HOW BIRDS DO IT

How do birds fly?

The simple answer is: with their wings. A more accurate answer is that everything about a bird's body is designed for flight, including its specialized feathers, hollow bones, and very strong flight muscles located in the breast. As a bird flaps its wings, the force of the wings does two things: lifts and propels the bird. As the wings push downward and backward, more air is moved below the wing than above it. This difference in the amount of air, or air pressure, is what causes lift, and results in upward and forward movement of the bird.

The concept of lift, such as that produced by a bird's wing, can be illustrated easily. Have your youngster hold his or her hand, flattened with fingers together, just outside the window of a moving car. When the leading edge of the hand tilted upward, the force of the wind immediately pushes the hand upward. This is exactly how the aerodynamic design of a bird's wing helps to create life and helps to hold a bird in the air in between flaps or while gliding. An excellent explanation of bird flight can be found in How Birds Fly, by John K. Terres (Harper & Row, New York).

How fast do birds fly?

Although they seem very fast to us, most birds do not fly more than 30 or 40 miles per hour at top speed. In general, small birds fly slower, and big birds fly faster. Birds as small as sparrows probably fly less than 20 miles per hour while some of the hawks fly as much as 50 or 60 miles per hour. We don't know much about how fast birds fly because it is very hard to measure. Improvements in technologies such as radar will probably allow us to answer some of these questions in the future.

What makes a bird a bird?

The first thing most people notice about birds is that they can fly, but that is not what makes them unique. Bats, bugs, and butterflies also take to the air, and they aren't birds. What makes birds different from every other kind of animal on earth are feathers. Feathers make it possible for birds to live a large part o their lives in the air. Feathers weigh very little, are strong (to survive long flights), and provide terrific insulation (which is why people living in the coldest parts of the world prefer jackets stuffed with goose down). Most birds also have hollow bones. If bird bones were solid, like human bones, birds would be too heavy, which would make flight very difficult.

Where do birds go at night?

Most birds spend the night sleeping, just as humans do. A few birds, like the owls are awake at night and rest during the day. The birds that rest at night find a safe place, such as a thick bush or shrub, where the nighttime predators will not see them. Some, such as woodpeckers, spend the night in holes in trees. Most ducks, on the other hand, sleep on the water.

Sleep in Birds

Like mammals, birds have cycles of NREM and REM sleep, but with some differences. One of the most striking differences is that both NREM and REM sleep episodes are quite short in birds; their NREM sleep episodes average only about 2 1/2 minutes, and REM sleep episodes only 9 seconds. Also, most birds do not lose muscle tone during REM sleep as consistently as mammals do, which is understandable, since many birds sleep while standing or perching. Some birds, such as pheasants and partridges, sleep on the ground. Water fowl can sleep while swimming. Some parrots sleep hanging down. It is suspected that some birds sleep aloft during long transoceanic flights. Once again, the importance of sleep in the animal kingdom is underscored by the amazing number of accommodations and circumstances during which it occurs.

Do birds fly at night?

Most birds can fly at night, but will only do so if necessary. The reason for this is that their eyes, like human eyes, are not designed to see in nighttime conditions. If a bird cannot see well, it risks injury by flying at night. Unless startled into flight by a predator, most birds will avoid leaving their nighttime roost.

Other species, such as owls and nightjars (nighthawks and whippoor-wills) fly primarily at night, their most active time, and sleep during the day. Songbirds, such as warblers and tanagers, which are active during daylight hours, do fly at night during migration, when they must travel long distances. It is thought that these migrants fly at night because the air is cooler, so there is less chance of their overheating during the long, strenuous periods of flight.

How do owls see at night?

Owls and other nocturnal birds have specially adapted eyes and ears that make it possible for them to sleep during the day and stay awake at night. The pupils of the eyes of these nighttime birds are much larger than the pupils of our eyes. The large pupils gather much more of the available light than our eyes do. In addition, there are two kinds of cells in most eyes, rods and cones. We human beings have more cone cells in our eyes, which allows us to see color. Owls have very few cone cells but many rod cells, that are efficient at gathering light.

