Front matter (continued 3)

Although the forces associated with an ordinary low-pressure area are by no means as intense as those associated with a tropical hurricane, the forces operating are much the same. Consequently birds conceivably might tend to be drawn toward a focal point near the center of the low, where the other factors already mentioned would tend to precipitate the entire overhead flight. Visible evidence of migration would then manifest itself to the field ornithologists.

CONCLUSIONS

1. Telescopic counts of birds passing before the moon may be used to determine reliable statistical expressions of the volume of migration in terms of direction and of definite units of time and space.

2. Night migrants fly singly more often than in flocks, creating a remarkably uniform dispersion on a local scale throughout the sky, quite unlike the scattered distributions observable in the daytime.

3. The nocturnal migration of birds is apparently preceded by a resting or feeding pause during which there are few migrants in the air. It is not to an important degree a non-stop continuation of flights begun in the daylight.

4. Nightly migrational activity in North America varies from hour to hour according to a definite temporal pattern, corresponding to the Zugunruhe of caged European birds, and expressed by increasingly heavy flights up until the hour before midnight, followed by a pronounced decline.

5. The visible effects of the time pattern are subject to modification at a particular station by its location with respect to the resting areas from which the night's flight originates.

6. Quantitative and directional studies have so far failed to prove that nocturnal migrants favor narrow, topographically-determined flight lanes to an important degree.

7. Flight densities on the east coast of Mexico, though of first magnitude, have not yet been demonstrated in the volume demanded by the premise that almost all migrants returning to the United States from regions to the south do so by coastal routes.

8. Heavy flights have been recorded from the northern coast of Yucatán under circumstances leading inevitably to the conclusion that birds migrate across the Gulf of Mexico in considerable numbers.

9. There is reason to believe that the importance of the Florida Peninsula as an April and May flyway has been over-estimated, as regards the numbers of birds using it in comparison with the numbers of birds using the Mexican and Gulf routes.

10. The amount of migration is apparently seldom sufficient to produce heavy densities of transient species on the ground without the operation of concentrative factors such as ecological patterns and meteorological forces.

11. The absence or scarcity of transients in some areas in fine weather may be explained by this consideration.

12. A striking correlation exists between air currents and the directional flight trends of birds, suggesting that most night migrants travel by a system of pressure-pattern flying.

LITERATURE CITED

Allen, R. P., and R. T. Peterson

1936. The hawk migrations at Cape May Point, New Jersey. Auk, 53:393-404.

Anonymous

1936-1941. Tables of computed altitude and azimuth. U. S. Navy Department Hydrographic Office. U. S. Govt. Printing Office, Washington, D. C., vols. 3-5.

1941. Airway meteorological atlas for the United States. Weather Bureau Publ. 1314. U. S. Dept. Commerce, Washington, D. C.

1945-1948. The American air almanac. U. S. Naval Observatory. U. S. Govt. Printing Office, Washington, D. C., 3 vols., issued annually.

1948a. Meteorological and climatological data for April 1948. Monthly Weather Review, April 1948, 76:65-84, 10 charts.

1948b. Meteorological and climatological data for May 1948. Monthly Weather Review, May 1948, 76:85-103, 11 charts.

Bagg, A. M.

1948. Barometric pressure-patterns and spring migration. Auk, 65:147.

Bergman, G.

1941. Der Fruhlingszug von Clangula hyemalis (L.) und Oidemia nigra (L.) bei Helsingfors. Eine Studie über Zugverlauf und Witterung sowie Tagesrhythmus und Flughöhe. Ornis Fennica, 18:1-26.

Bray, R. A.

1895. A remarkable flight of birds. Nature (London), 52:415.

Carpenter, F. W.

1906. An astronomical determination of the height of birds during nocturnal migration. Auk, 23:210-217.

Chapman, F. M.

1888. Observations on the nocturnal migration of birds. Auk, 5:37-39.

Davis, L. I.

1936-1940. The season: lower Rio Grande Valley region. Bird-Lore (now Audubon Mag.), 38-42.

F. [arner], D. [onald] S.

1947. Studies on daily rhythm of caged migrant birds (review of Palmgren article). Bird-Banding, 18:83-84.

Gates, W. H.

1933. Hailstone damage to birds. Science, 78:263-264.

Howell, A. H.

1932. Florida bird life. Florida Department Game and Fresh Water Fish, Tallahassee, 1-579 + 14 pp., 58 pls., 72 text figs.

Lansberg, H.

1948. Bird migration and pressure patterns. Science, 108:708-709.

Libby, O. G.

1899. The nocturnal flight of migratory birds. Auk, 16:140-146.

Lowery, G. H., Jr.

1945. Trans-Gulf spring migration of birds and the coastal hiatus. Wilson Bull., 57:92-121.

1946. Evidence of trans-Gulf migration. Auk, 63:175-211.

Mayhew, D. F.

1949. Atmospheric pressure and bird flight. Science, 109:403.

Overing, R.

1938. High mortality at the Washington Monument. Auk, 55:679.

Palmgren, P.

1944. Studien über die Tagesrhythmik gekäfigter Zugvögel. Zeitschrift für Tierpsychologie, 6:44-86.

Pough, R. H.

1948. Out of the night sky. Audubon Mag., 50:354-355.

Putkonen, T. A.

1942. Kevätmuutosta Viipurinlakdella. Ornis Fennica, 19:33-44.

Rense, W. A.

1946. Astronomy and ornithology. Popular Astronomy, 54:55-73.

Scott, W. E. D.

1881a. Some observations on the migration of birds. Bull. Nuttall Orni. Club, 6:97-100.

