africa

Type for Arvicanthis niloticus
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Mammals
Sex/Stage: Male;
Preparation: Skin; Skull
Collector(s): J. Loring
Year Collected: 1910
Locality: Rhino Camp, Lado Enclave, Uganda, Africa

Type specimen from ‘Egypt’.

Habitat and Ecology

Systems

• Terrestrial

As A. niloticus lives in colonial burrows, it requires some degree of ground cover, such as short bushes, trees, rocks, or termite mounds, under which it may nest. A variety of African habitats, including dry savanna, sub-desert, coastal scrub, open woodlands, grasslands, and cultivated areas, provide such protection. Exact altitudinal data are not reported, but A. niloticus is not believed to occur at high altitudes.

Habitat Regions: tropical ; terrestrial

Terrestrial Biomes: desert or dune ; savanna or grassland ; scrub forest

Other Habitat Features: agricultural

Agricultural areas and margins, canal and railway embank­ments with good cover, olive groves, and gardens. Recorded around, but apparently never in, human settlements. Presence in oases prob­ably due to humans.

A. niloticus is primarily herbivorous, feeding on grasses, leaves and stems of flowering plants, seeds, the bark of some woody plants, and cultivated crops. Arthropods are also eaten by this species. As different food types vary in their availability seasonally, A. niloticus will alter the intake ratio of food types. This flexible, generalist approach may improve its competitive ability. Caching does not appear to be a predominant behavior in this species, but has been observed when larger food items were offered to wild individuals.

Animal Foods: insects

Plant Foods: leaves; wood, bark, or stems; seeds, grains, and nuts

Foraging Behavior: stores or caches food

Primary Diet: herbivore (Folivore )

Aside from serving as prey to some African carnivores, A. niloticus also serves other important, though perhaps less desirable, roles in its ecosystem. It is an agricultural pest and competes with other African rodents, primarily natal multimammate mice, and savanna gerbils, for both natural and cultivated resources. Arvicanthis niloticus thus has a strong impact on plant diversity. Senzota (1983) also proposed resource partitioning of grasses by A. niloticus and some African ungulates, including blue wildebeest and Thomson’s gazelles, to reduce competition between the rodents and ungulates.

Arvicanthis niloticus also serves as a host and/or vector for a variety of organisms, including fleas, parasitic worms, and viruses. It has been implicated in many plant and human disease outbreaks as a carrier of a multitude of diseases, such as bubonic plague in ancient Egypt, Rice yellow mottle virus in parts of Africa, and Schistosoma mansoni, which causes intestinal schistosomiasis, a disease that sometimes occurs in severe outbreaks in parts of Africa.

Commensal/Parasitic Species:

• Viruses, such as Rice yellow mottle virus 
• Parasitic worms, such as Schistosoma mansoni 
• Fleas, such as Xenopsylla cheopis, which carries Yersinia pestis, the bacterium that causes bubonic plague

Some anti-predatory behaviors have been documented for A. niloticus. Individuals typically retreat immediately down runways back to the communal burrow, possibly stopping to hide under other ground cover from avian predators. Senzota (1990) noted that when no conspecifics were present outside the burrow, individuals of this species spent a substantial amount of time in vigilant behavior at the entrances of the burrow prior to emerging. Movement by predators resulted in retreat into the burrow by A. niloticus, although mere stationary presence would not. If conspecifics were present (foraging, “playing”, or maintaining runways), individuals would readily leave the burrow.

Given the widespread range of this species and the prevalence of predation upon small mammals, particularly rodents, A. niloticus may be preyed upon by a number of carnivorous African animals. It was the primary prey of barn owls, in the Nigerian savanna and accounted for 26.5% of the biomass of these barn owls' diet in one study. Direct predation on A. niloticus by dwarf mongooses, black-backed jackals, spitting cobras, long-crested hawk-eagles, black-shouldered kites, and black-headed herons has been observed in the field.

Known Predators:

• Barn owl
• Dwarf mongoose
• Spitting cobra
• Black-backed jackal
• Long-crested hawk-eagle
• Black-shouldered kite
• Black-headed herons

Arvicanthis niloticus is capable of perceiving touch and scent at birth, and hearing and sight both develop around 6 to 7 days of age. Communication in A. niloticus has not been adequately studied. However, squeaks and distress calls have been observed to begin between 4 and 6 days of age, and vocalization may be involved in its communicative repertoire. Olfaction is a common form of communication in many mammals, including rodents, and may also be utilized by this species. Because these animals are social and diurnal, both visual and tactile communiation likely take place, although details of these forms of communication are not available in current literature.

Communication Channels: visual ; tactile ; acoustic ; chemical

Perception Channels: visual ; acoustic

Active by day and night. Aggressive and difficult to capture .Digs a long, sinuous, rather shal­low burrow, complex with many entrances. Shorter burrows used for temporary shelter. Openings not plugged. Generally solitary or in pairs, though larger groups may congregate in burrows. Diet mainly grain, but also takes fruit, bark, etc. Predators include the Egyptian Mongoose Herpestes ichneumon, Swamp Cat Felis chaus, probably the Red Fox Vulpes vulpes, birds of prey, and snakes. Decimation of these predators thought to be responsible for its cur­rent large numbers. Gestation period about 20 days. Main breeding period thought to be June to November but may breed at other times. Litter size 5-6, possibly up to 10, and there may be up to 4 litters per year.

