Chapter V: Animal Life (2)

The polar bear is distinguished from its kindred, at least in a general way, by its large size and white or yellowish-white colour. These and other differences from its relatives have led naturalists to place it in a distinct genus, of which it is the only species. It is circumpolar in its distribution, and in America occurs along the coast, seldom travelling inland except during the breeding season, when it is sometimes met with 25 miles from the ocean. Its southern range on the Atlantic coast is in northern Labrador, but it is occasionally carried on floating ice as far south as Newfoundland. It inhabits the shores of Hudson Bay and the Arctic Ocean. On the west coast it reaches Bering Strait, and is carried on floating ice to the islands in the northern part of Bering Sea, and at rare intervals reaches the Pribilof Islands. It is probably strictly carnivorous, and lives principally on the seal. It is supposed to be the largest of the bear tribe, but is certainly approached if not rivalled in size by the brown bear of southern Alaska. As many arctic explorers testify, it is dangerous to man and will lead in an attack.

The famous grizzly or "silver tip" inhabits the Pacific mountains, but is best known in the Rocky Mountains and Sierra Nevada. Although like all kindred species presenting conspicuous individual variations, it is usually dark in colour, with white tips to some of the hairs. The pelage is long, almost shaggy, and gives the animal even a more formidable appearance than its great size and strength justifies. It is not only one of the largest of the American bears, ranking in this respect with the polar bear and the largest of the huge brown bears, but is also probably the fiercest, and not infrequently has been known to attack man, although it will usually retreat from the presence of human beings if an opportunity is available. Full-grown individuals are about 8 feet in length and weigh in the neighbourhood of 1,000 to 1,200 pounds.

The brown bear, of which there are perhaps three species, including the Barren-Ground bear of the north-central part of Canada, are, as their name signifies, of a brown or cinnamon colour, but present great variation in this respect. Some are of a decided yellow, while others become dark and are scarcely distinguishable from the true grizzly. They reach a great size, particularly in southern Alaska, and possibly in certain instances even exceed the polar bear in dimensions and weight. The tracks of one which I measured near Mount St. Elias were 16 inches long by 8 inches wide, and the stride was 64 inches. The range of the brown bear is confined principally to the Pacific mountains, but is of greater extent than that of the true grizzlies and includes central Canada.

The black bears are of almost continental distribution and occurred in all or nearly all wooded districts before the balance of natural conditions was disturbed by the coming of the white man. They are the smallest of the bear tribe on this continent and are usually harmless, but at times when attacked or approached suddenly, especially if accompanied by their young, become formidable enemies. Their colour is usually a glossy black, but much variation occurs, especially about the head, and this and other differences are thought by some to indicate specific distinctions. A seemingly well-marked variety occurring in southern Alaska, which has a thick bluish-black under-fur, has recently been described as a distinct species.

Near relatives of the bear are the racoons, of which several species are present, one being abundant in the eastern portion of the United States and the other in the Pacific mountains.

_The Cats._--The _Felidae_ are represented by two genera, _Felis_ and _Lynx_, each of which contains several species.

Of the true cats, the largest is the beautiful jaguar, or American tiger, _Felis onza_, which is nearly as large, and by some said to be equal in size to its Asiatic relative. It more nearly approaches the leopard, however, in the character of its spots as well as in its arboreal habit, but exceeds it in size. The jaguar is some 4 feet or more in length to the base of the tail, and the tail is about 3 feet long. Its general colour is a soft-yellowish passing into dark brown and black, with large rosette- or somewhat lozenge-shaped spots, which take the form of indefinite rings of dark fur with lighter centres, within which there are one or two dark dots or eyes. The skins are fully as beautiful as those of the tiger or leopard, and are highly prized for rugs, and in some cases have been used for clothing. A dark, nearly black variety (or perhaps more properly, examples of melanism) has been described as a distinct species, and is sometimes spoken of as the black tiger.

The centre of distribution of the jaguar is probably in the great Amazonian forest, but it ranges over nearly all of South America, throughout Central America, and extends northward to Texas and perhaps Louisiana.

