by Hal Borland
The capacity of birds for flight is one of the enduring wonders of nature. Albatrosses, vultures, and hawks can soar for hours without flapping a wing. The Arctic tern flies 22,000 miles a year in its incredible migrations. The ruby-throat hummingbird, which weighs only a little more than a bumblebee, makes its 500-mile migratory flight across the Gulf of Mexico without a stop, without food or drink. Such feats are all the more remarkable because of the physical limitations, especially of small birds. Their lives demand great quantities of energy, which is provided by a high rate of respiration, around 120 per minute when at rest, twice that when flying, and by high metabolism. Most birds feed almost constantly during the day and sometimes consume half their own weight daily. Nestlings of some species require their own weight or even more in food every day. These processes produce high body temperatures, as much as 108° Fahrenheit But the temperature may drop to around 100° at night when they are at rest, thus conserving energy. The metabolism of the hummingbirds appears to have a wide range, day and night. Hummers, incidentally, contrary to legend, do not subsist entirely on nectar; they also eat large numbers of small, flying insects. The nestlings of some species, notably wrens, pass through an early stage of cold-bloodedness which anthropologists say proves their reptilian origin. But their warm-bloodedness is soon established and persists the remainder of their lives. During that early phase they must be hovered by a warm-blooded parent during the cool night or during a chill, rainy day or they perish.
The speed of birds in flight is often overestimated. Most small songbirds fly about twenty miles an hour, with a top speed of not much over thirty-five miles an hour. Crows can fly as fast as forty-five miles an hour, but seldom do; their usual pace is less than thirty miles an hour. Few ducks can fly more than sixty miles an hour except with a strong tail wind, and most plovers have a top speed of about fifty miles an hour. I have seen it stated that swifts can fly 200 miles an hour, but I am skeptical. Birds of prey can attain high speeds in dives at their victims, but that isn’t what should be considered flight. Flight is straightaway travel through the air.
All birds are hatched from eggs, of course, and with the exception of a few parasitic species such as American cowbirds and European cuckoos they all make some kind of nest in which to brood those eggs and care for the chicks. Some sea birds lay their eggs and brood them on bare rocks, but they evidently consider the spot where they lay the eggs as their nest and guard it carefully. Of our common land birds, the nighthawks and whippoorwills make the crudest nests I know of. I have seen a nighthawk’s eggs in a “nest” on the bare roof of a city apartment building, nothing more than a spot where the roofing gravel was somewhat brushed away. And I have seen a whippoorwill’s eggs on bare ground in the woods with a few small twigs around them, a token nest if I ever saw one. At the other end of the scale are the orioles, which I sometimes think must have taught man the art of weaving. And when I watch a pair of barn swallows building their mud nest on a beam in my garage I shake my head in wonder at their patience and industry, not to say the skill they have to build such a structure with nothing but their beaks for tools, since their feet are inadequate for anything but perching.
Some birds can be lured to the dooryard with nesting boxes or houses, especially house wrens, purple martins, and bluebirds. The Audubon Society and other nature and conservation groups publish plans for such birdhouses. The critical dimension is that of the entrance, which must be just large enough to admit the wanted tenant, small enough to keep out troublesome intruders. A house wren, for instance, will not use a house with an entrance larger than a silver half-dollar. A bigger entrance than that will admit an English sparrow, and English sparrows destroy wren nests and eggs.
Nesting boxes are often put up for wood ducks on posts in shallow ponds. If such boxes are not too close to an occupied house the colorful ducks will use them year after year. Wood ducks also nest, and by preference, in hollow trees. But always near the water.
Anyone who insists on trimming every dead branch from the trees on his place is robbing himself of the company of many birds, both at nesting time and through much of the year. Not only owls and woodpeckers nest in deep knotholes in old trees and dead branches. Bluebirds nest in such places, and tree swallows, and other species from time to time. And, though this has nothing to do with birds, flying squirrels nest in such hideaways. Flying squirrels are good neighbors, though few people ever see them since they are nocturnal animals.
