Alfred Russel Wallace

“ Birds.—The genera of birds absolutely peculiar to the Nearctic region are not very numerous, because, there being no boundary but one of climate between it and the Neotropical region, most of its characteristic forms enter a short distance within the limits we are obliged to concede to the latter. Owing also to the severe winter-climate of a large part of the region (which we know is a comparatively recent phenomenon) , a large proportion of its birds migrate southwards, to pass the winter in the West-Indian islands or Mexico, some going as far as Guatemala, and a few even to Venezuela. ”

“ Previous to the glacial epoch there was probably a warm period, when every part of the range supported an abundant and varied fauna, which, when the cold period arrived, would descend to the lowlands, and people the country to the east, west, and south, with similar forms of life.
The first, and most important sub-division we can make, consists of the Eastern United States, extending across the Mississippi and the more fertile prairies, to about the 100°th. meridian of west longitude, where the arid and almost desert country commences. ”

“ To the south, in Georgia, Florida, and Louisiana, a sub-tropical climate prevails, and winter is almost unknown. To the north, in Michigan and New England, the winters are very severe, and streams and lakes are frozen for months together. These different climates, however, produce little effect on the forms of animal life; the species to some extent change as we go from north to south, but the same types everywhere prevail. This portion of the United States, having been longest inhabited by Europeans, has been more thoroughly explored than other parts of North America ”

“ The Eastern sub-region is by far the richest, nine-tenths of the whole number of species being found in it. The Alleghany Mountains form the richest portion of this sub-region, possessing nearly half the total number of species, and at least 24 species found nowhere else. The southern States have also several peculiar species, but they are not so productive as the Alleghanies. The Canadian sub-region possesses 32 species, of which nearly half are northern forms more or less common to the whole Arctic regions, and several of this character have spread southwards all over the United States. ”

“ Many of the species of Unio are very large, of varied forms, and rich internal colouring, and the group forms a prominent feature of the Nearctic fauna. By far the larger proportion of the fresh-water shells inhabit the Eastern or Alleghany sub-region; and their great development is a powerful argument against any recent extensive submergence beneath the ocean of the lowlands of North America. ”

“ This is undoubtedly the case if any fixed geographical boundary is taken; and it would thus seem that the "Nearctic" should, in birds, form a sub-region only. But, if we define "Nearctic genera" as above indicated, we find a considerable amount of speciality, as the following list will show. The names not italicised are those which are represented in Mexico or Guatemala by peculiar species:—
List of Typical Nearctic Genera of Land Birds. ”

“ It is for the most part an undulating or mountainous forest-clad country, with a warm or temperate climate, but somewhat extreme in character, and everywhere abounding in animal and vegetable life. To the west, across the Mississippi, the country becomes more open, gradually rises, becomes much drier, and at length merges into the arid plains of the central sub-region. ”

“ A considerable proportion of the passerine birds winter in Central America and the West Indian Islands, and go to the Middle States or Canada to breed; so that even the luxuriant Southern States do not possess many birds which may be called permanent residents. ”

“ To the north the limits are undefined; but as a considerable number of species and genera occur in the United States but not in Canada, it will be convenient to draw the line somewhere near the boundary of the two countries, except that the district between lakes Huron and Ontario, and probably Nova Scotia, may be included in the present sub-region. As far west as the Mississippi, this was originally a vast forest country ”

“ Its winters are far milder than those of the Eastern States in corresponding latitudes; and this, perhaps, has enabled it to support several tropical forms which give a special character to its fauna. It is here only, in the whole region, that bats of the families Phyllostomidæ and Noctilionidæ, and a serpent of the tropical family, Pythonidæ, are found, as well as several Neotropical forms of birds and reptiles.
Mammalia.—The following genera are not found in any other part of the Nearctic region. Macrotus (Phyllostomidæ) , one species in California ”

“ The crested birds in the middle of the picture (Oreortyx picta) , are partridges, belonging to the American sub-family Odontophorinæ. This is the only species of the genus which is confined to California and Oregon. The bird at the top is the blue crow (Gymnokitta cyanocephala) , confined to the Rocky Mountains and Sierra Nevada from New Mexico and Arizona northwards, and more properly belonging to the Central sub-region. It is allied to the European nutcracker; but according to the American ornithologist, Dr. Coues, has also resemblances to the jays, and certainly forms a distinct genus. ”

