BIRDS OF NEW YORK STATE 139 



The Distribution of Nesting Birds 



1 Life zones or range 



All of North America has been divided into transcontinental 

 bands, or zones, according to differences in temperature and 

 corresponding differences in plant and animal life. These bands, 

 called life zones, are bounded by definite isotherms. They are 

 naturally very irregular in contour because the mean temperature 

 of every locality is aiifected by so many different things, such as 

 altitude, presence of large bodies of vvrater, etc. 



In New York State there are three well-defined zones (Birds 

 of N. Y., p. 19-42), the Canadian or coolest, the austral or 

 warmest, and the transition or intermediate. The main portion 

 of the State is in the transition zone and the majority of birds 

 are typically transition species. The Canadian zone is found 

 throughout the Adirondacks and Catskill region and on hill tops 

 and in cool swamps in other parts of the State. The austral zone 

 predominates in the lower Hudson valley and along the south 

 shore of Lake Ontario where the temperature is modified by the 

 lake. One can tell in which life zone his locality lies by the 

 presence or absence of certain nesting birds. Thus where white- 

 throated sparrows, juncos, hermit thrushes and myrtle warblers 

 nest, one can feel sure he is in the Canadian zone. Where cardi- 

 nals, tufted titmice, Kentucky warblers and yellow-breasted 

 chats are found, it is the austral zone. Where the robin, wood 

 thrush, yellow warbler and rose-breasted grosbeak are common 

 nesters, it is the transition zone. On the tops of the highest 

 Adirondacks and Catskills there is a tinge of a fourth, the Hud- 

 sonian zone, where blackpoll warblers, Bicknell's thrushes and 

 three-toed woodpeckers are found. 



The distribution of birds within each zone is not always uni- 

 form, for some species are remarkably erratic or local in their 

 distribution. Thus while the blue jays and brown thrashers are 

 common in eastern and western New York, they are rare in 

 central New York. 



2 Habitat or environment 



The study of birds is greatly facilitated when one knows just 

 where to expect to find each species. Every species is adapted 

 for some particular habitat and though on its migrations it may 

 be found at a considerable distance from its favorite haunt, when 

 nesting begins and a bird's movements are more restricted, the 



