Chapter II: Introduction (1)

In looking back over the preparation of these sketches I feel as though each evening I'd gathered up the bits and pieces left over from the day's work and fashioned them into designs for my own amusement and the edification of my family. Truly it's as though I'd used stray feathers, fallen from the bird skins I'd handled, and fitted them together into something of wider interest than the original.

Much of my work now is museum research, working with bird specimens and books. In fashioning a research paper I always amass a great deal more material, that is to say, information and ideas, than I am able to use in it. In place of a lumber room I have a set of files with index headings that range from Abundance and Age, through such headings as Beauty, Feathering of Feet, Fictitious, Hysteria, Pterylography, Social, Song, Tail Feathers, Valentine's Day, to Zoogeography. Here I put the information that is irrelevant at the moment but too interesting to discard. Its source is varied. Some has been accumulated while studying specimens from localities as geographically separated as Alaska, El Salvador, Gabon, Tristan da Cunha, Nepal, Negros, and New Guinea; and while writing papers that range from describing new species to discussing secondary sexual characters and ecological competition. Some have been recorded while in the field on expeditions, trips that ranged from two years in Madagascar, three expeditions in New Guinea, and a season in the Philippines to trips nearer home from the Yukon to Nova Scotia, Florida, and Central America.

Gradually information builds up under each heading, and new ones are added. These items are too interesting to remain buried in the files. They are things people want to know about. So I began to draft them into articles for publication in the museum's monthly, _The Chicago Natural History Museum Bulletin_. The response was gratifying. The press picked them up and reprinted them. One was used in a Chicago _Tribune_ editorial. Several were used in commercial radio programs. Encouraged, I prepared more, soon overrunning the space available in the bulletin.

Most scientific papers are not written to be read for enjoyment. Conciseness as well as clarity are striven for, conveying certain information in a small compass. The correlations made are often obscure ones, appreciated only by scientists. Yet the material they contain is often intensely interesting, and if these papers were written in a more leisurely style, with more general correlations pointed out, they would provide both interesting and entertaining reading. In a few cases my own research falls in this class, and I've rewritten some of my own papers with this in mind (_see_ "Battle of the Sexes and Its Evolutionary Significance").

This collection of articles, if it were a painting, could be called a conversation piece. Or it might be compared to a well-filled whatnot. Each of the sixty chapters is an independent unit, illustrating some facet of birds, their behavior, or our study of them. Some of the facts may seem unusual or bizarre, but most of them are well known and well documented. The thing that is new, if there is anything new, is the setting in which I've placed them, the manner in which I've looked at them. Taken as a whole, they touch on many different birds from many different places in their less widely known aspects, and with a human interest slant.

"But what will your professional colleagues say?" asked a friend as he flipped through the cartoons. "These pictures don't approach the subject in a very serious manner." Quite true. But a discipline must be very lightly rooted indeed if it can't stand a few caricatures and cartoons and perhaps be the better for them.

The knowledge of most people about the hornbills of tropical Africa, the gulls of Australia, the penguins of Antarctica, and the crocodile birds of the Nile is probably pretty vague. To give a frame of reference in a biological sense is impractical in the compass of one slim volume.

But a ready-made frame of reference already exists: the parallels in bird and in human. These I have used. But in so doing I am not imputing human motives and attributes to birds. The actions are similar. The workings of the human mind I understand only vaguely; that of the bird I can study only through the actions of the birds. One set of behavior may be learned and rational, one rigidly innate, entirely instinctive, and inherited, or at most modified by experience. Be that as it may, the similarity in the end result in two such different vertebrate animals as man and bird when faced with similar problems is often close. Perhaps it is because the solutions are necessarily few; perhaps, and I incline to this feeling, it helps illustrate one aspect of the close relationship between all animate nature.

This series of articles is intended to be interesting and entertaining. I hope it will also make more people aware of the many ways birds act, here and in far places, how they have solved their problems and profited by their opportunities.

STRAY FEATHERS FROM A BIRD MAN'S DESK

BIRDS USING TOOLS

Man is the tool user pre-eminent in the animal world, but he does not stand completely alone in this. Here and there, in quite different groups of animals such as insects, mammals, and birds, a few kinds have forged a little ahead of the rest of their near relatives and show the very beginning of tool using.

