178 
PASSENGER TURTLE. 
unlike those of other birds, whose movements are 
considerably affected by temperature, are not under- 
taken, at any fixed period or season of the year', or 
frozen or cold, to a warmer climate, but are entirely 
regulated by the supply or want of food ; for Audu- 
bon, in his interesting account of this bird, remarks, 
“ It sometimes happens, that a continuance of a suf- 
ficient supply of food in one district will keep these 
birds absent from another for years. I know at 
least to a certainty, that, in Kentucky, they re- 
mained for several years constantly, and were no 
where else to be found. They all suddenly disap- 
peared one season, when the mast was exhausted, 
and did not return for a long period.” 
Their power of flight, indicated by the length of 
their wings and tail, is very great ; and, indeed, with- 
out a locomotive gift of extraordinary extent, it 
would be impossible for such countless numbers as 
are seen associated together to exist ; for the supply 
of food in the immediate neighbourhood of their 
roosting resort or their breeding-places, when they 
are necessarily engaged for months together, soon 
becomes exhausted, and they have frequently to tra- 
verse each day an immense distance in quest of a 
further supply. This is proved by facts naiTated by 
Wilson in his graphic history of this bird, as well as 
by Audubon, who mentions the extraordinary cir- 
cumstance, that “pigeons have been killed in the 
neighbourhood of New York, with their crops full of 
rice, which they must have collected in the fields of 
