Part 6

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.

SUBLEASES The snug, secure cavity that a woodpecker chisels in some tree trunk for its nest will last for many years, a shelter in which tree swallows, house wrens, screech owls, bluebirds, or wood mice may make headquarters and use as a nursery. In the strange forests of saguaro, a giant cactus of southern Arizona, the nest cavities of the gila woodpeckers and the gilded flickers in the cactus trunks seem necessary for the presence of many nesting birds. Without them the birds would have to go elsewhere for cavities in which to nest. In old woodpecker nest cavities the elf owl, pigmy owl, screech owl, sparrow hawk, ash-throated flycatcher, martin, and crested flycatcher commonly nest, and cactus wrens and even Lucy's warbler may use them. Their use is not confined to birds alone, for scaly lizards, snakes, rats, and mice have been found in them. In the Argentine there is a woodhewer that appears to depend on the domed mud nest of the red oven-bird for its nesting sites. It takes over a recently vacated or an old nest of the oven-bird and lines it with grass and feathers for its own use. In Africa and Madagascar the great domed nest of the hammerkop stork may find a secondary use in sheltering barn owls.

SANDPIPERS AND EAGLES But it is not only burrows and domed nests that when deserted by their original occupants are used by other birds. The solitary sandpiper of our northlands belongs to a group in which nest building is reduced to a minimum, usually little more than a hollow in the ground with a few bits of material added. But the solitary sandpiper, and the green sandpiper of the Old World have broken with tradition and customarily lay their eggs in the abandoned nest of some thrush. Our great homed owl is another bird that may use the discarded nest of a crow or hawk for its eggs and young. And age in the eagle's nest means little to the eagle. Frances Herrick, the noted chronicler of the life of the American bald eagle, writes of one nest in the crotch of a lofty tree that had been in use for thirty-six years. Each year more material was added until the nest became 12 feet high, 8½ feet across the top, and was estimated to weigh 2 tons.

Man has found, among others, the following two direct uses for two kinds of birds' nests: one he uses for food; of another he makes covering for himself.

The swift's nests used for food have been discussed in another chapter, "Birds' Nests and Their Soup," so here I will only tell of the use of birds' nests as human covering.

EIDER-DOWN BLANKETS An eider-down has come to mean a comforter, a sleeping bag, or even a padded jacket. But to an ornithologist eider down still has its older meaning: the down of an eider duck. It is this material gathered from the eider ducks' nests which forms the article of commerce. The eider's nest may contain grass, seaweed, and sticks, but it is notable for the blanket of down on which the eggs rest, and with which the female covers the eggs when she leaves them. This down is plucked from the breast of the female. If it is taken from the nest she replaces it with more, and it is on this principle that harvesting of the down is carried out. On islands and islets in the northern part of the North Atlantic eiders nest in great numbers in dense colonies. Some of these are jealously guarded by the local inhabitants, who gather the first blanket of down from the eggs, and later, after the eggs have hatched, gather the second crop of down with which the female has replaced the first to guard her eggs against the inclement weather of those boreal latitudes. Each nest may yield an ounce or so of the precious down, which is carefully cleaned and sent to market. It is this material, extremely light, extremely elastic, and one of the best non-conductors of heat, which finally becomes the important part of real eider-down comforters, sleeping bags, and padded jackets.

SYMBIOSIS--ANIMALS LIVING IN MIXED HOUSEHOLDS

Symbiosis, a term from the Greek, is what the biologist uses for the living together of two dissimilar organisms. In a broad sense it includes such diverse relations as the lice living on man and rats in his house, the union of an alga and a fungus to form a lichen, and the cross-pollination of flowers by hummingbirds.

The story of the burrowing owls of our Western plains living in amity with prairie dogs and rattlesnakes as one happy family comes to mind as an example. But "foolish nonsense" is how the noted biographer of North American birds, A. C. Bent, characterizes such stories. He then goes on to quote evidence as to what actually happens, and one can see how the story originated. The prairie dogs, which are really plump, dumpy, ground squirrels and not dogs at all, dig their burrows close to each other on the prairie in colonies which have come to be called prairie-dog towns, or dog towns or simply "towns." Burrowing owls also take up their residence in these towns, probably because they find burrows ready made and do not have to dig their own as they are quite able to do.

MODERATELY PREDATORY The owls may make an occasional meal of a young prairie dog, and a prairie dog may perhaps dine occasionally on owl eggs, but on the whole owls and dogs get along on terms of easy familiarity. Sometimes when alarmed, both may scuttle into the same burrow for safety, but each has its own burrow. With the rattlesnake it is different. The rattlesnake may live in burrows in the dog town, but when it is hungry it eats owl or dog as occasion offers. While the picture of a happy family of owl, dog, and snake is a myth, the symbiosis of owl and dog, at least in the same colony, is striking.

