CONCLUSIONS

The migration of birds as it is known today had its beginning in times so remote that its origins have been entirely obscured, and it can be interpreted now only in terms of present conditions. The causes underlying migration are exceedingly complex. The mystery that formerly cloaked the periodic travels of birds, however, has been largely dispelled through the fairly complete information that is now available concerning the extent and times of the seasonal journeys of most of the species. Many gaps, however, still remain in our knowledge of the subject. Much has been learned, and present knowledge is being placed on record, but it must be left to future study to clear away many of the uncertainties that continue to make bird migration one of the most fascinating subjects in the science of ornithology.

Each kind of bird seems to have its own reaction to its environment, so that the character of movement differs widely in the various species, and seldom do any two present the same picture. In fact, bird migration has been described as a phase of geographic distribution wherein there is a more or less regular seasonal shifting of the avian population caused by the same factors that determine the ranges of the sedentary species. If this view is correct, then it must be recognized that the far-reaching works of man in altering the natural condition of the earth's surface can so change the environment necessary for the well being of the birds as to bring about changes in their yearly travels. The nature and extent of the changes wrought by man on the North American Continent are easily apparent. Forests have been extensively cut away and their places have been taken by second growth or cultivated land, and wide stretches of prairie and plain have been broken up, irrigated, and devoted to agriculture. These great changes are exerting a profound effect upon the native bird populations, and the various species may be either benefited or adversely affected thereby.

The Federal Government, has recognized its responsibility to the migratory birds under changing conditions brought about by man, and by enabling acts for carrying out treaty obligations, it is now giving many important species legal protection under regulations administered by the Bureau of Biological Survey. Much is being done by legislation for the welfare of the birds. The effectiveness of these conservation laws, however, is increased in the same measure that the people of the country become acquainted with the facts in the life histories of the migrants and interest themselves personally in the well being of the various species. Long before the white man came to America the birds had established their seasonal lanes of migration throughout the Western Hemisphere, as here outlined. The economic, inspirational, and esthetic values of these migratory species dictate that they be permitted to continue their long-accustomed and still mysterious habits of migration from clime to clime.

BIBLIOGRAPHY[4]

[4] Since almost every faunal paper on birds has a bearing on the subject of migration, only a few can be listed in this publication. Those included were selected to aid the student wishing to pursue the subject further and to cover not only all cited in the text but also others consulted and used in its preparation.

(1) Allard, H. A.

1928. BIRD MIGRATION FROM THE POINT OF VIEW OF LIGHT AND LENGTH OF DAY CHANGES. Amer. Nat. 62: 385-408.

(2) Austin, O. L., Jr.

1928. MIGRATION-ROUTES OF THE ARCTIC TERN (STERNA PARADISAEA BRUNNICH). Northeastern Bird Banding Assoc. Bull. 4: 121-125.

(3) Baird, S. F.

1866. THE DISTRIBUTION AND MIGRATIONS OF NORTH AMERICAN BIRDS. Amer. Jour. Sci. (2) 41: 78-90, 184-192, 337-347.

(4) Clarke, W. E.

1912. STUDIES IN BIRD MIGRATION. 2 V., illus. London.

(5) Cooke, W. W.

1888. REPORT ON BIRD MIGRATION IN THE MISSISSIPPI VALLEY IN THE YEARS 1884 AND 1885. U. S. Dept. Agr., Div. Econ. Ornith. Bull. 2, 313 pp., illus.

(6) ——————

1904. DISTRIBUTION AND MIGRATION OF NORTH AMERICAN WARBLERS. U. S. Dept. Agr., Div. Biol. Survey Bull. 18, 142 pp.

(7) ——————

1904. THE EFFECT OF ALTITUDE ON BIRD MIGRATION. Auk 21: 338-341

(8) ——————

1905. ROUTES OF BIRD MIGRATION. Auk 22: 1-11.

(9) ——————

1905. THE WINTER RANGES OF THE WARBLERS (MNIOTILTIDAE). Auk 22: 296-299.

(10) ——————

1906. DISTRIBUTION AND MIGRATION OF NORTH AMERICAN DUCKS, GEESE, AND SWANS. U. S. Dept. Agr., Bur. Biol. Survey Bull. 26, 90 pp.

(11) ——————

1908. AVERAGING MIGRATION DATES. Auk 25: 485-486.

(12) ——————

1910. DISTRIBUTION AND MIGRATION OF NORTH AMERICAN SHOREBIRDS. U. S. Dept. Agr., Bur. Biol. Survey Bull. 35, 100 pp., illus.

(13) ——————

1913. DISTRIBUTION AND MIGRATION OF NORTH AMERICAN HERONS AND THEIR ALLIES. U. S. Dept. Agr., Bur. Biol. Survey Bull. 45, 70 pp., illus.

(14) ——————

1913. THE RELATION OF BIRD MIGRATION TO THE WEATHER. Auk 30: 205-221, illus.

(15) ——————

1914. DISTRIBUTION AND MIGRATION OF NORTH AMERICAN RAILS AND THEIR ALLIES. U. S. Dept. Agr. Bull. 128, 50 pp., illus.

(16) ——————

1915. BIRD MIGRATION. U. S. Dept. Agr. Bull. 185, 47 pp., illus.

(17) ——————

1915. BIRD MIGRATIONS IN THE MACKENZIE VALLEY. Auk 32: 442-459, illus.

(18) ——————

1915. DISTRIBUTION AND MIGRATION OF NORTH AMERICAN GULLS AND THEIR ALLIES. U. S. Dept. Agr. Bull. 292, 70 pp., illus.

(19) Cooke, W. W.

