Delany's swamp mouse (Delanymys brooksi)

Also known as: Delany's mouse
GenusDelanymys (1)
SizeHead-body length: 5 - 6 cm (2)
Tail length: 8 - 11 cm (2)
Weight5.2 - 6.5 g (2)
Top facts

Delany's swamp mouse is classified as Vulnerable (VU) on the IUCN Red List (1).

The only member of its genus, Delany’s swamp mouse (Delanymys brooksi) is the smallest member of the Nesomyidae family, and one of the smallest rodents in the world (3) (4) (5).

Delany’s swamp mouse is a very small climbing mouse with an extremely long tail and characteristically long hind feet (3). The pelage of this species is long and is typically slate-grey at the base of the hairs, and brown with a reddish-orange tinge towards the tips. The underside of Delany’s swamp mouse is pale yellow-brown to buff (2).

This species has long black guard hairs, which give it a darker colouration (3). The eyes of Delany’s swamp mouse are surrounded by short black hairs and there is a black patch on the nose, while a distinctive patch of pure white hairs is present on the throat (2).

Delany’s swamp mouse has large, round ears and its tail is longer than the combined head-and-body length. The tail is thin, almost hairless, and has scales forming ring-like patterns along its length (2) (3). The male Delany’s swamp mouse is slightly smaller than the female, and the young have brighter, hazel-coloured fur (3).

Delany’s swamp mouse is native to the Albertine Rift Valley in southwest Uganda, western Rwanda, Burundi and the extreme eastern Democratic Republic of the Congo (1).

Delany’s swamp mouse is largely confined to high-altitude marshes within bamboo or montane forests, at elevations of 1,700 to 2,400 metres or higher (1). A few individuals have been found in non-marshy habitats, such as dense, grassy vegetation (3).

The nocturnal Delany’s swamp mouse is extremely well adapted for climbing on grass and plant stems. Its feet are highly specialised, with long, spreading digits and numerous small, prominent tubercles on the palms and fingers which enable grasping and prevent slipping. The long, prehensile tail of Delany’s swamp mouse is used to provide balance and can even be curled around stems for additional support (1) (3).  Seeds make up the majority of this small rodent's diet (2) (4).

Little is known about the reproductive behaviour of Delany’s swamp mouse, although two pregnant females have been recorded with three embryos each, and one nest with four blind young has been found. This species constructs a small, round grass nest with two entrances, usually off the ground in a bush or other such vegetation (2).

The small geographic range and fragmented distribution of Delany’s swamp mouse make it very vulnerable to continuing decline. Habitat destruction, largely due to agriculture and the high human population density of the region, is one of the greatest reasons for this species’ decreasing population size (1).

No specific measures are currently in place to conserve Delany’s swamp mouse, despite it being the only surviving member of its subfamily, Delanymyinae (4). Much of its highland habitat is in the Kahuzi-Biega National Park in the Democratic Republic of the Congo. However, the lowlands remain severely threatened (1).

The population numbers of Delany’s swamp mouse need to be researched and monitored. Studies into the range, biology, ecology, habitat status and threats to this species are also needed in order to inform any future potential conservation measures (1).

Find out more about Kahuzi-Biega National Park:

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  1. IUCN Red List (November, 2011)
  2. Nowak, R.M. (1999) Walker's Mammals of the World. The Johns Hopkins University Press, Baltimore.
  3. Dieterlen, F. (2010) Pers. comm.
  4. Vaughan, T.A., Ryan, J.M. and Czaplewski, N.J. (2011) Mammology. James and Bartlett Publishers, LLC, Sudbury.
  5. Britannica Educational Publishing (2011) Rats, Bats, and Xenarthrans. Britannica Educational Publishing, New York.