12 A GUIDE TO THE BIRDS 



tion of any one species varies, largely according to the abun- 

 dance of the species, but also according to some unexplained 

 idiosyncrasy of the bird. The Yellow-rumped Warbler is 

 passing through sometimes for a period of over a month ; the 

 first Rusty Blackbird often appears late in March, and the 

 last in early May. Certain birds are seen much less fre- 

 quently in migration than one would expect from their abun- 

 dance northward ; the Winter Wren and the Sapsucker are 

 examples. Some birds have very different routes in spring 

 and fall ; the Connecticut Warbler is almost never found in 

 New England in spring, but is sometimes locally common in 

 the autumn, while the Blackburnian Warbler is much rarer 

 in the autumn than in the spring. Several birds, therefore, 

 the Yellow-bellied Flycatcher and the Bay-breasted Warbler, 

 for instance, occur as not uncommon migrants along the 

 Hudson, or even in the Connecticut Valley, though rare in 

 eastern New England. 



The spring is an easier time to identify migrants than the 

 autumn. Nearly all the males are in full song in the spring ; 

 very few sing at all in the autumn. Many birds change their 

 plumage in the summer, and lose their bright distinctive 

 marks. And yet, to an enthusiast, there is something very 

 fascinating in the study of the fall migrants. In spring, the 

 bird's song generally betrays his presence for some time be- 

 fore he is seen ; but in the autumn one is kept constantly on 

 the alert to discover in the flocks of small restless warblers 

 or sparrows, often dull colored and puzzling, some novelty 

 or rarity. 



Perhaps the most interesting experience connected with 

 the study of birds is to hear the notes of migrants passing 

 overhead on clear nights in August and September. The 

 tsip of Black-poll Warblers or the chink of a Bobolink fall- 

 ing from the darkness, brings home to one with startling 

 impressiveness the wonder of the long journey from northern 

 New England to the Equator and back again. 