The song thrush of Europe is perhaps a borderline case. It feeds in part on snails. To get the soft edible animal out of its shell, it carries or drags the snail to a favorite rock, its anvil, and there hits it against the anvil until the shell is broken and its contents exposed. The question is, can this be considered as using a tool? If the song thrush moved or prepared the rock, which it does not do, there would be no question that it was a tool. The sea otter brings a stone from the bottom of the ocean and places it on its floating body to use as a similar anvil in cracking hard objects, and this undoubtedly is the use of a tool. At the other extreme are many species of birds that beat their prey on branch or ground, wherever they happen to be. The song thrush is certainly an advance over that, and can, I think, be considered as using a tool in a primitive way.

A few other species, too, bring shellfish to special places. Gulls on our coasts pick up mussels and clams and, flying over a rock or some other hard surface, drop the shellfish, and follow it down. If the shell is broken, the dish is ready for the gull; if the shell is not broken the gull takes the shellfish up to a higher altitude and tries again. In places where hard-surfaced roads are conveniently located gulls have learned to use them as shell-breaking places, and such roads become littered with shells.

Crows of more than one species also use the same routine in breaking open shellfish, and they, too, have learned to use special hard surfaces, such as masonry walls, on which to drop the shellfish.

PAINTING A BOWER The satin bowerbird of Australia, a species known to science as _Ptilonorhynchus violaceus_, has also been considered as a case in point when discussing the use of tools. The birds are somewhat larger than a robin, the male glossy blue-black, the female greenish. The male of this species constructs an elaborate bower, presumably for courtship purposes. It makes it of sticks and twigs, and decorates it with bright and curious objects such as shells, feathers, bits of bone, and fruits, as do several other species of bowerbirds. But the satin bowerbird is unique in painting the inside of its bower. Fruit is crushed in its bill, and the bird, using its bill as the tool or paintbrush, smears the fruit juice on the sticks on the inside of the bower. While this is a wonderfully strange habit, and apparently unique in the bird world, it is doubtful if this behavior can be considered as using a tool. If the satin bowerbird used a twig, or a wad of moss or fiber, which it does not do, in spreading the paint, the case would be clear.

The clearest case is that of the woodpecker finch of the Galápagos Islands. _Camarhynchus pallidus_ is its proper name. It is one of a group of dull-colored finches restricted to the Galápagos Islands. Before it became known that one species used a tool, the chief claim to fame of the group was that it, along with some other Galápagos Island animals, such as the giant tortoises, had a great influence on Darwin's thinking which resulted in his working out the theory of evolution as set forth in his _Origin of Species_.

The woodpecker finch feeds largely on insects it gets by searching and probing on the ground, and on the trunk and leaves of trees. In searching crevices the woodpecker finch is handicapped by its rather short, thick bill, and to offset this, it picks up a slender, short length of stick, or the spine of a prickly pear, and with this in its bill, pokes into crannies. The insects, disturbed or driven out, are seized. Sometimes the woodpecker finch digs into the tree trunk and then gets a stick to probe with; sometimes it carries its probe about with it, poking in crannies until prey is disturbed. Then the stick is dropped and the food seized.

We have seen how several birds are perhaps borderline cases in using tools. They use certain special aspects of their environment in preparing their food, and use it time after time. It's probably instinctive behavior, but learning is shown in the gulls and crows coming to recognize and use a hard-surfaced road in breaking open their shellfish. The use of a probe by the woodpecker finch is a clear and unique case of tool using by a bird.

BIRDS AS BRIGANDS

Anti-social activities of humans such as those of brigands who plunder their fellow men find their parallels in the bird world.

The bald eagle is one of the best-known of the birds that practice such brigandage. Fond of fish, and capable of capturing it himself upon occasion, it is a common practice for the eagle to take fish from the osprey, plunder the osprey has just caught from the water. The osprey, with a fresh-caught fish, flies heavily. The watching eagle quickly overtakes the smaller, heavily laden bird and forces it to drop its catch, then dives down and usually catches the fish before it can strike the land or water. Rarely does the osprey escape with its food under such an attack. It is recorded that an eagle made several dives at one fish-laden osprey and, when these were not successful in making it lose its hold on the fish, the eagle dived under the smaller bird, turned over on its back, and with talons outstretched, snatched the fish from the grasp of the osprey and sailed away with it, as successful a pirate as ever sailed the seas.

