Mammalogy Department
 
 

Introduction

Otymus sloggetti
Ice Rat Otomys sloggetti | © W. Lubbe

The aims of this Department are:

  • To collect, study, monitor and preserve the mammals of the central interior of South Africa and Lesotho
  • To make collection material available for further research
  • To educate and to promote an awareness of our field of study and conservation in the general public

Small mammals

Few people know that approximately two thirds of all mammals (i.e. 66% - not the number of individuals, but the number of species!) are of the other kind. The kind that we often overlook when travelling, sight-seeing, hunting, taking wildlife photographs...the kind that we disregard when planning game reserves/ranches, or calculating stocking rates... small mammals!

Small mammals have been identified as valuable indicators of the health of grasslands. They react rapidly to habitat change, have small home ranges, are reasonably easy to catch, handle and study, and we already have a fair understanding of their general biology. Good quality habitat contains a high diversity of small mammals, while in disturbed or damaged habitat certain species dominate.

Visitors to our Departmental mammal reference collection are amazed to see how many different kinds of mice there are ... even more so when told of the densities of these creatures in their habitats. The four-striped mouse, for example, may occur at densities of > 200/ha (compared to 1 Large Stock Unit/8 ha), whilst sharing their environment with five other mouse species!

So why don’t we see them?

Indigenous species are independent of man and, unlike the exotic and commensal house mouse and house rat, very few of them are found close to human dwellings; a fair percentage of these species are solitary. Most of the mice and shrews spend almost 100% of their time in dense vegetation and are regarded as secretive. Furthermore, three species spend 99.9% of their lives underground, while two species spend most of their time in disused termitaria. Approximately 49 mammal species (60% of small mammals) are nocturnal or predominantly nocturnal. Taking all these factors into account, it is therefore not surprising that our indigenous mammal fauna appears more than 50% “poorer” to the average citizen.

Today we know that these small mammals are excellent indicators of ecosystem integrity (the health of the ecosystem). The following factors can give an indication of ecosystem integrity:

  • The presence or absence of specific indicators such as ecosystem engineers (i.e. animals that prepare the environment for other organisms to live in), or the predominance of certain species (e.g. the predominance of the multi-mammate mouse is an indication that some form of disturbance has taken place).
  • Healthy and diverse carnivore populations (this also includes smaller predators such as shrews) usually indicate that the diversity of prey species is intact.
  • Healthy specialist or top-predator populations indicate that links lower down in their food chain are intact.
  • A large variety of rodent species and a high specialist:generalist ratio indicate that the predator guild is complete.

It is, however, the combination of the above that sketches the full picture of the integrity of the ecosystem. The better the integrity, the more resilient and resistant (stable) the ecosystem – which, in itself, may ensure higher, sustainable primary productivity and thereby directly influence the stocking rates of farms, game farms and nature reserves.

Small mammals have diverse morphological adaptations to their environments. The relatively flat head of the dormouse enables it to enter even the narrowest of cracks, whilst the long, prehensile tail of the climbing mouse allows it to sit high on a grass stalk, freeing its "hands" to obtain seeds. Other small mammals use their long tails for balance when moving through treetops. The bipedal gerbil and the springhare of open areas rely on their relatively long legs to carry out fast hopping movements when escaping from predators. The long snout of the elephant shrew and the large ears of the bat-eared fox help them to locate prey, whilst the large ears of the large-eared mouse help it to evade predators. The long vibrissae and bristle-like hairs on the fore and hind feet of the common molerat may serve as feelers in their dark burrows. Does the African weasel use its striped pattern to “mimic” the appearance of the smelly polecat, or is it simply an effective camouflage similar to that used by the diurnal striped mouse, some skinks and grass snakes? What about its short legs? Do they allow this predator to effectively follow rats and mice into their burrows?

Did you know that one adult multi-mammate mouse (and her daughters) may potentially produce > 1 000 offspring in a 9-month breeding season, compared to the approximately 200 offspring of most other species? This mouse has 12 pairs of mammae and can raise more than 20 young at a time, compared to an average of six young in the similar-sized striped mouse. It also has a shorter gestation period and has its first litter at a younger age; as a result, this species is able to quickly recolonise an area after natural or anthropogenic disturbances, temporarily dominating the small mammal fauna.

Furthermore, did you know that the total weight of mice in a 1 ha area of grassland may amount to 5 kg (compared to the approximately 50 kg/ha of large stock); taking into account their relatively high metabolism, mice may be responsible for > 15% of the vegetation consumed by all mammals. Luckily (for us) mouse numbers drop dramatically (probably up to 60%) between the end of autumn and the end of winter. This drop is mainly caused by a shortage of food and social stress. Population numbers start to increase again with the appearance of new shoots after winter and reach peak densities at the end of autumn.

Traditional healers, for example, believe that if one buries a shrew near someone’s house, that person will be cursed. It is also believed that if you sprinkle the powder of a fruit bat over a jealous wife’s food, she will develop tunnel vision (or will be cured of her problem!).

Otomys sloggetti, the “ice rat”, is endemic to the high Maluti and Drakensberg mountains and is well adapted to the very cold conditions experienced in those open environments. Physically its relatively round body shape, short limbs and tail maximize the retention of heat. Like the other Otomys rats the body is covered in a thick blanket of hair and behaviourally it is strictly diurnal - its sun basking behaviour has led to its Sesotho name "Tadi ya maqwa" (≈ “the little old man of the snow”).

The Greater canerat, Thryonomys swinderianus, is bred and sold as a valuable protein source over its entire distribution area in Africa. It is also known as an agricultural pest in the sugar cane plantations of KwaZulu-Natal. Since the mid 1980s this mammal has infiltrated the Free State Province from the east (first Museum record – 1985, Reitz district), and was recently found on a farm c. 20 km west of Bultfontein; a westward increase in distribution range of 300 km in 18 years! Of great concern is that we do not know anything about the density, reproduction, social behaviour, etc. of this exotic mammal in our Free State ecosystems.