A monogamous African songbird performs a tap dance so fast it is invisible to the human eye, in an elaborate courtship ritual with steps for both partners, scientists said Thursday.
High-speed video cameras captured the previously unobserved rapid foot-tapping in a tiny finch with the catchy name "Blue-capped Cordon-bleu".
In what appears to the human eye as a single, quick leap from its perch, each bird in fact stamps its feet at a rate of three taps every 0.06th of a second (60 milliseconds), a team of German and Japanese biologists found.
The timing of the steps appeared to be coordinated with the songs they sang.
The fleet-footed songster, also known as a waxbill or Uraeginthus cyanocephalus, is native to east Africa, and one of few species of bird in which both sexes perform courtship displays.
They stand about 10 centimetres (4 inches) tall.
The male's head, body and tail are a striking sky blue, and the wings, belly and back are light brown. The female has similar colouring, except that the top of the head is also brown.
Courtship dances involve each bird holding a twig in its beak, head up high, while singing and bobbing up and down to drum out a rhythmical sound with its feet.
In the videos, male and female take turns.
"By recording these displays with high-speed video camera, we discovered that in addition to bobbing, their visual courtship display includes quite rapid step-dancing," the researchers wrote.
"Both male and female cordon-bleus intensified their dance performances when their mate was on the same perch."
This was the first-ever observation of such tap dance-like behaviour in a songbird, the researchers said.
And it challenged classical theory of sexual selection which postulate that elaborate singing and dancing courtship displays are performed only by males.
The research was conducted on 16 captive cordon-bleus—eight males and eight females, and the findings published in the journal Scientific Reports.
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Tap dancing birds: the multimodal mutual courtship display of males and females in a socially monogamous songbird, Scientific Reports 5, Article number: 16614 (2015) DOI: 10.1038/srep16614