Next to the jaguar in importance is the widely known panther. Unlike most of its relatives, this species has an essentially uniform colour. The fur on the back, head, and tail is of a tawny brownish-yellow, but varies somewhat with changes in seasons. The under parts are of a dirty white. The animal when full-grown is of a formidable size, the larger examples being nearly 5 feet long from the tip of the nose to the base of the tail. The stout cylindrical tail is from 20 to over 30 inches long. In spite of its size and great strength the panther is not to be feared so long as room for its escape is open, as it is a great coward. One of the most interesting facts concerning this species is its unusually great range. Before being disturbed by white men it inhabited practically the entire width of both North and South America, from Hudson Bay to Patagonia, an extreme range of some 110 degrees of latitude. It is most at home in the mountains and is seldom seen on open plains. It is still common in the Pacific mountains of the United States and Canada.

Of the smaller cats, several of which are beautifully marked, mention may be made of the ocelot of the Texas region and the lynx or American wildcat. The latter, of which there are at least three varieties, is yet common, and maintains approximately its original range, which embraces the entire width of the continent from the subarctic forest at least as far south as northern Mexico.

_The Wolves._--In the history of the establishment of English colonies in this country, and throughout the spread of civilization across the continent, many accounts are given of encounters with wolves. These stories as they have been handed down have probably in many instances been magnified, but there is no doubt but that the larger wolves, such as the gray timber-wolf, once common in the northern portion of the United States, when assembled in packs and pressed by hunger, were formidable antagonists.

Of the wolves, four species are usually recognised, but their great variation, in each instance, has led to the description of numerous varieties, some of which have by certain writers been given the dignity of distinct species. The largest is the gray wolf, which is white or grizzly gray in colour, and frequently 5 feet or more in length and weighs 50 to 60 pounds. Individuals have been killed, however, which exceed these measures. The range of this species, or group of species as the case may be, was originally continental, but more particularly in the forested regions. Its hair, which is frequently 4 inches or more in length, and the fine thick under-fur make the skins valuable for robes, but they are seldom used for clothing, except by the Indians and Eskimos. The hood of the outer garment worn by Eskimos, termed a parkie, is frequently fringed about the face-opening with the long warm hair of the wolf.

A smaller species, the coyote, is still common on the western plains, and is termed the prairie-wolf. It is a comparatively small animal, although frequently 3 feet in length of body with a bushy tail two-thirds as long, and is of a skulking, cowardly nature. Its colour is usually a yellowish gray, and its skin, although used for robes, is much inferior to that of the gray wolf. Its range is from northern Mexico northward throughout the great plateaus, and in the valleys of the Pacific mountains into Canada. It is usually the first of the larger mammals the traveller in that region learns the existence of, even at the present day. Several individuals frequently gather together just after sunset and make their presence known by barking and howling in concert. These serenades last but a short time, however, and are likely to be repeated in the morning just before sunrise. During the night the animals composing these bands seem to scatter and hunt for food singly, but reunite in the early morning, after which they again separate and seek secluded individual retreats.

_Brief Mention of Other Mammals._--In order to convey an adequate idea of the large variety and richness of the North American mammalian fauna far more space would be required than is at present available. Indeed, of the smaller mammals much more research is evidently needed before even the number of genera and species can be enumerated, much less their life histories and economic importance made known, as is indicated by the fact that a large number of species previously recognised has been described during the past two or three years.

Of the abundant smaller mammals, none are more attractive or beautiful than the arboreal squirrels, of which several species are widely known. One of these, the common red squirrel, is remarkable for its wide range and adaptability to a great variety of conditions. It is abundant in the valley of the Yukon and even north of the arctic circle, throughout the forest-covered portions of Canada, and as far south as the South Atlantic States. Of less extensive range is the gray squirrel and the black squirrel, common in New England, and the somewhat larger and yet more beautiful fox squirrel of the central part of the continental basin. There are also a large number of species of ground squirrels, and several species of flying-squirrels. The rodents are also represented by the marmots, certain species of which are exceedingly numerous near timber-line in many of the ranges of the Pacific mountains as far north at least as Mount St. Elias, and by gophers, chipmunks, lemmings, the musk-rat, porcupines, rabbits, hares, rats, mice, etc. The list might also be extended by enumerating the bats, shrews, and moles, but we are compelled to cut short this most interesting portion of our review.

_Mammalian Families Peculiar to America._--While there are many genera and species of mammals found only on this continent, the number of families that are peculiar to it is small. Among the characteristic families, most of which, however, extend into South America, none are of greater interest in the study of geographical distribution than the opossums, of which there are 3 genera and some 22 species, all of them confined to the New World. Of these, two species are common in North America: one, the Virginia opossum, abundant throughout the eastern portion of the United States to the south of New York, and the other and smaller species, which inhabits Mexico and extends northward into southern California and Texas. Many representatives of this same family occur in Central and South America, some of which are notable on account of their diminutive size. The opossums are of peculiar interest owing to the fact that they are the only representatives of the marsupials now living outside of Australia. Fossil species occur, however, in the Tertiary rock of Europe, so that the American forms cannot be considered as indicating a recent land connection between this continent and Australia.

