Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"
This week's article is a short one, about a short critter. This is a Fat Mouse, Steatomys pratensis. Many people are impressed by the big and spectacular animals of Africa, but few are aware how many fascinating and charming small ones there are. Of Africa's small mammals, the fat mouse is one of my favourites. This little mouse has a head and body length of about 9 cm/3.6" and a tail just half that long. It typically only weighs about 29 g/1 oz. even as fat as it is. Its fatness is indeed a natural, adaptive feature of it. When food is plentiful, it eats enough to put on a thick layer of subcutaneous fat. When there's no food, it spends its time in its burrow, sometimes in a hibernation-like torpor which can last for three weeks. Feast and famine is indeed a feature of its habitat. It occurs over most of sub-Saharan Africa except in dense rainforests and barren deserts. These regions are mostly covered by savannah woodlands and grasslands. Here the climate is variable, with the rain falling plentifully in summer, fuelling plant growth, but with drought lasting through all of autumn, winter and much of spring. The more weight the fat mouse can put on during the rainy season, the more easily it can endure the long dry season. These mice can get very fat indeed, looking like round little fuzzballs. But at the end of the dry season, most of the fat has been used up, and they are then sleek looking, much like other mice. Their weights can therefore vary wildly; female fat mice have the largest range, from 10 g/0.4 oz to 44 g/1.6 oz.
Apart from their plump roundness, fat mice can be recognized by their bright fur colour. Most mice are a dull brown or grey, but fat mice have light to dark rusty-brown upperparts and white bellies, throats and feet. Their fur is soft and shiny. They have large, round ears and comparatively short tails. They're somewhat hamster-like in appearance in spite of not being close relatives of them. They are similar in shape to another kind of African mouse, the Pouched Mouse, but this one has a greyish body colour. They lack the cheek pouches for which the pouched mouse is named.
There are six different fat mouse species in Africa. This one is the most widespread; one species in west Africa has a small range and can be considered vulnerable, but the others all are widely distributed as well. The fat mouse occurs rather patchily over its vast range. It is fairly indifferent to vegetation, but needs soil that is sandy, but still firm. This is so that they can excavate their deep burrows in it. They are frequently found in the dry terrain right beside rivers or swamps, or in patches of sand washed by rivers down into valley bottoms. They are also found in farmland where there is loose, ploughed soil. They need lush vegetation and plentiful food. They eat mostly seeds, bulbs, roots and grass, but will also catch and eat insects. They will store food inside their burrows, but it doesn't keep fresh long enough to last the entire dry season, hence the fat accumulation and periods of torpor. During the torpor, their metabolism slows down very much, and their body temperature drops to within a degree or two of the surrounding air temperature. They line their resting chambers at the bottoms of their burrows with dry leaves to help them preserve at least some of their body heat. A mouse taken from its burrow while in torpor, will take a long time to 'wake up' and become active.
Fat mice are rather lazy and slow. This makes them easy prey. They avoid most predators by being active at night. These mice live singly or as couples. They breed during the summer, the average number of babies per litter being three. They are not particularly plentiful compared to other mouse species, but they are not endangered either. Apart from the many mammals, birds and snakes that prey on them, they are also regarded as delicious snacks by some human communities in their range.