8 BIRDS OF MASSACHUSETTS 



its tributaries, drains three fourths of Middlesex, and one fourth 

 of Worcester Counties. The Ipswich, Mystic, Charles and Nepon- 

 set Rivers, with their tide-water marshes are the other important 

 streams of the coast. In northern Berkshire, the Hoosac River 

 flows northwestward, emptying into the Hudson River outside 

 the confines of the State. It seems probable that this valley may 

 serve as a highway along which southern and western species are 

 enabled to reach northern Berkshire. 



In Worcester County are the greatest number of lakes. Many 

 of considerable size occur also in the southeastern part of the 

 State, and there are a few large bodies of water in the Housatonic 

 Valley in southern Berkshire. 



The mean annual temperature of Massachusetts ranges from 

 44 F. in the northern part of the State to 50 in the extreme 

 southeast. During the summer months, the isothermal line of 

 65 dips into the northern part of the State on either side of the 

 Connecticut Valley, whither it is brought down by the mountain- 

 ous regions about Mt. Greylock and Mt. Wachusett. The isotherm 

 of 68 on the other hand swings up the Connecticut Valley from 

 the south, as far as the Holyoke Range. During the winter 

 months, the temperature averages from about 22 in the north- 

 west, to 30 and 32 along the south shore and the islands of 

 Martha's Vineyard and Nantucket. 



The average rainfall for the year is least in the extreme north- 

 western part of the State, and is greatest over a narrow belt ex- 

 tending from northeast to southwest across the east-central region. 

 Proximity to the sea reduces the quantity of rainfall along the 

 coast in summer, but causes great humidity in this region during 

 the cool seasons. 



Four life zones are represented by the breeding birds of Massa- 

 chusetts, viz.: the Upper Austral, the Transition, the Canadian 

 and the Hudsonian zones. These will be considered separately 

 as follows : 



Upper Austral : Representatives of this life zone are present as 

 a small, though fairly constant element of the breeding fauna in the 

 valleys of the Housatonic and Hoosac Rivers of Berkshire County 

 and the southern part of the Connecticut Valley in Hampden and 

 Hampshire Counties, as well as the valleys along the south shore 



