22 



catchers. But the laws of atmospheric movements remain unchanged, 

 and their effect on the movements of birds is the same in kind, but 

 slightly different in degree. A north wind still retards their move- 

 ments, but it comes with no icy breath, and when the fancy takes them 

 they move easily against its no longer dreaded force. 



May 3, the record began at 11 p. m., at which time there was an area 

 of low pressure in northeastern Dakota and Manitoba, the barometer 

 being very low at Qu'Appelle (29.38 inches). Most of the Mississippi 

 Valley was included between 29.7 inches and 30.0 inches, the latter 

 being the reading all along our eastern border. 



This low area produced southerly winds over most of the district, 

 there being nothing but S., SE., and SW. winds in the region north of 

 Saint Louis. The temperature was high (58° to 61°) along the Missis- 

 sippi and the lower Missouri to Saint Paul and Omaha, falling to 55° 

 at Saint Vincent and Bismarck, and falling rapidly around the lakes to 

 42° at Marquette. South of Milwaukee and Omaha the weather was 

 cloudy; north of these places, clear. During the night the low area 

 moved south to a point a little below Bismarck, the south wind still blow- 

 ing over the Mississippi Valley, with increased cloudiness in the north- 

 ern part. By 3 p. m. May 4, West Las Animas, Colo., was the center 

 of the low area, and there was a decided fall in pressure over all the 

 United States east of the Bocky mountains, causing the south wind to 

 blow still harder, with clouds and local rains in the Upper Mississippi 

 Valley. Such was the preparation for the bird wave of the night of 

 May 4, for after 3 p. ra. the low area turned northeastward and passed 

 directly across the upper rmrt of the district, being central at Yankton 

 at 11 p. m., with a pressure of 29.64 inches. Thus all the migration 

 during the nights of May 3 and 4 was on a falling barometer — on the 

 night of the 4th with cloudiness, and on both nights with warm south- 

 erly winds. 



In the study of migration in May, one must deal almost entirely with 

 the 11 p. m. weather observations, for towards the latter end of migra- 

 tion the movement is for the most part by night. It is true that a few 

 birds, the Warblers for instance, move a little during the daytime, pass- 

 ing slowly from tree to tree; but short distances only are made in these 

 journeyings, leaving the bulk of the movement to be performed at night. 



During the night of May 3 but few movements took place, and more 

 than half of these were around Saint Paul and to the northward, where 

 the influence of the low area in Manitoba was already beginning to be 

 felt. The full advance was postponed until the next night, which was 

 one of great movement over most if not all of the country between Saint 

 Louis and Manitoba. The districts which furnished but nine records 

 for the night of May 3, on the next night showed nearly seventy. The 

 wave seems to have been most pronounced in Iowa, northern Illinois, 

 southern Wisconsin, and at Saint Louis, with a heaver wave in Mani- 

 toba and another in northern Texas: but it is not unlikely that this 



