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Who's Kenn? Simply put, Kenn is a national treasure. A renowned birder, author, and conservationist, Kenn Kaufman has spent his life dedicated to observing birds, reading about birds, writing about birds, and sharing the world of birds with others. With all that birdy knowledge in his brain, he also acts as the field editor for ����APP magazine. So, whenever we have a bird question stumping us around the office, we just ask Kenn. And now you can, too! If you have a bird or birding question you'd like Kenn to answer, leave them in the comments below or on Facebook. Maybe next month you'll get the kind of thorough, thoughtful, and even humorous response from Kenn we've grown so fond of over the years. —The Editors 

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Q: I heard someone call a Bald Eagle a "trash bird"—why?

KK: I’ve been hearing the term “trash bird” applied to some birds all my life. Reasons for it seem to vary. For Bald Eagles, there is one odd connection to trash that might apply. These regal birds do sometimes hang around garbage dumps, literally eating trash with the gulls and crows. But another explanation is more likely: Some active birders use the phrase to signal that a bird is common and widespread, easy to find and frequently seen, and that is definitely true for the Bald Eagle.

At least, it’s true today. But that wasn’t always the case. As recently as 50 years ago, the species was seriously endangered and going downhill fast.

Precise numbers are hard to pin down, but Bald Eagles seem to have been declining (because of shooting and other human activities) for most of the first half of the 20th century. By the late 1960s, the Lower 48 States apparently had fewer than 500 breeding pairs. Many of those pairs were not producing any young, because the effects of persistent pesticides like DDT kept their eggs from hatching. After the use of DDT was banned in 1972, eagle populations began to build up again—gradually at first, and then at a faster pace.

Their recovery has been remarkable. The number of breeding pairs in the Lower 48 now numbers more than 10,000. And the buildup of numbers has been noted continent-wide. If you look up the species on ����APP’s cool “trend viewer” for the Christmas Bird Count, it shows increasing numbers in 49 U.S. states and 10 Canadian provinces—everywhere, in other words. 

In Ohio, where I live, the whole state had only four nesting pairs in the late 1970s; now the number is pushing 350 pairs. Their recovery is partly due to the removal of DDT from the environment, and partly due to other initiatives. On the federal level, the Migratory Bird Treaty Act, the Bald and Golden Eagle Protection Act, and the Endangered Species Act all played a part. On the state level, our Ohio Division of Wildlife worked hard for decades to protect the eagles and their nests. All of these efforts paid off. I’m lucky to live in the part of Ohio with the highest concentrations, the western Lake Erie marsh region. Dozens of pairs nest within a few miles of my house, and I can see Bald Eagles literally every day of the year.

So, are they too common to be exciting now? Never. Why should we appreciate a bird any less, just because we get to see it frequently? These eagles are among the most magnificent creatures anywhere, and I can’t forget that when I was a kid birder in the 1970s, we seriously thought they were headed for extinction. Their comeback has been glorious, and it proves that conservation efforts can work, that we can save birds for future generations. No matter how many Bald Eagles I see, I will never take them for granted, and they’ll never be trash birds to me.

Q: I love watching videos of murmurations—big swirling flocks of starlings in the sky—and started wondering about the word. If a murmur is a sound, why is murmuration applied to such a visual spectacle? 

KK: They’re among the most fascinating of all bird videos: Distant views of hundreds or even thousands of small birds flying close together in flocks that change shape as they swirl across the sky. As if directed by a cosmic choreographer, the flocks twist and turn, forming grand geometric shapes and designs that change moment by moment. Starlings are especially noted for being masters of such astounding aerobatics, and humans have been awed by them for millennia.

Watching one of these extraordinary displays of coordinated aerial grace, it’s hard to imagine how it’s even possible. Since the birds seem to be constantly changing direction, there can’t be any one bird leading the flock; individuals at the front at one moment may be all the way in the back a few seconds later, as the whole flock shifts course. Yet the group stays cohesive even as it morphs from a sphere to a twisted crescent to a double spiral to another fantastic shape. How do they do it?

