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 Rocky 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. m. the low area turned northeastward and passed 
directly across the upper part 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 besinuiy 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 heavy wave in Mani- 
toba and another in northern Texas; but it is not unlikely that this 
