1. Albion: migration negligible 2. Ottumwa: 4,600 (1,500) 3. Columbia: 1,400 (400) 5. Louisville: 1,700 (200) 10. Memphis: 6,600 (900) 12. Rosedale: 1,100 (100) 14. Mansfield: 1,700 (400) 18. Pensacola: migration negligible 21. Winter Park: 600 (100) 24. Progreso: 27,300 (3,000)] [Illustration: FIG. 45. Winds aloft at 10:00 P. M. on April 24 (CST). Winds at 2,000 feet above mean sea level are shown in black; those at 4,000 feet, in white. Velocities are indicated by standard Beaufort Scale of Wind Force. The numbers in circles refer to the stations shown in Figure 44.] Correction: Figures 41 and 45 were inadvertently transposed. [Illustration: FIG. 46. Comparison of flight trends and surface weather conditions on May 21-22, 1948. The meteorological data were taken from the U. S. Weather Bureau Daily Weather Map for 12:30 A. M. (CST) on May 22. The nightly station densities and the average hourly station density (shown in parentheses) are as follows: 2. Ottumwa: 6,900 (1,400) 5. Louisville: 1,500 (200) 9. Knoxville: 3,200 (500) 10. Memphis: 7,000 (1,200) 13. Oak Grove: 5,800 (800) 14. Mansfield: 2,500 (800) 18. Pensacola: migration negligible 21. Winter Park: 1,200 (200)] [Illustration: FIG. 47. Winds aloft at 10:00 P. M. on May 21 (CST). Winds at 2,000 feet above mean sea level are shown. Velocities are indicated by standard Beaufort Scale of Wind Force. The numbers in circles refer to the stations shown in Figure 46.] On the first night, following the passage of a cold front, migration at Ottumwa was comparatively low (6,900 birds in five hours). On the following night, when the trajectory of the winds was toward the north, the volume of migration was roughly twice as high (22,300 birds in eight hours). At Louisville, on May 21-22, the nightly station density was only 1,500 birds in seven hours, whereas on the following night, it was 8,400 birds in the same length of time, or about six times greater.