Part 3

This covering of the eggs by the parent is not unique in the bird world. The pied-billed grebe of North America also does this. When disturbed at the nest the incubating bird has been seen to use quick pecking motions to draw material from the edge of the nest over the eggs. Instead of leaving the eggs exposed the nest simply looks like a heap of trash and may thus escape the attention of a predator. It used to be thought that this grebe used to incubate only at night, leaving the eggs covered during the day to be incubated by the heat from the sun and from the decaying vegetation of the nest. However, recent studies have shown this is not the case, and protection by concealment seems to be the main advantage of this behavior.

Yet another species of quite a different group, the eider duck, covers its eggs on leaving them. The eider's nest is characterized by a blanket of down, plucked from the breast of the bird, and when the female has time, when she leaves the nest she pulls the edges of the down blanket over the eggs, perhaps for concealment, perhaps for the sake of the down's insulating properties, keeping the eggs warm in a northern climate during the parent's absence.

Here we have covering of eggs for what seems to be very different purposes: to keep the eggs cool; to keep them warm; and to hide them from view.

THE SNOWY OWL AS A TRADE INDEX

Angus Gavin was a fur trader at the Perry River post of the Hudson's Bay Company on the edge of the Arctic Ocean. White foxes were the chief fur brought in, and the Eskimos were the trappers. Sometimes it was necessary to advance credit to an Eskimo, against the expectation of a coming season's catch out of which the advance was to be repaid. Gavin, who was a keen naturalist as well as trader, writes, "I used my observation on Snowy Owl abundance to govern extension of credit...." When snowy owls were abundant he could extend liberal credit to the Eskimo with every assurance the white-fox catch would be good and that the Eskimo would be able to liquidate his debt. When snowy owls were scarce little credit would be extended, for the white-fox catch would be small.

In general we've accepted the value of birds to man, and are appreciative of the complicated web of life in which one animal affects many others. But this use of snowy-owl abundance as a guide in granting credit strikes me as novel. Actually, of course, it is quite sound, for it uses one part of the chain that links such diverse items as owls, lemmings, foxes, Eskimo, fur trader, and finally of course milady in her white-fox furs.

LEMMINGS IMPORTANT First of the factors involved is, of course, the vegetation; the grasses, herbs, and tiny dwarf shrubs of the Arctic barrens. The next are the lemmings, mouselike creatures of the Far North that eat the vegetation. They are the first step in turning grass into flesh and fur and feathers. One of the striking facts of lemming biology is the fluctuation in their numbers. Some years they swarm, lemmings are everywhere, and in places they erupt in vast emigration, the tundra and the sea ice being covered with masses of moving lemmings. We know this best from the accounts written about the lemmings of Norway, but the same thing occurs in the American Arctic. At other times they're scarce and it is difficult to find even one. Strangely there's a periodicity in this, and periods of abundance and scarcity tend to recur every four years. What happens or what causes it we don't know.

The Arctic fox, staple fur bearer of the Far North, and the snowy owl both prey on lemmings. Lemmings are so important to them that when lemmings are abundant the foxes and the owls prosper and multiply; when the lemmings are scarce the foxes and the owls starve or migrate, in any case where there are few lemmings there are few foxes or owls.

Thus we see how it is that an abundance of snowy owls can indicate that the Eskimo will make a good fox catch and the trader will do good business.

MONKEY BIRDS

Birds get their everyday names in a variety of ways in the countries where they live; from their looks, like the snake birds and the pond scroggins; from their color, like the cardinal and the blackbird; from their behavior, like the frigate bird and the creepers and the boobies and king-birds; from what they eat, or are supposed to eat, like the antbirds and plantain eaters and bee eaters; from what they say, like the poor-will and the more-pork; from how they say it, like the warblers and the screamers; from how often they say it, like the brain-fever bird and the wideawake terns; from where they nest, like the cliff swallow and the house martin and the chimney swift; and some from their non-bird associates, like the cowbird, moose-bird, and the monkey bird.

It is the monkey birds that have taken our fancy at the moment. The forests of Africa, the jungles of Borneo, and the forests of the Philippine Islands each have a bird that associates so often with monkeys that this habit became incorporated into its local name. The birds are not at all closely related. One is a hornbill, one is a drongo shrike, and one is the fairy bluebird. The hornbill goes in parties of their own kind, but apparently the drongo, and certainly the fairy bluebird prefer the society of monkeys to that of their own kind.

The stories we have of them stress the utilitarian aspect of the association; that the monkeys as they travel about through the trees scare insects out of their hiding places and the birds, being on hand, can snap up the insects more easily than if they had to search them out for themselves.

