Walking with … pigeons?
Dr Jim Usherwood studies the biomechanics of movement. As well as looking at the way people walk and run, he studies other species to gain further insights into the practicalities of locomotion. In a recent paper in ‘Nature’, he showed that the way pigeons fly throws up some interesting points about the best ways to get around, whether on the wing or on your own two feet.
How do you walk? Put one foot in front of the other. But every time you put a foot down there’s an inefficient ‘clunk’ in your motion. If you take smaller steps, there’s less of a clunk. If you had infinitely light legs, you could take infinitely small steps and essentially roll along. Evolution hasn’t invented the wheel though (not yet!), so we have to balance the efficiency of small steps with the benefits of long strides and find a compromise gait somewhere in between.
Pigeons, when flying at least, don’t have to clunk their feet on the ground, so you might think it would be possible for pigeons to use their wings in an optimally efficient way. Just like a human running round a bend, pigeons banking on a turn need to work harder to stay on course. In this case, you might expect that they would just flex their muscles and flap faster and flap harder. It turns out that while they do flap faster, it is with shallower beats of their wings.
This is somewhat counterintuitive but we need to think about more than just their muscles. Obviously a pigeon’s wings have mass, so what the pigeon might gain in mechanical efficiency by flapping harder, it would lose by the physical effort to do so.
Usherwood’s research reveals that there is a lot more to getting around than at first appears. The applications of his work include finding better ways to help people learn to walk – after a stroke, for example. It’s important to think about the muscles involved, of course, but it also helps if you understand the mechanics of walking – and it turns out that’s not so different from the mechanics of flying pigeons.
The video shows up to 18 pigeons flying in a flock measured with back-mounted GPS and Inertial Measurement Units, recorded in June 2010 (note: playback rate is triple the actual rate). The trails show the paths taken by the birds in the previous ten seconds. The different trail colours distinguish individual pigeons: trail width is proportional to height and the colours of the ‘head’ of each trail indicate the flapping frequency of each pigeon: red if above average and blue if below average. Thanks to Jim Usherwood for letting us show it here. I could watch this for hours…
- Usherwood, J., Stavrou, M., Lowe, J., Roskilly, K., & Wilson, A. (2011). Flying in a flock comes at a cost in pigeons Nature, 474 (7352), 494-497 DOI: 10.1038/nature10164