Exploring Kootenay Lake

A bird’s deployment of alulae is a remarkably transient event. If you blink, you will probably miss it, for each event lasts less than half a second. Yet, it is fun to spot these bits of aerodynamic wizardry which perform the same function for a bird as do the slats on an aircraft.

Half way along the leading edge of bird’s wing there is a bend that is analogous to a person’s wrist. An alula corresponds to a bird’s thumb. It is usually held flush to the wing to minimize drag during normal flight, and so passes unnoticed. Yet, birds have the same problem as do aircraft. To land, they must slow, but doing so decreases lift and control. To minimize this loss of lift, the bird tips back to increase its angle of attack. This can lead to a stall as the air ceases to flow smoothy over the upper surface of the wing. A bird’s deployment of alulae forces the airflow back over the wing’s upper surface, allowing the maintenance of adequate lift and control.

I was watching a heron hunting in a marsh. And although I felt that my twenty-five metre distance would not be threatening, the heron thought otherwise and flew farther away.

It flew low over the grass to a spot about double the distant. The Great Blue Heron cruises at about 40 km/hr and now must come to a graceful stop. If it were landing in a tree, it could approach from below and use gravity to slow. However, on a level surface, its wings need to do all the work.

It begins to tip back. The increased angle of attack increases drag slowing the bird and also partly compensates for the decreased lift at the lower velocity. Alas, it also increases the likelihood of a stall with its loss of control. At this time the alulae are deployed. They are the raised feathers halfway along the leading edge of the wing (at the wrists).

With its alulae still deployed, the heron tips back even further. The ruffled upper coverts (feathers that cover the wing) probably play the same role as vortex generators on aircraft wings.

Alulae are no longer needed as the heron swings its feet forward to alight.

And all of this was seen because the heron apparently wanted to double its distance from me. Successive landing pictures were separated by about a fifth of a second and the alulae were deployed in two pictures—about the time span of the blink of an eye.

I don’t suppose that any local birder would doubt that Wood Ducks breed around the Lake. Yet, they are remarkably secretive about doing so. Frequently seen are the chicks of Mallards, Common Mergansers and Canada Geese, but not Wood Ducks.

At least, this is the first time I chanced on Wood Duck chicks. Curiously, despite the large number of campers at Kokanee Creek Park, this skittish species was secreted not far from a busy campground.

There were at least four chicks, but only the mother and two of them appear in this grab shot taken though foliage just before they all vanished, presumably as a rebuff to my presence—although, I really wasn’t all that close. 

 
Male Red-naped Sapsucker, 2010

For a week I have been visited by sapsuckers. 

Early one morning a week ago, I first heard and then spotted two sapsuckers on a utility pole, but managed a picture of only one of them before they both flew off. That bird, posted to recent birds and reproduced below, is a male now identified as a Red-naped Sapsucker.  

Since that time, I have heard a sapsucker a half-dozen times but only managed a few more pictures, always of a female Red-naped (one of which is below).

The odd thing about this is that sapsuckers drill holes in trees and then sip the sap that flows. Certainly, that is how I have seen them before, as in the shot of a male working his way around a mountain ash (on the right). This time the sapsuckers seemed to confine themselves to the utility pole, something that clearly lacks sap. They were probably drumming on it to communicate, rather than feed.

This is the first sapsucker (male) seen a week ago.
Its partner went unrecorded at the time.

This is one of a few pictures of the female captured over the subsequent week as it hammered on the pole. Although it was primarily in the shade, there was a moment when shifting leaves allowed sunlight on its red crown.

The Grey-crowned Rosy Finch is not a bird that is often seen, at least not by valley dwellers. It breeds high in the mountains, usually in the vicinity of permanent snowfields.

So it was that on hike up to the Kokanee Glacier last Saturday, Doug Thorburn photographed one and noted:

I didn’t get to spot a nest, but I could hear them
feeding young somewhere nearby.

Doug Thorburn’s pictures are used with permission.