26 



as a basis of comparison, but also to serve as a model for observers in 

 future years. 



The expression li Urd wave" has been used many times. The term 

 is capable of two interpretations; consequently, two methods of study 

 are possible. 



(1) A "bird wave' 7 may be considered to consist of a very large num- 

 ber of individuals, of one or many species, which suddenly invade a 

 certain area. In studying such a wave it is necessary to ascertain the 

 species of which it is composed and the boundaries of the area over 

 which, it extends. 



(2) Certain species, known to be migrating in company on a given 

 day, may be considered to constitute a "wave," and their progress may 

 be watched from day to day and from week to week. 



This latter mode of study is applicable to the earliest waves only, for 

 it is only early in the season, if at all, that the same species which are 

 together in the south keep together during the entire journey. In all 

 the later waves the species migrating in company change from day 

 to day. Hence no attempt will be made to follow waves of this char- 

 acter; and the first, or bird waves proper, will alone be dealt with. 



It is usually believed that all birds reach their winter quarters by 

 the end of December, but in this respect the winter of 1883-84 was 

 exceptional. The fall of 1883 was very warm, and from latitude 39° 

 southward there was no cold weather before Christmas. About this 

 time, however, the real winter set in, and by January 2 it had extended 

 southward to latitude 33°. Hence, fall migration did not end until the 

 first week in January; and since spring migration began in central 

 Mississippi on January 11, but little time was left between the end of 

 the southward and beginning of the northward movement. It is to be 

 observed, however, that the southward movement of January 1 was con- 

 fined chiefly to the Thrush and Sparrow families, while the northward 

 movement consisted wholly of water-birds. As examples of this late 

 staying of birds at the north the following may be selected: Dr. G. S. 

 Agersborg reported from Vermillion, Dak. (latitude 42° 56'), that "in 

 early January birds were few, probably owing to previous mild weather. 

 On January 5 winter set in, with the thermometer at 34J° below zero, 

 and by the end of the month all our winter residents were here except 

 the Bohemian Waxwing, the Evening Grosbeak, and the Magpie. Pur- 

 ple Grakles and Cowbirds did not leave until December 26, a later date 

 by twenty-seven days than any noted since 1867, when I commenced 

 to record arrivals and departures." 



At Saint Louis, Mo. (lat. 38° 40'), the cold spell set in with a snow- 

 storm January 1, causing most of the Bluebirds, Shrikes, Bed-tailed 

 Hawks, Bed-shouldered Hawks, and Gulls to retreat southward, and 

 bringing down large numbers of Crows. 



From Anna, 111. (lat. 37° 30'), C. W. Butler reported : "Until Janu- 

 ary 2, I could pick strawberry blossoms growing out of doors and 



