Strange loon markings

Two friends and I saw this loon while out kayaking. What are the unusual tan markings on its lower back? Also, how does one tell the difference between a male and a female loon?
—Kate Amrein, Twelve Mile Bay, Ont.

At first, this photo had us stumped—we’d never seen a loon with markings like this. (And you don’t work at Cottage Life without seeing a lot of loons.) But as it turns out, the mysterious “marks” are actually just normal body feathers “caught in a strange light or in a position that is not regularly seen,” says Mark Peck of the ornithology department at the Royal Ontario Museum. Folks at the BioDiversity Research Institute in Gorham, Maine, and the Loon Preservation Committee in Moultonborough, NH, agree.

“What you’re seeing is the feathers that lie under the main body feathers,” explains Harry Vogel, a senior biologist and the executive director of the Loon Preservation Committee. Normally hidden, this downy layer insulates the loon.

As for the second part of your question? “That one is easy,” says Vogel. “The female is the one who lays the eggs.” No, really: “When you see a loon floating on the lake, it’s very hard to tell.”

Even if you see a pair of loons, it may be hard to tell. There are no real plumage differences, says Vogel, and though males are typically 20 to 25 per cent larger than females and have a somewhat larger head and thicker neck, some individual females are slightly larger than males. What if you saw an adult on a nest or with a baby on its back? Still no help: Unlike some other bird species, “loons share nesting and chick responsibilities,” explains Kathy Jones of Bird Studies Canada. (It’s not the ’50s anymore, hummingbirds.)

Male loons do make one call that females don’t: the yodel. They use the call—which sounds similar to a wail call, but has a number of repeating phrases—to advertise and defend their territory.