How to cross slick surfaces: lessons from birds

March 30, 2011 • 11:03 am

Via the New York Times, I found a new paper in The Journal of Experimental Biology that possibly has lessons for humans.  The lessons are about how to walk over slick surfaces without falling.  And although it’s coming a little late in the season, it’s good advice to remember for next winter.

The authors ran four helmeted guinea fowl (Numida meleagris) over tracks, training them on tracks with a sandpaper segment, providing good traction.  Then they let the birds run over both sandpaper tracks and tracks with a slick segment made of polypropylene.  As you might guess, some of the birds slipped.   Here are some recordings; be sure to watch them since they’re short and LOLzy:

Video 1: Control birds on sandpaper track

Video 2:  Experimental trial, polypropylene.  Bird crosses successfully

Video 3: Experiment trial, polypropylene.  Bird falls on its tuchus.  Note that in this case the bird had its front leg extended forward more than the previous bird.

Here’s the successful bird in a screenshot from video 2:

And the hapless bird from video 3:

The difference is obvious, and was borne out by the authors’ data: to cross slick surfaces, don’t extend a leg way out in front of you, but keep it closer to your center of gravity.

The crucial graph:  the “fall zone” occurs when the upper segment of the limb is at an angle of less than 70 degrees from the ground (legs right below you are 90 degrees).  The plot, taken from the paper, shows speed versus limb contact angle, SP = sandpaper, PP = polypropylene, dots are successful runs, triangles are falls (FAIL!).

What you should learn from this:  when crossing a slick piece of ground, especially ice, keep your steps short and your legs below the body, mincing rather than marching across.  Actually, this had previously been shown in several studies of human locomotion, but how many of us knew about those?


Clark, A. J. and T. E. Higham. 2011.  Slipping, sliding and stability, locomoter strategies for overcoming low-friction surfaces.  J. Exp. Biol. 214:1369-1378.

40 thoughts on “How to cross slick surfaces: lessons from birds

  1. Bipedalism 101? Forgive me, but isn’t this conclusion pretty obvious to anyone with a quarter of high school physics?

    1. Or to anyone who’s ever walked on ice? 😛

      I’m only jestingly criticizing the rationale for this study, but I do have a serious comment as well: It’s considered less than scientific to trust human intuitions on how to walk on ice, and yet here we are basing our knowledge on avian intuitions! I guess this makes nice converging evidence (presuming guinea fowl bipedal movement is physically similar to human bipedal movement), but at the same time I feel like it’s giving humans very little credit to be able to figure out how to move across different surfaces effectively….

      1. Well, with this study, we can say what angle seems to be the threshold of the “fall zone.” Scientific experiments should be done on things that are considered common knowledge. There are many things that we think are correct because it intuitively makes sense even though it isn’t.

  2. Well, it’s a good thing they we considerate enough of the birds to make sure they had their helmets on!

    Sorry…no, that’s okay…I can find my own way out….


    1. Arrhhh mannn – now you made me giggle. Not a very dignified behavior for +40 woman sitting at her editorial desk in an open-space office. Warn me next time, will’ya?

    1. Exactly! When I moved from St Paul to Chicago at the age of 10, I suddenly became a whiz at red rover when the paved playground was covered with ice. Never fell. Couldn’t explain why, it was just natural. Not that we don’t have winter in Chicago, it’s just nothing like St Paul.

  3. keep your steps short and your legs below the body, mincing rather than marching across.

    Even better: snap on a pair of these and kick in. I swear by the Sarkens. Added benefit is that you can use the long front points to catch any guinea hens that cross your path. Evolutionarily constrained locomotion is for the birds.

  4. I had a turkey fall on its butt in my driveway once. There was about a half inch of snow over sheer ice.

    The turkey left a wonderful impression of it’s tail fan in the snow.

    Normally, one just doesn’t think about a bird falling.

  5. Some years ago in the St Louis area we had three ice storms several days apart, with freezing temperatures the whole time. First day, we could hardly walk on the ice, and there were long waiting lines, at emergency rooms, of people who were injured from falling. However, by the time of the third ice storm, we were walking on ice without thinking about it, and falls were rare. Humans can be trained.

  6. Gee, I never thought of that. Always when I walk on ice I stick my leg out in front as far as it will go. Then I pick myself up and do the same with the other leg, and after a few hours of this I reach my destination, bruised but content.

  7. During those icy walks to lab when I lived in Ann Arbor, I always tried to keep my knees somewhat bent while trying to maintain roughly equal weight distribution on both legs. I guess that amounts to the same strategy as suggested here: keep your legs beneath your body.

  8. There is always a difficulty when generalizing the results from experiments done on animals to humans.
    I recommend a replication using undergraduates.

