The precocious brush turkeys of the Indo-Pacific could shed light on the most primitive birds and proto-bird dinosaurs, scientists suggest.
Although the Australian brush turkey (Alectura lathami) can fly the day it hatches, it usually prefers using its wings to help run up surfaces — and perhaps young proto-bird dinosaurs did something similar before they grew up, researchers Kenneth Dial and Brandon Jackson say.
To learn more about the way these unusual birds move, the researchers lugged adjustable ramps into a field, caught brush turkeys of various ages, and used high-speed cameras to film them as they ran up the ramps.
Surprisingly, the researchers found the infants could outperform their parents. Hatchlings were able to use their wings to help them not only to run straight up walls, but to run up walls that were leaning back toward them. Adults, on the other hand, had trouble going up even moderately sloped obstacles.
"The hatchlings are very comfortable with these extraordinary slopes, with no panting or stress, doing it over and over and over again. You can imagine they're preyed upon quite intensely, and do so to get to a refuge in the trees and cliffs and gullies where they live," Dial, an experimental functional morphologist at the University of Montana at Missoula, told LiveScience.
The mature brush turkeys rely more on their muscle-y legs. The adult is a far larger animal that has "these large legs with which it can use to run like the wind, outrunning all of its predators," Dial said. "The adults are much more invested in their legs to build and maintain these enormous earthen mounds where they have their nests."
This difference between hatchlings and adults could be much like that suspected in proto-bird dinosaurs, Dial said. Dinosaurs such as Velociraptor that were too large to be capable of flight as adults have nevertheless been discovered with feathered forelimbs. Others, such as Similicaudipteryx, apparently changed their plumage as they got older, suggesting that feathers might have served a variety of purposes that depended on the age of the creatures.
"A major question is, What is a proto-wing good for, one that is not fully capable of flight?" Dial said. "Proto-birds or dinosaurs that led to birds might have used these little winglike structures when small to lift themselves up, and as they got older, these limbs might have been used to help run or just been vestigial. The brush turkey could be a living model of how dinosaurs led to birds."
Dial said the researchers used hand nets to catch the birds of a variety of ages, from hatchlings weighing 0.2 pounds (100 grams) to adults weighing 4.4 pounds (2 kilograms).
"The babies are the easiest birds to work with, just extraordinarily docile," he recalled. "The adults were a royal pain in the ass. They just seem to get wilder and more paranoid and much more frenetic as they get older."
Dial and Jackson detail their findings online Wednesday (Nov. 3) in the Proceedings of the Royal Society B.