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Mammals

A Guide to Familiar American Species

St. Martin's Press

SEEING MAMMALS

Seeing mammals isn't as easy as seeing birds or flowers. Mammals keep out of sight. Some have concealing colors; some burrow; many are nocturnal. Yet they can be seen if you are patient, alert, and know where to look. Much about mammals is known, but much more remains to be discovered.

WHAT ARE MAMMALS? The name "mammal" refers to the female's mammary glands, which provide milk for her young. This characteristic sets off mammals among the warm-blooded, back-boned animals. Mammals are hairy; young are born alive. Most have varied teeth, for cutting, tearing, or grinding. The mammal's skull is unique; the brain more complex than in other animals.

HOW MANY ARE THERE? There are, the world over, about 15,000 kinds of mammals. Some 3,600 species and subspecies are found in North America. Species number about 650 in North America, 350 north of Mexico. Some are rare, others so common that scores may occur on a single acre.

WHERE ARE THEY FOUND? Mammals live on every continent — in mountains, deserts, arctic snows, marshes, meadows, forests, farms, cities, and the depths of the sea. Some have become adapted to specific environments; thus tree squirrels live only in forests, rice rats only in swamps. More adaptable mammals fit into a variety of environments; thus some rabbits live in woods, some in swamps, some in deserts.

RANGE IN SIZE Mammals range from the Pygmy Shrew to the Blue Whale. Large species, as some carnivores and hoofed mammals, are most familiar. Smaller ones are more common and, in the long run, more important. The larger the mammal, the more land needed to support it. Protecting mammals till their population exceeds the number that a given region will support may mean starvation for the surplus. This happened with deer and elk until hunters were allowed to keep the herds down.

ADAPTATIONS Mammals have developed effective ways of living. One is to care for the young inside the mother before birth. Tooth adaptations vary from the tusks of the peccary to the gnawing teeth of rodents. Feet with hoofs or padded toes are adapted for running, claws for digging, grasping, and climbing, and webs for swimming. Mammals can fly, glide, run, jump, crawl, swim, burrow, and dive. Internal organs show great adaptation, too. Some mammals can hibernate. Such adaptations have made mammals dominant today.

MAMMALS AND MAN Man, most adaptable of mammals, has domesticated and developed others he has needed. Dogs, cats, horses, cattle, sheep, and a score more have been domesticated. Most of these have been improved for human ends. A Holstein cow gives more milk than her ancestors. Those which did not fit our pattern, like the bison and the mountain lion, have suffered badly.

ECONOMIC VALUES Mammals helped make America. Pioneers depended on game for everyday food. The fur trade stimulated exploration and settlement. Some mammals are still taken for their furs. Hunting is more than a sport: on the business side, millions are spent yearly for equipment and supplies. Smaller mammals have less obvious values, but provide food for fur-bearers and other predators; many cultivate the soil. Some mammals carry diseases and contaminate foods. All species are so interrelated that each has a role in keeping the natural machinery in balance.

CONSERVATION Our wild mammals are a natural resource, which should be used wisely for the long-range benefit of all the people. National Parks provide complete protection for all wildlife, and here field trips can be most rewarding. State game refuges and those of the U.S. Fish and Wildlife Service protect threatened species such as bison, pronghorn, and elk. National forests are a reservoir of game and smaller animals. Even farms and woodlots can maintain a mammal population. When hunting and trapping are limited to removal of surplus animals, a future supply is assured. You obey hunting and conservation laws because they benefit you, your neighbors, and the country at large.

STUDYING MAMMALS Identification is the key to exciting hobbies. Once you have begun to study mammals, many possibilities open up.

OBSERVING MAMMALS means more than identification. See how they live, feed, protect themselves, and raise their young. This requires patience. Early or late, your time schedule must fit your subject. Binoculars are an essential. So are warm, comfortable clothes, a notebook, and sometimes a blind or camouflaged shelter. Most economic species have been studied by professional zoologists. Many smaller and less important species still need attention. Experienced amateurs, noting detailed observations, can make a zoological contribution by recording facts on feeding habits, burrows, runways, nests, calls, and behavior of local mammals.

PHOTOGRAPHING MAMMALS can augment your observations. Learn to know your camera first and the habits of your subjects next. Attempt simple, easy subjects first. Light is often poor, so a good lens or flash equipment is important. Animal photography cannot be rushed. Food and water bait often help. Learn to set up your camera so that mammals will take their own pictures.

UNDERSTANDING TRACKS Mammals leave tracks in soft earth, mud, or snow. Many of the tracks will enable you to identify the species without seeing the animal, and tell you the speed and direction the animal was traveling. To better learn to recognize tracks, casts can be made of these by pouring a thick solution of plaster of Paris and water over the imprint. When the plaster is dry, lift off the cast; then clean and label it.