At one time it was considered quite proper for amateurs to make collections of birds’ nests and eggs. Happily, that idea has now gone out of fashion. Only experts, collectors for museums and qualified researchers, do such collecting now. Birds’ nests should never be disturbed when they are in use, and eggs should be left in the nest. Winter nest-collecting is quite in order, of course, for those who like that sort of thing. But most birds have lice, and even abandoned Winter nests often have lice or louse eggs; if they are taken into a warm house they may soon become thoroughly alive. If you collect Winter nests, however, don’t be surprised if you find some of them occupied—by mice. Field mice often take over down-lined nests in low brush, roof them over with grass, and spend the Winter there, warm and snug.
Although most birds choose to sing and perch well up in the trees and bushes, a surprising number of the treetop songsters nest on or near the ground. Robins nest in tree crotches, often in dooryards, and bluebirds prefer to nest in holes in trees such as abandoned woodpecker holes; but hermit thrushes and veeries, though they are high singers, always nest on or near the ground, preferably in thick woods. Warblers’ nests show great variety not only in materials, ranging all the way from bark and grass to moss and mud, but in chosen situation. The prothonotary warbler often nests in a woodpecker hole. The Cape May, Audubon’s, black-throated green, Blackburnian, bay-breasted, blackpoll, pine, and several other warblers prefer to nest in conifers, some near the ground, some high up. All the sparrows are ground nesters or shrub nesters. One year I found a song sparrow nesting in a clump of phlox in my flower garden. Cardinals, which choose the highest branch from which to whistle, build a ragged nest of twigs and shreds of bark in a low bush. And brown thrashers, which also prefer to perch high when they sing, nest low, nearly always in bushes. If you have brown thrashers resident in your dooryard, look in your lilac bushes far their nest, especially bushes that are not trimmed too neatly at the base, so there is sufficient protection for a nest within two feet of the ground. Both thrashers and catbirds nest regularly in my yard. The catbirds build their nest five to eight feet above the ground in a big lilac clump twenty feet from the lesser lilac in which the thrashers nest.
If you have good eyes and are persistent you may find meadowlark nests in the nearest pasture or meadow. The nests will be on the ground in a tuft of tall grass—cups of deftly arranged dry grass, usually at least partially roofed over with a loose thatch that hides the nesting mother but gives her little real protection from the weather. Red-wing blackbirds’ nests will be found in wetland, often in clumps of reeds. In damp meadows you may find the open-topped nests of bobolinks, well-hidden grass cups.
Crows’ nests may be found in almost any kind of tall, deciduous trees, disorderly jumbles of twigs and grass assembled in a high crotch, sometimes as much as half a bushel or more of material. Gray squirrels from time to time appropriate a crow’s nest for the Winter, stuff it with leaves and dry grass for warmth.
The eyesight of birds is phenomenal. In proportion to their body size, the eyes of most birds are larger than those of any other vertebrate creature. The muscles that focus a bird’s eyes are so highly developed that a bird seems able to shift in a flash from examining something just beyond its beak to something else several hundred yards away. Hawks, eagles, vultures, and other high-flying birds of prey appear to have telescopic sight of unbelievable acuity. A hawk soaring a thousand feet in the air can distinguish a rabbit hiding in the grass, and I sometimes believe that a crow in full flight well above the highest tr
ees can see a kernel of corn in the garden. Some birds have highly specialized vision. The kingfisher, for example, has egg-shaped eyes with bifocal vision, one phase of which it uses in the air, the other under water. Owls, nighthawks, whippoorwills, and other night birds have night vision at least as acute as night-hunting animals. Unlike most animals, including dogs and cats, which see the world in blacks and whites and cannot distinguish colors, birds have satisfactory and possibly acute color vision. Color vision, incidentally, appears to be a rare attribute except among birds and monkeys and men.
All birds have an acute sense of hearing, but apparently they have little sense of smell or taste. Nor do they have much sense of touch, having no sensitive antennae, like insects, or fingers, like human beings. But the expression “bird-brained” is quite unjustified as a jeering characterization. The brain of a bird, in relation to the size and weight of the body, is larger than that of any reptile or insect and proportionately larger than the brains of some mammals.
