Wild Side: Birds use tails for steerage; birders use them for identification

File photo by Susan Safford

It’s nothing fancy – a clump of long feathers controlled by muscles at their base. But the basic model of a bird’s tail has evolved into a host of shapes and forms, sometimes playing highly specialized roles in the lives of birds. And the size or shape of a bird’s tail can provide useful hints for identification. So don’t underestimate this humble piece of avian anatomy!

Collectively, tail feathers with the long feathers on the tip and trailing edge of a bird’s wing are known as flight feathers. Designed to push against the air to provide lift or help the bird maneuver, flight feathers are remarkable structures, light and stiff, consisting of a central shaft and broad vanes of interlocked fibers. As with their less specialized body feathers, birds shed their flight feathers once or twice a year (in a process called “molting”). And birds spend a good portion of their time preening, or smoothing their feathers and removing parasites in order to keep these important structures in good shape. If you find a flight feather a bird has dropped, you can generally distinguish wing from tail feathers because, on the latter, the shaft is in the feather’s middle, while it’s offset to one side in wing feathers.

Birds rely on their tails, just as airplanes do, to pitch their bodies up or down in order to change altitude. Tails also twist to assist with turning in flight, and when it’s time to stop flying, a spread tail functions (along with the wings) as an air brake, to slow the bird to a safe landing speed. (In large birds, especially, the action of the tail is easy to observe in the field.) Birds can fly without their tails; it’s not uncommon, for example, to see a bird that has lost its tail in a narrow escape from a cat or other predator. But the loss of control that results is often easy to observe.

In some species, the tail is modified to assist with activities other than flying. In woodpeckers, for example, the shafts often extend slightly beyond the vanes, forming a row of prongs. Hanging vertically on a tree truck by its forward-pointing toes, a woodpecker snags the pointed tips of its tail feathers into the bark, producing a secure, three-point hold on the tree. This adaptation is even more pronounced in the brown creepers, one of our smallest songbirds, which spends virtually all its foraging time climbing vertically up tree trunks.

For many birds, a spread and raised tail is part of the mating display. The most obvious example for a Vineyard observer would be the tails on our feral turkeys: the males, or toms, strut optimistically before females in the spring, their magnificent tails spread and shaking like a fan. What hen turkey could resist? Similar behavior also occurs, though not as obviously, in many other species. For many songbirds, for instance, the male’s mating display involves some form of bowing combined with an elevated tail. And in a few other birds, like the Wilson’s snipe, specially modified tail feathers produce an odd, quavering whistle when the birds engage in dramatic, swooping courtship flights.

In some birds, the tail may have evolved, paradoxically, to be an inconvenience. The long tail of a cock pheasant, for example, requires a lot of resources to grow, and it surely does little to help the bird in flight. Some biologists see such a tail as a mechanism to favor the healthiest, most fit individuals; less well-adapted males, hindered by their remarkable plumes, are more likely than better adapted birds to die before they have a chance to mate. The counterintuitive result is that an unnecessary stress helps the species as a whole remain healthy.

Some tails display distinctive patterns of colors or markings. In many of our warbler species, for example, the tail shows white outer corners that vary in size and shape, depending on species. The pattern may serve the birds as a way to recognize their own species members when flying in flocks, or when courting. But for human observers, these tail “flash patterns” can be a powerful identification tool. The prominent white edges on a dark-eyed junco’s tail, for example, contrast strong with the otherwise gray back and tail, producing an unmistakable pattern.

Equally useful for an observer can be nuances of the shape of a tail. Sharp-shinned and Coopers’s hawks, for example, are dismayingly similar in plumage, and while the Cooper’s hawk averages larger, the two species overlap in size. Happily, a sharp-shin almost invariably sports a tail with a squared-off end, while the tail on a Cooper’s is generally rounded, sometimes widening slightly at the tip. It sounds like an obscure detail, but with a little experience, a birder will realize this field mark is apparent whether the bird is perched or flying.

The tail may be the last thing on a bird. But it’s often the first thing to look at.