How Do Birds Walk On Water To Woo Mates?

If you are a grebe, you had better update your dating skills. Grebes, the North American waterbirds, are a bit creative about the courtship season. Whether you are a male or a female, you will be rejected if you cannot 'walk' on the surface of water, according to nationalgeographic.

During the spring mating season, Western and Clark's grebes "rush", by sprinting up to 66 feet (20 meters) across the water in coordinated groups of two or more in amazingly fast speeds---just seven seconds. These are the largest vertebrates you could find who can walk on water, according to sciencemag.

But how on earth (or water) do they do it?

It's just a simple combination of up about 20 steps in a second, making some "forceful slaps on the water's surface with splayed feet", and getting into an unusual stride that can defy gravity.

Mapping the act in Journal of Experimental Biology, scientists point out that most animals that can stride over water are tiny insects that do it with the help of surface tension and lengthened limbs that can distribute their weight and prevent them from sinking, according to study co-author Glenna Clifton, a doctoral student at Harvard University in Cambridge, Massachusetts.

However, the bigger animals such as grebes cannot just bank on their surface tension, so Clifton used high-speed cameras to capture the rushing grebes at Oregon's Upper Klamath Lake. She took a clear shot of the birds' feet so that she could collate and assess their step rate and mobility.

Her assessment was that the birds make between 14 and 20 steps every second, while the the fastest humans can take five or six steps every second, she explains.

"Each grebe's step started with a splayed foot slapping the water, generating between 30 to 55 percent of the vertical force needed to keep the animals from sinking. The rest came from the bird actually pushing its foot underwater," according to Clifton.

After that, the grebe lifts its foot in an arc and repeats the cycle. "[It's] as if a ballet dancer were completely turned out and kicking their leg up to their ear," explains Clifton, who is a ballet dancer herself.

Perhaps the grebe's movement can be captured by robots that work on search and rescue operations---but that's another story!