MAMMALS AND COMMUNITIES Assemblages of animals and plants with similar environmental requirements can be grouped together in communities. The nature of the vegetation, substrate, climate, and many other factors all interact to affect the kinds of animals that can live in a community. Some communities in the United States with a characteristic mammal include desert (kangaroo rats), grassland-prairie (thirteen-lined ground squirrel), deciduous forest (eastern chipmunk), coniferous forest (red squirrel), and arctic alpine (pikas).

ECOLOGICAL NICHE Just as one mammal differs from another closely related species in certain skeletal or color differences, it also differs in occupying a distinctive habitat as well as distinctive feeding, breeding, and behavioral characters. Collectively, this makes up the ecological niche a given species occupies.

POPULATIONS The number of animals of a given species is dependent upon the quality of the habitat where it lives and the rate that new animals are added, as through births, or removed, as by deaths. Usually there is a balance between the numbers added and removed. However, the balance may be disrupted for a variety of reasons, and the species may be nearly exterminated or become overly abundant. Some species increase in numbers markedly with certain regularity and then have a distinct die-off. These are referred to as cycles and are noticeable in lemmings and voles.

HOME RANGES are established by most mammals much as with birds and other animals. One mammal may occupy a specific area for feeding, rearing young, courting, and resting, more or less to the exclusion of other individuals of the same species. Many species will vigorously defend this range. The size of the home range may differ in summer and winter, and for males and females.

MYTHS A variety of untrue stories about mammals persist. Lemmings do not migrate to the sea and commit suicide although Norwegian lemmings may undergo mass movements that proceed helter-skelter. Bats do not get in one's hair although in cramped quarters their sonar system may become confused and they may nearly fly into a person. Young opossums do not hang from their mother's tail. Porcupines do not shoot their spines, but these will fall out when the animals are shedding hair. Bears do not truly hibernate.

MUSEUMS AND ZOOS are fine places to study. Use them to supplement your field work. A list of well-known museums and zoos is given here, as well as a list of books for further study.

MAMMALS OF TODAY are probably descended from small- to medium-sized, active, flesh-eating reptiles — the Cynodonts. These reptiles, with mammal-like skulls, bones, and teeth, lived millions of years before the dinosaurs. The first true mammals developed about 190 million years ago, but for over 100 million years they remained an unimportant group of animals. When the dinosaurs died out 70 million years ago, mammals came into their own. By 50 million years ago, three main groups of mammals and most of their subgroups were well established. The egg-laying mammals, like the Duckbill and Echidna, are now a small, almost extinct group. The pouched marsupials, whose young are born incompletely developed, are represented by only one species in the United States — the Opossum. All other mammals fit into the great placental group regarded as about 16 living orders. General relationships of the principal orders are shown above. More detailed "trees" are appropriately placed in the book. Study them and become familiar with more detailed relationships.

MAMMALS OF YESTERDAY include some which lived in North America and have become extinct in the past 50 million years. At intervals land bridges from Asia formed, and new mammals came over to compete with and sometimes replace existing species. The Short-legged Rhinoceros lived about 10 million years ago. It became extinct soon after, but other species persisted in Europe till the ice age. The early camel (Procamelus) died out about the same time, but others lived here till the last ice age. More is told about these animals on the next page.

THE FIRST MAMMALS appeared in North America over 75 million years ago. New kinds developed; others came from Asia. About 25 million years later, mammals began to dominate the continent. Many ancient mammals died off, leaving no descendants. Others were ancestors of modern horses, camels, deer, beaver, bison, and rhinos — to mention a few. Smaller mammals were abundant too; their fossils are rarer. Species that have become extinct recently include:

Long-horned Bison was one of a number of species of bison widespread in North America during the ice age. Spear points found with bones of extinct bison show that man hunted them.

Saber-toothed Cats, also found in Europe, were larger in North America. Our species, with dagger-like teeth 8 inches long, survived until late in the ice age.

Short-legged Rhinoceros and kin, developed in North America, became extinct before the ice age. Some migrated to Asia and Africa, where descendants still live.

American Mastodon was one of our many elephantlike animals. Some had shovel-tusks; some, curved pointed tusks. The Woolly Mammoths, surviving into the ice age, were hunted by early man, perhaps Indians.

Giant Ground Sloth was an elephant-sized member of a group which today has few members. Heavy hind legs and tail suggest it squatted when feeding or resting. It was contemporary with early man in North America.

Early Camel (Procamelus) represents the midpoint in the development of the camel in North America. From here, types of camels moved into Asia and South America, where they live today. Other, larger kinds of camels survived here into the ice age.

OPOSSUM is our only native marsupial or pouched mammal. Baby opossums, which weigh only 1/15 oz. at birth, live in the mother's fur-lined pouch about 3 months. Up to 14 may be born; usually only 7 to 9 survive. Opossums hunt at night for small birds and mammals. They eat eggs and fruit also. When threatened by enemies, they "play possum" and collapse as if dead. Opossums are recognized by their white faces, coarse fur, and rat-like tails. Males and females are alike. Length: 33 in.

