December 22, 2014

Fisherman in the Swamp

The shape of an anhinga is quite distinctive, as if it is all open wings with no head, and a long neck that shifts from one direction to the other in quick succession. Also called the swamp turkey, its muted quack can be heard in freshwater swamps as it perches on low branches and opens its saturated wings to dry.

Or so goes the common wisdom. It was once thought that the spread-wing posture was to dry the wings, but it is now believed that this position is for thermoregulation- - to absorb solar energy to supplement their low metabolic heat production. The feathers are not water repellant, and they do get quite saturated even though they preen like other water birds to spread oil from the oil gland at the base of their spine onto their feathers. It is the feather structure itself which absorbs water, decreasing buoyancy, and thus allows the birds to pursue fish underwater.

It is called the snake bird, too. Just look at it in the water fishing and you can see why. Only the top of its neck and spear-like beak can be seen above the water. When it dives it spears, rather than grabs, its prey. After it impales a fish it must come out of the water to toss the fish up in the air then grasp it in its beak and swallow it head first. So another easy way to identify an anhinga is by its sharp spear-like beak.

In Africa, the same bird is known as a darter, deriving its name from its quick movements and dives.

Males and females are quite distinctive, though about the same size. Males are black with green gloss, and silvery whitle spots and streaks on their wings and upper back. During breeding season, early spring, they develop wispy plumes on the upper neck, and their facial skin becomes bright gold. Females have a buff- colored neck and breast. Immatures resemble females but are browner.

Nests are rough willow and other twigs. Chicks, downy and voracious, beg for fish brought and regurgitated by both parents.