It’s time to dip into the animal file, and today we’re going to talk about some relatives of our own native animals. Most of us are familiar with the ko'ko', the Guam rail, a flightless bird that disappeared from Guam after the brown tree snake was introduced.
Well, it turns out that we aren’t the only island with rails. The world's smallest flightless bird can be found on Inaccessible Island in the middle of the South Atlantic. Researchers originally believed that this bird arrived there by now submerged land bridges and they named it Atlantisia. Recently, Swedish biologists have shown that Atlantisia’s ancestors flew to Inaccessible Island from South America about 1.5 million years ago.
The researchers analyzed the bird’s DNA and determined its closest relatives are the dot-winged crake in South America and the black rail found in both South and North America. It probably also has relatives on the Galápagos.
This proved Percy Lowe’s theory wrong when he described the Inaccessible Island rail almost 100 years ago. Lowe classified the bird in its own genus and drew the conclusion that its inability to fly was a very old trait, and that it colonized Inaccessible Island by walking on land bridges and across continents that later disappeared into the ocean depths.
The Inaccessible Island rail has no natural enemies on the island and doesn’t need to fly in order to escape predators. Its ability to fly was lost through natural selection and evolution over thousands of years. The researchers emphasize the importance of continuing to prevent enemies of the Inaccessible Island rail from being introduced to the island. They say if that happens, it might disappear.
Ah, yes, here on Guam, we know all about that.
And now, we’re going to talk about some local superheroes. No, it’s not who you think it is. It’s our geckos.
Geckos are well-known for their acrobatic feats on land and in the air. They can run up a wall at 3 feet per second, they can glide, they can right themselves in midair with a twist of their tail and rapidly invert under a leaf running at full speed. And they can run at a meter per second over water. Nothing else can do that; geckos are superheroes.
Not only can they run on water, they can easily transition to speeding across solid ground or climbing up a vertical surface. Their speed on the water's surface exceeds the absolute swimming speeds of many larger, aquatic animals, including ducks, minks, marine iguanas and juvenile alligators, and they’re faster in relative speed than any surface swimmer except whirligig beetles.
In experiments with flat-tailed house geckos, common in south and southeast Asia, the researchers discovered they use several different strategies to run atop the water surface.
Surface tension is essential, because when soap was applied to eliminate surface tension, the geckos were much less efficient: Their speed dropped by half. They can also move using slapping, paddling movements with their four legs like larger animals. Leg slapping creates air pockets that keeps their bodies from being completely submerged, allowing them to trot across the water in much the same way they run on land.
Their smooth, water-repellent skin allows them to plane across the surface in a maneuver similar to hydroplaning. They also use their tail to swish the water like an alligator, providing propulsion as well as lift and stabilization.
So, wave to one of those geckos on your wall. They’re your live-in superheroes!