Exploring Kootenay Lake

No, the title does not contain a spelling mistake. I really do mean plane, not plain. 

This was an observation that would warm the cockles of the heart of any bird behaviourist: two male Common Mergansers were competing in their harassment of a female — and doing so while all were planing. 

About the harassment: This is the breeding season and the males chased the female back and forth across the water before mating. The mating took place behind a dock, but subsequent behaviour made it clear what had happened. I will let the pictures speak for themselves on the issue of harassment, and concentrate on the feat of planing.

When moving across a water surface, most birds, mammals, and boats are in displacement mode: they are supported primarily by buoyancy. Their speed is effectively limited by (what is known as) their hull speed. Some birds have the power to temporarily plane, just as can some recreational boats. (Among adult birds, those with the power to plane seem to be mainly divers.)

When planing, a bird or boat is supported primarily by the rush of the water against its tipped-up body. For a boat to plane, there also needs to be a sharp transition between the bottom of the hull and the transom to force a separation of the water flowing underneath. A bird has a rounded butt, which normally would prevent planing. However, when a bird wants to plane, it changes its shape by forcing its tail down into the water to create the necessary sharp transition. 

Male mergansers harass a female while all plane. Bodies are tipped up and tails are pressed down.

Planing is hard work. Sometimes when a bird tires, wings are used for supplemental power.

Little birds can hover, but not soar; big birds can soar, but not hover. 

By hovering, I mean (what is called) true hovering: staying aloft by flapping rather than by moving horizontally through the air and doing so for an extended period of time. The kingfisher is probably the largest bird capable of pulling this off. 

Occasionally, one does see an osprey or an eagle seemingly hover over a spot below. This is always done when flying into a brisk wind, so the bird actually is moving through the air, but has matched its speed to that of the head wind. Even then, the activity is so energy intensive that the bird can only maintain it for a few moments. 

A large bird wants to do this is so it can position itself for an attack on prey.

A Bald Eagle seems to hover in a brisk wind as it eyes a potential prey (probably a duck) below. It did so only briefly before plummeting to the lake surface, but it missed the target.

Ospreys are back.

I saw my first Osprey of the year fly by last Monday (April 10^th), but failed to get a picture. Others have seen them along the lakeshore throughout the week. Yesterday was the first time I managed a picture. Thus begins the nearly half-year local season of ospreys.

A (male) Osprey flies along the shore.

Lying in the sand is a male Mallard — at least it used to be.

Standing over it, the Merlin looks at me and says:

“If you try to take my breakfast, I will eat you, too.”

Why watch for Mountain Bluebirds each spring?

They are stunning beautiful.

Typically, Mountain Bluebirds arrive to breed in late March or early April. This year, a few turned up on schedule, but the insects they feast upon were tardy. Jaunts to see bluebirds found numbers to be sparse — until this last weekend. 

How could this creature be named anything other than bluebird?

The muted colour of the female gives better camouflage from predators.

A male had flown down to the dried grass in an unsuccessful raid on an insect.

“You needn’t even try to photograph me in flight; I am way too fast for you.”