How hummingbirds control flight

We have a new study out on how birds use visual cues in flight. Here is a summary:

Thanks to Charlie for helping to capture the video footage! The study is a collaboration with Tyee Fellows and Doug Altshuler at UBC.

For the experiments, we used eight high-speed black & white cameras to capture the entire length of the 5.5 metre-long flight tunnel (I only had space to show two in the Youtube video above). The cameras were part of an automated tracking system that tracked the birds’ motion, and determined the birds’ 3D flight paths from the different camera views. This works similar to the way multiple cameras are used to make 3D movies.

Hummingbirds were great subjects, not only because they are incredible fliers, but also because they are sugar fiends! They have to feed every 10-15 minutes throughout the day. This meant that we were able to design big experiments and test a wide range of visual conditions.

Here are two other clips that illustrate the data from the tracking system:

The best part about this project was that we started with a pilot study that seemed like a failure, at first. We tried to repeat what had been previously shown for other birds (based on a pioneering study of budgies), but we did not see the same results. At first, that can be pretty disappointing. But it also gives you the chance to think of new ideas, and then figure out ways to test them. I think this evolution from failed experiments to ones that work is the most exciting part of science! The catch is that it can take years to get there. I really started to appreciate this once I began working with birds in the lab.

Dakin, Fellows & Altshuer. 2016. Visual guidance of forward flight in hummingbirds reveals control based on image features instead of pattern velocity. PNAS, in press.

Feel the vibration

In between field work, I’ve been making a lot of videos lately – mostly for my students in the summer course in Ecology and the Environment. But my latest creation is entirely different: it’s for the upcoming American Ornithologists’ Union (read: bird nerd) conference.

It features slow-motion clips of peacocks vibrating their train feathers during their courtship displays. I used a special high-speed camera to film this behaviour at 210 frames per second – it was incredibly difficult to do, because the high-speed camera requires that you get really close, and males only perform the vibration when a female is nearby (and not a human one!). In the end, I was able to coax some hungry peahens practically into my lap by slowly doling out the treats. This allowed me to film males displaying at the females from just a couple of feet away.

From these videos, I estimated that peacocks vibrate their eyespot feathers at a rate of 25 Hz (i.e., the feathers move back and forth a whopping 25 times each second). That’s incredibly fast, but it’s hardly record breaking for birds. For instance, Teresa Feo and Chris Clark recently showed that hummingbirds vibrate their tail feathers at a rate of more than 80 Hz to produce a buzzy trill-like sound during their display dives. However, the hummingbirds do it passively, I believe.

Other birds are also making the news these days for their choreographic skills. Anastasia Dalziell and her coauthors at the Australian National University have shown that superb lyrebirds actually coordinate song and dance during their remarkable courtship displays.

Further Reading

  1. Feo and Clark. 2010. The Auk 127: 787-796.
  2. Dalziell et al. 2013. Current Biology. In press.

Super indelible flower colours

How do you fire a pollinator?

That was the question in last week’s Ecology, Evolution and Behaviour departmental seminar. The speaker was James Thomson, an evolutionary ecologist from the University of Toronto who specializes in the interactions between plants and their animal pollinators. His research shows that nectar-addled hummingbirds are like corporate ladder climbers. Bees, on the other hand, are always getting canned.

Pollination syndromes have been a major focus of Thomson’s work1. These are not garden ailments. “Syndrome” here refers to a suite of traits that tend to be found together, in this case because they help a plant attract a certain kind of pollinator.

Bird-pollinated flowers tend to be red and tube-shaped, producing lots of nectar but relatively little scent. Birds have sharp vision, and do not depend much on their sense of smell. Honeysuckle is an example of this type of flower – or anything that looks like a hummingbird feeder. Bee-pollinated flowers come in shades of yellow, blue, and purple, because bees cannot see the colour red. Familiar examples are sunflowers, snapdragons and wild pansies. These often have petals modified into special bee landing platforms. Flowers that specialize on birds and bees are common, but there are many other pollination syndromes. If a flower is orange-brown and smells like rot, it probably depends on carrion flies. Mammal-pollinated flowers often smell fruity, like synthetic grape flavouring.

In his talk, James Thomson reviewed a decade’s worth of work on beardtongue flowers from the genus Penstemon2. In 2007, Thomson and his collaborators used genetic analyses to build the evolutionary tree for close to 200 of the species in this group3. When flower traits were mapped on to the Penstemon family tree, interesting patterns were revealed.

First, the bird and bee pollinated species were distributed broadly throughout, implying frequent transitions between these two syndromes in the history of the Penstemon group. Like an evolutionary magnet, pollination by one type of animal or another exerts a strong pull on multiple flower traits in concert. Evolving species are drawn rapidly towards a new form, so you almost never find intermediates.

This lability or changeable nature of floral traits was not much of a surprise, but the Penstemon tree also suggested something incredible. Floral evolution was directional.

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