16 A GUIDE TO THE BIRDS 



found in each of the neighboring belts, and none not shared 

 by one or the other of them. It has therefore been called 

 the Transition Zone. Its boundaries to the north concern us 

 chiefly, for many birds (see p. 342) cease to be found when 

 we pass from this Transition belt to the Canadian. 



Nothing is sharply defined in nature, and so the bounda- 

 ries of these zones, though they may be well defined on maps, 

 have in the actual country a very indefinite outline, one area 

 fading almost insensibly into another. Moreover, certain 

 birds, though confined to the spruce belt, begin to appear at 

 its very margin, while others demand for a summer home 

 deep spruce forests, or other conditions which are attained 

 only well within the belt. Snowbirds, for instance, usually 

 appear with the first small patches of spruce, in Worcester 

 County, Mass. ; Brown Creepers only in large-sized spruce 

 forests, such as occur on Greylock and Monadnock ; and 

 Black-poll Warblers not until the Catskill or White Moun- 

 tain region is reached. Similarly, some of the Carolinian 

 birds, such as the Chat and the Orchard Oriole, are found 

 beyond the range of the others, far up the Housatonic Val- 

 ley or in eastern Massachusetts. 



The range of any particular bird in the breeding season 

 will be found in the account of that bird ; in many cases the 

 map which shows the Life Zones will give the area through- 

 out which the bird commonly occurs. Outside this area, the 

 bird may be expected to occur sparingly, in places which 

 approximate to the warmth or dryness of more southern re- 

 gions, or to the coldness and moisture of the north. Certain 

 lists given in this book (p. 341) should be studied in this 

 connection, and a list is also given on p. 348 of " local lists " 

 which may be either bought, or obtained in large libraries ; 

 these give the latest information as to species found breed- 

 ing in the various localities of which they treat. The student 

 cannot be too strongly urged to make out for himself, by 

 the use of the map and of the lists above mentioned, a list 



