Galapagos rice rat (Aegialomys galapagoensis)

Synonyms: Oryzomys bauri, Oryzomys galapagoensis
GenusAegialomys (1)
SizeHead-body length: c. 15 cm (2)
Tail length: c. 12 cm (2)

The  Galapagos rice rat is classified as Vulnerable (VU) on the IUCN Red List (1).

The Galapagos rice rat (Aegialomys galapagoensis) was first described from specimens collected by Charles Darwin during his famed 1835 voyage aboard ‘The Beagle’ (1). A small, brown rodent, the Galapagos rice rat has medium-brown fur on the upperparts and lighter fur on the underparts (3). It has large, almost hairless ears, black eyes and a pointed nose. The tail, which is virtually hairless, is as long as the body length (3) (4).

Male and female Galapagos rice rats differ in appearance, with the male being heavier and longer than the female (3).

The Galapagos rice rat is found only on the island of Santa Fé in the Galápagos Archipelago, off the west coast of Ecuador (4).

A subspecies Aegialomysgalapagoensis galapagoensis was endemic to the island of San Cristóbal until its extinction sometime after 1835.

Santa Fé is an uninhabited island in the Galapagos National Park, covered with desert-type flora, including cacti, small deciduous trees and shrubs. The Galapagos rice rat is common throughout the island (3) (4).

Like many rodents, the Galapagos rice rat is most active after dark (6). After dusk, this species will venture out from its burrow, which is typically situated in the hollow trunk of a cactus or beneath a rock (7). It feeds on a variety of plants, particularly grass seeds, as well as small invertebrates (6).

There is little information available regarding breeding in the Galapagos rice rat. The breeding season is thought to begin after the arrival of the warm season rains between January and May, when food is most abundant (4) (6). During the mating season, the usually nocturnal Galapagos rice rat becomes more active during daylight. Each litter contains between two and five infants, with the number of offspring thought to be dependant on the level of rainfall (4) (8).

The Galapagos hawk (Buteo galapagoensis) and the short-eared owl (Asio flammeus), both frequently prey on the Galapagos rice rat (4).

The Galapagos rice rat is thriving on Santa Fé Island, one of the few islands in the Galapagos which is currently free of any introduced rats or mice (5) (9).

However, the introduction of invasive predators or competitor species to Santa Fé is a constant threat, and should this happen, the Galapagos rice rat could rapidly become extinct (1) (9).

The extinction of the Galapagos rice rat from San Cristobal Island is thought to be due to introduced rodent species, such as the back rat (Rattus rattus) and Norway rat (Rattus norvegicus) (1) (5), and acts as a stark warning to the remaining rice rat population on Santa Fé.

Although the Galapagos rice rat is currently not the focus of any conservation measures,  the Galapagos Islands are internationally recognised as a site of incredible, unique biodiversity (10) (11). As a result, the Galapagos Islands receive much conservation attention, from which the Galapagos rice rat will naturally benefit.

It has been recommended that three strategies are implemented to ensure that the Galapagos rice rat on Santa Fé does not have the same fate as the population on San Cristobal. Firstly, the island should be regularly monitored for introduced rodents and other invasive mammals. Secondly, a rapid and effective emergency plan must be developed to eradicate exotic species in the case of an introduction. Finally, efforts should be made to establish captive populations as a safeguard to extinction (9).

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  1. IUCN Red List (November, 2010)
  2. Eisenberg, J.F. and Redford, K.H. (1999) Mammals of the Neotropics. Volume 3: The Central Neotropics. The University of Chicago Press, Chicago.
  3. Swash, A. and Still, R. (2000) Birds, Mammals, and Reptiles of the Galápagos Islands. Yale University Press, United States
  4. Clark, D. (1980) Population ecology of an endemic neotropical island rodent: Pryzomys bauri of Santa Fe Island, Galapagos, Ecuador. The Journal of Animal Ecology, 49(1): 185-198.
  5. Nowak, R.M. (1999) Walker’s Mammals of the World. The Johns Hopkins University Press, Baltimore, Maryland.
  6. Steadman, D.W. and Zousman, S. (1988) Galápagos: Discovery on Darwin's Islands. Smithsonian Institution Press, Washington, DC.
  7. Burton, M. and Burton, R. (2002) International Wildlife Encyclopedia. Marshall Cavendish, New York.
  8. Brosset, A. (1963) Satut actuel des mammifères des îles Galapagos. Mammalia, 27: 323-341.
  9. Dowler, R., Carroll, D. and Edwards, C. (2000) Rediscovery of rodents (Genus Nesoryzomys) considered extinct in the Galápagos Islands. Oryx, 34(2): 109-117.
  10. Galapagos Conservation Trust (May, 2011)
  11. Galapagos Conservancy (May, 2011)