Exploring Kootenay Lake

One does not have to spend much time in the company of robins to realize that earthworms have an uneasy friendship with them. Each time a robin invited one to lunch, the worm demurred.

This worm clung to its home so strongly that it took multiple invitations and much effort before the robin persuaded it accept a luncheon invitation.

However, in the end, the worm was persuaded to come for lunch.

Who can resist the sight of mommy duck parading her ducklings across the water? It is especially cute when the chicks hitch a ride on mommy’s back, as merganser chicks do.

However, this is not the only neat behaviour that these merganser chicks exhibit. In addition to hitching a ride, chicks both draft and plane.

Merganser chicks ride on mommy’s back as a way to keep pace with her swimming. 

While some of the chicks are hitching a ride on mommy, many of them are following behind in the water. Keeping pace with mommy in free swimming is a problem for, due to their lesser length, the chicks have a lower hull speed. The solution is to draft mommy. By travelling in a group behind her, water resistance is lowered and they can keep up. 

There is another way the chicks can keep up with mommy: They can plane. This is another method of getting around the problem of the speed limit imposed by their hull speed.

At a speed somewhat below the swimmer’s hull speed, the swimmer is in displacement mode, where support is (primarily) a result of buoyancy. When planing, support is (primarily) provided by the rush of the water against the tipped-up hull. However, to attain this new state requires considerable energy (as any pleasure boater will confirm).

It is true that owing to a lower threshold speed, planing is easier the smaller you are (chicks are better at it than adults), but it is also the case that a particular hull configuration is needed. In displacement mode, a rounded stern (for a boat) or butt (for a bird) is desirable: In planing mode a sharp underwater transition between the hull and transom is necessary. A bird normally has a rounded butt, so how does it make the sharp underwater transition it needs to be able to plane? Answer: It forces its tail feathers down into the water.

This picture shows two merganser chicks in planing mode (left) and one in displacement mode (right). The chick on the right has its tail feathers lying along (slightly above) the water surface. The two chicks on the left have forced their tail feathers as deeply as they can into the lake. Also the wakes look different whether the swimmer is in displacement or planing mode.

This image shows all three behaviours. There are chicks that solve the problem of the speed mismatch by riding on mommy’s back. There are also chicks that are keeping pace by drafting mommy. Finally, three chicks (upper left, centre, lower centre) are planing.

A birding guidebook says that the Great Horned Owl is a common resident of almost all habitats in our region. Fair enough, but just try to find one.

So, it was a delight to encounter one, and its chick, in the last few days. (OK, I didn’t find it on my own; Joanne Siderius, the senior naturalist at Kokanee Creek Park, showed me where to look.)

A Great Horned Owl perches high in the forest and watches trail walkers far below.

Nearby is one of its two chicks on its first day out of the nest.

Four species seen during a walk.

Usually found flitting about bushes, the Grey Catbird is named for its cat-like call.

This is a robin. The speckled breast reveals it to be a juvenile.

Two male Barrow’s Goldeneye Ducks seem to synchronize the examination of an intruder.

The Red-naped Sapsucker is a woodpecker that carves horizontal lines of holes in the bark of trees. Later, it returns to collect the sap and insects attracted to it. Earlier holes can be seen as a line of scars on the tree trunk.

This is the season to see chicks. This is also the season to notice a rather odd behavioural difference between birds that show sexual dimorphism and those that don’t.

A species with sexual dimorphism exhibits different characteristics beyond the differences in their sexual organs. Indeed, the male and female often look markedly different. In a species with sexual monomorphism the male and female are difficult to distinguish.

Some birds are monomorphic; some are dimorphic. Among dimorphic species, it is usually the male that has the brighter and fancier plumage, but now and then it is the other way around (kingfisher). Sexual differences in appearance seem to have evolved as a result of the mate selection by females.

Curiously, the visual difference is accompanied by a behaviour difference in parenting:

The lesser the similarity in appearance, the lesser the involvement in breeding duties by the more colourful bird (usually, but not always, the male). The greater the similarity in appearance, the greater the equality in breeding duties.

I was reminded of this yesterday while watching an impressive group of Wood Duck chicks and someone in the group wondered why the chicks weren’t accompanied by both parents. The short answer is the Wood Duck is sexually dimorphic.

The first picture shows the female (left) and male (right) Wood Duck (appropriately) perched in a tree. They are strikingly different in appearance (March 28, 2016).

Consequently, during yesterday’s observation of thirteen Wood Duck chicks, we expect to see only the mother with them. (The most Wood Duck chicks I had previously seen were three.)

Similarly, the (sexually dimorphic) Common Mergansers seen five days ago only shows mommy with the chicks.

Contrastingly, Canada Geese parents look much the same, and both tend chicks (May 31, 2011).

The similarity of Osprey parents implies that both have parental duties (July 19, 2013).