This past summer in my backyard on the edge of Mount Jumbo, a most unusual bird hopped across our native plantings. It looked like a Spotted Towhee or perhaps an American Robin, but had no tail. Seemingly unhampered by the absence of tail feathers, it then flew into a nearby serviceberry bush. From a distance I could see that it had settled on a nest that I had not noticed previously. Even with my binoculars little was visible but the signature red eye of the towhee.
Tail feathers are an important part of a bird’s flight control and guidance system. Fortunately, this towhee could sustain itself and its nestlings with help from its mate and by foraging for insects, berries, and seeds on the ground. It did not need the flight dexterity of a flycatcher that preys on winged insects.
Tail feathers, and tails in general, provide a variety of functions for different animal species. The prehensile tails of monkeys in Central and South America are the ultimate fifth appendage. These tails can be used for grasping and hanging from branches and manipulating objects. Curiously, while African monkey species often have similar tails, none have grasping prehensile tails.[1]
Another important feature of tails is coloration. The white-tailed deer’s tail serves as a communication device, particularly for female deer. White-tail does have larger and whiter tails than the bucks, and does are more likely to flag their tails and run when they sense danger. This is part of their matriarchal instinct to protect the herd. Solitary bucks are much less likely to flag their tails and run, as I can vouch from tracking them. Instead, they are as likely to sneak over the ridge and perhaps into the scope of a hunting partner.
Many bird species exhibit some white tail feathers, often along the edges of the tail. The humble junco is a case in point. These ground-feeding birds often forage in flocks and, when alarmed, flash white outside tail feathers as they dart off. These white tail feathers may communicate danger to the rest of the flock.
I have also wondered whether this trait could be maladaptive. Could flashing white tail feathers allow a predator to better track the fleeing bird?[2]
I recently read a study that may shed some light on this quandary. In northern snowbound latitudes weasel species generally turn white in the winter. Two of these species, the long-tailed weasel and the short-tailed weasel, sport black tips on their tails in contrast to otherwise white bodies. These black tips would seem to make the camouflaged weasels more visible.
One hypothesis is that the black tip provides a survival advantage to weasels by distracting a predator away from more critical body parts. To test this hypothesis researchers trained three Red-tailed Hawks to attack a brown-colored model of a long-tailed weasel which they pulled along a track. They then substituted three winter-colored weasel models: one was all white; one was white with a black-tipped tail; and the third was white with a black spot on the back. As hypothesized, the hawks were less successful at taking the weasel model with the black-tipped tail. Apparently that black tip confused the focused hawk attacks.
And let us reconsider our nesting Spotted Towhee bereft of its tail feathers. In its fully feathered state its tail feathers would have sported white markings along the margins. Were these white spots enough to confuse a marauding neighbor cat who came away with tail feathers and not the whole bird? One can only speculate.
I’m Edward Monnig for Field Notes, brought to you by the Montana Natural History Center, providing natural history education for schools and the public throughout Montana. For information about upcoming events and programs at the Center, call 327.0405 or visit our website at MontanaNaturalist.org.