16 ON THE MIGRATION OF BIRDS. 
easily distinguish them when flying, and I find that 
such feathers are never replaced while these birds re- 
main with us. Great numbers of young Swallows 
retire in autumn before the exterior feathers of their 
tails have acquired their full length, yet the tail- 
feathers of those birds which return in spring are 
always perfect in their growth. To these facts I shall 
add a few extracts from Mr. Pearson’s account of his 
experiments, made for the purpose of preserving 
Swallows alive through the winter, as given in 
Bewick’s ‘ British Birds,’ vol. i. pp. 250, 251, which 
are decisive as to the moulting of this species. The 
first year’s experiment failed ; but the second attempt 
was completely successful, as Mr. Pearson states that 
“the birds throve extremely well, they sung their 
‘song through the winter, and soon after Christmas 
began to moult, which they got through without any 
difficulty, and lived three or four years, regularly 
moulting every year at the usual time. On the re- 
newal of their feathers it appeared that their tails 
were forked exactly the same as in those birds which 
return here in the spring, and in every respect their 
appearance was the same. These birds were exhibited 
to the Society for Promoting Natural History on the 
14th day of February, 1786, at the time they were in 
a deep moult, during a severe frost, when the snow 
was on the ground.” The account is concluded by 
Mr. Pearson in the following words :—“Jan. 20, 
1797. Ihave now in my house, No. 21 Great New- 
