Take the plunge for love, like a hummingbird

A male broad-tailed hummingbird (left) flashes its iridescent throat feathers while another flies upward to make a U-shaped dive to attract female attention.
A male broad-tailed hummingbird (above) flashes its iridescent throat feathers while another flies upward to make a U-shaped dive to attract female attention.PHOTOS: UNIVERSITY OF CALIFORNIA, BERKELEY; ROCKY MOUNTAIN BIOLOGICAL LABORATORY
A male broad-tailed hummingbird (left) flashes its iridescent throat feathers while another flies upward to make a U-shaped dive to attract female attention.
A male broad-tailed hummingbird flashes its iridescent throat feathers while another (above) flies upward to make a U-shaped dive to attract female attention.PHOTOS: UNIVERSITY OF CALIFORNIA, BERKELEY; ROCKY MOUNTAIN BIOLOGICAL LABORATORY

In the bird world, males often go to extremes to attract female attention, through dance, colour and sophisticated home decor, for instance.

Hummingbirds are no exception.

Broad-tailed hummingbirds (Selasphorus platycercus) fly up to 30m in the air before diving down towards a perched female, then climb back up for a subsequent dive in the opposite direction.

At the Rocky Mountain Biological Laboratory in Gothic, Colorado, home to a population of breeding broad-tailed hummingbirds, researchers from Princeton University have been investigating how these tiny dynamos combine speed, sound and colour in their displays. Their work appears in the journal Nature Communications.

"The dives are truly amazing feats for such small birds," said Dr Benedict Hogan, a postdoctoral research associate in ecology and evolutionary biology, and the study's lead author. "We know from previous work that the males can reach really high speeds. They combine that speed with intriguing noises generated by their wing and tail feathers, and of course with their brightly iridescent plumage."

To explore how the different components fit together, and what a dive might look and sound like to a female, Dr Hogan and Dr Mary Caswell Stoddard, an assistant professor of ecology and evolutionary biology and the study's senior author, created video and audio recordings of 48 dives performed by wild male broad-tailed hummingbirds. They used image-tracking software to estimate each male's trajectory and speed throughout the dive, said Princeton University in a statement.

Combining these estimates with the audio data, the researchers measured the precise time at which the males produce a mechanical "buzz" with their tail feathers.

Using multi-angle imaging and an ultraviolet-sensitive camera, they created special photographs, which were combined with a model of hummingbird colour vision and details of the U-shaped flight path, allowing the researchers to estimate a female "bird's-eye view" of the male's iridescent throat feathers.

Putting it all together, Dr Hogan and Dr Stoddard determined how the events in a hummingbird's dive unfold, said the university.

"We discovered that the most dramatic aspects of the dive - high speed, the mechanical buzz and a rapid iridescent colour change - happen almost all at once, just before the male soars past the female," said Dr Stoddard.

"These aerial acrobats deliver an in-your-face sensory explosion."

A version of this article appeared in the print edition of The Straits Times on December 22, 2018, with the headline 'Take the plunge for love, like a hummingbird'. Print Edition | Subscribe