NEMESIS OF VULTURES Besides taking fresh-caught food from the osprey the bald eagle has been seen pursuing vultures and making them disgorge their meal of carrion. The eagle, if unsuccessful in catching the disgorged food in the air, may land on the ground and eat it there. We know also that the aerial flights the eagle uses to frighten the vulture into relinquishing his food are not idle threats, for an eagle has been seen to strike and kill a bird that refused to disgorge.

Not only does our American eagle adopt such practices, but related species in other parts of the world behave in similar ways. The New Guinea sea eagle harries the osprey there, and on the west coast of Africa a sea eagle robs pelicans and cormorants of their prey.

Certain long-winged birds of the tropical seas, such as _Fregata magnificens_, are known popularly as man-o'-war birds or frigate birds, reflecting their well-known character as pirates and tyrannical freebooters. The man-o'-war birds get part of their food from many creatures which swarm at the surface of the sea, but they also get much of their food by forcing terns, cormorants, boobies, and pelicans to deliver up their catch.

In a tropical bay a school of small fish comes to the surface, perhaps driven by large fish below; from far and near terns gather, darting down to seize the fish that jump into the air. Above them circle the frigate birds, ready to dive down and chase and harry a successful tern until it drops its fish and leaves its prey to the freebooter.

BOOBIES ARE VICTIMS Frigate birds may sail about, also, where a colony of nesting brown boobies is located, waiting for the birds laden with food to return home. When such a food-laden booby returns, the frigate bird dashes down at it, buffets it with its wings, snaps at it with its long, hooked bill, until the booby finally drops its fish for the man-o'-war bird to enjoy.

The skua, a big, dark relative of the gull, is also known as a pirate. Its chief food is fish but it also eats many other foods from the sea. It rarely takes the trouble to fish for itself but watches until some other bird, perhaps a gull or a tern, has been successful in its hunting and then gives chase, forcing the unfortunate hunter to relinquish its food. Several of the skua's smaller relatives, the jaegars, have similar habits. It is written of the pomarine jaegar off our New England coast that they are notorious pirates and freebooters, the highwaymen among birds that prey on their neighbors on the fishing grounds and make them stand and deliver. The jaegar gives chase to a tern that has caught a fish and follows it through every twist and turn as if the two were yoked together. Finally the harassed tern drops its fish and the jaeger swoops down and seizes it before it can strike the water.

BIRDS BATHING

The toilet of most birds includes wetting their feathers in water and shaking the feathers and preening them with the bill. This bathing probably helps remove foreign matter from the birds' plumage and helps keep it in good condition. In addition it is probable that in summer the birds derive enjoyment from the coolness resulting from the bathing. But birds bathe in cold weather as well as warm and have been recorded doing so when the temperature of the air was only 10 or so degrees above zero.

The sparrows and robins that come about a birdbath usually hop right into the water. They squat down, fluttering their wings, and duck their heads into the water, splashing and rolling it over their backs. They may become quite drenched. Then they fly to some perch to sit and preen and dry their soaked feathers.

But some birds take shower baths. During a shower in late summer I have seen marsh hawks sitting in the rain with wings spread, apparently enjoying the wetting the shower gives them, and a buzzard has been recorded as deliberately flying to an open perch in a rainstorm and sitting there with its wings spread and sometimes shaking them until the shower was over, when it flew to a sheltered place.

SPRINKLERS A BOON The artificial showers of lawn sprinklers provide an opportunity for birds about our gardens to take a shower bath in fine weather. A robin or a flicker may hop into the shower and squat there and indulge in bathing antics on the wet grass. Hummingbirds have been seen to fly into the dense spray of a lawn sprinkler and hover there for a moment, gradually assuming a vertical position and spreading the tail, then slowly settling to the ground, and finally "sitting" on the grass, body erect and tail spread out fanwise, the wings continuing to vibrate slowly. In a few moments the bird may rise into the air and repeat the whole performance.

In wet tropical forest it is probable that many of the treetop birds bathe in the water that collects on the surface of the leaves, pushing their way through clusters of wet leaves and over wet surfaces of others until they are as wet as if they had actually been bathing in water. This is not restricted to tropical birds, for even in our latitudes towhees have been recorded as bathing thus, and thrushes and flickers have been seen to rub themselves over the wet grass and then go through the actions of bathing followed by preening.

