Nesoryzomys swarthi 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Mammalia Rodentia Cricetidae

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

Assessment Information [top]

Red List Category & Criteria: Vulnerable D2 ver 3.1
Year Published: 2018
Date Assessed: 2017-01-15
Assessor(s): Dowler, R. & Weksler, M.
Reviewer(s): Amori, G.
Contributor(s): Tirira, D.G. & Boada, C.
This species is assessed as Vulnerable under criterion D2 because it has a very restricted population which is potentially threatened by the possible introduction of exotic species (rats, mice, and cats) to the island. The species has an extent of occurrence (EOO) of approximately 636 km², an area of occupancy (AOO) 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 rodent 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.
Previously published Red List assessments:

Geographic Range [top]

Range Description:This species is endemic to Galápagos Islands, where it occurs on Santiago (= San Salvador, James) Island (Dowler et al. 2000, Patton and Emmons 2015).
Countries occurrence:
Ecuador (Galápagos)
Additional data:
Number of Locations:1
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:This rat is locally common (Dowler et al. 2000). This species is restricted to James Bay, Sullivan Bay and La Bomba. (Patton and Emmons 2015). 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 threatened status of this species. No other populations of Nesoryzomys swarthi were found while searching for potential sites on western Santiago (Charles Darwin Research Station 2005).
Current Population Trend:Unknown
Additional data:
Population severely fragmented:No

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 is restricted to occurring in mature cactus thorn-scrub dominated by endemic cactus (Opuntia galapageia), which indicates a relationship exists between this plant and the presence and survival of the rice rat Nesoryzomys swarthi (Charles Darwin Research Station 2005, Patton and Emmons 2015).

Threats [top]

Major Threat(s): This species is potentially threatened by non-native rodents introduced to Santiago Island, including Rattus rattus and Mus musculus. It also has a highly restricted occurrence (Patton and Emmons 2015).

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).

Citation: Dowler, R. & Weksler, M. 2018. Nesoryzomys swarthi. The IUCN Red List of Threatened Species 2018: e.T14709A22390617. . Downloaded on 19 September 2018.
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