The monkey bird in Africa, which is a hornbill, follows, along below the monkeys in the lower branches of the trees. It used to be thought this was for the fruit the monkeys dropped, but then it was found the hornbills were insectivorous. Instead of being scavengers the hornbills are using the monkeys to beat out their game for them.

Hamba Kerah, the slave of the monkeys, is what the Malays of Borneo call the racket-tailed drongo. This is from its habit of stationing itself behind a band of monkeys traveling through the forest. But Mr. Ridley, who watched them, decided it was the other way around; the monkeys, unwittingly of course, were working for the drongo, acting as beaters to drive out the insects which the bird snapped up in the air.

In the Philippines it is "the sentinel of the monkey" that is applied to the fairy bluebird. The bluebird seldom associates with its own kind, but is almost invariably associated with a band of crab-eating macaques. But here again it seems the monkeys are acting as beaters for the bird, driving out insects.

This is a sort of unconscious co-operation one finds in the bird world. One animal helps out another without being aware of it. Birds are ever ready to profit by such behavior, and when it proves of enough benefit, the habit can become usual for the species, as in the cowbird-cow relationship, or indispensable as with the oxpecker-hoofed-animal association.

BIRD-MADE INCUBATORS

Incubators as we know them on chicken farms are electrical gadgets with thermostats to control the temperature, or at least with oil lamps to supply the heat necessary for the young chick in the egg to grow. Naturally we wouldn't expect anything so artificial as this in the bird world, but there is one group of birds that does not brood its eggs but has employed another method of incubating.

The birds that do this are fowl-like birds of the Australasian area. They are variously called "mound builders" from the nest mound they construct, "megapodes" from the large size of their scratching feet, or bush turkeys, presumably from their edible qualities. These birds bury their eggs and leave them thus to hatch without any brooding by the bird. The birds have adapted their habits to two different sources of natural heat. On some of the Pacific islands there is local volcanism making the sand warm. To such places the birds come to bury their eggs.

But in many of the tropical forests there is not this convenient natural heat. Another method is employed. The birds take advantage of the heat generated by rotting vegetation. They scratch up the surface litter of the forest floor into mounds--structures that may be a yard or two high and five or six yards across. Some much larger have been observed. It is into these the hens burrow and lay their eggs. The temperatures in them have been recorded as 95° to 96° F., which compares with normal bird temperatures of just over 100° (bird temperatures are a few degrees higher than normal human temperature).

The bush turkeys from Queensland have been bred in captivity, and have given some extremely interesting data, according to an article by Mr. Coles in the proceedings of the Zoological Society of London for 1937. It was the male who did all the building of the mound. Though the female started to cover the eggs laid singly in burrows in the mound, the male finished this. And it was the male that looked after the nest mound during the incubation period, continually scratching over the surface layer. Both parents helped the young emerge, by digging burrows into the mound which the emerging young, who had started to burrow out, could use.

The young are in a very advanced state and apparently are able to fly and look after themselves upon emerging. On the day after hatching one chick is reported as able to flutter up to a perch six feet high. In the captive birds mentioned above, the parents, though they were attending to the mound and helped the chick out, appeared to take no further interest in the chick once it was out.

There are a few other cases when birds cover or bury their eggs. With the grebes it has been said they covered them and left them to be incubated, but that is doubtful. Certainly the megapodes are the only ones to present a dear case of "artificial" incubation.

This burying of eggs by the megapodes of course brings to mind the way some reptiles, such as turtles, bury their eggs. And considering that from an evolutionary viewpoint birds are really only modified reptiles, it is perhaps not surprising that they too have this habit. But that it is really an ancestral trait retained by the megapodes is doubtful. Rather I'm inclined to think it's another example of the many ways birds have evolved, or changed their habits so as to utilize as much of the environment as they can in as many ways as possible.

CORMORANT FISHING

In western Europe, when falconry was in favor for taking game on land and in the air, there was a certain vogue for training cormorants to take fish. Like the falcons, the cormorants were hooded and carried on the wrist, but of course where the falcons flew to their game, the cormorants swam to theirs.

It was in China where cormorants were domesticated, "completely and perfectly," as that eminent Sinologist Dr. Laufer says. Extensive breeding establishments have been maintained. The eggs of the breeding flock of cormorants are given to a hen to hatch, for cormorants as mothers prove unsatisfactory under domestication. When the eggs hatch the young cormorants must have special care; for, unlike the young of ducks and geese, young cormorants at hatching are not down-covered and able to run about, but are weak, helpless things sensitive to cold. They are placed in cotton batting, artificial heat provided when necessary, and they are fed by hand on a diet composed basically of chopped eel.

