[Illustration]
Of course birds can learn. Indeed there's a trite saying that no animal
has been discovered so low that it cannot learn. One of the simplest
cases of learning is shown by parts of some experiments I carried out
years ago on the curve-billed thrasher. I had raised a number of these
thrashers by hand, and in connection with finding out about their
tasting abilities I first fed them on the white of egg, hard-boiled and
cut into little squares. They liked it. Then I soaked more squares of
boiled egg white in evil tasting (to me) formalin. The birds came to
the dish, and also ate them. But after that for a week they refused to
eat such egg white. They had quickly learned to avoid the ill-tasting
food.
BAD-TASTING FOOD Once I hand-raised a barred owl from a nestling to
adulthood. Sometimes getting food for it was a problem, and upon
occasion I fed it frogs, which it seemed to like well enough. But then
came a day when I fed it a toad. The owl seized the toad at once.
Now toad skin, presumably as a defense weapon of the toad, secretes
a substance irritating to the mucous membranes of some animals. And
this was evidently irritating to the owl, for it did not hold the toad
long in its bill. It spat it out, and the owl's face gave evidence of
disgust. After that the owl not only refused to take toads, but it also
refused to take frogs such as it had found palatable before. Evidently
frogs looked too much like toads. The learning was effective, and
extended not only to the original object, but also to other, similar
objects.
BUCKET-DRAWING When in Florida with the Archbold Expeditions I was
studying blue jays. A very simple but amusing thing that chickadees
learn is to sit on a perch and pull up a little container of food that
dangles far below the perch on a string. Jays, along with crows, are
among the most clever of birds, as I've said before, and I gave two
jays in one cage a chance to learn the trick. In three days one of
the jays was regularly and quickly pulling up the little bucketlike
container and getting its food from it. The process was simple: the
jay reached down, seized the string in its beak, secured the slack
under its foot, and reached down again for another pull. Sometimes five
separate pulls were needed to raise the food bucket the eight inches to
the perch.
The jays were regularly fed in this manner. Soon I noticed that only
one of the two birds pulled up the bucket, though the other also fed
from it. In effect one was depending on the work of the other. After
this had gone on for a month, I wondered if the second jay, which had
never done any of the work, would be able to pull up the bucket if left
alone. Certainly it had had lots of opportunity to learn by seeing
its cage mate go through the motion. So I left it alone in the cage.
This second jay, despite its chances to learn by observation, took
one day longer to learn how to pull up the bucket of food than had
the first jay. The jays certainly learned the trick quickly through a
trial-and-error process, but simply watching the process seemed to be
of little help in learning it.