Part 11

All the larger herbivores are attended by oxpeckers except the elephant and the hippo, but the favorite seems to be the rhino, and for this he's sometimes called the rhino bird as well as tickbird and oxpecker. The rhino gives the bird its food, and in return the bird provides a service of a value difficult to evaluate. It acts as a sentinel and may warn the rhino of the approach of hunters, for which habit it is execrated by sportsmen.

It would seem that such relationships could have developed only where the supply of big game was large. With the introduction of cattle and other domestic animals it was natural the oxpecker should turn its attention to them. Here the question arose as to the attentions of the oxpeckers being harmful or otherwise to the herds. Mr. R. E. Moreau, formerly of the East African Research Station at Amani, has investigated the problem. He finds that white men who own herds tend to consider the oxpecker a nuisance; Africans tend to consider it beneficial and some African cattle owners object to having the birds killed; the beasts themselves tolerate the birds.

There is the possibility on the one hand of oxpeckers spreading certain cattle diseases that are mechanically transmitted, and on the other hand they may help reduce disease by eating ticks, the vectors of certain diseases. Of course dipping the cattle takes care of ticks on them, and here we see another indirect effect of civilization on bird life. When cattle have been dipped the oxpeckers disappear from the herd. Perhaps it is because there is no longer food for them there; perhaps they get enough of the poison dip left on the beasts' hair to be lethal.

WINGS IN FEEDING

The obvious adaptation of a bird's wings is for locomotion; to fly in the air. It is true that some few birds are flightless, and some like the penguins use their wings for underwater swimming, but this does not spoil the generalization.

Secondary uses, some with special adaptations, occur: the owl at bay spreads its wings wide, with the effect of increasing its apparent size and being more terrifying to a predator. The young bird, begging to be fed, flutters its wings in a characteristic way, and the female, in some of her mating behavior, may also flutter her wings like those of a young bird.

In courtship the wings may play an important part in display. In the Australian rifle bird they are held out, fully spread on each side of the bird like a velvet curtain against which the vivid iridescence of the throat patch stands out more vividly. The argus pheasant has the inner secondaries greatly elongated and ornamented in a fashion recalling the decoration of a peacock's tail and these he spreads to show in his courtship, while the ruffed grouse uses his wings to make instrumental music, his drumming.

Wings in geese and swans may be used in fighting, and tame birds may severely buffet humans who take too close an interest in their young. In the related screamers of South America the bend of the wing is equipped with long, very sharp spurs, which undoubtedly make formidable weapons in fighting.

In addition wings are used in at least three different ways in feeding. The red-tailed hawk may spread its wings as it sits on its prey, perhaps a behavior adapted to help the bird maintain its balance when dealing with struggling prey, perhaps to help smother the struggles of its prey.

The secretary bird of Africa is said to feed on snakes, poisonous and non-poisonous ones, and is said to use its huge wings as shields for its body in attacking them.

But the strangest use of wings in feeding is that practiced by a blackish African heron. In feeding in shallow water it takes a few rapid steps, apparently to bring it within reach of fish it has sighted, then spreads its wings, bringing them forward until they meet, and with the tips of the quills in the water. The head is in the canopy formed by the wings, and apparently it is here under this canopy that the fish on which it feeds are caught. The suggestion as to the correlation that presents itself is that the dark canopy thrown over the fish confuses them and makes them easier to catch.

INSTRUMENTAL MUSIC OF BIRDS

Vocal music bulks large in our avian springtime chorus, but don't overlook the instrumental music that accompanies it. The drumming of the downy woodpecker on the dead limb of a maple near my bedroom window is as much a part of my spring as is the cheery cheerup of our robin. It's not that woodpeckers are voiceless that they drum. The flicker can be called in with his particularly rich repertoire to repudiate it vociferously. All day the downy woodpecker goes about pounding his head against tree trunks, with his bill chiseling out wood-boring insects to eat. What more natural when springtime comes and he wants to tell the world, and especially other woodpeckers about it, to select a dead limb with a nice tone in my maple tree and hammer out a rolling tattoo--his love song and his challenge.

A DRUMMER The gray-brown ruffed grouse of a wood lot we used to have in the Chicago area is a drummer I miss. "Thump-thump ..." he started slowly, and then quickened to a roll that filled the forest with hollow sound and you wondered whence it came, unless you happened to know, as I did, that an old log in the patch of gray birch was the old cock's favorite performing stand. There he came to roll out his invitation to the demure hen grouse. A drummer, I've called him, yet he has no drum. It's his wings, striking the air, that thump and build up into a roll, its volume testifying to his great breast muscles as well as does the whir of wings as he hurtles away through the air when I come too close.

The snipe of a nearby marsh makes music with feathers and wind, music that is more enthralling to me than the song of the yellowthroat or the vocal imitation of stake driving by the bittern. Circling high, then with a change of pace, his "winnowing" or "bleating" spring song comes drifting down. There is still room for argument, but probably it's air rushing past the outer tail feathers that makes the sound. One year a short-eared owl nested in the nearby meadow. Owls generally are vocalists, even if we don't rate very high their hoots or yelps, but the short-eared owl also has an instrumental performance. Sometimes, when giving his mating song on the wing, a series of "toots," he interrupted this by a dive in which he brought his wings together under his body, with a clapping sound. It's part of the performance, but not, as might be said, the owl applauding his own show.

