Game Ranging / Field Guiding Course. Small Mammals

Transcription

1 1 Module # 7 Component # 2 Small The term small mammals is not a taxonomic one. Small mammals are not inter-related unless viewed from a much broader sense in that they are mammals and small in size. One of the groups examined here is the Hyrax or Dassie. Oddly enough this small mammal is more closely related (taxonomically) to the elephant, than it is to any other small mammals. Small mammals are a frequently overlooked group. This is not due to any deliberate action but rather because they are seldom seen and are often difficult to find even when looking for them. This does, however, not make them any less important ecologically than the larger mammals frequently seem. In terms of biomass (see the glossary) they more than equal that of their larger counterparts and play an equal or more important part in the functioning of most given ecosystems. In terms of species diversity, as well as actual populations, small mammals as a group are far more numerous than their larger counterparts. For this reason, each subset of the small mammals can only be practically described in broad terms with no specific species accounts given.

2 2 Order: Insectivora As a group, insectivores are generally considered to be the most primitive of living placental mammals. Their primitive characteristics include: Small brain Few wrinkles to decrease surface area Primitive teeth Primitive features of the auditory bones and collar bones Plantigrade gait Generally, insectivores are small animals with narrow, mobile snouts. All of them are plantigrade and most have short limbs with five digits on each foot. The eyes and ears are relatively small. Elephant shrew Insectivores which occur in Southern Africa fall into three families: Family Soricidae (Shrews) Family Erinaceidae (Hedgehog) Family Chrysochloridae (Golden moles)

3 3 Family Soricidae: Shrews Members of this family are small, secretive mammals. They possess long, narrow and pointed muzzles They have very small eyes - their vision appears to be poor Their senses of smell and hearing are acute Both sexes possess musk glands For their size shrews, are remarkably fierce and are always ready to bite. Shrews are born with their final set of teeth which are extremely sharp. Their first set of teeth are shed or resorbed during embryonic development. Ecologically shrews are important in that they break down animal tissue and return raw materials to the soil. Typically, terrestrial, they spend most of their time foraging in and under fallen vegetation searching for insects and carrion. Some species also eat seeds, nuts and other plant material. There are 15 species of shrew in Southern Africa: Forest shrew Long tailed forest shrew Dark footed forest shrew Greater dwarf shrew Lesser dwarf shrew Least dwarf shrew Swamp musk shrew Maquassie musk shrew Reddish grey musk shrew Grey brown musk shrew Lesser red musk shrew Tiny musk shrew Peter s musk shrew Greater musk shrew Giant musk shrew Climbing shrew

4 4 Family Erinaceidae: Hedgehog Only one species occurs in Southern Africa - the South African hedgehog. The body plan of hedgehogs is regarded as primitive except for their spines and the associated muscles Their eyes and ears are well developed The snout is long, the tip is mobile They possess powerful legs with strong claws. The most distinctive feature of the hedgehog is its spines. Spines are modified hair ending in a needle-sharp point. To lighten the load each spine consists of many small chambers each filled with air. Connected to the base of each spine is a small muscle whose function it is to pull the spine erect when danger threatens. Hedgehogs are additionally protected by their ability to curl up into a ball, thereby protecting the belly, legs and head. This is achieved by having a larger skin than is necessary and a powerful muscle beneath the skin, which on contraction causes the hedgehog to curl. Hedgehogs feed on a wide variety of prey and some vegetation. The earthworm is their first choice followed by beetles, earwigs, slugs, millipedes and caterpillars. They will also scavenge on remains of any animal found dead and take eggs and young from the nests of birds. All hedgehogs are capable of undergoing periods of dormancy (hibernation). This enables them to survive periods of food scarcity by reducing energy requirement to a very low level.

5 5 Family Chrysochloridae: Golden moles Members of this family are solitary, burrowing insectivores. Golden moles spend more time burrowing in search of food than any other activity. They have short limbs with the forelimbs being equipped with strong digging claws There are no visible tails and the eyes have almost been lost The eyes and ear openings are covered with fur The nostrils are shielded by a leathery pad which protects them from soil during excavations Golden moles are highly sensitive to vibrations Most species dig elaborate burrow systems with specific chambers. Golden moles can orientate themselves. When parts of the burrow system have been destroyed, they are able to construct new tunnels to link up with the existing ones. Their food consists of earthworms, insect larvae, slugs, snails, crickets and spiders. Prey found on the surface is dragged down the burrow where it is consumed. 15 species of this family are endemic to the Southern African Sub-region, they include the: Cape golden mole Giant golden mole Rough haired golden mole Grant s golden mole Arend s golden mole Van Zyl golden mole Visagie s golden mole Duthie s golden mole De Winton s golden mole Sclater s golden mole Gunning s golden mole Juliana s golden mole Hottentot golden mole Zulu golden mole Yellow golden mole

