[Illustration]
Through selection birds have become adapted to their environment. In
most cases this is successful adaptation. Occasionally, however, we
come across instances in which the adaptations do not work out. Such
cases, where the actions of the birds are not beneficial or are even
detrimental to it, come as surprises.
Since the introduction of the Tartarian honeysuckle (_Lonicera
tatarica_) into the United States from Asia, its planting as an
ornamental shrub provides each autumn a display of juicy red fruit.
This fruit contains saponin, a substance that has the effect of an
anesthetic and muscle poison and may paralyze the greater nerve
centers (in sufficiently large doses saponin causes death by cardiac
paralysis). A condition of intoxication has been recorded for robins
feeding extensively on these honeysuckle berries: "... this drunkenness
has been seen in every shade of severity, from mild unsteadiness to a
degree of incoordination sufficient to cause the birds to fall to the
ground. It seems to make some of the birds utterly fearless and perhaps
a bit belligerent, for they become quite unafraid of passers-by and
interested spectators. A few dead robins have been found about these
honeysuckle bushes--presumably poisoned by the berry diet." Fortunately
the poisoning of birds by this honeysuckle seems to be uncommon.
In the Philippines the local people gather the juice of the coconut
inflorescence in bamboo tubes placed in the crowns of the palms. This
juice ferments quickly and provides a refreshing, mildly intoxicating
drink. A little parrot of the Philippines, the hanging parakeet, has a
taste for this drink, comes and drinks from the containers, sometimes
becomes drunk, falls in, and drowns.
The California woodpecker ordinarily differs from many birds because
it does not lead a hand-to-mouth existence but stores food. These
woodpeckers feed extensively on acorns, and one way they store them is
by drilling holes in the bark of a tree and fitting an acorn into each
hole. The whole trunk of a tree thus may be pitted with stored acorns.
When the acorn crop fails and the nuts are scarce the woodpecker
goes through the same storage activities but, being unable to find
sufficient acorns, it stores pebbles instead. These pebbles are, of
course, quite useless to the woodpecker, and this is an interesting
example of an instinct "gone wrong."
Sometimes these woodpeckers have another method of storing their
acorns. This is by dropping them into cavities in tree trunks, but when
stored in such a way there seems to be no way for the birds to reach
them. Here again we have a blind impulse to store acting in such a way
that the bird gains nothing by the act.
The raven is ordinarily and quite correctly considered one of the most
intelligent of birds, but a raven I kept in captivity and fed small
fish attempted to store some of them by pushing them through a knothole
in the back of its cage. The fish fell about fifteen inches below the
knothole, where the raven could not possibly reach them. After pushing
each fish through the raven peered through the knothole though it
could not see the fish. Here again we have the instinctive storing act
carried out in such a way that it produced no benefit to the bird.
The late George Latimer Bates, noted ornithologist, studying the birds
of West Africa, found a most surprising thing in connection with one of
the honey-guides. As a group, these birds are noted for the habit of
attracting the attention of human beings and leading them to bee trees,
presumably so that they will break down the bee tree for the honey, and
the birds can feed on the scraps left over. Bates found that the West
African species is parasitic on other birds in its nesting habits and
its young have been found in the nesting hole of a little barbet. This
barbet was a much smaller bird than the honey-guide and the entrance
to the nest hole was so small that Bates doubted that the honey-guide
would have been able to get in to lay its egg. He suggested that the
egg may have been laid elsewhere and deposited in the nest by the
parent's bill. It is difficult to understand how the young honey-guide
would be able to get out, for when fully fledged it would have been far
too large to squeeze through the entrance that admitted the tiny body
of its foster parents, the barbets. This is an almost incredible story
and if true looks like a case of maladaptation.