The porcupines are also representative of the New World fauna, although not strictly confined to it, and belong mostly in the northern continent. The Canadian porcupine is found throughout nearly the entire forested portion of the boreal region and extends as far south as the Middle Atlantic States, and an allied species, but of larger size, inhabits a portion of the same region and extends to the Pacific mountains and occurs in Alaska.

The racoons are strictly American and inhabit both continents. They are common in the forests of Central America and Mexico, and extend as far north as central Canada.

Of the several families of smaller and less well-known mammals peculiar to this continent, mention may be made of the pouched rats of California.

All of the animals to which attention has thus far been directed are now living; should one attempt to describe the great number of fossil forms whose bones have been discovered in the rocks, the menagerie would be vastly enlarged, and many exceedingly strange species, genera, families, and even larger divisions of the animal kingdom, added to the extended procession.

THE BIRDS

When one attempts to write an account of the birds of North America, the heavens seem darkened with such a multitude of varied and beautiful forms and the air filled with such a discordant clamour mingled with the sweetest of music that failure to convey an adequate idea of the countless numbers and diversity of the feathered throng within the compass of a few pages must be recognised from the start.

The important place held by the birds of North America in the avifauna of the world, may perhaps be best indicated by noting first of all what orders and families are without representatives among them.

The orders under which the birds of the world are arranged in the scheme of classification adopted by Wallace in his great work on the geographical distribution of animals are as follows:

CLASS--AVES

ORDERS. EXAMPLES.

1. Passeres Includes the greater number of the smaller birds, such
as kingbirds, flycatchers, larks, jays, crows,
blackbirds, finches, sparrows, warblers, chickadees,
swallows, thrushes, etc., numbering in North America
some 328 species and many subspecies.

2. Picariae Woodpeckers, cuckoos, toucans, kingfishers, swifts,
goat-suckers, humming-birds, etc.

3. Psittaci Parrots only.

4. Columbae Pigeons and the dodo.

5. Gallinae Grouse, pheasants, quail, jungle-fowl, turkeys,
guinea-fowl, etc.

6. Opisthocomi The hoazin of Guiana and Brazil only.

7. Accipitres Eagles, owls, vultures, hawks, buzzards, falcons, etc.

8. Grallae Rails, snipes, plovers, cranes, herons, storks,
flamingoes, etc.

9. Anseres Ducks, geese, gulls, petrels, pelicans, penguins,
loons, auks, etc.

10. Struthiones Ostrich, rhea, cassowaries, emeus, apteryx.

Of these ten orders, all but two are abundantly represented in North America. The missing orders include the ostrich-like birds, of which the only species in the New World is the rhea, of the southern portion of South America, and the peculiar hoazin, represented by a single species found in Guiana and Brazil.

The eight orders under which the birds of North America have been arranged (other classifications, however, have been adopted by various naturalists) have again been subdivided into families, genera, species, etc. According to Wallace's summary, the 8 orders referred to contain 124 families, of which 75 are not represented in North America to the north of the lowlands of Mexico, while 47 families are present. Of these 47 families, 25 are essentially of world-wide distribution, and only 1, containing a single species, a small wren-like bird of the genus _Chamaea_, found in California, is peculiar to the fauna of the continent.

As the North American continent under the arrangement adopted for the series of books of which the one in hand forms a part, is considered as including the West Indies, Mexico, and Central America, the above summary does not represent its entire bird fauna, but presents, perhaps, the best general idea of it that is at present attainable. To include the birds of the tropical portion of the continent would add greatly to the number of species, but I believe not materially to the number of families and orders, as given above.

In reviewing the distribution of the land birds of North America to the north of Mexico, but including lower California, J. A. Allen places the total number of genera, as given in the check-list of the American Ornithologists' Union, at 181. Of these, 55, or 30 per cent, are circumpolar or otherwise wide-ranging Old World forms; 126 genera, or 70 per cent, are American, of which 35, or 28 per cent, are essentially tropical, leaving 91 genera, or about 50 per cent, as distinctly North American.

