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Using their large feet and fast stride, the Western and Clark’s grebes
can run as far as 20 meters on water, making them the only bird and the
heaviest animal on Earth capable of doing so.
If you exclude Jesus Christ, whose biblical feat of walking on water is
literally considered a miracle of the New Testament, only a handful of
creatures are known to be able to walk or run on water. Most of them are
small insects, but there is also a small basilisk nicknamed the Jesus
Christ lizard for very obvious reasons, but the largest of them all are
two bird species – the Western and Clark’s grebes. They can run on water
for up to 7 seconds and distances of about 20 minutes as part of an
impressive mating ritual.
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Unlike the spiders and gnats that rely on their extremely lightweight
frames to stick to the water’s surface, Western and Clark’s grebes rely
on other unique advantages to run on water. These birds usually weigh
between one and a half and four pounds, making them considerably heavier
than other animals capable of walking on water. In fact, they are the
heaviest animals capable of this remarkable feat.
For years, the ability of Western and Clark’s grebes to remain afloat
for considerable distances as they ran on water eluded experts. Then, in
2015, a team of American scientists analyzed footage recorded using
high-speed cameras to try and understand how the birds moved their feet.
They found that the grebes relied on their big feet and extremely fast
strides in order to perform their little miracle.
Specimens from these two species of birds use their broad, lobed feet to
slap the water’s surface, which generates about half the force needed to
counteract their weight. The way they lift their feet out of the water –
to the side – also helps to reduce friction. But this alone isn’t
enough. The grebes are also capable of moving their feet at a very high
speed, taking up to 20 steps a second.
Interestingly, both Western and Clark’s grebes only perform their water
run, also known as ‘rushing’, during their mating rituals, which means
scientists can’t just take specimens into a laboratory and have them
replicate the ritual. Because ruching has so far only been analyzed in
the wild, using video footage, some mystery still remains around the way
grebes use their feet underwater.
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Although 7 seconds of running on water may not seem very long, it’s
actually extremely impressive for such a large, heavy bird as the grebe,
and some scientists refer to their ability as a sort of ‘magic’.
Once considered the same species, Western and Clark’s grebes are nearly
identical and the unique characteristics each has are so subtle that
only experienced birders can tell them apart.
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