In Africa there is a tiny falcon only about eight inches long which is called a pygmy falcon because of its small size. When Dr. Friedmann was studying the social weavers in South Africa, birds which nest in large colonies under a common roof they make in a savanna tree, he found these falcons occupying nest chambers in thriving weaver colonies. There was no friction between the weaverbirds and the falcons, and they were sometimes seen to sit side by side. When Friedmann collected three of these falcons he found bird remains in their stomachs but they were not remains of the social weavers. Apparently the falcons were feeding largely on small birds, but they did not molest the weaverbirds which had made the nests the falcons were using.

PARROT-DUCK-OPOSSUM MÉNAGE We occasionally find a mallard nesting in a tree, on an old crow or hawk nest, and there are ducks like the wood duck and the golden-eye, which usually nest in holes in trees, but a South American duck called the tree teal habitually nests in a parrot's nest. The parrots, called monk parakeets, make their nests in compact colonies in the branches of trees, so close together that they form a single mass. The tree teal's usual manner of nesting is to lay its eggs in one of the chambers in this apartment-house colony. At first the eggs are laid on the rough twig floor of the nest, but as the eggs increase in number a lining of down, plucked from the breast of the bird, is added until it may even extend out the entrance of the nest. Apparently parrot and duck both get along amicably in their pendant treetop cradles. An opossum sometimes also finds these parrot nests to its liking, though one wonders if it may not have a meal of young parrot or duck in mind. But be that as it may, in different chambers of a single communal nest of these parrots, parrots, a duck, and an opossum have been found.

On islets off the New Zealand coast lives a rather large-sized lizard called Sphenodon. It's rather well known by name, at least, for it is one of those relics of a formerly more widespread group which are called living fossils. It is also noted for its remarkable development of a pineal eye, the remnant of an important sense organ in ancestral forms, and formerly an organ some philosophers supposed to be the seat of the soul. But here we are interested in the fact that petrels swarm to these same islands to dig their burrows and lay their eggs in them, and it is in these same burrows that Sphenodon spends its daylight hours. Apparently the insect-eating Sphenodon and the oceanic-feeding petrels share the burrows amicably, adding still another example of a rather long list of dissimilar organisms whose lives are associated.

BIRD APARTMENT HOUSES

Every now and then in our press appear blasts against crowded living conditions in our cities, and the tenements where people are crowded together. Often there is the implication that this type of thing is unnatural and abnormal. And yet when we look about us in the bird world we see that gregariousness is a common trait. We have only to remember the great flocks of starlings and blackbirds in the autumn, or the massed flights of water fowl. Not only in traveling and in feeding, but also at nesting time birds may gather together, and some birds nest in such close association that the term "apartment houses" or "tenement" is really applicable.

The martins' house on our lawn with perhaps dozens of closely spaced rooms (some houses have as many as two hundred rooms) is a case in point. The neat martin house, made of boards, is a man-made thing, but even before the white man came to this continent, and before the Choctaw Indians hung up groups of hollow gourds for the martin colonies to use, the martins nested in colonies. Even in recent years certain colonies we might consider unprogressive have been reported as using such diverse nesting situations as among the boulders of a lake shore in Minnesota, and the closely spaced woodpecker holes which riddled a dead pine in Florida. And probably it was always thus. The martins liked company at nesting.

CLIFF DWELLERS, TOO Perhaps it would not be proper to consider a colony of bank swallows, each with a separate burrow in the same small cut bank and roofed with the same few square yards of turf of mother earth, as a real apartment house of cliff dwellers. But the term has been used in connection with a West Indian woodpecker, where a dozen pairs were nesting in a single dead tree, and "the trunk was a veritable apartment house." A similar situation exists with the naked-faced barbet of West Africa. This bird too makes a hole in a dead tree for its nest, like a woodpecker, and colonies of thirty to fifty birds may be found nesting in a single dead tree, while other dead trees nearby, apparently equally suitable, are untenanted. Colonies of hundreds of nests of cliff swallows, the nests touching and overlapping, may be under the eaves of a single barn, or as they used to be and some still are, on the sheltered side of a cliff. But as these birds had nothing to do with the making of the roof, perhaps these too do not deserve to be rated as apartment houses.

In southern South America there is a monk parakeet that makes a real tenement. It nests colonially in treetops, and the nests of sticks are placed so close together that they merge and form a single mass, up to nine feet across, in which each parakeet has its own nest. Similar to this is the palm chat. This West Indian bird is small and thrush-sized, dull in color, brownish with a streaked breast, nothing remarkable to look at, but it carries amazingly large sticks, little thinner than a lead pencil and as much as two feet and more long up to the top of a palm tree, and there it makes its bulky community nest.

BUILD NESTS CO-OPERATIVELY These stick nests, which may be four feet and more across, are conspicuous and regular features of the landscape in Hispaniola. The colony consists of four to eight pairs of birds, and each has its own apartment in the bulky structure, and its own passageway to the outside. But in the parts of the community nests that hold the individual nests together and cover them there are roughly defined passages running through the interlacing twigs of the top of the nest so that the birds can creep about under cover. Apparently some of the work is carried on in common, for as many as half a dozen birds may be working close together, pulling and twisting twigs more firmly into place.