Tag / biomechanics

by Roslyn

Flight school

Our research on hummingbird flight is featured in the July 2017 National Geographic!

The article is all about hummingbird science, and how new techniques are allowing us to see aspects of their behaviour that aren’t available to the unaided eye. You can read the print article here, see a beautiful video summary here, and another one here. Here’s one of an Anna’s hummingbird in a wind tunnel. He’s remarkably good at keeping his head steady as the wind ramps up:

The photographer, Anand Varma, took a great shot of my vision experiments at UBC that shows a bird perching in a strange, Tron-like environment of glowing green stripes:

Hummingbird in the virtual reality flight tunnel

Photography and video by Anand Varma in National Geographic.

Between getting the scene right, adjusting the lighting, and then waiting for the bird to act in just the right way, this one photograph took an entire week of work (hands on work that is, no photoshop!). Given all the other complex shorts in the article, it’s easy to see how the whole endeavour took a couple of years – much like a scientific study. Working with Anand that week, it was interesting to see how many other parallels there are between what he does and our research. A lot of trial and error, a lot of patience, and a lot of coping with the quirks and surprises of animal behaviour.

The article ends with a scene from the summer when the writer, Brendan Borrell, spent a couple of days with me in the lab. I have the honour of being described as emerging from the lab with a “sheen of sweat” on my forehead. It is embarrassing, but true! It was a hot day and we were working hard in that room.

There is also a nice editorial about the project here.

by Roslyn

Bird-inspired drones

This Christmas the strong winds decorated the trees with shiny new drones:

(photo by Rod Croskery)

Drones of the future are going to get a lot more maneuverable.

A group at Imperial College London has now built an aquatic diving drone with wings that can tuck in for protection during rapid plunges, inspired by the hunting behaviour of seabirds in the family Sulidae (gannets and boobies).

And a Swiss team has developed a drone with feather-like elements that allow the wing to fold into a range of configurations, analogous to the way birds can overlap their wing feathers. This allows the drone’s wings to be adjusted to suit the conditions – reducing wing area in strong winds, for example.

These advances should make it possible for drones to maneuver in a greater range of tough-to-access environments, just like birds.

Both studies are published in a new issue of Royal Society Interface Focus:

Siddall et al. Wind and water tunnel testing of a morphing aquatic micro air vehicle.

Di Luca et al. Bioinspired morphing wings for extended flight envelope and roll control of small drones.

by Roslyn

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.

by Roslyn

Peacock physics

We have a new paper out!

Biomechanics of the peacock’s display: how feather structure and resonance influence multimodal signaling

In this study we describe the rapid feather vibrations that peacocks use during courtship. These vibrations – at a rate of about 26 Hz on average – represent a substantial mechanical and metabolic challenge for the birds, especially given that they are performed using a massive array of feathers with widely varying lengths.

IMG_3139

A peacock shows his stuff. His train feathers range from 10 cm to > 150 cm in length, and the whole thing weighs about 300 g. Photo by Roslyn Dakin.

We recorded high speed videos of peacocks displaying in the field. We also used lab experiments to test whether the peacocks move their feathers at resonance (which would be an efficient strategy), and to understand how the colourful eyespots can remain so steady during these vibrations. One surprising result was that the peacocks with the longest trains actually used slightly higher vibration frequencies overall – making their displays a greater challenge to perform. The next step is to understand how these feather motions influence the iridescent colour patterns as viewed by the peahens (the females), and ultimately, the hens’ choice of a mate.

Media coverage has been great – here are a few of my favourites:

…and Suzanne reports that her husband met a couple in the Netherlands who had just read about our study in that newspaper. Pretty gratifying to hear that!

The videos associated with the paper are available here.

by Roslyn

SICB Portland

Here is the poster we presented at SICB Portland last week on the biomechanics of peacock displays (click to enlarge):

SICB poster

I think it turned out pretty well, although I’m not sure it could stand alone without an interpreter.

We had a constant stream of awesome visitors. My coauthor Suzanne brought feathers and a model peacock to demonstrate what we were talking about – brilliant! We also had a touchscreen mounted to the left of the poster to display the supplemental videos, but to my surprise we didn’t use it much. It was too slow to load for every new visitor, although it did come in handy for people who wanted an in-depth look. I realize now that videos should really be integrated spatially with the poster content. This could be done if whole display was a touchscreen, for example.

One of the highlights of the meeting was seeing how folks in Stacey Combes’ lab are tracking the movements of individual bees by gluing tiny QR codes onto the bees’ backs (the codes are automatically recognized on video of the bees entering and exiting their hives by tracking software). Another highlight was Ken Dial’s talk about the influence of predation on the development of flight in nestling birds. Portland had lots of good food and drink and exciting views of 1000s of crows roosting late at night downtown.

Thanks to Owen, Suzanne, Jim and Bob for such a fun project!

by Roslyn

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.