MOLES are small, plump, underground creatures, with velvety fur, no visible ears, and eyes reduced or absent. They have powerful shoulders, a short neck, muscular front legs with shovel-like feet, and heavy claws — all features useful in digging. Sensitive snouts and sensory hair on front feet and tail keep moles from bumping into tunnel walls. Distinguish the Hairy-tailed Mole by its hairy tail and short snout. Star-nosed Mole is identified by an odd, pink, disc-like fringe on its snout. Moles tunnel in rich woods and lawns, feeding on grubs and worms. The Broad-footed Mole, one of several western species, is almost blind. It resembles the Eastern Mole (here), but with a more fleshy tail. The Shrew Mole has a long snout and hairy tail. The smallest mole (5 in.), it spends more time at the surface than others. In many features, it is intermediate between moles and shrews. Other moles range from 5½ to 8 in. long.

THE EASTERN MOLE or common mole makes the mounds that dot your lawn. You are unlikely to see any moles, for they stay underground unless molested. Moles dig two types of tunnels: deep tunnels (to 2 ft. underground) where they nest, spend the winter, and remain during drought; and shallow tunnels seen on lawns, along which they find insects and earthworms. Length: 7 in.

PYGMY SHREWS are the smallest shrews, and shrews, in general, are the smallest North American mammals. The Pygmy Shrew weighs only 1/14 ounce — less than a dime. As it darts through dry woods and clearings, where it lives, people mistake it for a mouse. Note its velvety, soft, mole-like fur, slender body and legs, and short tail. Shrews feed on small insects, which they hunt constantly. Because of their activity and small size, they consume several times their weight in food every day. Shrews spend more time above ground than moles. Their eyesight is better, too. Enemies: common carnivores, owls, hawks, snakes. Length: about 3 in.

SHREWS, our smallest but fiercest mammals, attack and kill prey several times their weight. Two shrews may fight till one kills and consumes the other. The young (four to five), born in a hollow stump, log, or burrow, can fend for themselves within a month. The life span is short — one and a half years at most.

Masked Shrew is a common, widespread, long-tailed shrew, found in moist forest localities. Length: 4 in.

Arctic Shrew is similar to Masked Shrew, but larger, with a longer tail. Its coat is brown above, gray-white below, changing in winter to a darker brown or blackish above and almost white below. Length: 4½ in.

Least Shrew, small and short-tailed, inhabits grassy abandoned fields. Feeds on insects, possibly mice.

Desert Shrew, pale, ashy-gray in color, lives amid cacti and sagebrush in more arid places than any other of our shrews. Not often found. Length: 3 in.

Short-tailed Shrew, with stubby tail, is one of the commonest mammals of eastern woods. Its slightly poisonous saliva aids in paralyzing prey. Length: 4½ in.

Water Shrews can run on water, with their large, broad, hairy feet. They also swim and dive, feeding under water on insects, fish, and fish eggs. Length: 6 in. Northern Water Shrew is more black; the Pacific species is more brown.

BATS are the only flying mammals. Flying squirrels glide, but only bats fly. Bats' forelimbs are greatly modified and form wings very different from those of birds. In bats, the fingers are greatly lengthened to support a thin membrane. This membrane extends to the hind legs. The legs and usually the tail support the membrane.

Bats have limited eyesight. In flight their large ears form part of a unique system for locating and avoiding objects. Bats emit a sound, too high-pitched for us to hear, which is echoed back like a radar beam. Picked up by the bat's sensitive ears, this echo indicates the direction and distance of obstacles to be avoided and of flying insects that may be seized for food.

About 2,000 kinds of bats inhabit temperate and tropical regions. The 65 or so kinds found in the United States are primarily insect-eaters. Some larger, tropical bats feed on fruit, and the Vampire Bats of South and Central America feed on blood. Long-nosed Bats feed on pollen of night-blooming flowers. Bats rest during the day, hanging upside down in caves, in deserted buildings, under cliffs, and in trees. At dusk they fly out to feed on insects. Their erratic flight and the darkness make identification difficult. For positive identification, find some at rest during the day. Catch them in barns, under cliffs and in caves. Release them after you have studied them.

PIPISTRELLES are the smallest American bats (length: 3 in.). The erratic flight, in early evening, and small size are clues to identification. Eastern Pipistrelle has reddish-brown fur, black at base, and brownish ears. Western Pipistrelle has grayish-brown fur, blackish ears. Both hibernate.

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Excerpted from Mammals by Herbert S. Zim, Donald F. Hoffmeister, James Gordon Irving. Copyright © 1987 St. Martin's Press. Excerpted by permission of St. Martin's Press.
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