XIV PREFACE. 



are generally cognizant of a migration in a given species only 

 when the great " bird wave" sweeps entirely past us either to 

 the north or south. Some species, however, seem actually 

 fixed at all seasons, and are really essentially non-migratory, 

 as the Spruce Partridge, and Quail (Ortyx Virginianus) are in 

 New England. But only a small proportion, doubtless, of the 

 so-called non-migratory birds at any given locality are really 

 so.* 



"In connection with this topic of migration, the fact that some 

 of the young or immature individuals of our marine birds, as 

 the Herring Gull (Larus argentatus) and other species of that 

 family, and several of the Tringse, linger on our coast daring, 

 summer, while the adult all retire northward, is one of some 

 interest. Mature and strong birds only, in species that breed 

 far to the north, evidently seek very high latitudes. Birds of 

 the first year also appear to roam less widely than the older. 

 In different species of the Gull family it is generally only the 

 mature birds that in winter are seen far out at sea, though in 

 the same latitudes the young may be numerous along the coast. 

 All observant collectors are well aware of the fact that those 

 birds that first reach us in the spring, of whatever species, are 

 generally not only very appreciably larger, but brighter plum- 

 aged and in every way evidently more perfect birds than those 

 that arrive later ; and that in those species that go entirely to 

 the north of us there is a much larger proportion of paler col- 

 ored and immature birds, especially among the Sylvicolidce, or 

 warblers, towards the close of the migrating season than ear- 

 lier. Hence the presence here of a few individuals in summer 

 of species that usually go farther north is not always sufficient 

 evidence that the species breeds with us." n 



Good illustrations are of great assistance to young students, 

 teaching them, better than words, characteristic details of 



*"In respect to the proof whereon this proposition rests, see my remarks on 

 this point in the Memoirs of the Boston Society of Natural History, Vol. i, Ft. iv, 

 p. 488 (foot note)." 



11 Several passages or sentences have, for convenience, been omitted in this 

 extract. 