The number of species in the avifauna of the continent, according to the latest check-list published by the American Ornithologists' Union (1895), is 768, together with a large number of subspecies. If the tropical portion of the continent were included, this number would be greatly increased and possibly doubled.

A further generalization has been advanced by Allen, who states that in the arctic portion of the continent the number of genera of birds present during the breeding season is 65, of which only 5 are exclusively American. In the cold temperate belt 120 genera are represented, of which 98 are circumpolar and 22 American. In the warm temperate belt 95 genera occur which do not range into the cold temperate belt, and of these only 12 are Old World forms, while 83 are exclusively American, and in addition 60 genera are common to both the cold and the warm temperate zone, of which 46 are represented in the fauna of the Old World, while 14 are American. This gives 155 genera for the warm temperate zone, of which 58 are Old World and 97 exclusively American. There are besides 50 essentially tropical genera which extend into the warm temperate zone, of which 43 are American and 7 tropicopolitan. The avifauna of the warm temperate zone thus contains a total of 205 genera.

The above enumeration indicates the rapid increase in the variety of bird life met with as one travels from the arctic to the Gulf coast of the continent, and in this connection it is to be remembered that the land contracts in breadth towards the south. In number of individuals, however, it is doubtful if there are less per square mile at the north than at the south during the breeding season.

There is a decrease in the number of Old World forms inhabiting North America from north to south. A similar decrease in mammalian species common to America and Eurasia has previously been referred to, and the same explanation applies in each case, namely, the near approach of the land areas of the Old and the New World at the north, and the actual union of the two continents in late geological time.

As has been shown by Allen, the species of birds of the temperate and boreal zones of North America were derived in part from the Old World, in part from types almost universally distributed throughout the warmer latitudes, and in part from tropical America, but to a marked extent the species present developed where they are now found. This generalization is in harmony with the geographical relations of the continent to other land areas, and with the fundamental principles of evolution.

_Migrations._--Among the many facts of interest to the geographer in connection with the bird life, none present a more fascinating field for study than the annual migrations in which a very large number of the species participate.

As one travels northward from Mexico or the Gulf States, the number of species of birds which remain in essentially the same area throughout the year, or the _residents_ as they are termed, becomes less and less. In New England and about the southern shores of the Great Lakes there are about 30 species which remain all winter and may justly claim to be citizens. Besides these, there are several visitors that come from the north and belong to the vast army of migrants, but which are contented with a comparatively small change of position during the periods of greatest cold or heaviest snow. In the far north the number of residents is still more restricted. On the tundras fringing the arctic coast even the snow-owls, snow-buntings, and the ptarmigans, the hardiest of birds, move southward during the winter to the shelter of the subarctic forest, and bird life on the vast frozen morasses is practically, if not absolutely, wanting.

The millions of birds that journey southward each fall begin their return migrations at the first promise of spring. Even during unusually mild spells of weather in winter, temporary northward movements occur. The migratory birds are actuated by such a strong desire to regain their nesting places and summer homes that they embrace every opportunity to journey towards them, and not infrequently suffer severely for the risks they take. In some instances species which have begun their northward flight too soon are killed by thousands owing to a return of severely cold weather or die for lack of food.

The first definite northward migration in the southern portion of the Mississippi Valley begins during exceptionally favourable years as early as the end of January, but the great movement of the feathered hosts is not usually at its height before the middle of March or the first of April. In New England the current of migration begins between the middle of February and the first of March, and increases in strength until the middle of May, when it is at its height, and then rapidly declines and is practically over by the beginning of June. In the far north, the first arrival from the southward, and that a species which does not make a long annual journey, usually appears early in April. At Point Barrow, the most northern portion of Alaska, as was observed by John Murdock in 1882 and 1883, the first harbinger of spring was a snow-bunting, which arrived the first year on April 9th. The northward-flowing tide of bird life ends early in July in the region of the Yukon, and by the middle of that month the vast flocks have been separated and the many mates have found their nesting places. The time taken for the general movement is thus in the neighbourhood of four months.