  9. Somewhere in the background of this paper there was a dare to publish work in re. chickens crossing the road.

  10. You guys’re starting to make me nervous, you know.

    I mean, we all know that ice is something that comes in the form of small cubes that you remove from the freezer and add to your drink, right? The whole notion of giant sheets of it covering the ground is just one of those silly religious myths that godbots use to frighten their children. Can you just imagine the size of the freezer you’d need to make ice “cubes” that big? And think of the conspiracy it’d take to hide the industry where they’re made, the delivery vehicles, and the rest — the notion that any of that could possibly happen is simply preposterous.

    Y’all can stop pretending now. No really! It’s okay. The kids are all in bed and asleep.



  11. My first 1977 strapped-on leg was the same copper riveted tin & leather tech used in the 1920’s.

    Since the 1940’s (or perhaps earlier) anti-personnel device design has been about disabling rather than killing. This, plus the recent improvements in battlefield medicine & the swifter delivery of the injured to the knife & the saw ~ has meant boom time in the prosthetics & robotics markets.

    Now I’m using a carbon fibre, silicon & plastic construction attached via suction. But…

    The knee technology is still mostly passive with little ‘feel’ (feedback) for the dynamics of speed, acceleration, friction & [long list continues here]. A simple example ~ no nerve signals reaching my brain about the nature of the physical contact area underfoot.

    As an amputee I welcome these kinds of studies of gait patterns. As a rule I don’t think anything should be assumed as “pretty obvious to anyone with a quarter of high school physics” in systems that are not entirely mechanical.

    In biologically dynamic systems ~ there are subtleties introduced by animal behaviour & perception.

  12. In four years as an undergraduate at NAU in Flagstaff, Az, I never fell once (or twice or multiple times). Even on “black ice.” Short steps, even after a few (too many) beers was the key.

    Didn’t need to watch no dinosaur descendants to figger that out!

  13. If the surface is so sick, why are you risking taking a step anyway? I just slide my feet by small increments.

  14. There’s another aspect that applies well too, that I use (and try to teach people) when walking in streams with rocky bottoms: weight distribution.

    Plant one foot firmly and know that it’s secure, and extend the other one out without shifting weight from the first. Find and secure the footing under the extended leg, then allow yourself to shift your weight forward. Allow weight to settle onto the extended foot, don’t push off of the planted one to shift the weight.

    This is great for places where you can’t see where your feet are going (muddy streams,) and can even work to a limited extent where the rocks have a fine coating of silt and algae, probably the slipperiest surface I’ve encountered. With $1000+ of photo equipment strapped on, you find ways to keep your feet 😉

  15. It also gets interesting when the surface is slick . . . but unlevel.

    I’m thinking of the sidewalk phenomenon post-snowfall in Chicago (surely it happens elsewhere, as well).

    During/after a significant snowfall, many businesses/property owners shovel/sweep the sidewalk in front of their respective property(ies).


    Still, there are expanses of sidewalk that go unswept (stretches of vacant lots, unoccupied premises, etc.) that nevertheless see foot traffic.

    Trudge, trudge, trudge. Trudge, trudge, trudge.

    Snow gets stamped down by a variety of footwear impressions. Night settles on the city. Temperature plummets.

    Trampled snow ices over, becoming a treacherous field of glazed and broken geography to baffle even the fevered dreams of Dale Chihuly. The wind whistles over the surface in a ghostly call that beckons pedestrians to sacrifice upon the rimed parabolas their ankles, asses, and arms.

    Good times.


    If anyone has an extra slice of Pat’s Pizza (from the South Clark pizzeria in Printer’s Row, please, not that place up in Lincoln Park), by any chance could you do me a tiny favor and hold it close to your broadband connection? It’s been so long . . .

    Still learning,


  16. As to the study’s conclusions–well, DUH! Cute vids, though. Till you think about it–just HOW did they goose those guineas to run precisely when and where they needed them to? And to hit the middle of the center platform in perfect stride?

  17. I learnt the hard way to walk a bit like that in Tromsoe – rain on snow & ice then more ice etc… place the feet down flat, not heel first or…
    Ouch! Gluteus maximus gets it again…

  18. That’s great advice for a guinea fowl, but humans can’t hope for the same data to extend to them as is. On a flat smooth surface I move as if I were skating (I often wish there were enough ice to skate). On a steep incline I grind my teeth and take small steps, preferably on the crushed bits, hoping I don’t slip. On 1-4″ of unpacked snow I walk along as if there were no ice and on all other icy surfaces I scream and curse.

  19. This is common knowledge in certain parts, where the short stride is referred to as “the penguin walk.”

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