Exploring Kootenay Lake

Bufflehead Ducks might be seen throughout the year, but they become fairly common during cold months. In the past couple of weeks, buffleheads have been appearing around the area. They are our smallest duck: a black and white male and a brownish female with a white cheek patch.

The description of the male as being black and white is a tad deceptive for the black feathers on its head (although not elsewhere) can be strikingly iridescent. Five weeks ago, I showed similar magpie iridescence. The process with male buffleheads is the same: the duck’s iridescent feathers contain a basal melanin layer, which produces the black by absorption, but above that are reflecting platelets, which produce iridescent colours. The iridescence arises in a similar way as those in a slick of (burnt) oil on black pavement. Light reflected from the base of the slick interferes with that from the top of the slick to preferentially select various wavelengths. 

However, the effective spacing between the reflective layers depends upon the viewing angle so sometimes one colour is seen, sometimes another, and sometimes nothing but black. The trick is to have the proper geometry between the sun, the duck and the observer.

A group of male and female Bufflehead Ducks swim by. There is a hint of iridescence on the heads of the two males at the front. However, the bufflehead at the back (right) has his head turned and he shows no iridescence at all.

The male duck at the rear turns its head. Suddenly, a beautiful range of colours appears.

Surf Scoters are really uncommon visitors to this region.

In the summer, Surf Scoters breed beside small boreal lakes, all of which are at least 800 km north of here. They winter along the Pacific coast, over 400 km to the west. Scoters have scant reason to pass this way during migration and so are rarely seen. However, now and then, storms drive them astray.

A male Surf Scoter visits.

Warm-season insectivores leave the region in October as the supply of insects and spiders diminishes. Many head for the southern USA, Mexico, or Central America. Three of these soon-to-be departed species were seen on a walk in yesterday’s sunshine.

A Savannah Sparrow flies to another perch, but soon will fly far to the south.

Another Savannah Sparrow hunts a diminishing supply of insects from a branch.

A Chipping Sparrow hunts near the ground.

My favourite shot is of a female Common Yellowthroat. She, too, will fly south soon.

Magpies do not favour this region because it is highly forested. These birds prefer open habitats with occasional clumps of trees. Consequently, there are few opportunities to capture pictures of magpie iridescence.

The pigmentation of a magpie’s feathers produces a plumage that is strictly black or white. Yet in some lightings, the black feathers on the wings and tail produce brilliant colours, particularly blues and greens. These colours do not result from pigmentation, but iridescence.

Cells in the iridescent feathers contain a basal melanin layer, which produces the black by absorption. Above are stacked reflecting platelets, which produce the iridescent colours when light reflected from one layer interferes with that from another. The resulting colours are bright, pure and strongly directional. A bird can use this for flashing a signal in one direction, while remaining inconspicuous to a predator in another direction. 

Of the handful of pictures of the Black-billed Magpie I have taken, only a few of them show the blue-green iridescence of the wings. In this picture, taken two days ago, the tail just looks black.

However, contrast that black tail with the brightly iridescent tail of the same bird seen a half-minute later. Who knows what signal it is attempting to send?