Because the eyes of owls are so large, they do not move from side to side and up and down the way human eyes do. An owl cannot look off to the side without moving its head, which is why owls have a special adaptation that allows them to turn their head almost all the way around without breaking their necks!

Owls and other nocturnal birds also hear better than we do. The small bones in an owl's ear that record sound are more sensitive than ours. What's more, an owl's ears are not symmetrical; that is, the ear on one side of the head is lower than the ear on the other, meaning that sound reaches one ear slightly before the other. This tiny difference is enough to permit an owl to know exactly where a sound came from. Because of this highly sensitive hearing, owls can find a small animal, such as a mouse, even when there is no light at all.

Why do birds migrate?

Not all birds migrate. Some, such as cardinals, live their whole lives within a fairly small area. Many birds migrate long distances, however. Birds migrate primarily for two reasons, to avoid bad weather and to find food. Many geese and ducks leave the north in winter because the water there freezes, and these birds need open water to survive. Warblers, which eat mostly insects, leave North America and go south to the tropics, because there is no food for them in the north in winter.

How do birds know where to go when they migrate?

This question has fascinated scientists for centuries, and we are only beginning to know how some birds find their way during long migrations. Birds are born knowing that they must migrate, but knowing that is not the same as knowing how to get from a woodlot in Wisconsin to a jungle in Brazil or from a sea cliff in Alaska to a feeding ground in the Antarctic. We know that some birds are born with a "star map" coded into their brains that allows them to navigate by the position of the stars and the moon. Some birds use the earth's magnetic field to find their way, and some use subsonic sound, the low-level noise created by ocean waves. Still others, like geese and swans, make their migrations in family groups, led always by an older bird that has made the flight before. There is still much to learn, however, about how birds make such long flights and find precisely the right spot.

How do birds stay warm in the winter?

Birds have a number of ways to beat the cold, but none so important as their feathers. You may have noticed how on a very cold day the birds at your feeder seem rounder and more puffed-up than usual. This is a way of keeping warm by raising the feathers to create pockets of warm air and enhance insulation. In addition, may species change their plumage, molting into a fresh thick set of feathers prior to the colder months.

Especially helpful are the very fluffy and soft body feathers known as down. These feathers provide super insulation, much like the goose down we use in coats and comforters.

At night, birds can dramatically slow down their body's metabolic rate (the rate at which the body consumes energy), and lower their body temperature, to conserve energy. During very cold nights, small birds such as chickadees and nuthatches may find a tree cavity or birdhouse where they can spend the night, huddled together with several other birds of the same species. Such communal roosting permits the birds to share body heat. There have been reports of as many as 20 pygmy nuthatches sharing a single tree cavity. Ducks can swim in water that is almost frozen because their feathers have natural oils and are waterproof. Waterproof feathers retain all of their insulating avility. Ducks have a netlike system of blood vessels in their legs that brings warm blood from the heart, alongside cold blood returning from the feet, keeping the feet warm in icy water.

Some birds are not adapted to survive cold winter weather. These species are known as migrants, since they must migrate in response to changes in weather. The osprey, an eagle-like bird that dives into the water from a great height for fish, lacks down feathers in its plumage. The osprey cannot keep its feathers from getting wet, and it has no insulating down, so it must leave the northern portion of its range when cold weather arrives. When warm weather returns to the area, so does the osprey.

Why are male birds more brightly colored than females?

This is not true for all bird species, but it is true for many birds we find in North America, such as the cardinal. The male cardinal is brilliant red, with a red crest and a striking black face. The female is a dull, gray-brown imitation. The reason? Males birds need to be conspicuous in order to attract a mate's attention, and to defend a breeding territory from competing males.

Females, on the other hand, are inconspicuous, which helps to protect them from the sight of predators and competitors during the nesting process. A brightly colored female cardinal would be easily spotted by a hungry hawk or owl. But in her drab attire, she blends well with the viney tangles and brambles in which cardinals prefer to nest.

Why do woodpeckers peck on trees?

Woodpeckers are named for the method in which they find food: pecking, hammering and digging in wood to reach insects, grubs, and even sap. But woodpeckers also use their bills to excavate holes in which to live and nest. They also hammer on tree trunks to advertise their territory and presence to other woodpeckers.