The northward flight of the birds is seldom, if ever, one continuous journey, but like many other movements in nature, progresses by pulsations. Well-defined "bird-waves" have been recognised especially in the Mississippi Valley. The direct or immediate cause of the starting of these waves of life is the coming of a wave of heat. Secondary or modifying conditions are furnished by strength and direction of the wind, cloudiness, rain, etc. As the weather in spring-time is fickle, and its variations not the same for any two consecutive years, so the gathering of the birds into flocks and their northward flights vary, although for a term of years the arrival of a given species at a particular station does not depart far from a mean date. With the northward sweep of the waves of bird life over the temperate and boreal portions of the continent comes the awakening of plant life, but the birds, to a marked extent, precede the unfolding of the flowers. This marvellous renewal of the life of the land after the long cold winter makes the budding and nesting spring-time the most joyous portion of the year, and one which exerts a marked effect on human thought and activities. The spring-time awakening in all nature is like a resurrection, and has apparently exerted an influence on the religions of the world.

The bird-waves referred to above are characterized at the start by the presence of great numbers of a single species, but as they progress, scattering occurs, and at the time of the greatest movements in the northern portion of the United States a large number of species frequently arrive at a given locality in a single night. At sunset the groves may be nearly tenantless and silent, while at sunrise they are alive with the flitting of wings of many colours, and the air pulsates with many different songs.

Judging from extended observations on migrations made in the Mississippi Valley, the definite waves of bird life which sweep northward with the spring-tide of temperature are in some instances 100 or 200 miles long and have a breadth of perhaps a score of miles. The distance between the waves varies with variations in the weather and perhaps other causes, and as they progress they apparently become less definite and at the north have yet to be recognised.

The migrations of the birds are performed principally at night. In the northern part of the United States during the hours of darkness in early spring, even when cloudiness prevails or the land is veiled in mist, the voices of geese may frequently be heard overhead, proving that unseen flocks are then winging their way northward. About the lighthouses along the coast and on the shores of the Great Lakes, when migration is in progress, dead birds are frequently found in considerable numbers and of various species. In these cases the birds are evidently attracted by the lights and killed on striking the windows that protect them. This occurs particularly on stormy or cloudy nights, when the birds fly low. Several of the larger species of birds, as the geese, ducks, cranes, etc., which are strong of wing, make long flights without resting. In many instances a single stage in a journey may include 500 or 600 miles. Most of the smaller birds, however, fly comparatively short distances between the pauses made for rest and food.

A species on reaching the northern portion of the route over which it usually migrates scatters, and the individuals mate, nests are built, and young reared. At the approach of cold weather reassemblage occurs, frequently great flocks being formed, and the southern movement begins. The southward migration is less conspicuous in most instances than the movement _en masse_ of the birds in the spring, and so far as now seems to be recognised is not divided into definite waves.

While the winter habitat of most birds in the temperate and boreal portions of the continent is to the south of their summer homes, the annual migration is not in all cases great in amount. Some species move only a few hundred, or possibly a few score, miles. Even the winter residents make short migrations, dependent on weather conditions. The greater part of the migratory birds, however, pass the winter in the Gulf States, Mexico, the West Indies, and Central and South America. In some cases they go well to the south of the equator. The annual flight going and coming measured in a straight line, between the nesting place and the winter home, cannot be less in many instances than from 8,000 to 10,000 or 12,000 miles. An interesting fact in this connection is that certain species follow definite routes. The region moved over annually, if marked on a map, would resemble two open or partially opened fans, with their handles pointing towards each other and connected by a narrow band.

The causes of the annual migrations of birds have received much study and been the subject of much speculation. The general consensus of opinion in this connection seems to be that the birds are controlled largely by what we in our ignorance term instinct. The true beginning of the migration seems to be in the fall, when the birds are driven from their homes by cold or, perhaps more accurately in most cases, by scarcity of food. This, however, is not the whole story, since many species start southward before cold weather approaches and while food is yet abundant. Then, too, crippled individuals have been known to survive the winter in regions from which their summer companions have departed. Instinct, therefore, plays a part in even the fall migration, where at first glance sufficient physical reasons may seemingly be claimed for it. During the spring migration the birds are moved by a strong impulse to regain their breeding-grounds. Each species seems to have adapted itself to certain conditions of temperature, food, etc., through long ages of development, and acquired a subtle faculty of regaining the environment to which it is best adapted, as soon as the adverse conditions that caused it to leave its home are ameliorated. How a particular bird is enabled to return to the nest it built the year previous is not known. The study of the homing instinct of pigeons assists in this direction, however, and suggests that birds are endowed with something answering to a sixth sense--that is, a sense of direction or of orientation.

_Spring-time Music._--The northward-flowing tide of life each spring brings to the temperate zone of North America a marvellous change not only in colour and movements, but in sound. This is the season of bird courtship and more than usual happiness among the feathered millions. From shore to shore of the continent a chorus more seductive than sirens' songs pulsates on the breezes.

