PREFACE. Xtii 



of its breeding near Springfield. The casual visits of northern 

 birds in winter, which we may suppose sometimes results from 

 their being driven south by want of food or the severity of the 

 season, are also less remarkable, it appears to me, than the 

 occurrence here of southern species, as of the two Egrets, the 

 Little Blue Heron (Florida Ccerulea) the Gallinules and other 

 aquatic species, which never, so far as known (with one excep- 

 tion perhaps), breed so far north. In" the latter case they are 

 generally young birds that reach us towards fall in their chance 

 wanderings. 



" It may here be added that the cause of the migration of our 

 birds* still offers an interesting field for investigation. Obser- 

 vers are of late noting that in the case of some northern spe- 

 cies that reach us only occasionally in their winter migrations, 

 young birds only are at first seen, but if the migration contin- 

 ues the older birds appear at a later date. But sometimes 

 young birds only are seen. This frequently happens in the 

 case of the Pine Grosbeak (Pinicola eneudeator). The cause 

 of their visits is not always, it is evident, severe weather ; the 

 last named species appearing sometimes in November, weeks 

 before severe cold sets in while at other times it is not 

 seen at all during some of our severest winters. The probable 

 cause is more frequently, doubtless, a short supply of food, as 

 last winter was remarkable in this state for its mildness and 

 for the great number of northern birds that then visited us. 

 It has repeatedly been observed that on their first arrival these 

 unusual visitors are generally very lean, but that they soon 

 fatten ; an argument in favor of the theory that their migra- 

 tion was compelled by a scarcity of food. 



"Probably fewer birds are actually permanently resident at 

 a given locality than is commonty 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 



