Heron drag

This posting is about the aerodynamic drag on a flying Great Blue Heron. So why open with pictures of the Sandhill Crane? Well, the two species are often confused. Further, they have different strategies for minimizing aerodynamic drag.

We see both species: the Sandhill Crane is a warm season visitor to the south end of the Main Lake; the Great Blue Heron is a permanent resident of all the Lake. And for good measure, I toss a swan into the discussion.

Now, I start with the flawed tradition of offering a digression on a digression (heron > crane > cranberry), I note that the cranberry is named after the crane; it is literally the crane berry. This close view of bare skin on the head of a Sandhill Crane suggests why.

Here are two Sandhill Cranes on the Creston Flats.

And here are two Great Blue Herons on the West Arm. At a casual glance, the one might be mistaken for the other, both being big birds with long necks and legs. However, cranes and herons even belong to different families.

This view of a heron, which has just taken to the air, illustrates the reason that long-necked birds need to address the problem of aerodynamic drag. The S-shaped neck sets up turbulence in the airflow across it, so increases the drag. Quickly it will adjust its neck.

The Sandhill Crane, with a somewhat less flexible neck, flies with it fully extended.

So do both of our swan species. This is a Trumpeter Swan.

The heron adopts a different solution to the problem of drag. In sustained flight, the heron tucks its head tightly against its back to provide a smooth flow of air across its head and back. One does wonder whether the crane or the heron adopted the better solution.