- Two small mammal groups — Rodentia (like mice, beavers, squirrels) and Eulipotyphla (like shrews, moles and hedgehogs) — together contain nearly half of all known mammal species.
- A new study provides an updated picture of where all of the globally threatened species from the two groups occur.
- The study also identified regions that are home to rodents and eulipotyphlans currently classified as data deficient or DD — species whose conservation status we simply don’t know.
- The authors say they hope the study will not just get people excited about working with small mammals, but also encourage funders to invest in conservation or research projects focusing on these long-neglected but species-rich animal groups.
Think of a mammal that’s at risk of extinction. What comes to mind? A charismatic tiger, perhaps? Or a grand herd of majestic elephants? What about the Mount Lefo brush-furred mouse (Lophuromys eisentrauti), a rodent found only on Mount Lefo in Cameroon? Or the Sclater’s shrew (Sorex sclateri) that lives in Mexico?
Both the mouse and the shrew are critically endangered species. But if you haven’t heard of them, you’re not alone. Many small-bodied mammals, those typically weighing less than a kilogram (2.2 pounds), still remain poorly studied and understood, even by researchers and conservationists. This is despite the fact that two small-mammal groups — Rodentia (animals like rats, mice, beavers, porcupines, chipmunks, marmots, voles and muskrats) and Eulipotyphla (shrews, moles, hedgehogs and solenodons, among others) — together contain nearly half of all known mammal species.
Now, a new study has published an updated picture of both super-diverse mammalian groups. By mapping the distributions of rodents and eulipotyphlans, using the latest information from the IUCN Red List, researchers have identified hotspots where all of the globally threatened species from the two groups occur.
They’ve also identified regions that are home to rodents and eulipotyphlans whose conservation status is currently classified as data deficient, or DD. These are species for which we don’t have sufficient knowledge about population, distribution, or threats to their survival. In the absence of this information, we don’t know their conservation status.
“We hope that this study helps to direct people to hotspots where their actions can have the maximum impact,” said Rosalind J. Kennerley, the lead author of the study and co-chair of the IUCN’s specialist group for small mammals. “We’d like to see more people both choosing to do research on small mammals and of course taking part in active conservation efforts to conserve them.”
Being tiny has meant that many threatened rodents and eulipotyphlans are sliding toward extinction unnoticed. About 76 of the known 454 eulipotyphlan species are globally threatened. These include animals that are one of a kind, like the only two living species of the solenodon, one of the few venomous mammals on our planet. The Cuban solenodon (Atopogale cubana) is currently listed as endangered.
The study found that almost 40% of the at-risk eulipotyphlan species occur within just six regions: Cameroon, the Albertine Rift (covering parts of the Democratic Republic of Congo, Rwanda, Burundi, and Uganda), Tanzania, Ethiopia, Sri Lanka, and the Southwestern Ghats in India.
When it comes to rodents, 324 of the 2,231 known species are threatened with extinction. Nearly 34% of these threatened species are found in 10 regions, including Mexico, the Cameroon Highlands, Southwestern Ghats, Sri Lanka, Peninsular Malaysia, Sumatra, and Java.
The forests and deserts of Mexico, for instance, are home to 27 threatened species, including eight critically endangered ones, like the big pocket gopher (Orthogeomys lanius).
“We suspected that we would see these overall findings, but the number of hotspots still came as a wake-up call,” Kennerley told Mongabay in an email. “We have an enormous task on our hands to ensure small mammals are on the conservation agenda in all of these regions.”
Small mammals are, however, rarely the focus of conservation programs, the authors write. Even protected areas are seldom designed with mice, moles, shrews or other small mammals in mind.
“In general small mammals are relatively ignored if you compare them with some of the more obvious charismatic large mammals,” Kennerley said. “Megafaunas tend to be the ones where there’s more media coverage, there’s greater amounts of research, and there’s certainly more funding directed towards them. That inevitably means that when protected areas are being created and managed, it’s the larger species which people consider rather than the smaller ones.”