Finally the young are full grown and fully feathered. The training is now started. First the young are tied to a stake at the water's edge. A whistle signal is given and the young cormorant is pushed into the water. Thus he learns to know and obey the signal to go into the water. Then the trainer throws him little fish. These the cormorant catches in its beak and when he does the trainer whistles another signal, to bring the bird back to him with the fish. And the cord tied to the bird is used to demonstrate what is meant and make sure its done. So the training goes on until the bird has graduated to a class taught from a boat. Sometimes a small float is attached to the cormorant by a short cord, and it can be drawn in with a bamboo hook. If young birds are trained in the company of trained birds, it takes but half as long. Finally the training is complete and the fisherman sets out with his birds. This is no sporting event; it is the serious business of life, getting a living from fishing. On the sampan or the bamboo raft there may be from two to a dozen birds; sometimes they may have special perches built for them along each side of the boat. Sometimes the cormorant has a cord or band around its neck. The reason for this is disputed. Some say its a place to attach a cord; a place to get hold of the bird; some say each man's cormorant is thus specially marked for identification; some that it's to prevent the bird from swallowing its prey. With well-trained cormorants it is sometimes dispensed with. At a signal the cormorants go into the water, swim, and dive seeking fish. The fisherman, by stamping his feet, by voice or whistle, and by hitting the water with a bamboo directs and encourages the birds. When the cormorant catches a fish it brings it back to the boat, and the fisherman may use a net, or may lift up the cormorant onto the boat on an oar or pole, and take the fish from the bird. If a bird is lazy it's encouraged by beating the water near it with a bamboo pole. As cormorants' plumage is only partly waterproof they cannot stay in the water indefinitely, and this, as well as fatigue, probably determines the rest periods when the birds are lifted aboard. Sometimes the fisherman helps attract fish to the boat for the cormorants to catch by scattering grains of rice in the water.

When the day is finished the cormorants are collected, fed, and the fisherman goes home with the sustenance for his family, gathered by a bird.

In Japan the cormorant is also used, but apparently somewhat differently. There cormorant fishing may partake of the nature of a sport. Sometimes the cormorants are "harnessed" into a team, each attached by a cord to a single line, directed by one master. In China the fishing is usually done during the day, but in Japan night fishing is common, the scene being illuminated by fires in braziers or cressets on the boat, or lanterns.

THE SHRIKE'S LARDER

Our northern shrike is a songbird which has developed feeding habits along the lines of those of a hawk. Whereas most birds its size are content with fruits, seeds, or insects of a size it can beat or bite and then swallow whole, our northern shrike takes not only small insects but prefers large ones, and mice and birds too big to be swallowed whole. It is an opportunist and takes what is most abundant and easily accessible. The shrike's strong hooked bill is a powerful weapon, used with a nipping motion that is directed at the back of the head or neck of mouse or bird.

Now with the dead sparrow or mouse the shrike is at a disadvantage. With a powerful bill hooked at the tip its feet are still those of a songbird and are not strong enough to hold its large prey while pulling it to pieces. Only small insects are held in one foot and pulled to pieces. To meet this need for holding large dead prey the impaling habit was evolved. The result of this is the so-called larders, which form a fancied resemblance to meat hanging in a butcher shop, and have given the birds their name of butcherbird. A thorn tree, a splintered end of a branch, or even the barbs of wire fencing may serve. The shrike flies to one of these, carrying the prey in its bill (rarely in its feet), and with a pulling motion fixes the prey on a projection point. Sometimes instead of impaling the mouse or bird it pulls it into the fork of a branch, and so wedges it there. Now the food is firmly held, and the shrike can use its bill effectively to pull off pieces of flesh and swallow them. When the bird has fed, it leaves the rest of the animal hanging where it was. It may return to this food and make repeated meals of it if not spoiled, or dried up, until the whole is devoured. But often parts of meals are left hanging and discarded. If suitable thorn bushes are scarce the shrike may return time after time to the same tree with its prey, and in time this tree may come to be decked with many partly devoured carcasses. Such trees are the so-called "larders." There is another aspect of shrike behavior that adds to these larders. The shrike, even when replete, may seize any prey that appears and impale it. The bird's organization is such that the sight of a small moving animal may start the actions that end with impalement even when the bird is not hungry. This food usually is not eaten later.

Thus the shrike's "butcher shop" is not primarily a store of food, even though it sometimes serves as such when in times of scarcity remains of old meals are eaten. It is not a gathering of food in time of plenty and saving it for a later use. Rather the placing of many items in one tree is the result of its being a favorable impaling place. And the impaling is behavior developed to overcome the weakness of the claws in a bird whose disposition and strong beak enable it to prey habitually on larger animals which otherwise it could not tear to pieces and eat.