Woodpecker territorial drumming increases in frequency in the early spring months, before the breeding season.

Why does a male cardinal attack our window every spring?

Many reports come in every spring about crazy birds fighting with windows. In most cases a bird is seeing its reflection in the pane of glass and assuming the other bird to be a rival or intruder. The real bird attacks the reflected bird to drive it away, but is never successful in doing so.

This may continue for several weeks until the real bird tires out, or until something, such as a screen, is placed in front of the window to break up the reflection. Once the bird can no longer see its rival, it will go about its business.

Amazing Bird Facts: What Birds Eat

· house wren can feed 500 spiders and caterpillars to its nestlings during a single summer afternoon.

· A chimney swift can devour 1,000 flying insects in a single day.

· A barn owl can swallow a large rat whole. After digesting its meal, the Owl coughs up a pellet containing the rat#&146s bones and fur.

· A northern (Baltimore) oriole can eat as many as 17 hairy caterpillars in a minute.

· Quail, sparrows, and other seed-eating birds sometimes swallow fine gravel, which they store in a special part of their digestive system. This gravel, known as grit, helps to break up hard seeds to make them easier to digest.

· More than 70 different bird species have been observed drinking nectar from hummingbird feeders.

Amazing Bird Facts: Feathers

· Herons and egrets were once shot by the thousands so that their ornate feathers could be used to decorate women#&146s#&146 hats. The shooting of most migratory birds is now illegal.

· A tundra swan#&146s plumage contains more than 25,000 feathers.

Birds Alone on a Winter's Night
Two winters ago Glenn Geyer found two dead bluebirds inside one of his 15 nest boxes in Union, Missouri. Assuming they had frozen to death, he took the boxes down for the rest of the winter to prevent future mishaps. We turned to wildlife biologist Scott Shalaway to find out how birds stay warm at night.

Ever wonder where birds sleep? Especially on cold winter nights?

A general answer is that birds sleep anywhere they safely can stay warm. Some ducks sleep in icy water. Bobwhites sleep on the ground. Crows and turkeys roost in trees. Screech-owls and many other cavity-nesters sleep in their favorite cavities and nest boxes.

Wherever a bird sleeps, its first line of defense against cold is its feathers. Feathers repel water and efficiently insulate warm bodies from the much colder air. Each feather is controlled by a group of small muscles that can raise and lower it. By fluffing their feathers, birds create many tiny air spaces that drastically reduce heat loss (the same principle that makes down jackets so warm in winter).

On extremely cold nights, birds reduce heat loss further by burying naked body parts into their feathers. This is why birds tuck their bills into their shoulder feathers and why many water birds often sleep with one leg held tightly up against the body. Birds also have an amazing network of blood vessels in their feet and legs that minimizes heat loss. Sleeping quarters also protect birds from the elements.

Songbirds such as cardinals, blue jays and finches retire to dense thickets of vegetation. Take a walk at dusk through such habitat and you'll be amazed at the commotion as birds settle in for the night. Tangles of briars, grape vines and brambles protect birds from all but the hardest driving rains.

Even greater protection is found in evergreen refuges such as conifers and ivy-covered walls. This is a good ecological reason for every bird-friendly backyard to include some evergreens.

Woodpeckers, wrens, titmice and nuthatches sleep in cavities much like the ones in which they nest. In the Rocky Mountains, pygmy nuthatches sometimes roost by the dozens in large tree cavities.

Roosting cavities cannot guarantee survival, however. Sometimes it just gets too cold, and birds freeze. And sometimes birds at the bottom of the heap suffocate. About 18 years ago I found four dead bluebirds in a nest box after one particularly frigid Oklahoma cold snap.

Other avian sleeping arrangements are a bit more unusual. Bobwhite sleep in a tight circle on the ground, all heads facing outward. The contact enables them to conserve precious body heat, and the outward orientation allows wary eyes to detect danger in all directions. And when there's lots of snow cover, ruffed grouse sometimes bury themselves in snowdrifts, where the snow itself insulates them from plummeting outside air temperatures.

Despite their relatively small size and lack of large amounts of body fat, birds use peculiarities of anatomy, physiology and behavior to make it through the coldest winter nights.


