Planing loon

A year ago in planing waterbirds, I wrote about an uncommon behaviour of some swimmers.

When swimming across a water surface, water birds usually float. Called displacement mode, a bird is primarily supported by its buoyancy (static pressure). However, its swimming speed is constrained by the waves it makes to what is known as the hull speed (see, muskrat hull speed). To swim faster, a bird can either dive, or switch to planing mode.

In planing mode, a bird is primarily supported by the lift provided by the rush of water against its slightly tipped-up body (dynamic pressure). The problem is that for a bird (or boat) to plane requires not only much greater power, but also the right body (hull) shape. These things were explored in the essay.

While I knew that a Common Loon could plane, I hadn’t managed a picture of it until this last week. Present were all the characteristics (which are shared by planing boats):

• It travelled at a much greater speed than possible in displacement mode.
• The bird’s breast was lifted slightly allowing water to rush against a tipped-up body.
• The tail was pressed downward to mimic a boat’s sharp transition between hull and transom.
• The wake took the form of a rooster tail. 

Other aspects of loon behaviour seen on this occasion will be explored in the next posting.

A Common Loon planes across the Lake.