As to the other senses, touch is not highly developed except about the
bill, where it reaches a climax in birds like the wood-cock, which probe
for unseen earthworms in the soft soil. Taste seems to be poorly
developed, for most birds bolt their food, but there is sometimes an
emphatic rejection of unpalatable things, like toads and caterpillars.
Of smell in birds little is known, but it has been proved to be present
in certain cases, e.g. in some nocturnal birds of prey. It seems certain
that it is by sight, not by smell, that the eagles gather to the
carcass; but perhaps there is more smell in birds than they are usually
credited with. One would like to experiment with the oil from the preen
gland of birds to see whether the scent of this does not help in the
recognition of kin by kin at night or amid the darkness of the forest.
There may be other senses in birds, such as a sense of temperature and a
sense of balance; but no success has attended the attempts made to
demonstrate a magnetic sense, which has been impatiently postulated by
students of bird migration in order to "explain" how the birds find
their way. The big fact is that in birds there are two widely open
gateways of knowledge, the sense of sight and the sense of hearing.