Produced by Chris Curnow, Tom Cosmas, Joseph Cooper, The Internet Archive for some images and the Online Distributed Proofreading Team at http://www.pgdp.net A Quantitative Study of the Nocturnal Migration of Birds BY GEORGE H. LOWERY, JR. University of Kansas Publications Museum of Natural History Volume 3, No. 2, pp. 361-472, 47 figures in text June 29, 1951 University of Kansas LAWRENCE 1951 UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY Editors: E. Raymond Hall, Chairman; A. Byron Leonard, Edward H. Taylor, Robert W. Wilson UNIVERSITY OF KANSAS Lawrence, Kansas PRINTED BY FERD VOILAND, JR., STATE PRINTER TOPEKA, KANSAS 1951 [Union Label] 23-1020 A Quantitative Study of the Nocturnal Migration of Birds By GEORGE H. LOWERY, JR. CONTENTS Page INTRODUCTION 365 ACKNOWLEDGMENTS 367 PART I. FLIGHT DENSITIES AND THEIR DETERMINATION 370 Lunar Observations of Birds and the Flight Density Concept 370 Observational Procedure and the Processing of Data 390 PART II. THE NATURE OF NOCTURNAL MIGRATION 408 Horizontal Distribution of Birds on Narrow Fronts 409 Density as a Function of the Hour of the Night 413 Migration in Relation to Topography 424 Geographical Factors and the Continental Density Pattern 432 Migration and Meteorological Conditions 453 CONCLUSIONS 469 LITERATURE CITED 470 LIST OF FIGURES Figure Page 1. The field of observation as it appears to the observer 374 2. Determination of diameter of cone at any point 375 3. Temporal change in size of the field of observation 376 4. Migration at Ottumwa, Iowa 377 5. Geographic variation in size of cone of observation 378 6. The problem of sampling migrating birds 380 7. The sampling effect of a square 381 8. Rectangular samples of square areas 382 9. The effect of vertical components in bird flight 383 10. The interceptory potential of slanting lines 384 11. Theoretical possibilities of vertical distribution 388 12. Facsimile of form used to record data in the field 391 13. The identification of co-ordinates 392 14. The apparent pathways of birds seen in one hour 393