BATHING WHILE FLYING Watching swifts or swallows coursing low over the surface of a lake and occasionally touching it leaves one with the impression sometimes that the birds are bathing rather than picking up insect food or drinking. With some other birds the habit of bathing from the wing is more definite. Sometimes drongo shrikes that are sitting up on a perch near the edge of a pool will fly out over the water, drop directly into it with a little splash, and then rise and fly back to their perch, where they either repeat the performance or sit and preen their feathers.

POST-PRANDIAL ABLUTIONS Ospreys have been recorded as bathing while on the wing in a rather striking manner. They have been seen flying along just above the surface of the water, then descending into it, adopting a sort of vertical American-eagle attitude while flapping the wings, then rising a little, flying on, and repeating the process. It has been suggested that the osprey is washing its feet in this manner after finishing its meal. One observer makes this still more definite. He says that the osprey finishes its meal of fish on a perch in a tree and then flies low over the lake. Dropping both its legs, the osprey drags them through the water, flapping its wings all the time. Then it immerses its beak and head into the water while still flying along, apparently washing off the scales and slime that it had gotten on itself while making its meal of fish.

HOW BIRDS ANOINT THEIR FEATHERS

A bird's plumage receives a great deal of care from the bird that wears it. The bill is the only implement for this grooming, and it is run through and along the feathers it can reach, helping clean them and making sure they lie in their proper place in the bird's dress. There are parts of the plumage that the bird's bill obviously can't reach, as that of the head, but ducks at least surmount this difficulty by rubbing their head against their body.

Many birds have oil glands (the only external glands that most birds have), a pair of glands just above and in front of the root of the tail, on the back. They contain an oily substance, and the usual explanation of its use is that the secretion of these glands is used in dressing the feathers. Certainly birds that have oil glands seem to use them, nibbling at them as though to press out the oil, touching them with the bill, and then rubbing the bill through the feathers, and rubbing the head against the oil gland.

The beautiful, soft, whitish bloom seen on some birds' feathers, such as the pale gray of a male marsh hawk and filmy appearance of some herons' plumage, is caused by specialized feathers called "powder down." Sometimes this powder down is scattered through the plumage; sometimes it is in patches, such as the particularly conspicuous ones in the herons. The tips of the powder down are continually breaking off and sifting over the rest of the plumage, giving it the bloom that with handling quickly rubs off.

WALNUTS AS A COSMETIC But birds sometimes rub foreign substances over their feathers--just why we don't know. Grackles have been known to use the acid juice of green walnuts in preening.

In Pennsylvania starlings have been seen to come to walnut trees when the nuts were almost three-quarters grown, in June, and peck a hole in the sticky hull of a nut, clip the bill into it, undoubtedly wetting the bill against the pulpy interior, and then thrust the bill into their plumage.

They did this from June to August, especially on hot, dry summer days, but some birds continued this even during light rain. Some years before the above was recorded, when this sort of thing was less known, Edward Howe Forbush, noted ornithologist, cautiously used a similar record in his classical _Birds of Massachusetts and Other New England States_. He writes that his colleague, J. N. Baskett, says he saw a bluejay lift its wing and rub pungent walnut leaves repeatedly into the feathers beneath.

BEER AND MOTH BALLS Since then such things have been recorded a number of times, including a catbird that anointed its feathers with a leaf and a grackle that found a moth ball and, holding this in its bill, rubbed it against the underside of its spread wing and the side of its body. After several applications the grackle dropped the moth ball and preened its feathers; then again it picked up the moth ball and treated the other wing as well as its belly.

Recent experiments with tame song sparrows have shown that they may use beer, orange juice, vinegar, and other things made available to them in dressing their plumage, and it appears that this may be correlated with a little-understood type of activity known as anting, in which live ants are placed on the feathers.

TRAVELING BIRDS' NESTS

In spring and fall many of our birds make long journeys under their own power, some of the most publicized being the migration of the Arctic tern, a bird that may spend the northern summer north of the Arctic Circle and, before returning there next season, may have visited south of the Antarctic Circle. The golden plover that makes a nonstop flight to Hawaii is another famous traveler, and many of our smaller songbirds are no mean travelers either. The barn swallow that nests about an Illinois farm in the summer may spend the winter in Argentina. The tiny hummingbirds' feat of crossing the Gulf of Mexico nonstop is worthy of mention too. Such travels have become commonplace through familiarity. We have come to accept even the possibility of occasional transatlantic passages of small perching birds, helped by transatlantic vessels, and of such birds as starlings, making their way from place to place by boxcar.