1915. THE YELLOW-BILLED LOON: A PROBLEM TN MIGRATION. Condor 17: 213 214.

(20) Coues, E.

1878. BIRDS OF THE COLORADO VALLEY, A REPOSITORY OF SCIENTIFIC AND POPULAR INFORMATION CONCERNING NORTH AMERICAN ORNITHOLOGY. U. S. Dept. Int. Misc. Pub. 11, 807 pp., illus.

(21) Gätke, H.

1895. HELIGOLAND AS AN ORNITHOLOGICAL OBSERVATORY, THE RESULTS OF FIFTY YEARS' EXPERIENCE. (Transl. from the German by R. Rosenstock.) 599 pp., illus. Edinburgh.

(22) Grinnell, J.

1931. SOME ANGLES IN THE PROBLEM OF BIRD MIGRATION. Auk 48: 22—32.

(23) Gross, A. O.

1927. THE SNOWY OWL MIGRATION OF 1926-27. Auk 44: 479-493, illus.

(24) Harrison, T. H.

1931. ON THE NORMAL FLIGHT SPEEDS OF BIRDS. Brit. Birds 25: 86-96.

(25) Lincoln, F. C.

1917. BOHEMIAN WAXWING (BOMBYCILLA GARRULA) IN COLORADO. Auk 34: 341.

(26) ——————

1922. TRAPPING DUCKS FOR BANDING PURPOSES: WITH AN ACCOUNT OF THE RESULTS OBTAINED FROM ONE WATERFOWL STATION. Auk 39: 322-334, illus.

(27) ——————

1924. BANDING NOTES ON THE MIGRATION OF THE PINTAIL. Condor 26: 88-90.

(28) ——————

1924. RETURNS FROM BANDED BIRDS, 1920 TO 1923. U. S. Dept. Agr. Bull. 1268, 56 pp., illus.

(29) ——————

1926. THE MIGRATION OF THE CACKLING GOOSE. Condor 28: 153-157, illus.

(30) ——————

1927. NOTES ON THE MIGRATION OF YOUNG COMMON TERNS. North eastern Bird Banding Assoc. Bull. 3: 23-28, illus.

(31) ——————

1927. RETURNS FROM BANDED BIRDS, 1923 TO 1926. U. S. Dept. Agr. Tech Bull. 32, 95 pp., illus.

(32) ——————

1928. THE MIGRATION OF YOUNG NORTH AMERICAN HERRING GULLS. Auk 45: 49-59.

(33) ——————

1934. THE WATERFOWL FLYWAYS OF NORTH AMERICA. U. S. Dept. Agr. Circ. 342, 12 pp., illus.

(34) Magee, M. J.

1928. EVENING GROSBEAK RECOVERIES. Northeastern Bird Banding Assoc. Bull. 4: 56-59.

(35) May, J. B.

1929. RECOVERIES OF BLACK-CROWNED NIGHT HERONS BANDED IN MASSACHUSETTS. Northeastern Bird Banding Assoc. Bull. 5: 7-16, illus.

(36) Palmén, J. A.

1893. REPORT ON THE MIGRATION OF BIRDS. Transl. from the German by C. W. Shoemaker. Smithsn. Inst. Ann. Rept. 1892: 375-396, illus.

(37) Phillips, J. C, and Lincoln, F. C.

1930. AMERICAN WATERFOWL: THEIR PRESENT SITUATION AND THE OUTLOOK FOR THEIR FUTURE. 312 pp., illus. Boston and New York.

(38) Rowan, W.

1925. RELATION OF LIGHT TO BIRD MIGRATION AND DEVELOPMENTAL CHANGES. Nature [London] 115: 494-495.

(39) ——————

1926. ON PHOTOPERIODISM, REPRODUCTIVE PERIODICITY, AND THE ANNUAL MIGRATIONS OF BIRDS AND CERTAIN FISHES. Boston Soc. Nat. Hist. Proc. 38: [147]-189.

(40) Rowan, W.

1930. EXPERIMENTS IN BIRD MIGRATION. II. REVERSED MIGRATION. Natl. Acad. Sci. Proc. 16: 520-525.

(41) ——————

1930. THE MECHANISM OF BIRD MIGRATION. Sci. Prog. 25: 70-78.

(42) ——————

1931. THE RIDDLE OF MIGRATION. 151 pp., illus. Baltimore.

(43) Watson, J. B., and Lashley, K. S.

1915. AN HISTORICAL AND EXPERIMENTAL STUDY OF HOMING. Carnegie Inst. Washington, Dept. Marine Biol. Papers 7: 1-60, illus.

(44) Wetmore, A.

1923. MIGRATION RECORDS FROM WILD DUCKS AND OTHER BIRDS BANDED IN THE SALT LAKE VALLEY, UTAH. U. S. Dept. Agr. Bull. 1145, 16 pp., illus.

(45) ——————

1926. THE MIGRATIONS OF BIRDS. 217 pp., illus. Cambridge, Mass.

(46) Winkenwerder, H. A.

1902. THE MIGRATION OF BIRDS WITH SPECIAL REFERENCE TO NOCTURNAL FLIGHT. Wis. Nat. Hist. Soc. (n. s.) 2: [177]-263, illus.