Two particular attributes, their colorful plumage and their voices, distinguish birds among all creatures. Only such insects as moths and butterflies can rival birds in physical beauty of color, and even they have no such seasonal color changes as many birds have. In most instances the male birds are more brilliantly colored, at least when in Summer plumage. But some, even such spectacularly beautiful ones as the goldfinches, change to quite drab Winter garb. The goldfinch, brilliant in black and dazzling yellow all Summer, is as sparrow-dull in color as his modest mate all Winter. But who can see a cardinal, an Indigo bunting, a Baltimore oriole, a scarlet tanager, or half a hundred other birds in full color and fail to marvel?
As for voices, the birds are the world’s memorable songsters. No other living creatures except the occasional human being can create such sweet sounds. Only a few birds, such as the pelican and the cormorant, are voiceless. Some, such as the crow, have harsh voices with little or no music in them. But scores of birds not only have beautiful voices but a variety of melodies.
We think of most birds as having only a very few songs which they sing over and over. Actually, many of them have an extensive repertoire. Aretas A. Saunders, an outstanding authority on bird songs, has recorded fifty-three different songs from one male meadowlark in less than an hour. And the meadowlark is not generally known as a versatile songster. The thrushes have long been noted for the quality of their music, but not many people think of even them as being endowed with a great variety of song. Yet all thrushes have a considerable repertoire. Saunders says that the robin, probably the best known and most often heard of all American thrushes, has eight or ten different musical phrases that can be put together in a great variety of ways. And the hermit thrush, sometimes called the greatest of all American songsters, has at least ten different phrases, each composed of eight to twelve notes, which can be put together in almost countless combinations. The catbird, cousin of the versatile, sweet-voiced mockingbird, has been recorded by Saunders imitating more than twenty other birds as well as using seventy-four different song phrases of its own.
The warblers are also notable songsters, though not as vocally spectacular as the thrushes. Experiments have shown that warblers especially, but some other birds too, often sing notes and whole phrases above the range of the human ear. So it seems likely that most of us hear only a part of the bird songs that fill the air every Spring day.
There is even a variation in the songs sung by individuals within most species. Of the various Baltimore orioles that nest each year near my house I can usually distinguish four or five by their voices or the songs they sing most often. One of them, a few years ago, persistently sang a phrase identical with one from “I’ve Grown Accustomed to Her Face,” a song in the musical comedy, My Fair Lady. We finally named that oriole ’Enry ’Iggins. And every year we learn to identify several robins by their characteristic songs.
I have a well-worn tape recorder, bought some years ago for quite another purpose, with which I have from time to time made tapes of bird songs for my own amusement and information. All the recordings have been made from here in the house or on the front porch, most of them through open doors and windows. The microphone I use is an ordinary voice microphone, not one of the extremely sensitive microphones used by those who make professional bird recordings. Mine are strictly amateur tapes, and they include early-morning choruses of all the birds nearby as well as individual songs such as the ecstatic outpouring of a house wren that one year nested in the big spruce just outside my study window. They also have crow calls, the jeering of blue jays, alarm calls of robins with nestlings learning to fly, night calls of the repetitious whippoorwill, the hooting of owls.
Such tapes can be made by anyone with a tape recorder. No special equipment is needed, though I do have a twenty-foot extension for the microphone line for use on the porch. I dub in the dates of the recordings and when I can I identify the birds, all for my own information. Thus I have a record, of sorts, of the birds that sing or call within earshot of my own house the year around.
Far better recordings, with accurate identifications, are available commercially, both on tapes and on records. These recordings are of great help to anyone trying to learn to identify birds by their voices. But homemade recordings can be of help, too, if only for comparison with the professionally made ones to make identity certain. I have found that the best time for recording is around sunup, when the birds are most vocal and in best voice. The best time of the year is the Spring, April and May, while the birds are nesting and the males are most articulate. I have never tried using the battery-powered portable tape recorders, which could be carried into the woods and open fields, but such an instrument should be completely satisfactory. Mine is a house-current recorder bought originally about fifteen years ago. Much better ones are available today.