But when it is time for birds to make their nests and rear their family we expect them to give up their traveling for a time and to settle down in one place. We expect, with our songbirds, to have the male arrive first, pick out a territory, and announce to his species that other males are to keep out and that a mate is welcome. The female arrives and chooses her mate or territory, and a nesting ensues. Many species defend the area around the nest against others of their kind. So it comes as a surprise to find nests built in such a situation that they are not stationary but move back and forth, along with part of their environment.

BY BOAT Tree swallows nest on the ferryboats that ply between Ogdensburg, New York, and Prescott, Ontario, across the St. Lawrence River where it is more than a mile wide. The nests are tucked into suitable openings on the ferries, and the frequent trips back and forth across this mile of water and the docking at different piers do not seem to disturb the birds. They gather their nesting material of feathers and straws and leaves from either shore, and when the young are being fed, insects may be gathered about the Canadian or the United States shore, depending on where the ferryboat is docked.

Another example comes from Western Australia, also of a swallow, the welcome swallow which is nearly like our barn swallow. A pair of these birds nested on a boat used for visiting local coastal stations. If there were eggs or young in the nest when the boat sailed, the old birds would accompany it, once following her on a trip of thirty-five miles and back.

BY TRAIN Barn swallows have been noted nesting on railway trains that run across the two-mile portage between Atlin Lake and Lake Tagish in British Columbia. In the summer the train makes the trip almost daily, and for many years a pair, or a succession of pairs, has made its nest and raised its young in one of the open baggage cars. Members of the train crew took an interest in the birds and put up a cigar box for a safe place for their nest. Here the family seemed to prosper, undisturbed by the proximity of people and baggage and the clatter as well as the movement of the train.

MALADAPTATION IN BIRDS

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.

FEATHERED BABY SITTERS AND CO-OP NURSERY NESTS

Co-operative nurseries, where a few parents look after the young while the rest of the adults, temporarily freed of the care of their offspring, can go about their other affairs, appear in the bird world.

The wild turkey of our Eastern United States commonly steals away singly to lay its eggs and incubate them in its nest on the ground. But occasionally it happens, Audubon writes, that several hen turkeys associate together and lay their eggs in one nest, and raise their young together. With the turkey apparently there is little division of labor, as Audubon writes of finding three hens sitting on forty-two eggs, but he says that one of the hens is always on the watch at the nest so that natural enemies have no chance to rob it.

A GREGARIOUS BIRD What is of only occasional occurrence in one species may be the regular course of events in another, and in the ani we find it customary for a number of birds to nest together. The anis are moderate-sized cuckoos living in the tropical Americas. The smooth-billed ani is perhaps the best known, for Dr. D. E. Davis, when studying at Harvard for his doctor's degree, made a special trip to Cuba to study them in the field. The smooth-billed ani goes in flocks the year round. Usually there are about seven birds in the flock, but there may be as many as twenty-four. The nest is a bulky structure of twigs and fresh leaves. When nest building starts usually one bird is most active, but as many as five birds were seen carrying in sticks at one time. When the nest of sticks and leaves is finished several females may lay their eggs in it. But apparently only one bird incubates at a time, and the male takes his turn at incubating. When the young hatch, after about thirteen days, most of the adults in the colony help feed the young.

Eider ducks may nest in dense colonies, but each bird has its own nest in which it lays its own eggs, and in which the female alone incubates. But after the young hatch and the mother leads them to the water, the young may band into larger flocks, accompanied by a number of females, and the young seem to be independent of their particular parent, but attach themselves to and are tended by the nearest duck.

PENGUIN SOCIAL GROUPS A much more elaborate system for caring for the young has been evolved by certain penguins. The sexes alternate in their care of the young in the early stages. But when the young are partly grown the family unity breaks up for a communistic type of social organization. The young are now grouped into bands of up to twenty or more birds and are left under the care of a few old birds, while the rest of the adults go to the water, which may be some distance away. Periodically they return with food for the young. Apparently the individual young is not recognized by the parent, which goes to the particular group of which its young is a part, and there may feed any one of the "child groups."

Here we have two definite cases of a social organization that has resulted in division of labor: in the incubation of the ani, and in the care of young penguins. In addition we have two less specialized cases of the same thing, showing the sort of raw material on which evolution can operate to produce new behavior patterns.

