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An adult male Nelson's small-eared shrew, alive and well
A tiny species of shrew has been rediscovered in the wild, more than a century after first being described.
In 1894, a handful of specimens of the Nelson's small-eared shrew were collected in southern Mexico.
But the shrew was never seen again, and was considered by many experts to already be extinct.
That was until two researchers found three shrews in a small patch of forest, a find that is reported in the journal Mammalian Biology.
The Nelson's small-eared shrew (Cryptotis nelsoni) is named after the man who first discovered it.
In 1894, Edward Nelson and Edward Goldman collected 12 specimens some 4,800 feet up the slopes of the San Martín Tuxtla volcano in Veracruz, Mexico.
A year later, the creature was formally described for science, and the specimens were stored away in the drawers of the National Museum of Natural History in Washington DC, US.
That was the last time the shrew was seen alive for 109 years.
The biology of the shrew has remained a mystery. It was even believed to have become extinct because it had gone unrecorded so so long.
That changed when two mammalogists based in Mexico decided to look for it.
Fernando Cervantes of the National Autonomous University of Mexico teamed up with Lazaro Guevara of the University of Veracruz in Mexico.
In 2004, they set off for the forest slopes of the San Martín Tuxtla volcano to search for the long-lost shrew.
The skull of an adult female Nelson's small-eared shrew
Setting 100 pitfall traps a night for four nights, they eventually caught three shrews - one adult male, one juvenile male and an adult female.
Since then, the researchers have been validating their find.
"We have reviewed [all the] papers about Cryptotis. We visited several biological collections and museums," says Guevara.
"A recent study on the mammalian diversity of Sierra de Santa Martha, Veracruz, did not record the presence of C. nelsoni. Therefore, we believe that no more specimens exist."
The shrews are tiny, measuring less than 10cm from nose to tail. They have sooty brown fur, which is darker than a related shrew species C. mexicana. It also has a larger and heavier, but flatter skull than its relative.
The researchers found the animals scurrying around a patch of cloud forest, that local people know as "dwarf forest" due to its small trees.
"We know very little about its behaviour," says Guevara.
The shrew's last stronghold, in the forests of Veracruz, Mexico
He says that after 100 years or more, it was acceptable to think that the Nelson's small-eared shrew had gone extinct, especially as shrews tend to be overlooked by many scientists.
The surviving shrews are still so scarce that they must be considered critically endangered, say the researchers.
The volcano upon which they live erupted in 1793, destroying all the vegetation around the crater. Despite this eruption, the shrew managed to survive.
But so few now exist that any small change to their habitat could prove disastrous, says Guevara.
"A small habitat alteration may cause changes in the population that may lead to their extinction," he says.
Subsistence crops and livestock are reared in the region, "and any conservation plan needs to involve communities, government and schools to promote the dissemination of the importance of this species," says Guevara.
"In Mexico, the shrews are very poorly known, even by the people who coexist with these beautiful animals."
Guevara explains that, when they started their search they knew that the last record of the species was from 1894. "We thought it was very important research," he says. "We thought that was risky but high value for wildlife conservation. So, we travelled to find it. When we found it, we (were) very pleased."