Nelson’s Small Eared Shrew
(Cryptotis nelsoni)
This medium-sized shrew is thought to be endemic to the forested slopes of a small volcano in southern Mexico. It was discovered in 1894, but not seen again for more than a century, leading researchers to fear it had gone extinct. However, in 2003, two researchers set out to search for the species in the same region from which it was first discovered. Their expedition met with success, and they found three individuals in the vicinity of the type locality. Although good news for the species, the researchers discovered that the species’ tiny range is under pressure from human activities, including logging, cattle grazing, induced fires and agriculture. Urgent conservation action is needed if this Critically Endangered shrew is to survive.
Urgent Conservation Actions
Research is needed into the current population status of this species in order to develop a conservation action plan.
The volcano upon which the tiny shrews live erupted in 1793, destroying all the vegetation around the crater. Despite this eruption, the shrew managed to survive.
Evolutionary Distinctiveness
Order: Soricomorpha
Family: Soricidae
Shrews are a highly successful group of insectivores, comprising the third most speciose mammal family (Soricidae). They occur throughout most of the world, with the exception of Australasia and much of South America. They are often portrayed as “primitive” animals; indeed, the earliest mammals are often portrayed as shrew-like. However, soricids are a relatively modern group. The earliest shrew fossils have been found in North America from the middle Eocene (45 million years ago). They are known from Asia and Europe from the early Oligocene (34 million years ago), and in Africa from the middle Miocene (14 million years ago). The Soricidae is divided into three sub-families: the Crocidurinae (white-toothed shrews), the Myosoricinae (African white-toothed shrews) and the Soricinae (red-toothed shrews). Red-toothed shrews are so-called because their teeth have a reddish appearance because of a deposition of iron in the outer layer of enamel, which may increase resistance to wear.

The genus Cryptotis (small-eared shrews) belongs to the Soricinae.
Head and body length: 55-100 mm (for Cryptotis)
This small to medium-sized shrew has sooty brown fur that is darker than that of the related C. mexicana.   It has a pointed snout, minute eyes and small, inconspicuous ears. The skull is larger and heavier than that of C. mexicana, with a larger, flatter braincase.
Very little is known about the ecology of this species – it had remained undected for so long that it was widely presumed extinct. In general, shrews have a high metabolic rate and consequently a voracious appetite. They must eat very frequently, and so are active throughout the day and night. Nelson’s small-eared shrew is believed to feed exclusively on insects.
Occurs in evergreen tropical forest comprising large trees and areas covered by layers of volcanic sand and ashes. The vegetation on the slopes of the volcano changes within the species’ range from dense primary forest on the lower slopes to montane grassland above 1,525 m. The 2003 specimens were taken from cloud forest.
Until recently this species was known only from the western slope of the extinct San Martín Tuxtla volcano in Veracruz, Mexico. It has been recorded from 1,463 m up to the summit of the volcano at 1,650 m asl.

In 2003, 109 years after it was last seen, three of these tiny shrews were found near the type locality: ton he south face of the volcano and just to the north west of the nearby Catemaco Lake. The shrew may occur in suitable habitats throughout the Sierra de Santa Martha.  However, recent surveys in the region have not recorded its presence, leading researchers to belive it is endemic to the small area arounf the volcano.
Population Estimate
Population Trend
Classified as Critically Endangered (CR B1ab(i,ii,iii)) on the 2009 IUCN Red List of Threatened Species.
The species occurs in an extremely small area which is completely surrounded by a high density of human settlements. Its habitat is gradually changing or disappearing as a result of logging, cattle grazing, induced fires and agriculture, which are occurring within the Los Tuxtlas Biosphere Reserve. Deforestation is as much as 90% in the area of the type locality, and the annual deforestation rate is 6.2%.
Conservation Underway
The entire range of this species falls within the Los Tuxtlas Biosphere Reserve and Los Tuxtlas Biological Station.
Conservation Proposed
Further research is urgently needed to determine the current distribution and population status of this species. A Species Conservation Strategy is needed to ensure steps are taken to protect and restore the species’ habitat. This should be developed alongside and agree with the management plan of the Biosphere Reserve.
Cervantes, F. A. and Guevara, L. S. 2010. Rediscovery of the critically endangered Nelson’s small-eared shrew (Cryptotis nelsoni), endemic to Volcán San Martín, Eastern México. Mammalian Biology - Zeitschrift fur Saugetierkunde 75(5): 452-454..

Woodman, N. 1999. Geographic Variation and Evolutionary Relationships Among Broad-Clawed Shrews of the Cryptotis goldmani-Group (Mammalia: Insectivora: Soricidae). Zoology NEW SERIES, NO. 91.

Woodman, N., Matson, J., Cuarón, A.D. & de Grammont, P.C. 2008. Cryptotis nelsoni. In: IUCN 2009. IUCN Red List of Threatened Species. Version 2009.2. <www.iucnredlist.org>. Downloaded on 18 January 2010.

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