Exploring Kootenay Lake

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. 

The Merlin is the larger of our two regular falcons. It often takes songbirds by approaching them rapidly from below and behind in their blind spot. On this occasion a juvenile Merlin had captured and killed a Grey Catbird. 

The juvenile Merlin was seen standing over its prey, and partially blocking a side road. It held its ground with a look that said: “This bird is mine; Stay clear of me.”

We just waited by the side of the road for passage (but took pictures) as it continued to feed. Meanwhile another catbird (the prey’s mate?) was calling from the branch of a tree above us.

After a while, the merlin became skittish and flew off. It and another Merlin complained bitterly about our presence, so we just drove off.

The final flight picture is courtesy of Finn Fraser Grathwol.

Our three regular hummingbirds arrive in April to breed. First males come, soon followed by females. The three species are Rufous, Calliope, and Black-chinned. I have not seen a Calliope since early May (although others have) so I only show the other two.

Rufous males don’t stick around after breeding and begin their migration to western Mexico by early July. So the males are gone. The females stick around for only another few weeks, and are then followed by juveniles in August. It is now mid July and we are still being visited by Rufous females, one of which stopped by a few times this week.

The Black-chinned female is the most frequent visitor. She may be tending a nest, but seems more or less unconcerned by an adjacent human clicking a camera.

Occasionally, a male Black-chinned comes by. He is distinctly skittish. If the watching human so much as twitches, he is off.

The infrequency of the male’s visits made it difficult to obtain a shot of him flashing his purple gorget. Here is one attempt.

By watching eaglets over the last month or so, I discovered pin feathers. Mind you, I would have discovered them much earlier had I done more reading — or kept chickens.

A pin feather is just a feather during its formation. Normally, a feather is composed of non-living material, but when growing, it is enclosed in a protective keratin sheath and is supplied with nurturing blood. What is seen is the long whitish tube extending from a partially completed feather — a somewhat strange sight.

The problem with spotting pin feathers on a recently hatched chick is that the chick is usually deep inside the cup of a nest which is, itself, located high above eye level. By the time the chick emerges, the feathers have already formed.

However, I occasionally watched a nest of Bald Eagles from high on a distant bank, which placed my eye almost at the same height as the shallow nest. Further, the eaglets would occasionally spread their wings in practice flight, and in doing so, display some pin feathers on their wings.

I set the stage with a picture taken in mid-June (2021/06/14). I had used it earlier to illustrate that Bald Eaglets had mainly dark brown plumage, and so were readily confused with Golden Eagles. Most of the feathers shown here had already formed.

However, in a picture taken a week earlier (2021/06/06) white extensions can be seen from some flight feathers. At the time, I thought these were the feather shafts without realizing that they were actually enclosing keratin sheaths and were called pin feathers.

A picture of an eaglet’s spread wing in mid-June (2021/06/14) shows pin feathers on both the flight feathers and dramatically on the underwing coverts.

However, by mid-July (2021/07/11) all feathers look completely formed. Will flight be far off?

I include this picture of the two chicks, just because I like it (2021/06/29).

I then searched through my pictures of nestlings. The only one where I was looking down into the nest was one of robins. The pin feathers are apparent on the heads of the chicks (2016/07/14).