The winter is characteristically a season of silence. The sounds heard at a distance from human habitations are mainly those produced by inanimate nature. The wind causes varied discords amid the bare branches of the deciduous trees or sings weird melodies in the pines. Strange muffled roars come from the frozen lakes, as the ice contracts and breaks during periods of excessive cold. The frost in tree trunks causes sharp explosions. The ice-covered streams are still except where cataracts interrupt their even flow. In the profound silence of a calm winter night the distant dismal howl of a wolf, the cry of an owl, or the bark of a fox alone reminds one that life still continues, but these animate sounds are far more frequently absent than present. With the coming of the spring there is a marvellous awakening and unfolding. The brooks, swollen to overflowing by the melting of the snow, make music as they run. The northward flight of the birds brings to every grove a chorus of song. A host of batrachians and reptiles bestir themselves after a long winter sleep and vociferously proclaim their presence. The insect world, with its unnumbered legions, takes wing. The air vibrates with millions of voices. The trees put forth their leaves, each a harp-string which responds to the touch of the fingers of the wind. The organ-notes of the thunder again startle the hibernating echoes. As the winter is the silent season, so the spring is the time of music.

One of the most charming of the many phases of nature's concert season is the matin songs of the birds. Ere the eastern sky along the New England coast becomes roseate with the first blush of morn, the twitter of birds may be heard amid the shadowy branches of the trees. Soon a thrush or a warbler awakens in full song, and is followed by a host of other voices, until the air pulsates with music. As the sun rises and his first level rays reveal the varied tints of the tree tops, the many-voiced chorus passes the height of its ecstasy and the music gradually subsides. But the glad tidings of the coming of the day are passed westward from grove to grove and from meadow to meadow, and a wave of song sweeps on ahead of the wave of light, induced by its coming. The song-wave spreads to the north and south and flows steadily westward over the forest-covered mountains, across the great central basin of the continent, breaking on the treeless plateaus into many streams which follow the grove-fringed rivers, passes through the depressions in the Rocky Mountains, and although weakened in the arid valleys beyond, is not checked. The larks there listen for its coming and pass the joyful message westward. The timid dwellers in the great forests of Oregon awaken at the magic sound and the lofty tree tops are made to thrill with the voices of unseen choirs while it is yet night in the silent aisles below. The onward rush of sound is not reflected or turned back by the lofty Cascades, but flows through their passes and only ceases when the sea-birds of the Pacific renew a note that was dropped on the distant Atlantic coast.

One of the most fascinating incidents in the life of the explorer in his lonely camps in the great forests or amid the solemn mountains is the coming of the wave of song in the spring and early summer-time which precedes and accompanies the rising of the sun.

* * * * *

The fascination of the field of study touched upon in this chapter invites an attempt to present an account of some of the more characteristic birds of North America, and to endeavour to convey to the reader some idea of the varied reptilian, fish, and invertebrate life of the continent, but the limitations of space prohibit such a review. Even the great problems dealing with the intimate relation that exists between geographical conditions and the distribution of animals cannot be given more attention than the suggestions already offered.

LITERATURE

ALLEN, J. A. _The Geographical Distribution of Animals_, in
Bulletin of the United States Geological and Geographical Survey
of the Territories, vol. iv, Washington, 1878, pp. 313-377; _The
Geographical Distribution of North American Mammals_, in
Bulletin of the American Museum of Natural History, vol. iv, New
York, 1892, pp. 199-243.

HEILPRIN, ANGELO. _The Geographical and Geological Distribution of
Animals_. International Scientific Series, London and New York,
1897.

OSBORN, H. F. _The Rise of the Mammalia in North America._ New
York, 1893.

COPE, E. D. _Geographical Distribution._ In the Annual Report of
the Smithsonian Institution for the year ending June 30, 1898,
Washington, 1900, pp. 1199-1234.

MERRIAM, C. HART. _Life-Zones and Crop-Zones of the United
States_, United States Department of Agriculture, Division of
Biological Survey, Bulletin No. 10, Washington, 1898; _Results
of a Biological Survey of the San Francisco Mountain Region and
Desert of the Little Colorado, Arizona_, United States
Department of Agriculture, Division of Ornithology and Mammalogy
[Bulletin] No. 3, Washington, 1890; _The Geographical
Distribution of Life in North America_, in Proceedings of the
Biological Society of Washington, vol. vii, 1892, pp. 1-64.