Chapter 10
Sun, Moon, Stars, and Weather
Powerful as he is, man cannot divert the hurricane or temper the blast of a lightning bolt, let alone alter the orbit of the least star in the heavens. All around him every day of his life play the eternal forces of the universe, to be watched in awe and wonder.
IT SOMETIMES SEEMS THAT the atmosphere around us and the natural phenomena in the skies, the sun, moon, and stars, are more taken for granted and are less generally known than any other aspect of nature. True, we are all aware of the weather, even though we live in air-conditioned houses or apartments, because we encounter it every time we step outdoors; and the weather is the atmosphere in action. But even the weather is, for most of us and most of the time, little more than a topic for forecasters to discuss and something for us to enjoy or regret, not something to understand and appreciate. Yet the atmosphere, which creates both weather and climate, is our lifelong environment, and the sun, moon, and stars are our neighbors and mysterious companions in this remarkable voyage we are making through the universe. It would seem only fitting that we be at least as aware of them, whether we understand them or not, as we are of the robin in the dooryard and the dandelion on the lawn.
There isn’t room in this chapter, or this whole book for that matter, to discuss the atmosphere and the skies in any detail, but perhaps we can find a few guideposts and suggest a few paths into this fascinating and all-encompassing area. Let’s start close at hand, with the atmosphere and the weather.
The atmosphere is the film of air that surrounds the earth. The specialists call it the earth’s atmospheric envelope. Proportionately, it is even thinner than the skin on an apple, and it is invisible to the human eye. At least half of it, by weight, is concentrated in a three-and-a-half-mile layer next to the earth’s surface. At sea level the atmosphere consists of approximately 78 per cent nitrogen, 21 per cent oxygen, and varying amounts of water vapor, carbon dioxide, and other gases. Five miles up the oxygen becomes scarce, as climbers of high mountains have learned. Five hundred miles up the atmosphere consists almost entirely of hydrogen and helium, and from there on up it thins away until there is nothing but str
ay atoms of gas and dust in outer space.
Science divides the atmosphere into four layers. The one closest to the earth is the troposphere and is about five miles deep at the poles, eleven miles deep at the equator. Then comes the stratosphere, reaching up to about fifty miles. Then the ionosphere, extending out to about 650 miles. Beyond that is the exosphere, about which we know very little.
Man and all other animal life live in the troposphere, which is a kind of universal ocean of oxygen-rich air. We are as dependent on it as a fish is on water. We cannot swim in it, though birds can, but we are partially supported by it as we move about. Its oxygen feeds the fires of life, and its pressure holds our bodies together.
Weather is a result of what happens in the troposphere, though it is affected by changes and movements in the stratosphere. But what happens in this lower layer of air creates all our weather and dictates our climate. It is this layer of the atmosphere which makes the earth habitable for the kind of life we know. The heat radiated by our parent star, the sun, is essential to life, but without this atmospheric envelope the earth would be incredibly hot in daytime and abysmally cold at night. The moon, which has no atmosphere, has daytime temperatures as high as 212° Fahrenheit, the boiling point of water, and night cold reaching 238° below zero. Our atmosphere filters and moderates the daytime heat, allowing less than half the sun’s radiation to reach the earth, and acts as a blanket at night, preventing the earth from radiating all its warmth back into outer space.
Being a gas, the air is easily compressed, expands when heated, and shrinks when chilled. When warm, it can hold a vast quantity of water vapor. When chilled, it precipitates that moisture as rain or snow. Air flows somewhat as water does, but it is very restless and flows much more swiftly. Heat it in one place and it expands and rises, leaving a pocket. Cold air from elsewhere rushes into that pocket, and that moving air is wind. If it begins to swirl it may become a tornado. If the swirl sets a great mass of air into motion it may become a hurricane.