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Nesoryzomys swarthi

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA MAMMALIA RODENTIA CRICETIDAE

Scientific Name: Nesoryzomys swarthi
Species Authority: Orr, 1938
Common Name(s):
English Santiago Galapagos Mouse

Assessment Information [top]

Red List Category & Criteria: Vulnerable D2 ver 3.1
Year Published: 2008
Date Assessed: 2008-06-30
Assessor(s): Tirira, D., Dowler, R., Boada, C. & Weksler, M.
Reviewer(s): Amori, G. (Small Nonvolant Mammal Red List Authority) & Schipper, J. (Global Mammal Assessment Team)
Justification:
This species is listed as Vulnerable due to a very small or restricted population which is currently threatened by the possible introduction of exotic species (rats, mice, and cats) to the island. The species has an extent of occurrence of approximately 580 km², an area of occupancy that is likely less than 20 km², and is found in just one location (Santiago Island). Efforts are needed to monitor this species and eradicate invasive species. This species was first collected on the island of Santiago in 1906, but remained undescribed until 1938. When described, it was suggested that the species might be extinct as no further collections had been made. However, the discovery of a skull in 1965 which was attributed to this species lead to speculation that a population still existed. Subsequent surveys in the 1970s and later field surveys by personnel of the Galápagos National Park only found the introduced species Rattus rattus and Mus musculus. Field work by Robert Dowler and his team in 1997 at two sites on the island resulted in the rediscovery of the species when 74 individuals were trapped over two nights at one of the sites. From this limited information it is difficult to know the full-size and extent of the population. But from all accounts it is highly restricted and so merits a Vulnerable listing pending further fieldwork. It is interesting that the species has persisted despite the introduction of aggressive invasive species.
History:
2000 Vulnerable
1996 Extinct

Geographic Range [top]

Range Description: This species is endemic to Galápagos Islands. It occurs on Santiago (= San Salvador, James) Island (Dowler et al., 2000).
Countries:
Native:
Ecuador (Galápagos)
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: This rat is locally common (Dowler et al., 2000). Two new populations were discovered on the northern coast of the Island during a monitoring expedition in March 2005, population densities at these sites are low, but they represent a significant increase in the known population of the species. This range extension does not alter the highly endangered status of this species. No other populations of N. swarthi were found while searching for potential sites on western Santiago (Charles Darwin Research Station, 2005).
Population Trend: Unknown

Habitat and Ecology [top]

Habitat and Ecology: This species is poorly known. It is terrestrial and nocturnal. There is no information about its diet. This species co-occurs with black rats (Rattus rattus) and domestic mice (Mus musculus). It has been captured in lowland areas (Dowler et al., 2000). This endemic rice rat occurs in dry forest and shrubs areas with a large quantity of the endemic cactus (Opuntia galapageia), which indicates a relationship exists between this plant and the presence and survival of the rice rat N. swarthi (Charles Darwin Research Station, 2005).
Systems: Terrestrial

Threats [top]

Major Threat(s): This species is threatened by non-native rodents introduced to Santiago Island, including Rattus rattus and Mus musculus.

Conservation Actions [top]

Conservation Actions: To preserve this species it is to important develop an eradication or control program of the introduced species (Rattus rattus and Mus musculus).

Bibliography [top]

Musser, G. G. and Carleton, M. D. 2005. Superfamily Muroidea. In: D. E. Wilson and D. A. Reeder (eds), Mammal Species of the World: a geographic and taxonomic reference, pp. 894-1531. The John Hopkins University Press, Baltimore, USA.


Citation: Tirira, D., Dowler, R., Boada, C. & Weksler, M. 2008. Nesoryzomys swarthi. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 03 September 2014.
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