INTRODUCTION 13 



THE LIFE ZONES OF THE REGION 



In spite of the relatively small size of the Region as de- 

 limited above, it is remarkably diversified, and birds are 

 surprisingly abundant. With the exception of high moun- 

 tains and deserts, almost every type of habitat calculated to 

 attract birds is found locally, and the coast line and the 

 Hudson River Valley are well known highways of migration. 

 It remains to be determined whether the Delaware Valley 

 and the Kittatiny Ridge on our western boundary is not 

 another highway of migration. In spite of the presence of 

 one of the largest cities of the world, with a large suburban 

 area, and even more distant summer resorts, there is a large 

 amount of unspoiled and relatively untouched country still 

 remaining. 



The great variety of bird-life in this vicinity, however, is 

 not so much due to natural advantages of habitat and the 

 fact that migratory hosts pass through twice each year, as to 

 certain other more fundamental causes. It is a curious fact, 

 as yet but partly understood, that groups of species of animals 

 and plants range over almost identical areas, and are not 

 found, at least in the breeding season, either north or south of 

 limits which are definable with a fair degree of accuracy. 

 Whatever the natural causes may be that govern the ranges 

 of these species, they are taken as indices of natural life zones 

 or faunal areas. The change from one faunal area to another 

 is, of course, a gradual one, except where high mountains 

 cause a rapid change in temperature and climate with the 

 change in altitude. In relatively level country no sharp lines 

 of demarcation can be drawn, and between any two faunal 

 areas a neutral zone will exist in which occur species char- 

 acteristic of each. The New York City Region happens to 

 be situated in territory occupied or touched by three different 

 life zones. The Upper Austral or Carolinian Zone reaches its 

 northern limit in parts of our area, or extends but little 

 beyond it along the coast and up the Hudson River Valley. 



