Part 17

Their functions seem to be to give something for the pair to do; something they can share. It helps fill up the pair's day and keep them together. It is something that helps strengthen the bond between them, against the day when both will be working together raising a brood.

THEY TURNED THE TABLES

Most birds prey on animals enough weaker than themselves to be in no danger from their prey; their hunting is more like that of the gunner after rabbits than that of the hunter after lions. But there are exceptions.

The great blue heron, armed with a spearheadlike bill, lives largely on fish. These it spears in the water, stalking about after them on its long legs, or waiting like a bird on a Japanese screen, as patient as any fisherman, for its prey to come within striking distance. The heron's size and its great bill render it safe from most enemies. But it sometimes overestimates its ability. Audubon recorded one on the Florida coast that, standing in deep water, up to its belly, struck a fish too large for it. The fish dragged the bird for several yards, now on the surface, now underwater. Finally, after a severe struggle, the heron freed itself. It was exhausted, and stood near the shore, head turned away from the sea. As if, Audubon said, it was afraid to make another attempt at fish catching.

A more serious encounter for the bird was recorded in Field and Stream magazine. The heron had caught a shad about a foot long. He tried to swallow it, but it was too big to go down. He tried to disgorge it, but the fins of the fish, acting as barbs, kept it from slipping backwards and out. The result was death for both bird and fish.

CAUGHT BY A CLAM The oyster catcher, a large black and white relative of the sandpiper, feeds on, among other things, shellfish. Mussels and oysters look like hard nuts to crack, even with a stout, wedgelike bill such as that of the oyster catchers. The oyster catcher's favorite feeding times are when the tide has fallen and the shellfish are first exposed to the air and before they have closed up their shells, and again when the tide is rising and the shells are just beginning to open. The oyster catcher stabs into the shell, and with its bill cuts the strong adductor muscles that hold the shells of the bivalves together. The rest is easy. But a danger lurks here: what about stabbing into too big a shellfish, or making an inept stab? And this very thing has happened. On the South Carolina coast Mr. W. P. Baldwin found a trapped, drowned bird. It was held, with the tip of its bill caught in the shell of a hard-shell clam, as if in a trap. Apparently the rising tide had flooded and drowned the bird.

The raven eats most anything, living or dead, and except for man has little to fear in the northern forests where it lives. Yet from Wisconsin comes a record of one that met his death through a porcupine. The porcupine's quills are a dreadfully prickly covering that one would think would protect it from most encounters. Yet one animal, the fisher, kills and eats it as a matter of course, and wolves and bears sometimes eat them without too many ill-effects from the spines. The slow-moving porcupine has little regard for automobiles, and many are run over on country roads. A porcupine is too big and tough for a raven to kill and the Wisconsin raven had probably fed on a dead porcupine. Stuck through its gizzard was a quill, and another, which had apparently caused its death, was stuck in its heart, having apparently worked there from the digestive tract.

Many small insectivorous birds eat spiders as well as insects. This they do almost with impunity in temperate latitudes, where only occasionally do spiders make webs strong enough to trap a bird. But in the tropics, where there are more large spiders, their webs must be a greater hazard to birds. That the hazard exists in both climes, however, is shown by a goldfinch reported caught in a spider's web in Cape Cod, Massachusetts, and a dusky flycatcher caught in a spider's web in Cameroons, West Africa.

SURVIVAL OF THE UNFIT

To care for the weak, the unfit, and the cripple is usually considered an extremely highly developed altruism in our society. As our society progresses, more and more provisions are made for the unfit.

In nature the unfit usually is soon weeded out. If an animal is unable to feed itself it is doomed; or if it is less successful than its fellows it has less chance of leaving progeny. That is natural selection.

Hence on both counts it comes as a surprise to find two well-authenticated cases of crippled birds, unable to search for food for themselves, surviving for long periods.

The first is T. R. Peale's record in 1848 of a brown booby on Enderby Island in the Pacific. An adult bird whose plumage indicated it was several years old was found on the island, and it had only one wing, the other having been lost by some accident and the wound completely healed. The bird was unable to go to sea and get its own food, and was being fed by its fellows.

The second was a frigate bird, found on the Revillagigedo Islands, reported by A. W. Anthony in 1898. This bird, too, was fat, and had one wing withered and useless, evidently from hatching. It had never flown. Frigate birds are masters of the air that snatch their food on the wing from the surface of the water, and a flightless frigate bird would be as badly off as a flightless swallow. The cripple had been fed all its life by its neighbors.

