A bird’s wings may be his most conspicuous features, but his tail is no less amazing. Without tails, many birds would have difficulty landing, perching and taking off gracefully -- let alone turning mid-flight. Sans tails, some birds would have trouble wooing mates. For others, tails also serve specialized functions.
Bird tails are deceptively simple. Essentially, they're just a bunch of long feathers controlled by muscles at their base. There's more to them than meets the eye, though. Tail feathers are specialized plumage that's lighter and stiffer than body feathers. The same is true of feathers at the tip and trailing edge of their wings -- along with their tails, they're collectively called "flight feathers." Birds shed all of their feathers once or twice a year. Despite their similarities, it's easy to tell the difference between wing and tail flight feathers. The former has an off-center shaft; the latter has a central shaft. According to UC Davis and other academic sources, birds probably first evolved feathers for thermoregulation and, later, specialized feathers for flight.
Birds use their tails to create lift and control drag during slower flights and to help steer during turns. They also furl their tails to reduce drag during faster flights. Although a wider wingspan could accomplish some of these ends, it would prohibit other abilities afforded by tails, according to a 1996 article in the "Journal of Theoretical Biology." Despite established and emergent research, science hasn't exhausted the topic of bird tails and flight. The delta-wing theory -- devised to predict the aerodynamics of high-performance aircraft -- fails to predict the shape of bird tails during flight, according to a paper published in 2002 in "The Royal Society." A new or modified theory is needed to accommodate their morphology, according to the authors.
The Tell-Tale Tail
In many species of birds, tail feathers have distinct markings that serve no obvious purpose in aviation. That's because many male birds fan their tales and strut during the spring to impress potential mates. With stunning plumage topped with eye-like designs, the flagship bird in this category is obviously the peacock. Regardless, turkeys and even songbirds display similar behaviors. Many birds' tail markings and designs are species-specific, which suggests they help birds recognize members of the same species -- i.e. compatible mates. Birds may also use tail feathers to identify their coterie in flocks throughout the year and during migration.
Balancing Acts and Whistling
Bird tails have evolved to serve a number of specialized roles apart from flight and display. A woodpecker's tail, for instance, has a row of prongs that helps her hang against tree trunks while she jackhammers the bark. Her tail acts as a stabilizer that forms a tripod with her legs. Brown creepers' tails afford them similar vertical foraging. Bird tails can stand in for bird calls, too. The most dynamic example is probably Wilson's snipes. During courtship, their tail feathers whir and whistle as they engage in dizzying dances.
- Journal of Theoretical Biology: Why Do Birds Have Tails? The Tail as a Drag Reducing Flap and Trim Control
- The Martha's Vineyard Times: Wild Side -- Birds Use Tails for Steerage; Birders Use Them for Indentification
- Natural History Magazine: Tails -- Caudal Appendages Adapted by Nature to the Needs of Her Creatures
- Cornell Lab of Ornithology: Feather Structure
- UC Davis: The Origin of Feathers -- A Display Hypothesis
- International Wildlife Encyclopedia: Peafowl
- The American Naturalist: How Natural Selection Shapes Birds' Tails
- Arizona State University: 23 Functions of Feathers
- Illinois Natural History Survey: What Makes a Bird a Bird?
- The Royal Society: How Do Birds' Tails Work? Delta-wing Theory Fails to Predict Tail Shape During Flight
- U.S. Fish and Wildlife Service: The Feather Atlas
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