BIRDS' NESTS AND THEIR SOUP

In caves near the ocean in the Far East nest myriads of tiny swiftlets whose chief impact on the civilized world is that their nests provide an edible article of commerce. "Birds' nest soup" at once comes to the mind of the Occidental, few of whom have ever eaten of the nests, or even seen the birds to know them. For those who would like to see the nests, some museums have them on exhibition, such as in the Chicago Natural History Museum, where two nests are placed in their natural setting, and beside them is a quantity of the material of commerce in its raw state.

The birds themselves are dusky-colored swifts only a few inches long, and belong to a group of swifts that represents perhaps the most puzzling problems of species identification in the bird world. As yet we do not know even how many species there are. The genus is called _Collocalia_. Only some of its members make the edible nests; others mix so much moss into the nest that it is useless for soup. One species has the scientific name of _esculenta_, given in reference to the supposed edible nature of the nest, but through error the name was applied to a species whose nests are not edible. In habits all these swiftlets seem very similar, flying about with a rather weak flight for a swift, catching their insect food on the wing.

A number of swifts, including our chimney swift, use the secretion of their salivary glands as a glue to stick together their nest, and to stick it to the wall of a cave, the inside of a hollow tree, or the inside of a chimney. But some of the edible-nest swifts go further and make their nest entirely of this secretion from their enormously enlarged salivary glands. This material, as it comes from the mouth of the bird, resembles a saturated solution of gum arabic and is very viscid. If one draws out a strand from the mouth of the bird and sticks it on a rod, by rotating the rod and winding up on it the thread of saliva one can empty the salivary glands of the bird. This material dries quickly, and is the material of which the nest is made. When the bird makes its nest, which it does in large colonies in caves, it flies up to the rock wall, applies the saliva to the rock in a semicircle or horseshoe. Gradually a little shelf is built out, and in the finished nest one can see the many little strands that have gone into the structure. It may take the birds as long as three months to make this nest, even if undisturbed. The birds lay their two eggs in the nest, and raise their naked, helpless hatchlings into facsimiles of themselves in it.

But in the Orient, especially in China, the nests are highly prized by epicures as a delicacy. As the supply is limited the price is high. A note with some material we saw stated that the price was $12 to $36 a pound in Siam.

The climbing for and collecting of these nests requires daring, skill and is not without danger. The nests may be far back and high up in the cave. Ropes and poles may have to be fixed in place to aid the climber, who has a flaming torch in one hand and carries a sack or basket for the nests. In Siam, at least, the collecting of these nests was hereditary, father training son. The rights to collect nests are valuable. In Siam, where the rights to collecting the nests were vested in the state, revenue of as high as £20,000 has been received from the rights for this collection.

The nests are said to be of highly nitrogenous material, and contain about 50 per cent of protein and 7½ per cent of mineral matter. Their use as food is an Oriental custom, but an Occidental opinion of their flavor is that it is bland, and an appreciation of it needs to be cultivated. The price of these nests is so great that unscrupulous persons have manufactured spurious nests. These nests are made from agar-agar, the jelly made by boiling down certain seaweed, and are so cleverly flavored that only connoisseurs can detect the fraud.

We usually think of these nests in connection with birds'-nest soup, which may be made with chicken or beef broth and then the cleaned material of the nest added like tapioca or vermicelli. Sometimes a sweet soup is made. Sometimes lotus seeds, sugar, and the nest material are used in the preparation of the dish. But in the Orient, at least formerly, they're considered to have medicinal qualities, too. It is said that when combined with ginseng they are capable of restoring life to a person on the point of death. In Northern China where the winter is bitterly cold, it is a general belief that the blood congeals and can only be thawed out by drinking a soup made of these nests. The list of further benefits, such as against tuberculosis, as a tonic, stimulant, and a pacifier of the stomach, recall advertisements of patent medicines.

WALLED WIVES OF HORNBILLS

For long it has been written that the male hornbill walled up his mate in her nest in a hole in a tree at nesting time, and one author even wrote that the male plucked out the female's feathers at this time. The facts underlying these statements have different interpretations, but the nesting of the hornbill is still one of the most extraordinary of animal habits. Travelers and naturalists in Africa had brought back tantalizing bits of information, to add piecemeal to our knowledge of these birds. Now all this is synthesized and corrected by R. E. Moreau, onetime resident in East Africa, who made a study of certain species, raised young birds by hand, and gave us a comparative study of their behavior. Even this study must be considered preliminary, for, of the twenty-six African species, we have breeding data on only sixteen of them.

