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How Birds Do It
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.