and noted the combination of weather conditions described above 

 was ideal for mass migrations of ducks during November. During 

 this period, observers at Delta, Manitoba, south to Louisiana 

 recorded a tremendous flight of ducks as the proper conditions of 

 barometric pressure, temperature, wind, and cloud cover passed 

 across the central United States and Canada. An example of the type 

 of weather system that is often associated with mass movements is 

 illustrated in Fig. 12. 



Records of lapwings on Newfoundland and the Gulf of St. 

 Lawrence appear to be the result of a particular series of 

 meteorological events (Bagg 1967). The lapwing is a European 

 species rarely found in the New World. If cold air moves into western 

 Europe from the east, lapwings move westward into England, Wales, 

 and Ireland. Occasionally, the development of an anomalous weather 

 pattern over the North Atlantic including an elongated low from 

 Europe to eastern Canada causes some birds to be literally "blown" in 

 the counter-clockwise airstream across the Atlantic to the Gulf of St. 

 Lawrence. 



During spring migration, weather conditions conducive to strong 

 movements of birds are somewhat the opposite from those in the fall. 

 Migrants will move north on the warm sector of an incoming low. 

 When a high pressure area has just passed, the influx of warm moist 

 tropical air is extended and intensified (Bagg et al. 1950). However, 

 during this time, cloudiness and rain associated with the low may 

 curtail migration or squeeze it into a narrow period proceeding along 

 the warm front. If a fast moving cold front approaches from the 

 northwest, the rapid movement of migrants will be sharply curtailed 

 or even grounded until more favorable conditions occur. 



The incessant crescendo note of the ovenbird is ordinarily 

 associated with the full verdure of May woods, but this bird has been 

 known to reach its breeding grounds in a snowstorm, and the records 

 of its arrival in southern Minnesota show a temperature variation 

 from near freezing to full summer warmth. Temperatures at arrival 

 of several other common birds vary from 14 between highest and 

 lowest temperatures to 37, the average variation being about 24. 

 North American species spending the winter months in tropical 

 latitudes experience no marked changes in temperature conditions 

 from November to March or April, yet frequently they will start the 

 northward movement in January or February. This is in obedience to 

 physiological promptings and has no relation to the prevailing 

 weather conditions. For migratory birds the winter season is a period 

 of rest, a time when they have no cares other than those associated 

 with the daily search for food or escape from their natural enemies. 

 Their migrations, however, are a vital part of their life cycles, which 

 have become so well adjusted that the seasons of travel correspond in 

 general with the major seasonal changes on their breeding grounds. 

 With the approach of spring, therefore, the reproductive impulse 

 awakens, and each individual bird is irresistibly impelled to start the 

 journey that ends in its summer home. 



53 