Refinetti (2004) reports an average longevity of 2 years in captivity, with a standard deviation of 1 year for A. niloticus. Nowak (1999) claims that the longest lived individual of this species in captivity died at the age of 6 years and 8 months. Little is known about longevity in the wild; however, Packer (1983) estimates that females in one colony lived for an average of 10.2 months, with a maximum of 20 months.

Range lifespan

Status: wild: 20 (high) months.

Average lifespan

Status: wild: 10.2 months.

Range lifespan

Status: captivity: 6.6 (high) years.

Average lifespan

Status: captivity: 2 years.

Average lifespan

Status: wild: 10.2 months.

Average lifespan

Status: captivity: 2 years.

Average lifespan

Status: captivity: 6.7 years.

Maximum longevity: 6.7 years (captivity)

Relatively little is known about the mating structure of this species. Packer (1983) studied one colony in Tanzania and reported that the colony averaged 2.6 females and 3.1 males. Only males immigrated into the colony; new females were born in the colony and presumed not to disperse. All females successfully reproduced, and all males had descended testes, indicating the capability of breeding. Therefore, it is most likely that multiple members of an A. niloticus colony are breeding simultaneously.

Senzota (1990) studied two study sites with multiple A. niloticus colonies and indicated that colonies were mainly equally composed of males and females, with females more often outnumbering males than vice-versa. All-female and all-male colonies were also observed, but Senzota found that males were more likely to disperse than females, confirming Packer's findings.

Arvicanthis niloticus is capable of breeding year-round under highly favorable conditions. However, it usually experiences a sexual rest period beginning in March. This is during the hot dry season prior to the rainy season, and the rest period is induced at this time by long days, dry air, and high temperatures, which have an inhibitory effect on the gonads.

During the breeding season, gestation may take 18 to 25 days, averaging 23 days. Females have two equipotential ovaries and a duplex uterus. Birth weights of pups range from 3 g to 6 g, and litter sizes range from a few to 12 pups, averaging around 5 pups. Females experience a post-partum estrus and thus may be consistently pregnant and lactating, giving birth every 23 to 25 days, during the breeding season (October to March).

Young are weaned at the age of about three weeks and are considered sexually mature at 3 to 4 months. Males were observed to disperse from their natal colonies around 9 to 11 months of age.

Breeding interval: African grass rats breed every 23 to 25 days during the cold dry season in restricted habitats.

Breeding season: Mating occurs throughout the cold dry season (October to March) in restricted habitats and may occur year-round in highly suitable environments.

Range number of offspring: 4 to 12.

Average number of offspring: 5.

Range gestation period: 18 to 25 days.

Average gestation period: 23 days.

Average weaning age: 21 days.

Range time to independence: 1 to 4 months.

Average age at sexual or reproductive maturity (female): 4 months.

Average age at sexual or reproductive maturity (male): 4 months.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); fertilization ; viviparous ; post-partum estrous

Average birth mass: 4.15 g.

Average number of offspring: 5.

Average age at sexual or reproductive maturity (male)

Sex: male: 45 days.

Average age at sexual or reproductive maturity (female)

Sex: female: 45 days.

Comprehensive examination of parental care in this species is lacking. However, mothers have been observed to defend their young prior to weaning. Lactation lasts about 21 days, and it is most likely, given preliminary data, that females rarely disperse from their natal nest, whereas males often disperse. Thus, parental care beyond lactation may occur. However, Senzota (1990) noted that wild A. niloticus did not defend their sub-adult offspring in the presence of predators but instead retreated immediately to their burrows.

Male parental care is not well-documented. Males may be kept in captivity with their mates and offspring throughout lactation but have occasionally been observed to commit infanticide, which is not uncommon in captive rodents. However, given the communal social structure of A. niloticus, it is likely that males are at the least indifferent to and at most actively parenting their offspring.

Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); post-independence association with parents

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Species: 3
Species With Barcodes: 1

This species does not appear to be in any danger. The IUCN red list does not have a data entry for A. niloticus; however, it does list its congener, Arvicanthis blicki as near-threatened. The US Federal list and CITES have no information on A. niloticus.

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: least concern

Native, resident.

Least Concern.

Common.

Population

Population Trend

Major Threats

Conservation Actions

Arvicanthis niloticus is considered an agricultural pest throughout much of Africa, and active pest management programs are currently in effect. Also, this species has been implicated in the transmission of multiple human and crop diseases, including bubonic plague in Egypt, intestinal schistosomiasis, and Rice yellow mottle virus.

Negative Impacts: injures humans (causes disease in humans , carries human disease); crop pest

Given its rapid breeding capabilities, diurnal activity patterns, and small size, A. niloticus has value in laboratory research in medicine, physiology, behavior, and other related fields. Most rodent-based research in these disciplines utilizes either Norway rats, or house mice. However, both of these species are nocturnal, and captive A. niloticus colonies have been validated as diurnal and are thus more similar in certain respects to humans and other diurnal mammals than typical lab rats or mice.

Positive Impacts: research and education