At first the uncritical might think, What altruism, what charity, for the healthy to feed these two cripples. But an explanation involving less advanced principles, principles more in keeping with what we know about bird behavior, is possible. Remember that young birds that are unable to begin feeding themselves at the proper time may continue to beg for food, and be dependent for a long time, as I have shown with young shrikes under the chapter, "Conditioning in Birds." Remember that a young bird begging for food may be fed by adults, not its parents, and even by other young birds (shown in "Bird Helpers at Nesting Time"); and we have the clue.

The cripples, hungry, begged for food; the healthy birds responded by feeding, as they might do to other begging young, and owing to the unusual circumstances both were continued.

These certainly are cases where the unfit survived. Natural selection has not operated. But such cases are rare exceptions.

DUST AND SNOW BATHING

The taxidermist preparing a bird specimen for the museum sometimes has to deal with one whose plumage is soiled or stained. He may have to wash it with water. Then, to dry the plumage, fluff it, and help in arranging the plumage so it will lie smooth and natural, he may use a powder: corn meal, sawdust, plaster, or plaster and potato starch may be worked into the feathers, then dusted out again. It is interesting that birds themselves use and have used long before taxidermists a similar method of using dust in dressing their feathers, a fact that anyone who has watched domestic hens for any length of time must be aware.

A DIRTY BATH Recently I watched a house sparrow dusting by the railway track in the city of Chicago. The dust may have been in part "clean" earth, but in part it was soot, city dust, and soft-coal debris. The sparrows here were dingy, all had their plumage heavily impregnated with city grime, and looked very different from the sparrows in the country. And this sparrow I was watching when it had finished dusting was the worst of the lot. These city sparrows, even when they bathe in water, seem never to get much of the grime out of their feathers.

This reminded me that Oscar Heinroth once wrote that birds do not bathe to get themselves clean, but bathe as an aid in bringing their feathers into order and making them lie smoothly. Perhaps he is right. Certainly my sparrow did nothing to clean himself.

It is in arid countries, plains and deserts especially, where many of the birds take only dust baths. In more humid regions water bathing is the rule. But some birds do both, like our flicker and our house sparrow, bathing now in water, now in sand.

In northern climates, when the land is held in the grip of winter, the water frozen over, and the earth covered with snow, neither dust nor water bathing is possible. Then, it has been recorded, some birds find a substitute in snow. Among other cases, in Alaska the hawk owl has been seen to perch in the snow on the tops of telephone poles, and go through the motions of bathing; in England a rook was recorded as bathing "in crisp powdery snow as if it were taking a bath in dust or water"; and in New England in midwinter juncos have been recorded bathing "in light dry snow, just as other sparrows take dust baths in hot weather."

The snow evidently is used as a substitute for dust in these northern latitudes.

DECORATION IN THE HOME

To use a bunch of flowers or a spray of leaves in decorating a room in a house is a refinement of civilization. As the flowers fade, or the leaves wilt, they are replaced with fresh ones. Sometimes a winter bouquet is used that will serve for months.

There are several birds that habitually deck their nests with green vegetation, and when it is wilted, it is renewed with fresh. The reason is not clear. It has been suggested it is to supply humidity and, by evaporation, coolness; it has also been suggested that its use serves a sanitary purpose. But whatever the reason in birds' eyes, it looks like decoration to human eyes.

This habit is common with a number of different hawks: for example, the red-tailed hawk is reported sometimes to have its nest, a bulky flat, basin-shaped structure in the crotch of a tree, "profusely and beautifully lined with fresh green sprigs of white pine, which are frequently renewed during incubation and during the earlier stages in the growth of the young." The golden eagle is said to add green grass, or green leaves often attached to the twigs from time to time to the lining of the nest, especially after the young are hatched; and the broad-winged hawk is said to add green leaves to the lining of its nest. In quite another group of birds the same thing also occurs. A carrion crow's nest in England was visited periodically from March to August. Strangely no eggs were laid during this whole period, but the birds remained in attendance. When found, fresh sprigs of oak leaves were interwoven around the rim of the nest. On subsequent visits the oak leaves were found to have been replaced with fresh ones, and the leaves were kept fresh until late August.