With high-definition, slow-motion videos of flocks of thousands of starlings, scientists have analyzed movements of individual birds to come up with . There is no force directing movements of the whole group. Instead, the cohesion of the flock is maintained because each individual starling is reacting to the movements of its six or seven closest neighbors. The formations are tightest and most elaborate when the birds are reacting to a predator, like a nearby Peregrine Falcon. To keep from being an easy target, each individual starling tries to stay as close as possible to its neighbors; so, if a nearby part of the flock starts to turn in a different direction, others will instinctively follow. They may all appear to be shifting at exactly the same instant, but in fact their reactions are just so quick that a change in direction sweeps through the flock in a fraction of a second. When different parts of the flock are turning different directions at the same time, we see these swirling, mesmerizing patterns that defy imagination.

But why are they called murmurations, anyway? Actually, this is just a new use for an old word.

Collective nouns for groups of animals have been at the center of mildly popular fads, off and on, for years. I first became aware of these as a teenager when I ran across a book called An Exaltation of Larks, by James Lipton. This volume listed more than a thousand group nouns, many of them applying to birds and animals: A leap of leopards. A parliament of owls. A fall of woodcocks. For a while I was trying to memorize all the bird ones, until I realized that hardly anyone actually used these terms in a practical way. But they’re fun to consider, and new collections of these words are still published at a rate of one or two every decade.

However, for the origins of many of these words, we have to go back to The Boke [book] of Saint Albans, published in England in 1486. An oddity that featured sections on hunting and falconry, it also included a long list of such group nouns. is “a murmuration of stares.” (At that time, starlings were generally known in English as staers or stares, with “starling” applied to young ones, as with duck and duckling. Only later would “starling” become the general name for the species.) The word “murmuration” was already in use to describe a low, continuous sound. It wasn’t a surprising choice for a group of starlings, since their flocks typically keep up a steady level of noise when perched.

So the phrase “a murmuration of starlings” has been around for more than 530 years, but for most of that time it simply referred to a group of starlings. As far as I can determine, it wasn’t applied to these spectacular aerial formations until recently—not until people had the means to take videos of the motions of the flocks and share them easily online. Once these aerobatic displays were being widely viewed and discussed, people wanted a term to describe them, and a memorable, poetic word was readily available.

Does that mean it’s incorrect to use a word that had been just a collective noun for starlings as a term for these swooping, swirling flights that may or may not involve starlings? Of course not. Language is a living thing, and words, like birds, can evolve. I embrace the idea of calling these flock dynamics “murmurations,” and I think we should encourage everyone to watch for them and appreciate their wild beauty.      

Q: How do nuthatches walk so freely on the sides of trees without falling off? 

KK: The actions of nuthatches are wonderful to watch. Other tree-climbers, like woodpeckers and Brown Creepers, cling with both feet and brace themselves against the trunk with strong, stiff tail feathers as they go hitching upward. But nuthatches don’t use their short tails at all in climbing, and they don’t just climb up: They can walk up, down, and around trees, clambering about on vertical surfaces with an ease that Spider-Man would envy.

How do they do it? Like most birds, nuthatches have four toes on each foot, three pointing forward and one pointing back, with a curved, sharp claw at the tip of each toe. On a nuthatch, the claws are quite narrow and the hind toe (the hallux) is unusually well developed and strong. When the bird is moving up a tree, it’s clinging to the bark or to rough spots in bare wood with the three front toes on each foot. Going down, it’s held up mainly by the hind toe on each foot.

It’s not just foot structure, though—the nuthatch also has specific climbing strategies. It seldom goes straight up or down a tree; usually it’s moving at an angle, circling the trunk instead of going vertically. When it pauses, its body is usually at an angle to the axis of the trunk, not parallel to it. The bird keeps its feet spread far apart, almost always with one foot higher than the other. On the upper foot, when the bird is going sideways or downward, the claws grip the tree but the sole of the foot is pulled away from the surface. The lower foot is pressed flat against the tree, helping to brace the bird in position. 

These might not seem like enough adaptations and actions to allow such agile climbing—but remember, these birds hardly weigh anything. The White-breasted Nuthatch, the largest of our species, tips the scales at about three-quarters of an ounce. The other three species in North America are closer to one-third of an ounce, or about as much as four pennies. If a Pygmy Nuthatch perches on your hand, it feels weightless, as if you were holding the shadow of a bird. It doesn’t take much for such a wisp of a creature to resist the pull of gravity.

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Have a bird or birding question for Kenn? Leave it in the comments below, and maybe he'll answer it in a future column.