1881b. Migration of birds at night. Bull. Nuttall Orni. Club, 6:188.

Siivonen, L.

1936. Die Stärkevariation des Nächtlichen Zuges bei Turdus ph. philomelos Brehn und T. musicus L. auf Grund der Zuglaute geschätz und mit der Zugunruhe einer gekäfigten Singdrossel Verglichen. Ornis Fennica, 13:59-63.

Spofford, W. R.

1949. Mortality of birds at the ceilometer of the Nashville airport. Wilson Bull., 61:86-90.

Stebbins, J.

1906. A method of determining height of migrating birds. Popular Astronomy, 14:65-70.

Stevens, Loyd A.

1933. Upper-air wind roses and resultant winds for the eastern United States. Monthly Weather Review, Supplement No. 35, November 13, pp. 1-3, 65 figs.

Stone, W.

1906. Some light on night migration. Auk, 23:249-252.

1937. Bird studies at Old Cape May. Delaware Valley Orni. Club, Philadelphia, Vol. 1, 1-520 + 15 pp., pls. 1-46 and frontis.

Thomson, A. L.

1926. Problems of bird migration. Houghton Mifflin Company, Boston.

Van Oordt, G.

1943. Vogeltrek. E. J. Brill, Leiden, xii + 145 pp.

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1897. Observations of the passage of migrating birds across the lunar disc on the nights of September 23 and 24, 1896. Science, 6:409-411.

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1927. Migration and the telescope. Emu, 26:220-222.

West, R. H.

1896. Flight of birds across the moon's disc. Nature (London), 53:131.

Williams, G. G.

1941-1948. The season: Texas coastal region. Audubon Mag., 43-50.

1945. Do birds cross the Gulf of Mexico in spring? Auk, 62:98-111.

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Winkenwerder, H. A.

1902a. The migration of birds with special reference to nocturnal flight. Bull. Wisconsin Nat. Hist. Soc., 2:177-263.

1902b. Some recent observations on the migration of birds. Bull. Wisconsin Nat. Hist. Soc., 2:97-107.

Transmitted June 1, 1949.

23-1020

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—E. Raymond Hall, Chairman, Editorial Committee.

This series contains contributions from the Museum of Natural History. Cited as Univ. Kans. Publ., Mus. Nat. Hist.

Vol. 1. (Complete) Nos. 1-26. Pp. 1-638. August 15, 1946-January 20, 1951.

Vol. 2. (Complete) Mammals of Washington. By Walter W. Dalquest. Pp. 1-444, 140 figures in text. April 9, 1948.

Vol. 3. 1. The avifauna of Micronesia, its origin, evolution, and distribution. By Rollin H. Baker. Pp. 1-359, 16 figures in text. June 12, 1951.

2. A quantitative study of the nocturnal migration of birds. By George H. Lowery, Jr. Pp. 361-472, 47 figures in text. June 29, 1951.

Transcriber's Notes

With the exception of the typographical corrections detailed below and some minor corrections for missing periods or extra punctuation (item 28 in List of Figures), the text presented here is that contained in the original printed version. A transcription of the Data presented in Figure 12 was added (see below) to illustrate the information contained on that sheet. Some text was moved to rejoin paragraphs.

There are two notes in the original text indicating that the images for Figures 41 and 45 were transposed. The correct images have been placed with the captions and the two notes were removed. Lastly, the cover image was compiled from a copy of the original cover with two of the graphics contained in the article added and the list of UK pulications was moved to the end of the document.

Typographical Corrections

Page Correction

385 flght ⇒ flight

394 diargrams ⇒ diagrams

404 Determinaton ⇒ Determination

411 obsever ⇒ observer

419 Morover ⇒ Moreover

425 Mississippii ⇒ Mississippi

425 a ⇒ as

430 at ⇒ and

431 inserted "a" ("…traveling along a certain topographic feature…")

442 concensus ⇒ consensus

472 Stephens, Loyd A. ⇒ Stevens, Lloyd A.

Transcription of the Data in Figure 12 ORIGINAL DATA SHEET DATE 24-25 April 1948 LOCALITY Progreso, Yucatán OBSERVERS Harold Harry; George H. Lowery WEATHER Moderate to strong "trade" winds along coast, slightly N of E. Moon emerged above low cloud bank at 8:26. INSTRUMENT B. & L. 19.5 Spotting Scope; image erect REMARKS Observation station located 1 mile from land, over Gulf of Mexico, at end of new Progreso wharf -----------+------+-------+-------------------------------------------- TIME | IN | OUT | REMARKS -----------+------+-------+-------------------------------------------- C.S.T | | | 8:26 | -- | -- | observations begin; H.H. observing 50 | 4:30 | 9 | slow; small 56 | 3 | 10 | medium size 9:00 | 2 | 10:30 | very small 11 | 5 | 9:30 | moderately fast 25 | 5 | 10 | very small; rather slow 26 | 3 | 11 | " " 36 | 5 | 10 | medium size 40 | 3 | 10 | " " 43 | 5:30 | 9 | " " 46 | 3:30 | 10 | small 56 | 4:30 | 10 | medium size 9:58-10:00 | -- | -- | time out to change observers; G.L. at scope 10:05 | 4:30 | 11:30 | small 06 | 3 | 11 | 12 | 5 | 8 | very small 25 | 5 | 12 | very fast; small 30 | 4 | 10 | small 32 | 4 | 11 | " 32 | 2 | 11 | " 33 | 5 | 11 | " 33 | 4 | 1 | " 33 | 5:30 | 11 | " 35 | 4:30 | 10 | swallow-like 36 | 5 | 1:30 |