8 Birps 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 
