xxii PKEFACE. 



" Probably fewer birds are actually permanently resident at 

 a given locality than is commonly supposed, for species seen 

 the whole year at the same locality, as the Blue Jay, the Tit- 

 mouse, the Brown Creeper, and the Hairy and Downy Wood- 

 pecker, etc., in Massachusetts, are represented, not by the 

 same, but by different sets of individuals, those seen here in 

 summer being not those seen in winter, the species migrating 

 north and south, en masse, with the change of season. We 

 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 Tringae, linger on 

 our coast during summer, while the adult all retire north- 

 ward, 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 to 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 plumaged 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 colored and immature 

 birds, especially among the Sylvicolidce^ or warblers, towards 



" In respect to the proof whereon Boston Society of Natural History, VoL 

 this proposition rests, see my remarks i, Pt. iv, p. 488 (foot note)." 

 on this point in the Memoirs of the 



