428 REPTILES AND BIRDS. 
the space of twelve hours, it follows that they must have travelled 
the above space at the rate of a mile a minute. One of these birds, 
if able to keep up this velocity, could visit the European continent 
(from America) in less than three days.” 
It is not for the purpose of seeking a warmer climate that they 
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IK 
Fig. 163.—Migratory Pigeons, 
undertake their journeys, but to procure food when the acorns 
become scarce in the woods which they inhabit. Their migrations, 
consequently, are irregular as to date. Looking at the innumerable 
and closely packed masses of passenger Pigeons which take part in 
these voyages confuses the mind. Audubon one day endeavoured 
to count the flocks which passed above him in one hour. He counted 
163 in twenty minutes, but he was soon obliged to give up, the 