Birds Are Always on Their Toes
Humans usually have five toes on each foot, important for balance but not critical to carrying out activities of daily survival. Birds' toes and feet, however, are much more utilitarian, similar to our hands.

Ordinarily birds have four toes on each foot, three fanned forward and one pointed to the rear. While our feet are pretty much the same from one person to the next, birds' feet can be quite specialized, as in webbed for swimming. Songbirds stand on their toes, not the flat of their feet as humans do.

The feet of perching birds -- sparrows, wrens, warblers, thrushes, to name a few -- can do almost anything, from walking to hopping and nimbly holding onto nearly any object. When a bird lands on a perch, a tendon in the back of its leg tightens so the toes lock. This involuntary reflex keeps a sleeping bird from falling off a perch. The bird simply stands up and straightens its legs to unlock the tendon.

On most woodpeckers the toes are arranged with two turned forwards and two backward. This gives them better balance and stronger support for climbing or standing on rough and sometimes vertical surfaces.

The stubby legs of white-breasted nuthatches give them perfect balance no matter what their position. Their long toes and down-turned claws adhere to the slightest rough surface, permitting them to dash headfirst down a tree in search of bugs in the bark.

And then there are hummingbirds, which do most of their feeding on the fly, so to speak. Their feet are tiny and so weakly developed that hummers are classified as the order "Apodiformes," which literally means "without feet."

Birds' feet and toes are mostly tough tendons and bones, covered with heavily scaled skin. There is a limited supply of nerves, blood vessels or muscles. This is why their feet do not stick to metal feeder perches when temperatures plummet. And when songbirds roost, their belly feathers cover their feet to keep them warm. If the weather is especially cold many songbirds will squat to cover their feet as they eat. Mother Nature has adequately provided birds with effective protection against wintry weather.


Don't Even Think About It!
Can wild birds "think"? Probably not, although people tend to be anthropomorphic enough to believe they can. Especially when we watch woodpeckers work on a treat-filled suet cake or blue jays caching seeds in the bark of trees.

What birds do have is "instinct." This is somehow transferred from generation to generation, ensuring that any particular species continues to do things in the same way as its ancestors.

Each instinct triggers necessary tasks, such as finding food and mates, building nests and raising the young, in exactly the same way as called for by its species blueprint. None ever really tries a "new" approach. This means, for example, that all migrants know the prescribed course for flying thousands of miles over land or water between North and South America.

Of course it really looks like the local four-footed bushy tails are "thinking" as they figure out how to get at our protected seed feeders. But what we probably are witnessing is nothing more than instinctive feeding patterns.

Which is not to say, however, that squirrels are not capable of learned behavior. If they are able to get on a feeder one way today, they likely will try the same thing again tomorrow.

It's also (fortunately for those who feed them) what causes wild birds to put our feeders on their mental lists of places to eat. This learning can become so patterned that they may well stand on the sill and peck at the window when "their" feeder stands empty.

They may be connecting their experiences and learning. But they are not really "thinking." Which really doesn't matter to those who feed birds. We find their behavior appealing however they come up with it.

Evolution
Quite unusual in this day and age, a new bird has been "discovered," high in the Andes Mountains of Ecuador. It is a species of antpitta, a very reclusive, long-legged, non- migratory bird that hops on the forest floor, feeding on large insects. With some 9,000 known species of birds in the world (90% of which are not seen in North America), only about one new one a year is discovered.

Paleontologists examining fossils from China of small, meat eating, ground-living, two-legged dinosaurs are persuaded that birds evolved from them. Others, however, say the similarities are coincidence. One new fossil species had a cluster of feathers at the end of its tail, some perhaps eight inches long. Another had feathers over much of its body. Both lived at least 120 million years ago. Meanwhile, the oldest established bird, which apparently could fly, lived about 147 million years ago in southern Germany.

