No. 429.] RELATION OF WIND TO BIRD MIGRATION. 751 
4. When the wind is favorable and approximately parallel to 
the direction of migration, hawks fly and sail at a "eu altitude 
and occasionally soar in circles. 
5. When the wind is favorable but sna perpendicular to 
the migratory direction (the favorable component being small), 

riot 
Map III. — EASTERN CANADA AND EASTERN UNITED STATES. 
The dotted lines are the isobars of September 18, 1900. A low barometric pressure is 
centered off the Maine coast. The small arrows indicate the direction ot the wind, and 
its velocity in miles «si hour is given in a number of cases. The mean velocity of the 
wind records on the map as it is given here is over seventeen miles per hour. 
hawks fly low and soar continually, often alternating soaring 
with the wind and flying or sailing nearly against it. 
6. That hawks migrate during the daylight, and, other con- 
ditions being the same, they are most abundant in migratory 
flights when the atmosphere is clear. 
