346 SWALLOWS. 
more northern parts than from the southern, is not 
invariably abided by, and perhaps as temperature 
and food both operate on them in determining the 
time of their migrating, one of these (most likely*the 
former) or both might be so far favorable in some 
particular district or county, as to cause the Swal- 
lows or Hirundines as a whole there resident to 
protract their stay. At all events after the Swallows 
of our own neighbourhood have disappeared, flocks 
arrive hither and rest awhile previously to under- 
taking their passage over the seas, thus on October 
15th, 1831 an immense flock was collected on the 
buoy of a reservoir adjoining the coast of Plymouth 
Sound, another flock was seen departing Oct. 23rd ; 
about October 28th, 1834 a large company was seen 
approaching the coast ; on November Ist, 1835 a 
flock settled at a village not far from Plymouth, and 
after recruiting their powers mounted high in the 
air and departed in a south-eastern direction. So 
far as | am able to decide, our own Swallows quit 
us at different periods and in different distinct com- 
panies from the latter end of September to about 
the 5th of October ; flights have more than once 
been noticed on October 16th, but these most likely 
came from more northward situations. Food has 
great power in determining the time of their quitting 
us, but no doubt temperature or weather generally 
has still more, especially as this may itself greatly 
influence the supply of the former. ‘The compa- 
rative powers of these two circumstances, together 
with other useful information might be gained, if 
naturalists would take means of comparing the times 
of departure and the circumstances attendant there- 
on as regards food and weather in different situa- 
tions. But if weather is granted to be of so much 
consequence, the difficulty of explaining the long 
protracted delays of some few individuals becomes 
so much the more increased, unless we be content to 
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