Adapted from Jim Conrad's online book A Birding Trip through Mexico, This excerpt from "Hot & Steamy at Témoris Station"
in western Chihuahua state
BLACK-THROATED MAGPIE JAYS
In late afternoon the canyon wall across the river darkens with its own shadow so that the still-lit butterflies flowing downstream over the river appear as thousands and thousands of bright, pulsating points of light. The mood of this strange and beautiful scene is suddenly shattered when three crow-size, long-crested, streamer-tailed, boldly blue, white, and black Black-throated Magpie Jays kite from the wall of my side of the canyon across the river to the other wall. The stately passage of these large, elegant birds above the river of yellow butterflies, all highlighted by tropical sunlight with the dark canyon wall behind them, is thrilling.
Magpie jays are related to North America's Steller's Jays and Blue Jays but, whereas Steller's Jays are only about twenty-eight centimeters long (eleven inches) and the Blue Jay a bit shorter, Black-throated Magpie Jays reach over seventy centimeters (about twenty-eight inches). About two-thirds of that length is tail.
The dark blue tail, embellished along its edges with white spots, stiffly streams behind the birds as they fly across the river. It's obvious from the birds' steady flight that the tails stabilize the flight through what must be highly unstable air.
When not flying, maybe the long tail can be problematical. I watch a jay perched on a limb inside a tree across the river try to turn in the opposite direction, but the tail catches on neighboring branches. The jay works himself along the branch to a more open spot but again it's the same thing. Later I watch a jay perching quietly on a limb minding its own business when a rogue updraft catches that tail, carries it upwards like the handle of an old water pump, and the poor jay topples over as if an invisible hand were pushing him from behind.
Why has nature equipped this species with such an impractical tail? Both males and females have them, so it's not a case like the peacock's, where the male's tail impresses the female. It's not to counteract the aerodynamic effects of the large crest, for Steller's Jays also have large crests.
After thinking about it for a while, the only conclusion I can draw is that Black-throated Magpie Jays have long tails with white spots along their edges because, having them, they are so pretty. Sometimes Mother Nature simply expresses herself with panache.