Science and conservation for the world’s 2800 small mammal species

Small Mammal FAQs

– Are all small mammals small?

As the name of this IUCN Specialist Group suggests, the great majority of species in the three groups of “small mammals” are small-bodied in comparison to most other mammals. The mean body size of all rodent, insectivore and tree-shrew species is less than 1 kg, and some species are truly tiny – the world’s smallest mammal, the Etruscan pygmy shrew (Suncus etruscus), weighs on average only 1.8 grams. However, some so-called “small mammals” are actually relatively large. The world’s largest rodent, the capybara (Hydrochoerus hydrochoeris), can weigh more than 50 kg, and several other rodents (such as porcupines, pacas and pacaranas) can also reach over 10 kg. Conversely, many other mammal species – such as bats, lagomorphs, tenrecs, small marsupials and even many carnivores – can also weigh far less than 1 kg.


– What’s so special about small mammals?

Despite their generally small body size, small mammals – rodents, insectivores and tree-shrews – display an otherwise incredible diversity of successful adaptations and modes of life. From the fishing mice of South America and the river-dwelling desmans of the Pyrenees and southern Russia, to the venom-injecting solenodons of the Caribbean and the eusocial naked mole rats of Africa, these species showcase the many different ways that mammals can make a living in almost any terrestrial ecosystem.


– What’s the most incredible small mammal species?

The diverse range of small mammals contains many poorly-known species with unusual, memorable, or simply endearing names. For example, have you ever heard of the moon-toothed degu, the fire-footed rope squirrel, the crafty vesper mouse, the beautiful squirrel, the monster rice rat, Dickie’s deer mouse, the pleasant gerbil, or the tuco-tuco of the dunes? And many other species have truly remarkable adaptations to match. Possibly the greatest small mammal “superhero” is the aptly-named hero shrew (Scutisorex somereni) of tropical Africa. This innocuous-looking species has evolved an incredibly strong backbone supported by elaborate interlocking spines and projections, which accounts for 4% of the shrew’s total body weight. This unique anatomy allows the shrew to withstand being trodden on by a fully-grown human – but the evolutionary reason for developing such a strengthened backbone remains unknown.


– Why are so many small mammals threatened with extinction?

Some small mammal species – notably black, brown and Pacific rats, house mice, and musk shrews – have become adapted to living alongside humans and exploiting the opportunities that we provide for food and shelter. However, the great majority of small mammals are less ecologically flexible, and are instead dependent upon the existence of intact natural environments for their survival. As human-caused habitat destruction continues to escalate at a global scale, the habitats that small mammal species depend upon have become increasingly threatened. In addition, many small mammal species are also threatened by invasive species – such as foxes and cats in Australia, and American mink in the UK – as well as by the effects of climate change and overexploitation for human use.


– Have humans already caused the extinction of any small mammal species?

Unfortunately several small mammal species have already died out in recent centuries as a direct result of human impacts. The Caribbean Islands experienced a major small mammal extinction event following the arrival of Europeans and their associated invasive mammals (rats, cats, dogs and mongoose), which led to the disappearance of several species of solenodons and hutias (large-bodied rodents), and wiped out the entire family of endemic nesophontid island-shrews. More recently, the introduction of cats, foxes and other invasive species to Australia led to widespread extinctions in the endemic rodent fauna. Today further extinctions of small mammal species, such as the Brasilia burrowing mouse (Juscelinomys candango), are also being documented from larger continental regions as a result of habitat loss.