746 THE AMERICAN NATURALIST. [Vor. XXXVI. 
EFFECT OF TEMPERATURE CHANGES ON THE MIGRATORY 
MOVEMENTS OF Hawks. 
To what extent these flights of hawks and other land birds 
are due to changes of temperature is difficult to determine. 
An examination of the data given in Table I, however, shows 
the following facts : 
1. The direction of the wind at Boston at the 7 and 
8 A.M. observations on days when twenty-four flights of 
hawks occurred was as follows: north, six days; north- 
west, eight days; west, ten days. Total, twenty-four days. 
2. The mean velocity of the wind for the twenty-four days 
(morning observations) was thirteen miles an hour, maximum 
twenty-four miles per hour, minimum eight. (In many cases 
the wind increased considerably during the day.) 
3. Mean change of temperature in past twenty-four hours 
of twenty-four days on which flights occurred was — 5.7 degrees. 
4. The number of days with higher temperature than the 
preceding day was four (+ 5 -- 2 4- 2 + 1). 
5. The number of days with lower temperature than pre- 
ceding day, but less than three degrees change, was six 
(—2—2—3—2—2-— 93) 
From the above it is seen that on ten days of the twenty- 
four in the table the temperature was either higher than the 
preceding day (in four cases) or lower by not more than three 
degrees. It seems evident, therefore, that the chief causes of 
the great migratory movements that occurred on the days given 
in the table were the favorable winds and not diminution of 
temperature. 
Time or Day DURING WHICH HAWKS MIGRATE. 
When hawks occur in flights during the autumn migrations 
they usually make their appearance some time after sunrise and 
continue flying all day, the maximum of the flight occurring 
in the forenoon in southeastern Connecticut and in the after- 
noon near the New York state line. In the former locality 
the sharp-shinned hawks begin to appear soon after sunrise and 
