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1855.] ^ t. ti fj^ _ 491 
I . . 
THE SENSE OF SIGHT IN BIRDS. 
A udubon lias written an amusing 
book, I had almost said of fables, 
called Ornithological Biography. By 
a number of cruel experiments, he has 
proved to his own entire satisfaction, and 
that of many others, that vultures are 
led to their food by the sense of sight 
alone; the sense of smell, which they 
were supposed to possess in an exqui- 
site degree, affording them not the 
slightest assistance. His experiments 
prove quite too much for his purpose, 
for they equally deprive the poor bird in 
question of both sight and smell. It is 
certain that this bird possesses both 
senses in great perfection, and equally 
certain that neither nor both are the 
sole means it employs for obtaining its 
food. Though the senses in animals 
are means of obtaining them food, they 
are not the sole means, as we very weU 
know. 
It is a most curious question, and weU 
worth more attention than it has ever 
yet received. For want of a better ex- 
planation, we usually say there is an 
instinct that enables animals to find 
tlieir food. Many go from great dis- 
tances directly to it. Pigeons find out 
newly-sown fields immediately, and will 
frequently go several miles to afield the 
very first morning after it is sown. 
Wild ducks that feed at night, are equal- 
ly quick in finding their food ; and in 
this case, I would bo glad to know what 
sense they employ. Tlio red-deer inva- 
riably knows when the shepherd’s patch 
of grain is fit for his food, and will fre- 
quently come down in such numbers as 
to cat up the entire crop in a single 
night. In fact, all birds, whatever their 
food may be, have an instinctive power 
of discovering it immediately, and that 
from such distances as no acuteness 
of either sight or smell will account for. 
Without allowing this, you cannot ex- 
plain facts too numerous, and too well 
authenticated, to be doubted. It is pre- 
cisely the same faculty, whatever it may 
be, that enables the carrier-pigeon to 
find its way home, take it what dis- 
tance, and any way covered up, you will. 
Toss it up in the air, and, after circling 
for a few moments, it adopts its line of 
flight, without hesitation and without 
mistake. Audubon himself furnishes an 
instance of the exercise of this facul- 
ty, in his description of the razorbill. 
“ The instinct or sagacity which ena- 
bles the razorbills, after being scattered 
in all directions, in quest of food, during 
the long night, often at great distances 
from each other, to congregate towards 
morning, previously to their alighting 
on a spot to rest, has appeared to mo 
truly wonderful : and I have been 
tempted to believe that their place of 
rendezvous had been agreed upon the 
evening before.” 
In disputing about the comparative 
value of the senses of sight and smell in 
birds, authors notice a much more curi- 
ous fact — the great power birds possess 
of altering the focal length of their eyes. 
To see equally well an object at a dis- 
tance of many miles, and a minute seed 
or insect an inch from the bill, may well 
amaze us. Observe the first person of 
yoiu* acquaintance you meet, Avho hap- 
pens to wear spectacles. If he looks at an 
object near him, he looks through his 
glasses : if at a more distant one, over 
them. Go to a practical optician and 
desire him to construct an instrument 
that will enable you to do what birds 
are constantly doing in this, and ho will, 
most likely, teU you the thing is im- 
possible. 
Man probably surpasses birds in ex- 
tent of vision, as much as birds suiq^ass 
man in sharpness. Ross, in his voyage 
to Baffin’s Bay, proved that a man, un- 
der favorable circumstances, could see 
over the surface of the sea 150 miles. 
It is not probable that any animal can 
equal this for extent. In sharpness of 
sight, on the other hand, birds greatly 
excel us. The eagle, soaring at such a 
hight that he seems a mere speck, 
sees the grouse walking in the heather, 
which it so closely resembles in color 
as readily to escape the sportsman’s 
eye. Schmidt threw to a considerable 
distance from a thrush a number of bee- 
tles, of a pale gray color, which the un- 
assisted human eye failed to detect, 
yet the bird observed them immediately. 
Many birds readily perceive insects on 
branches where the sharpest sighted 
person can detect nothing. 
The eyes of birds are remarkable for 
their great comparative size, the great 
convexity of the cornea, and for having 
the sclerotic coat formed anteriorly 
to a circle of bony plates. The optic 
nciu'cs are very large, and unite so 
