What is a Mammal mammals mammals typically have a high body temperature usually about 95 to 100 F 35 to 38 C They are homeothermic meaning that this temperature is normally kept fairly constant throughout the animal’s life Mammals are also referred to as endotherms meaning that the warmth is generated internally making them largely independent of external sources of heat such as the warmth of the sun Their offspring are born as active babies and fed on milk secreted by the mammary glands of the mother Echidnas pp 50 51 and the platypus pp 52 53 are exceptional in producing eggs but still nourishing their young with milk Parental care which sometimes lasts for years is normal among mammals and allows the offspring to learn from older animals Generally families are small and the young are well looked after to achieve a higher survival rate Many species also live in social groups in which individuals cooperate to raise their young more successfully Most mammals have a hairy or furry coat which helps insulate them and maintain their high body temperature Some whales for example are nearly hairless as an adaptation to their particular way of life but insulation is then provided by large amounts of fat blubber under the skin In conjunction with their warm body mammals also have a very efficient blood circulatory system It works faster and at higher pressures than in all other animals except birds Endothermic homeothermy warm bloodedness and an efficient blood system enable muscles and nerves to work faster speed up digestion of food help babies grow more rapidly and generally assist mammals in living a much more active life than most other creatures Variations on a Theme The basic mammal body plan including four feet each with five toes has been modified to allow the 4 development of highly efficient diggers runners swimmers and fliers The teeth are also specialized to cope with many different kinds of food from meat to nuts leaves fish grass blood and insects These characteristic features of mammals enable them to live in a wide variety of habitats more independently of their surroundings air temperature for example than any other animals Mammals occur on all the continents in the polar regions deserts mountaintops and jungles Some can make prolonged dives into deep oceans Mammals can survive successfully in a wider diversity of habitats than any other animal group of comparable size One species our own has even left this world to visit another no other animal ever did that Mammals and People Some mammals have become very abundant and widespread Many such as horses dogs cattle and sheep have also played a key role in the success of our own species helping humans in their conquest of the planet by providing us with meat milk leather transportation and muscle power Some assist in medical research to aid our own species but others are significant pests and carriers of disease The History of Mammals The first mammals evolved when dinosaurs ruled the world about 100 million years ago Mammals are therefore a comparatively new group of animals many others have a much more ancient origin Reptiles for example first appeared over 200 million years earlier The first mammals were small and insignificant creatures that looked like today’s solenodons and gymnures From simple beginnings mammals have evolved into a wide assortment of species based on shared features and now include the blue whale pp 22 23 the largest animal ever The smallest mammal
WHAT IS A MAMMAL The earliest mammals were small inconspicuous insect eaters like the long extinct Megazostrodon above Over the last 200 million years mammals have come to dominate the planet and now the group includes animals as diverse as bats kangaroos elephants left and human beings own survival or a danger to domestic animals Large mammals are also in danger simply because of their size Elephants for example take up a lot of space and need a great deal of food every day An African elephant pp 36 37 might eat the same amount as say two cows but the same vegetation cannot feed both The same patch of ground cannot grow grass and leaves for elephants and other large wild mammals while at the same time producing crops for people Often the expansion of farmland has pushed wild animals back into less suitable areas and their numbers have dwindled Sometimes the wild mammals large and small are forced to steal from the crops planted on the land they used to occupy They are then called pests and eliminated with guns traps and poisons Even using more humane forms of control such as putting up fences instead of killing the animals forces them to live in smaller areas that 5 is the Etruscan shrew at about 2 grams it is smaller than many beetles Over the last one to two million years enormous changes have taken place in the variety of mammal species present in different parts of the world Many have become extinct or been reduced to critically small numbers Why Are Mammals at Risk In historic times mammals have suffered heavily from attacks by humans particularly the larger species and those perceived to be fiercer such as the cheetah pp 8 9 leopard pp 10 11 and mountain gorilla pp 30 31 that were considered to be a threat to our
cannot support such high numbers It is the larger species that have suffered most simply because they need large amounts of space just as we do Get rid of an elephant herd and it creates room for 100 people and their crops As numbers of humans have increased wild mammals have been pushed aside For example during a 30 year period when elephants declined drastically in Kenya the high human birthrate there meant that the lost elephants were replaced by almost exactly the same total tonnage of people Domestic mammals such as cattle sheep and goats have everywhere increased in numbers replacing their wild relatives and competing for the limited amounts of available food Exploitation Some wild mammals have been specially hunted for their skins ocelot for example meat banteng or other products such as wool from vicuñas ivory from African elephants pp 36 37 or blubber from whales pp 20 25 Overexploitation has led to catastrophic population declines This particularly affects the larger species because they do not breed rapidly having few young and taking a long time to The lifeless body of a gray whale washed up on a beach after it was ensnared in a discarded fishing net Accidental deaths ranging from roadkills to incidents such as this claim the lives of mammals the world over reach breeding age Populations cannot cope with large numbers being killed and they collapse Larger mammals also tend to live longer often more than 20 years That allows time for poisons and other pollutants such as heavy metals and polychlorinated biphenyls known as PCBs to accumulate and take effect preventing breeding and causing sickness and sometimes even death The accumulation of poisons is less of a problem for animals that naturally live for only a short time Some mammals such as whales and many large land species are thinly spread over a wide area Their distribution therefore suggests a level of abundance that is misleading They seem to be common but widespread populations that are thin on the ground are vulnerable to fragmentation Once the population is broken into small groups they often include too few to be viable and they die out one after another Some The lack of natural food sources as a result of habitat disturbance can result in young being abandoned and conservationists intervening Here bats are fed from a syringe on goats milk
WHAT IS A MAMMAL Percentage of mammals threatened 0 7 7 12 12 17 17 100 Southern hemisphere countries that have the highest percentage of threatened mammals above include Australia Madagascar and Indonesia species are at risk from interbreeding with their domesticated relatives creating hybrids Smaller Species Small mammals have problems too Their size makes them vulnerable to predators and to cold weather At least half of all known mammal species are rat sized or smaller One third of all mammals are rodents rats mice squirrels and so on and one in five is a bat These animals are often difficult to study and are normally largely ignored This means that we simply do not know what their real status is Their numbers are unknown and not monitored Many may go extinct without ever being officially recorded as being present These are special problems for mammals but like other animals the mammals also suffer from habitat destruction Those that are adapted to a particular way of life suffer heavily from the cutting down of trees or the mass removal of their food such as fish to feed humans This is a particular problem where populations are small to start with Numbers of Threatened Species in Each of the Major Mammalian Groups Rodents mice squirrels and beavers Bats Carnivores dogs cats bears and otters Primates monkeys apes and lemurs Ungulates horses rhinos hippos deer and antelope Marsupials 461 253 98 224 149 61 Rodents which constitute 30 percent of all mammals represent the highest number of threatened species above The Situation Today There are about 5,500 species of mammal but more than 10,000 species of birds and almost 40,000 fish About 80 to 90 mammal species have become extinct in the last 300 years and many subspecies and local varieties are also extinct or nearly so Of the living species about 3 4 percent are now Critically Endangered 8 2 percent Endangered and 9 0 percent Vulnerable More than one quarter of all known mammals are threatened in some way That is about twice the proportion of threatened birds The highest proportion of endangerment is among the primates 49 percent of primate species are threatened 7
