II. BIRD MIGRATION. 



GENERAL DISCUSSION OF MIGRATION.* 



The semi-annual migration of birds, north-ward in the spring, and 

 south-ward in the fall, is familiar to all who have paid any attention to 

 ornithology. Only a very small proportion of our birds remain with 

 us throughout the year, and, although we have quite a number of 

 species present through the winter, after our summer species have 

 left us, the greater number are visitors from farther north. 



According to the character of their migration, the birds of any 

 locality are generally arranged under four heads : 



Residents, are those which are present throughout the year. In 

 many cases however, these are more numerous in summer than in 

 winter. 



Summer Residents; those which breed at the locality under con- 

 sideration, arriving from the south in the spring and returning again 

 in the fall. 



Transient Visita7its breed farther north and winter farther south, 

 passing through the specified locality on their migrations. 



Winter Visitants occur during the winter, arriving from the north 

 in the fall and returning again to their breeding grounds in the 

 spring. 



The habit of migration, probably, originating in the seasonal 

 change of climate and failure of the supply of suitable food, has 



* Every one interested in this subject should consult Mr. William Brewster's 

 instructive paper on " Bird Migration " (Memoirs of the Nuttall Ornithological 

 Club, No. I. Cambridge, Mass., 1886. Published by the Club.), which is a 

 most valuable review of the subject, based upon the author's extensive expe- 

 rience. The observations of the Delaware Valley Ornithological Club, so far 

 as they go, coincide entirely with Mr. Brewster's statements, and in the pres- 

 ent chapter several direct quotations or abstracts have been taken from his 

 paper as most clearly explaining the points under discussion. 



Another valuable paper which should be consulted is " Report on Bird Mi- 

 gration in the Mississippi Valley, by W. W. Cooke (Edited and Revised by Dr. 

 C. Hart Merriam), U. S. Dept. of Agriculture, Division of Economic Orni- 

 thology, Bulletin No. 2. Washington, 1888." 



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