First we must not generalize too far as to "the hornbills," for there are Asiatic and Malayan species as well as African, and African species differ among themselves, the ground hornbill being especially aberrant in its habits.

It is quite true that in many African species the female is walled up in her nest, and the period when she is enclosed may last three to four months. But it cannot be interpreted as an imprisonment forced on her by the male, and presumably she could, if she wanted to, open the entrance at any time, as she does finally on emerging.

Among the African species the details vary, but the nest is usually located in a hole in a tree, and except in the case of the ground hornbill the entrance is plastered up so that only a narrow slit is left, about wide enough for the passage of the bird's bill. The female takes an active part in the walling up of the opening, and might be said to wall herself in. When the opening to be filled in is wide, the male may bring earth, which he mixes with saliva in his gullet, and presents to the female, who does the actual plastering. In some species the walling up of the entrance may take months.

The female may wall herself in some days before she lays her first egg. Throughout incubation she remains there. Depending on the species, she may peck her way out, or burst out when the young are partly grown, or she may stay until the young are ready to fly.

During the time the female is walled in the male brings food for her, and later for the young, also. That he is a good provider is indicated by the fatness of the female and her young. This is proverbial with the natives of Africa. The method of feeding varies with the species. The male may bring a bit of food in its bill, pass it in to the female, and then go for another, or in other species we might think more intelligent, the male carries a quantity of berries in its gullet, and these are regurgitated one by one and passed to the waiting female; such species make trips to the nest less frequently.

Apparently shortly after the female goes into the retirement of her walled-in nest, she molts all her flight feathers, so that she is flightless, and then begins to grow them again.

When the female bursts out of the nest with the young only partly grown, the young that remain in a still very undeveloped state in the nest, using material in the nest such as remains of food and rotten wood, replaster the hole! The young, perhaps only halfway through their fledgling period, wall themselves in! The female then helps the male care for the young.

Such is an outline of what some of the African hornbills do at nesting time. The habit is unique in the bird world. One species appears not to wall up its nest. In an Asiatic species it is said that if the male is killed other hornbills help to feed the female in retirement. The whole procedure is an amazing behavior pattern, and one for the development of which it is difficult to find a functional explanation.

BURIED EGGS AND YOUNG

The crocodile bird, or Egyptian plover, has enjoyed a dubious publicity because of its reputed habit of entering, and coming out of, crocodile mouths. As Herodotus put it, the crocodile's mouth is infested with leeches, and when the crocodile comes out of the water it lies with its mouth open facing the western breeze. Then the crocodile bird goes into the crocodile's mouth and devours the leeches, to the gratification of the crocodile, who is careful not to harm the bird. Though there are some more recent observations corroborating this, modern observers who have had abundant opportunity have watched for this behavior and have not seen it.

As one authority on African birds puts it, it is evidently not an everyday occurrence.

But the crocodile bird has other habits that are just as bizarre and interesting. It lives along the sandy shores of African rivers, and when it lays its clutch of two to four eggs these are buried in the sand so there is no sign of them aboveground. The bird sits on top of this spot. A. L. Butler, who studied this bird in the Sudan, thought that the sand might be scraped away from the eggs and the eggs brooded in normal fashion by night. The young birds are very precocial, and feed themselves on tiny insects, but they follow the parent. When danger threatens the young squat motionless in some depression. The toe mark of a hippopotamus is a favorite place. Then the old bird, with her bill, throws sand over the young until they may be completely covered. Not only does this happen when the birds are very small, but continues up until the time the birds can fly. Dr. W. Serle in Sierra Leone once saw a crocodile bird burying something and found the disturbed spot fairly easily, as recent rain had beaten the sand beach smooth and hard; a fully fledged young was unearthed. It squatted motionless until prodded from behind, then it ran swiftly, rose, and flew away strongly.

The burying is not only protection from immediate enemies; A. L. Butler believed it was normal for the young when not feeding to be buried for safety or as protection from the burning sun. For a further protection from the sun the parent moistens the sand by regurgitating water over it.

Butler on one occasion saw a crocodile bird drink at the water's edge, run up onto a sand beach, regurgitate water, then settle to brood. Butler marked the spot, went to it, and, scraping away the dampened sand, found a tiny chick about one inch below the surface.

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.