For the first time ever, scientists have documented the elaborate tap dancing courtship displays of cordon-bleu songbirds. Invisible to the naked eye, these birds execute their rapid-fire steps in as little as 20 milliseconds.
Normally, male songbirds sing to attract females. But as a new study by an international team of researchers shows, both sexes of the blue-capped cordon-bleu songbird (Uraeginthus cyanocephalus), a waxbill species native to sub-Saharan Africa, perform courtship displays involving both singing and complex visual displays. By using high-speed video cameras, the ornithologists were able to document an astoundingly fast tap dance that both birds perform during the display. The results of their work now appears in the latest edition of Scientific Reports.
For the study, lead author Masayo Soma from Hokkaido University in Japan, and co-author Manfred Gahr from the Max Planck Institute for Ornithology in Germany, recruited eight male and eight female blue-capped cordon-bleus. The researchers paired the birds randomly for multiple two-hour sessions, amassing more than 200 hours of footage in the process.
When analysing the video — shot at 300 frames per second — the researchers noticed the rapid-fire step-dancing. For each burst, the birds performed an average of three to four rapid steps, with each step lasting no longer than 0.02 seconds, or 20 milliseconds.
Credit N. Ota et al., 2015/Scientific Reports
Remarkably, the dancing increased in intensity when another bird was positioned on the same perch, which means the vibrations might add a tactile element to the ritual. In other words, these birds are producing non-vocal sounds to supplement vocal chirps. Alternately, the dancing/vibrations could be part of a larger display that includes singing, bobbing, and even the inclusion of a piece of nesting material in their beak.
The researchers also noticed that the dance performances did not differ between sexes, but varied among individuals. And though both male and female cordon-bleus chose to court with particular individuals (they were surprisingly choosy), high-motor performance birds weren't necessarily popular among the opposite sex. In the words of the researchers: "Assortative mating did not tend to occur with respect to dance performances."
The authors conclude thusy: "The fact that both sexes of this socially monogamous songbird perform such a complex courtship display is a novel finding and suggests that the evolution of multimodal courtship display as an intersexual communication should be considered."
The next step is to study how singing, bobbing, and stepping behaviours are coordinated between individuals and partners, which should tell the researchers something about how and why these behaviours emerged.
Read the entire study at Scientific Reports: "Tap dancing birds: the multimodal mutual courtship display of males and females in a socially monogamous songbird".