6 6 Order: Lagomorpha This order is represented by one family - Leporidae - in Southern Africa. Family Leporidae (Rabbits and Hares) Lagomorphs were originally classified as rodents because of their gnawing incisors. But unlike rodents they possess a second pair of small, peg-like incisors behind the constantly growing pair in the upper jaw. The hind legs are long and adapted for running The ears are very large and mobile The eyes are also large and adapted to low light conditions The fur is usually long and soft and their feet are fully furred Their nostrils can be opened and closed by a fold of the skin above The lagomorphs are herbivorous and have a digestive system highly modified which can cope with large quantities of vegetation. The ceacum situated between the large and small intestines, contains bacterial flora which aids the digestion of cellulose. Many products of the digestion can pass from the ceacum directly into the blood-stream. Others such as the important vitamin B12 would be lost if it were not for the fact that lagomorphs eat some of their faeces and pass them through their gut twice. The practice of re-ingesting one s own faeces is known as coprophagy. The difference between rabbits and hares is often confused. Some have attempted to differentiate the two based on morphology, habitat and ecology. However, this is not a successful technique and quickly gets the user into trouble. There is a very clear cut way to separate the two groups. Hares bear precocial young. This means that their offspring are born fully furred with their eyes open and are capable of movement Rabbits bear altricial young. These young are born blind, naked and feeble. Rabbits also use secluded burrows for the most part and therefore these conditions are more conducive to altricial offspring. Lagomorpha that occur in Southern Africa are: Cape hare Scrub hare Natal red rock rabbit Jameson s red rock rabbit Riverine rabbit (currently one of the our most endangered species)

7 7 Order: Rodentia Due to this order being made up of a great many families, we will only cover characteristics common to all rodents. Rodents occur in almost every habitat and have high powers of reproduction. Most are small and have short limbs and a tail. They all have a single pair of razorsharp incisors which grow continuously throughout their lifetime as they are constantly being worn down. Rodents have no canines. Some species have cheek pouches. These are folds of skin and are lined with fur. Rodents that possess cheek pouches can build up large stores of food. Their sense of smell and hearing are acutely developed. They have long, touch-sensitive whiskers (vibrissae). Most rodent species are plantigrade. Their nails are claw-like and may be elongate in some burrowing species such as the Cape mole-rat. Most rodents eat a range of plant products, from leaves to fruit. Rodents have a relatively large ceacum which contains bacterial flora whose function it is to separate cellulose into digestible carbohydrates. However, only in the stomach which is higher up, can absorption take place. To overcome this, the rodent reingests the bacterially treated food taken from the anus. On its second visit to the stomach the carbohydrates are absorbed. Order Rodentia includes: Molerats, springhares, dormice, squirrels, gerbils and porcupines (the largest rodent that occurs in Southern Africa). Dassie rats, whistling rats, vlei rats, canerats and giant rats. Grooved tailed mice, spiny mice, striped mice, desert mice, water mice, woodland mice, house mice (introduced), pygmy mice, multimammate mice, tree mice, rock mice, white tailed mice, pouched mice, large eared mice, climbing mice, fat mice and rock mice. These animals have been classified into 34 Families, 354 Genera and a remarkable 1685 different species. There is little doubt that rodents are indeed one of the most successful groups of animals anywhere.

8 8 Order: Macroscelidae This order comprises of one family: Macroscelididae. Family Macroscelididae (Elephant-shrews) Elephant shrews are widespread in Africa but rarely seen as all species are secretive. They are strictly terrestrial mammals with long legs: the hind legs are much longer than the forelegs and adapted to jumping. They have long snouts for foraging and large eyes. They possess rat-like long tails. Some species clear, maintain and defend complex trail networks to enable them to traverse their territories easily and quickly. Every day individuals of a pair separately traverse much of their trail network, removing leaves and twigs that have fallen during the night, with swift side-strikes of their forefeet. These trails enable the elephant-shrews to take full advantage of their running abilities. At least eight species are endemic to Southern Africa. These include: Four-toed elephant shrew Round-eared elephant shrew Short-snouted elephant shrew Peter s short-snouted elephant shrew Smith s rock elephant shrew Rock elephant shrew Cape rock elephant shrew Bushveld elephant shrew

9 9 Order: Hyracoidea This order comprises one family: Procariidae. Family Procariidae (Hyraxes): Hyraxes are small and solidly built with a stump for a tail. The feet have rubbery pads which contain numerous sweat glands There are four digits on the front feet and three digits on the hind foot All the digits end in nails except for the inner digit of the hind foot which is armed with a claw They have one pair of enlarged upper incisor teeth and two pairs of lower, the other front teeth are absent They have a dorsal gland (in the centre of their backs) surrounded by a circle of hair. The hair stiffens when the animal is excited or showing aggression. The gland secretes a chemical the members of the group use for close range identification. Hyraxes have retained certain primitive features - they bite with the molars instead of the incisors - a relatively inefficient cropping method, poor regulation of body temperature and short feet. They have efficient kidneys which enable hyraxes to function on minimal moisture intake. In addition, they have a capacity for concentrating urea and excrete large amounts of undissolved calcium carbonate. Hyraxes always urinate in the same place and crystallised calcium carbonate forms deposits which whiten the rocks. These crystals were used as medicine by several South African tribes. Hyraxes have a poor ability to regulate body temperature. Heat loss is prevented by huddling together (often in dark crevices), long periods of inactivity and basking in the sun. It is when they huddle that the identification gland on their backs is most useful as it tells everyone who surrounds them. Hyraxes feed on a wide variety of plants. Representatives of the order that occur in Southern Africa are: Rock dassie Kaokeveld rock dassie Yellow-spotted rock dassie Tree dassie