Over our public school each evening in early summer a nighthawk booms. He has a voice, and he uses it, calling "beep" as he circles high. But the climax of his performance is instrumental, wind on feathers. He heads down, wings high, toward the flat gravel roof on which his mate is sitting. As he approaches the roof he moves his wings down; the air rushing past the quills gives a tearing boom as he comes out of the dive and mounts skyward again.

At dusk, at a damp corner of our old wood lot, in the spring, I listened for the woodcock's flight song, a twittering of wing music as he circles up, and sweet music, too, for a wild fowler's ears, is the whistling of the wings of a passing pair of black ducks on their way in the early darkness.

CONDITIONING IN BIRDS

The classical experiment in conditioning and reflexes is that of Pavlov. It consisted of sounding a bell each time food was given to a dog. Finally the salivary response resulted even when the bell was rung, without the food being given to the dog. The dog was conditioned to the bell. First it had responded to the food, then to the food and the bell, and finally to the bell alone, by a flow of saliva. The beauty of this experiment is in its simplicity, dealing as it does with a single reflex.

Though much behavior is more complex, experiments have been worked out to show how the environment, in a broad sense, can influence inherited behavior. An illuminating example of this is the one I made dealing with young loggerhead shrikes and the duration of their infantile behavior. Young shrikes, as with young passerine birds in general, while in the nest are fed directly by the parents, who place food in their mouths. One of the earliest behavior patterns these young birds perform is to stretch up with widely opened mouth, fluttering wings, and buzzing calls, in anticipation of being fed. This we call begging. Though typically infantile behavior, it may reappear in courtship, but this latter we will not consider here.

Ordinarily this infantile begging behavior is discontinued shortly after the young birds leave the nest and become able to feed themselves. Observations indicate that in a state of nature this change is probably hastened in part by the young birds themselves, who come to avoid having food thrust down their gullets, and prefer to pick up the food for themselves, and in part by the waning interest of the parents in the young, which confers an advantage on the young who early become self-supporting.

CASE OF RETARDED DEVELOPMENT Certain observations made from time to time have indicated that though the age at which young birds changed from infantile begging for food to self-supporting independence was a fixed thing, started by instinct, certain external factors, notably the amount of care the young received, could affect the age at which this change occurred. Indeed there was a record of a young cedar waxwing raised by hand who never learned to feed itself.

When I secured a brood of four young loggerhead shrikes, or butcherbirds, the material was available to conduct a controlled experiment. The young birds were raised together by hand to the stage where they were ready to begin to pick up things, to feed themselves, and to begin to abandon their infantile behavior of begging for food. This was when they were twenty-one days old. They were then divided into two lots and housed separately. One couple had a supply of food kept in front of them, and hand feeding was gradually discontinued and stopped as soon as possible. At the age of twenty-eight days they fed themselves well, though they still begged freely when I approached. By the time they were thirty-nine days old they begged rarely, and after the age of forty-five days they were not seen to beg.

The other couple had no free food available at any time, and they were fed completely by hand, the food being placed in their mouths. At the age of twenty-eight days they had made no effort to feed themselves. By the time they were fifty-three days old they made efforts to feed themselves, trying to peck the food from the fingers instead of having it thrust into their mouths, and evidently would have changed quickly to independent self-feeding and abandoned their infantile begging behavior. But hand feeding was continued. At the age of seven and a half months, when the experiment was discontinued, though these birds were capable of feeding themselves, as was seen when food was accidentally dropped on the floor of their cage, they still begged for food from their human foster parent.

OBJECT LESSON FOR PARENTS These four birds used in this experiment were nestmates, and had similar heredity and early environment. The birds in the lot which received only enough care to ensure proper development became self-feeding, independent, and lost their infantile begging behavior when they were about a month and a half old. The other lot, which received an excessive amount of care in the latter part of infancy, and were hand fed without being allowed to develop the behavior that would have made them independent, retained the infantile behavior pattern of begging to be fed until the end of the experiment. They were then seven and a half months old, and their nestmates, under a different set of conditions, had lost their infantile behavior six months earlier.

With some birds it appears excessive care can be a conditioning factor. It can delay the loss of infantile behavior and the acquiring of the normal independence. Though instinctively the young shrikes tried to develop their independent behavior, when this was not possible they continued their dependent, conditioned behavior.

POISONOUS BIRDS

Poison we know perhaps best in the plant world, whence comes, for example, strychnine. The deadly nightshade, a common weed, is another well-known poison plant. In the animal world we know poison best as something that is injected into the body by stings of bees, bites of spiders, the bites of insects, and even bites of shrews. In addition some animals having irritating, bad-tasting, or poisonous secretions which presumably protect the possessor from predators. This has received most attention in the insect world, the bad-tasting grasshoppers being examples. Toads have an acrid secretion from their skins which deters many would-be toad eaters, and pickerel frogs have somewhat the same thing.