That’s not to say that small mammals don’t have any formal protection. Protected areas established for larger, more charismatic species do sometimes include the ranges of small mammals in the area.
“No doubt, rodents and shrews do not get the love they deserve,” Stuart Pimm, the Doris Duke professor of conservation at Duke University, who was not involved in the study, told Mongabay in an email. “But, we may be doing a good job of protecting them anyway.”
Pimm and his colleagues have previously mapped the distribution of small mammals and found that the world’s protected areas, both small and large, at least partially protect the ranges of several small mammals.
Even then, living inside a protected area doesn’t guarantee protection, especially if conservation and research efforts in the parks remain focused solely on the larger mammals, while their smaller counterparts continue to be ignored. Moreover, just because a protected area exists on paper, it doesn’t necessarily mean that that area is indeed well protected, said Kennerley: “On the ground there could be many different activities happening to damage species and habitats.”
Overall, the study found that five eulipotyphlans, such as the Sclater’s shrew, Phillips’ Congo shrew (Congosorex phillipsorum) and the Andaman spiny shrew (Crocidura hispida), and 44 rodents, such as the Elvira rat (Cremnomys elvira) and the emperor rat (Uromys imperator), have ranges that fall completely outside of any protected areas.
Clearly, small mammals are an understudied lot. But knowing which ones are threatened and where those species live can be useful to plan and kick-start conservation actions to better protect them, the authors say.
For several rodents and eulipotyphlan species, though, we have almost no information: nearly 17% of species in the two groups are currently listed as data deficient by the IUCN. That’s a higher percentage than mammals as a whole, where about 14% are listed as data deficient. Their populations could be increasing or declining. Some species may even be nearly extinct — we simply don’t know.
One big reason why small mammals are studied less is because, well, they’re small, Pimm said. “And they are often nocturnal, which makes things even worse.”
Many small mammals also live in hard-to-access landscapes. Then there’s the complexity of taxonomy, the science of describing and classifying different species. With the availability of better techniques to study taxonomy, what were once considered single species are now known to be made up of several, Kennerley said. “Whilst we are learning more about the true diversity within these, there is often still not a huge amount of information known about the newly described species, meaning that they are often listed as DD.”
According to the study, most data-deficient eulipotyphlan species occur within three regions: the Congo Basin, southern and central China, and Laos and Vietnam. On the other hand, most data-deficient rodents occur within 18 regions, including in the northern tropical Andes, Argentina, Brazil, Borneo, Sulawesi and New Guinea.
“In regions of high aggregations of DD species we want to encourage more researchers to focus on small mammals and undertake ecology studies,” Kennerley said. Knowing where these species are distributed, what their population trends look like, the kinds of habitats they prefer, and the threats they face, would be crucial to moving them out of the data deficient category, she added.
The authors say they hope the study will not just get people excited about working with small mammals, but also encourage funders to invest in conservation or research projects focusing on these long-neglected but species-rich animal groups.
“It’s great to now have this objective research to call upon, so that when we speak to potential funders, we can confidently explain why small mammals matter and be able to show proof of why certain regions or species are important to focus on,” Kennerley said.
“The diversity of small mammals is amazing, so the more people we can get enthused, the better!”
Kennerley, R. J., Lacher Jr., T. E., Hudson, M. A., Long, B., McCay, S. D., Roach, N. S., … Young, R. P. (2021). Global patterns of extinction risk and conservation needs for Rodentia and Eulipotyphla. Diversity and Distributions, 27(9), 1792-1806. doi:10.1111/ddi.13368
Pimm, S. L., Jenkins, C. N., & Li, B. V. (2018). How to protect half of earth to ensure it protects sufficient biodiversity. Science Advances, 4(8). doi:10.1126/sciadv.aat2616
Banner image of a Cuban solenodon illustration via Wikimedia Commons.