Peacocks, with their colorful fan of intricately-detailed feathers, are arguably more known for their impressive plumage than any other bird species. In fact, the trains, made up of the trademark eye-spotted covert feathers, are believed useful for both attracting mates and warding off competition from other males.
The impressive size of the peacock’s train does imply that all this decoration is challenging to haul around, and could even make them more vulnerable to predators. In fact, some scientists have even supposed that the physical burden of those trains ensures that only the fittest birds survive and reproduce. Researchers in the biological sciences department at the University of Leeds set out to question the notion of the train as a handicap, and they were surprised at their findings.
Scientists used high-speed film to capture images of captive-bred peacocks taking off in flight between two perches, both with and without their trains. They also used wind tunnel tests to determine how aerodynamic the trains were. They used their captured images to calculate the birds’ velocity at takeoff and after second wingstroke, as well as kinetic and potential energy and power requirements at take-off.
The peacock’s train was found on average to be 6.9 percent of the bird’s total body weight, yet the velocity of the birds at and just after take-off were not very different between those with and without trains. That was a little surprising to lead researcher Dr. Graham Askew.
"Intuitively, you expect that the train should affect flight performance so, yes, not finding a detectable effect was a bit of a surprise,” Askew said. "But I then went on to measure the drag on the train in a wind tunnel and found that although the parasite drag on the bird is doubled, the power needed to overcome parasite drag is such small component of the total flight power that its requirements are trivial.”
Peacocks don’t generally spend much time in flight, preferring to stay on the ground where they can find the insects and seeds that make up most of their diet. Most of their airtime is spent between the ground and a branch where they roost. Askew said the two perches used for flight measurement in this study created a steep flight path, but one that was an accurate simulation of the way they might move to escape a predator. Even for that limited amount of flight, Askew said the peacock’s flight muscles generate an enormous amount of power.
"Per kilogram of muscle, the flight muscles of peacocks generate one of the highest powers of any muscle in the animal kingdom!” he said. "All that power is used to move air and flap the wings and generate an aerodynamic force on the wing.”
The fact the trains aren’t handicapping male peacocks from escaping predators doesn’t mean that they don’t come free of cost. Askew estimated about 3 percent of the males’ daily energy requirements goes toward feather production in the six months they take to create. He also pointed out that we still don’t know whether the trains could slow the bird down as it walks or runs, or whether the conspicuous feathers could make peacocks easier for a predator to grab onto if it didn’t manage to fly away in time. More research is needed to help quantify the costs of sexually aesthetic traits like the peacock’s impressive train.
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