BIRD FLAVORS

Particularly in the study of insects it has been shown that bright or contrasting and conspicuous colors tend to be associated with ill-flavor in the animals that wear them, while insects with a good flavor tend to be so colored that they are difficult to see. The first is a warning coloration--advertising to a predator that he will not enjoy eating this insect and better leave it alone; the other is concealing color, its function apparently to keep predators from finding their prey. The tasters in the experiments that have been used to work out the above generalizations were usually birds, but, as checks, a variety of other animals were used, and the magpie moth (_Abraxas grossulariata_), for instance, was found to be distasteful to certain spiders, frogs, lizards, various birds, a bat, and finally "the late Dr. Hans Gadow (one of the leading ornithologists of his day), who made a practice of sampling caterpillars, remarked on trying an _A. grossulariata_ that it was quite one of the worst he had ever eaten!" Apparently ideas in taste are similar throughout large sections of the predatory animal world. Reversing the usual role, and using insects (hornets) as tasters of bird flesh, the celebrated British naturalist, Dr. H. B. Cott, has recently studied the question of the palatability in birds and their coloration. Naturally Dr. Cott, with his customary thoroughness, compared hornets as tasters with other animals, including cats and men, and found a surprisingly close agreement in the results.

The experimental procedure was to expose the flesh of two different birds (without feathers) at the same time, and see which the wasps ate first. Thus a graded series was built up of the 38 species of birds tested, with a palatability rating of from 1 to 38. The wryneck and the crested lark stood at the top of the list, and the pied kingfisher and the white-rumped black chat, as the least palatable, at the bottom with Numbers 37 and 38.

Then, surveying the coloration of the birds, and their habits, Dr. Cott made the important correlation that in general the birds whose flesh was most edible were protectively colored, and those whose flesh was least palatable tended to be conspicuous in color and behavior!

To relate it to the theory of evolution Cott concludes that selective pressure by predators seems to have forced vulnerable species along two divergent lines of specialization: leading in those which are relatively palatable toward concealment, and in those which are relatively distasteful toward advertisement.

HOW MANY FEATHERS HAS A BIRD?

The question as to the number of feathers on a bird seems a simple one without complication. Dr. Wetmore, the well-known ornithologist who was secretary of the Smithsonian Institute, has given us some data. The number varies with the species, of course: the smallest bird, a hummingbird from Cuba, had the fewest, 940 feathers; larger birds had more, the robin 2587, and the mourning dove 2635 feathers. A glaucous-winged gull had 6540; a mallard 11,903 feathers; a Plymouth Rock chicken was said to have 8325 feathers; and a later investigator reported 25,216 feathers on a swan.

But as one thinks of it, more questions arise, as in any investigation. The answer to one question poses two more. The first question is, do not the birds in winter need a wanner plumage to keep out the cold than they do in summer, when it is warm? Do they have more feathers then? This was definitely true in the case of the goldfinch: a bird in summer dress had only 1439 feathers, while one in winter plumage had 2368 feathers, obviously an adaptation for cold weather.

The next question is more abstruse, but eminently practical: the smaller a body, the larger exposed surface for its weight it presents. That is, for its weight a small bird has a proportionately much greater surface from which heat is lost than does a larger one. With equal heat-producing mechanism and metabolism, a small bird would need more insulation than a large one. Reduced to its simplest: one would expect small birds to have relatively more feathers than large ones: more feathers per gram of weight. Is this true? Two members of the Department of Poultry Husbandry at Cornell University, Dr. F. B. Hutt and Lelah Ball, supplied the answer. Small birds do have more feathers per gram of body weight than do larger ones. A hummingbird weighing 2.8 grams had 940 feathers or 335 feathers per gram; a nighthawk weighing 67.9 grams had 2034 feathers or 29 feathers per gram; while a swan weighing 6123 grams had 25,216 feathers or 4 feathers per gram of body weight.

Presumably there are still other relations: Do the birds that live in the tropics where it is warm have fewer feathers than species of the same size of arctic climates, as one would expect? Are certain types of feathers such as those of aquatic birds better insulated than those of land birds, so that the bird requires fewer of them to keep warm? Does a dense coat of down reduce the number of feathers needed to keep warm? Do the loose feathers of ostriches, lacking barbules, necessitate some adjustment in numbers? The things we've learned point the way to other questions to be investigated.

LAST YEAR'S BIRDS' NESTS

The wisdom of our fathers is sometimes embodied in what we call old saws, to wit, "Many hands make light work," to which the iconoclast retorts, "Too many cooks spoil the broth." And when we come to the phrase, "As useless as a last year's bird's nest," we must reply, "Circumstances alter cases." For many a bird's nest of yesteryear still has its use; some a biological use to other birds; some to feed and clothe man.