PREFACE. xxi 



also come to light. It is perhaps not remarkable that a pair 

 of birds of species that regularly breed in northern New Eng- 

 land should now and then pass the summer and rear their 

 young in the southern part, as has been the case in certain 

 known instances in the Snow Bird (Jwnco hyemalis), the 

 Pine Finch QGhrysomitris pinus), and the White-throated 

 Sparrow (^Zonotrichia alhicollis) ; but it is otherwise with the 

 Snow Bunting (^Plectrophanes nivalis), which rarely breeds 

 south of Labrador, of which there is a single well authenti- 

 cated instance 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 caerv^ 

 lea) the Gallinules and other aquatic species, which never, so 

 far as known (with one exception 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. 

 Observers are of late noting that in the case of some northern 

 species that reach us only occasionally in their winter migra- 

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

 continues the older birds appear at a later date. But some- 

 times young birds only are seen. This frequently happens in 

 the case of the Pine Grosbeak (^Pinicola eneucleator). The 

 .cause of their visits is not always, it is evident, severe 

 weather ; the last named species appearing sometimes in No- 

 vember, — 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 sup- 

 ply 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 migration was compelled by a scarcity of 

 food. 



