It is one of the most remarkable resurrection stories in Mexican mammology. Nelson's Small-eared Shrew was described in 1894 from a single specimen from San Martín volcano, Veracruz. It was not recorded again for over a hundred years, until field expeditions rediscovered it in 2004 on that same mountain.
It lives exclusively in the cloud forest covering the slopes of that isolated volcano, with no other population known anywhere else in the world, making it one of the most range-restricted shrews on the entire continent. Its rediscovery did not eliminate the risk it faces: it remains considered one of the hundred most threatened species on the planet according to various conservation priority assessments. All its known biology comes from a handful of specimens captured during very specific expeditions, making it one of the least documented Mexican shrews despite its fame.
Nelson's Small-eared Shrew is a small-medium sized shrew with uniform dark brown fur, a long, mobile snout, and tiny, barely visible eyes. In hand, it can be confused with other broad-clawed shrews from eastern Mexico. Its exclusive presence on San Martín volcano, with no geographical overlap with sister species, is the most reliable key for field identification.
Tiny track, barely 1 cm, rarely visible except on very fine substrate. Tiny, dark droppings, a few millimetres long, containing insect chitin remains, left scattered along paths under the damp leaf litter of cloud forest. Nelson's Small-eared Shrew builds shallow tunnels under the leaf litter and spherical nests in hollows under fallen logs, typical of the damp undergrowth where it lives. However, given the species' rarity, these tracks and signs are rarely attributed with certainty without direct capture.
Mountain cloud forest, with humid soil and abundant leaf litter, on the slopes of San Martín volcano. Endemic to this single mountain in the Los Tuxtlas region, Veracruz state, eastern Mexico, with no known presence anywhere else.
Insectivorous, it feeds on insects and other invertebrates from the damp soil of the cloud forest.
Its habits are poorly documented due to the scarcity of field records. Its activity is probably continuous, divided into short periods throughout the day and night, like other shrews of its genus. Its extreme restriction to a single mountain makes it extremely vulnerable to any local alteration of the cloud forest.
After more than a century without records, its rediscovery in 2004 confirmed that a population of Nelson's Small-eared Shrew survives on San Martín volcano. However, its current population trend is unknown due to a lack of ongoing studies on the species.
Deforestation and fragmentation of the San Martín volcano cloud forest, driven by agricultural and livestock expansion, are significant threats. Nelson's Small-eared Shrew's extreme geographical restriction to a single mountain makes it vulnerable to any adverse local event.
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