The Drying Darter

Although the Indian Darter (Anhinga melanogaster) is a common sight across India and further south east, down to Brunei, it is classified as near threatened in the IUCN red list. When you look at the reasons, they are the same depressing lot: habitat loss due to human activity such as damming of rivers and creation of other water management systems, pollution and effluents. Like much of threatened wildlife today, they are accidental road-kills on the way to progress. It is nice to have a place like Bharatpur’s Keoladeo National Park where you can forget these problems for a day or two and look at darters in water.

I stood next to a small body of water and watched one dive into the water, for a while only its long neck could be seen at the apex of a clean wake. Could this be the reason they are also called snakebirds? Then it was gone, completely submerged. It had turned under water, because it came up in a completely different direction, near a dead tree with only a few branches jutting out of the water. It hadn’t caught a fish, so I couldn’t get a photo of it tossing its catch in the air before catching it in its beak, like a chef with a pizza. Instead I admired the way it managed to camouflage itself against the branches.

It doesn’t need to. It is large enough that adults don’t have natural predators among birds (chicks can be taken by raptors). It is same from most other hunters because it mostly nests and roosts in trees sticking out of the water, like the perch it now pulled itself up to. I had a wonderful view of the large webbed feet with which it grasped the branches. It craned its neck to look around. Why is it so alert to its surroundings when it is out of the water? It is certainly not looking for things to eat, since its food is all below the surface. I keep wondering whether it has predators.

You usually spot a darter by its very characteristic pose, when it perches on a tree or sits at the edge of water with its wings spreads out to dry. A sight like this always raises the question why a duck does not need to dry its feathers whereas cormorants and darters do. It was once believed that this was due to special properties of a “preening oil” which covers the surface of feathers. In the 1940s textile industries did some research on the waterproofing properties of this oil, and quickly realized that it is no better than commercially available waxes and polishes. Today we understand that it is the spacing and width of individual barbs in feathers which determine whether they get wet when immersed in water. There are conflicting demands on feathers from a bird’s ability to fly and its ability to resist wetting, and different genus of waterbirds have responded to these conflicts in different ways. There is more subtlety to the darter’s characteristic posture than appears at first glance!