Another interesting aspect of bird evolution involves the finches of the Galapagos Islands, off the coast of Peru. They are famous for providing Charles Darwin in 1835 with the most significant single clue supporting his theory of the origin of species. All are descended from a single line of birds that arrived from the South American mainland long ago. Being confined to the Galapagos, they represent an ideal example of the results of natural evolution in a small, localized population. When they arrived, there were no finches on the Islands. They all were seedeaters. But as they rapidly spread through the available space, the birds soon were competing with each other for territory and food. In response, some adopted tree habitats, some in cacti and others on the ground. Beyond that, these different populations developed different food preferences, and their beaks changed shape to accommodate these. Somewhat isolated by ecology and geography, the groups did not interbreed. Today the Islands have 14 finch species.


Feathers Fall: Time to Molt
Not all birds migrate, but all do "molt." Feathers are key to birds' lives and must be in good shape for birds to remain healthy and to manage arduous travel. Most of our feeder birds molt once a year, usually beginning in late summer after all the breeding is finished. Molting is a gradual process of losing feathers and replacing them with strong new ones a few at a time. When birds molt, the feathers usually fall out symmetrically on either side of the body, a few at a time. Although gaps appear, the birds still are able to fly but may temporarily lose some ability to maneuver quickly. Year 'round residents, such as chickadees, cardinals, jays and woodpeckers, add thousands of insulating down feathers to help keep them warm during the winter. Another permanent resident, the American goldfinch, molts twice a year, undergoing a drastic plumage change in the fall from canary yellow to drab olive green. Among the migrants, scarlet tanagers fade from brilliant red to greenish-yellow and many warbler species lose their distinctive markings by the time migration begins. As the days of summer become shorter, the diminished daylight signals that it's time again to be on the wing. Migrations are determined by geography, weather and availability of food. Some hearty warblers stay until October, feeding off berries and seeds. The phoebe leaves when its supply of insects runs out, but the robin stays longer because it switches from worms and grubs to late berries. In some places, another migrant moves in as others depart. For example, some songbirds leave their northern breeding grounds just as juncos arrive from even farther north. White-throated sparrows that nest from northern Wisconsin, across most of Canada up almost to the Arctic Circle winter from Illinois and New York south to the gulf states. These winter visitors will help you clean up your fall garden if you let some of the wilted plants go to seed. They will pick off any remaining flower heads along with the millet you provide on your platform feeders. You may notice a heavy increase in activity at your feeding stations as birds flock in preparation for migration. While fall feeding can help to enlarge the bird population in your neighborhood, the availability of food will not induce migratory birds to remain behind.


Variety
The variety of nature has as its basis the fact that the giant molecules of life do not always copy themselves precisely. In fact, the tiny errors that creep in allow life to perform an experiment with every new generation. The distribution of the great tit Parus major throughout Europe and Asia affords an outstanding example of the way geography can give rise to diversity. From Europe through Asia Minor and up to Siberia, the great tit has a green back and yellow belly, and interbreeds freely. The result is that local differences quickly become eliminated. To the south this tit overlaps and interbreeds with a variety that has a gray back and white belly. But because of geographic barriers, the overlap of the gene pool is not sufficient and the distinctive characteristics of the species are maintained. Further south, where the species has a pale green back and a white belly, this species cannot interbreed with the European/North Asian, and so the two behave as separate species.


Was It a Bird Or a Dinosaur?
Perhaps birds are not descended from dinosaurs after all. Recent rediscovery and re-examination of fossils dug up in central Asia 30 years ago now seem to be from a reptile with feathers and not scales as first thought. The four-footed animal, Longisquama insignis, lived some 220 million years ago. While this was not long after appearance of the first dinosaurs, it was 75 million years before the first known bird, archaeopteryx. Scientists believe the reptile probably could glide but not fly. Since the most bird-like of the dinosaurs, such as velociraptor (remember Jurassic Park?), lived 70 million years after the earliest bird, scientists now question whether there ever were any feathered dinosaurs. This discovery, unfortunately, does not solve the dilemma of the origin of birds. It simply raises more questions. Or as one of the scientists put it, "The exact relationship of Longisquama to birds is uncertain."


What's in a Name?
While bird names often are apt and logically descriptive -- red-winged black birds for example -- there are questionable appellations. The red-bellied woodpecker looks as though it should be called redheaded or at least red-naped. What red there is on its belly is pale to almost indistinguishable.

The common nighthawk neither confines its flights to the evening, nor is it a hawk. It is a member of the nightjar family. The bird captures insects like a hawk, though, and is so adept at snagging them on the wing that it can catch more than a thousand bugs per day.