“ But although somewhat deficient in the total number of its families, this region possesses its full proportion of peculiar and characteristic family and generic forms. No less than 13 families or sub-families of Vertebrata are confined to it, or just enter the adjacent Neotropical region. These are,—three of mammalia, Antilocaprinæ, Saccomyidæ and Haploodontidæ; one of birds, Chamæidæ; one of reptiles, Chirotidæ; two of amphibia, Sirenidæ and Amphiumidæ; and the remaining six of fresh-water fishes. The number of peculiar or characteristic genera is perhaps more important for our purpose ”

“ Birds.—The birds of this sub-region have been carefully studied by American naturalists, and many interesting facts ascertained as to their distribution and migrations. About 120 species of birds are peculiar to the east coast of the United States, but only about 30 of these are residents all the year round in any part of it; the bird population being essentially a migratory one, coming from the north in winter and the south in summer. The largest number of species seems to be congregated in the district of the Alleghany mountains. ”

“ Even now, we find fertile valleys and plateaus of moderate elevation, penetrating the range on either side; and both to the north and south there are passes which can be freely traversed by most animals during the summer. ”

“ Its use may be to keep out the earth from the mouth while the animal is gnawing roots. A mouth so constructed is found in no other animals but in these North American rats. In the distance is a herd of bisons (Bison americanus) , the typical beast of the prairies.
Birds.—This sub-region has many peculiar forms of birds, both residents, and migrants from the south or north. Among the peculiar resident species we may probably reckon a dipper, (Cinclus) ; Salpinctes, one of the wrens; Poospiza, Calamospiza, genera of finches; Picicorvus, Gymnokitta, genera of the crow family ”

“ It is thus well distinguished from the Palæarctic region by its Procyonidæ, or racoons, Hesperomys, or vesper mice, and Didelphys, or opossums, among Mammalia; by its Vireonidæ, or greenlets, Mniotiltidæ, or wood-warblers, Icteridæ, or hang-nests, Tyrannidæ, or tyrant shrikes, and Trochilidæ, or humming-birds, among birds, families which, extending to its extreme northern limits must be held to be as truly characteristic of it as of the Neotropical region; by its Teidæ, Iguanidæ, and Cinosternon, among reptiles ”

“ That Coleoptera are pretty numerous is shown, by more than 800 species having been collected on the shores of Lake Superior; 177 being Geodephaga and 39 Longicorns.
Greenland.—This great arctic island must be considered as belonging to the Nearctic region, since of its six land mammals, three are exclusively American (Myodes torquatus, Lepus glacialis, and Ovibos moschatus) , while the other three (Vulpes lagopus, Ursus maritimus, and Rangifer tarandus) are circumpolar. Only fourteen land-birds are either resident in, or regular migrants to the country ”

“ Allen's tables it appears, that more than 200 species are regular migrants to Canada in the breeding season, and nearly half of these are land-birds. Among them are to be found a considerable number of genera of the American families Tyrannidæ and Mniotiltidæ, as well as the American genera Sialia, Progne, Vireo, Cistothorus, Junco, Pipilo, Zonotrichia, Spizella, Melospiza, Molothrus, Agelæus, Cyanura, Sphyrapicus, and many others; so that the ornithology of these northern regions is still mainly Nearctic in character. ”

“ Species of Vitrina, Zonites, Pupa, and Succinea, are found in Greenland; and Eastern Palæarctic species of Vitrina, Patula, and Pupa occur in Alaska. More than 30 species of shells living in the Eastern States, are found fossil in the Post-Pliocene deposits of the Ohio and Mississippi.
Fresh-water Shells.—North America surpasses every other part of the globe in the number and variety of its fresh-water mollusca, both univalve and bivalve. The numbers up to 1866 were as follows:—Melaniadæ, 380 species; Paludinidæ, 58 species; Cycladidæ, 44 species; and Unionidæ, 552 species. ”