Birds frequently are named for the locations where they first were identified (the Kentucky warbler), for specific characteristics (yellow warbler) and for people. The Baltimore oriole was named for a colonial landowner, Lord Baltimore, because its colors were the same as his family crest. Bachman's warbler, Baird's sparrow and Harris' hawk honor colleagues of John J. Audubon. Audubon himself was commemorated with Audubon's warbler (now called yellow-rumped warbler) and Audubon's shearwater.

When you see a Brewer's blackbird, remember that it was named after a 19th century Boston editor, Thomas Mayo Brewer, who championed the introduction of the house sparrow into the United States.

The Berwick wren gets its name from Thomas Berwick, an English wood engraver and author of the illustrated A History of British Birds.

The mourning dove was so named because it was thought that the markings on its breast were suggestive of the black clothing of grief for the dead.

Famous Americans whose names are attached to birds they discovered include Merriweather Lewis (Lewis’ woodpecker) and fellow explorer William Clark (Clark's nutcracker). Both birds first were identified in the summer of 1805 while the two men were on their famous cross-country expedition.

The mechanism that enables a bird to perch while sleeping is a little more involved than the poster suggests. Not only is the tendon stretching over the ankle important, but the same tendon in the area of the toes has special properties that help to keep a bird firmly atop its perch. The undersurface of each toe tendon has a bumpy or ridged surface. The portion of the tendon sheath (tube-like covering of the tendon) that is adjacent to the ridged undersurface of the tendon is also ridged, on its inner surface. When the bird rests its weight on the perch, the ridges of the toe tendons and ridges of the tendon sheaths mesh. Once these two structures “lock”, the bird’s grip is sufficient to permit the relaxation of its body muscles in sleep. Pretty neat!

Although most of us see birds almost daily, the basic anatomy of a bird’s leg is often misunderstood. Birds do not walk on or perch with their feet, but with their toes! What many puzzle over as a “backward bending knee” is actually the bird’s ankle. The area from ankle to knee is the lower leg (often called drumstick), just as it is in mammals. However, a bird’s leg is not as easy to see, tucked up alongside the body and covered with feathers; hence the confusion.

Activity: Tendons In Action

Objective: Better understanding of function of tendons

Materials: Bare forearm

When we think of tendons, we generally think of some basic component of our anatomy that is out of sight, deep within our body. However, this is not necessarily true - we can easily see some of our tendons in action without any special preparations - we just have to look in the right place.

1. Initially, we need a subject to demonstrate so students know what to look for. Select someone whose arms have rather distinct muscles and “bony” hands (men have less fat just under their skin than women and make better subjects for this demo). They should bare their forearm, have their hand in clear view, palm down, and then wiggle their fingers as if they’re typing. As the fingers move, it should be easy for everyone to see the tendons on the back of the hand (chord-like structures) move in concert with the fingers. These tendons can’t move on their own but are responding to the muscle movements in the forearm which MAY be visible on some subjects.

2. Pair up your students and have each bare one forearm. Student A can demonstrate the “typing” activity as student B watches but with one variation. Have student B place a hand around the upper part of student A’s demo forearm (just below the elbow). As student A moves his/her fingers, student B will not only be able to see the tendons move on the back of the hand, but will be able to feel the muscular movement of the forearm that makes this possible. Now have student A and B reverse their roles.

3. Be sure to emphasize to the students that tendons connect muscles to bone. This demonstration shows how shortening (contracting) of the forearm muscles pulls on the attached finger tendons and moves the fingers.

4. Now have each demo student raise his fingers several times as if they’re telling someone to stop, so the other student can feel the muscles on the “hairy or top” of the forearm contract. Now have the demo student lower, or curl, her fingers back against her own palm so the muscles on the underside of the forearm can be felt. They should quickly see the connection between muscle, tendon, and finger movement. When muscles on the top part of the forearm contract, the fingers are pulled upward, when muscles on the lower part of the forearm contract, the fingers are pulled downward.

People regularly confuse ligaments with tendons so you may what to reiterate that:

tendons connect muscle to bone

ligaments connect bone to bone.