Distinguishing Waterfowl: The Differences Between Loons and Ducks 

Distinguishing Loons from Ducks by Appearance

Let’s apply these basics to ducks and loons, starting with their appearance.

Plumage color and pattern

Both ducks and loons change plumage over the course of the year. Of the five species of loons found in North America, only the Common Loon breeds in the lower 48 United States. Its breeding plumage is distinctive, pairing a black head with a high-contrast, black-and-white checkerboard back. No North American duck looks at all similar.

So if you happen to be spending the summer by a northern lake, telling a loon from a duck by plumage alone is easy.

For the rest of us, who are more likely to see loons in non-breeding plumage during migration or on their wintering grounds, things are a bit more complicated. With some subtle differences across species, non-breeding loons are grayish above and pale below. And while that not-very-satisfying description does in fact distinguish winter loons from most winter ducks, the biggest difference is their shape.

Size and shape     

Loons have elongated bodies, streamlined for efficient diving, and pointed bills, ideal for catching fish. Speaking very generally, ducks have a rounder, more compressed silhouette, and flatter bills. There are, of course, some exception to this generalized duck shape:

●   Canvasbacks are large diving ducks with long bodies, but their sloping foreheads and flat bills give them a very different silhouette than a loon.

●  Common and Red-breasted Mergansers are also long-bodied diving ducks and – to add to the confusion – have sharp bills. Seen well, the bright red of the mergansers’ bills distinguishes them. Seen not-so-well – the more typical experience – forget about color, and focus on size, shape and how the bill is held. A Common Loon’s bill is much heftier and dagger-like than that of a merganser. Red-throated Loons have thinner bills, easier to confuse with those of a distant merganser. However, mergansers hold their bills straight, while Red-throated Loons usually hold theirs angled upward.

As suggested above, silhouette is also important in distinguishing between different loon species. That’s especially true in the winter, when their plumage differences are subtle, at best. Of the three species most likely to be seen in the Lower 48 United States, Common Loons are the largest, with the heaviest and most fearsome bills; Red-throated Loons are the smallest and slimmest, with bills habitually held pointing up; and Pacific Loons fall between the two extremes. (Bonus tip: silhouette can also help differentiate between loons and large grebes, their close relatives.)

In flight, loons of all species share a distinctive silhouette. Their legs, set far back on their body for efficient diving, trail behind in the air. Their outstretched head and neck, held slightly down, give flying loons a humpbacked appearance.

Behavior and Habitat of Loons and Ducks 

Ducks occupy a wide range of habitats and display an equally wide range of behaviors, while loons as a family are more specialized. Knowing about loons’ behavior and preferred habitats can help you find and identify them.

Habitat     

While some ducks breed in one habitat and winter in another, all loons do so. During the summer, loons can be found on freshwater lakes and ponds. In the winter, loons relocate to large bodies of open water. Typically, that means salt water, though Common Loons also winter on large inland lakes.

Feeding behaviors

Unlike ducks, which depending on species may dabble on the water’s surface, graze on shore, or dive in search of small fish and other prey, all loons feed by diving for fish (the bulk of their diet) and other aquatic creatures. Diving loons can reach a depth of 200 feet, much deeper than even the deepest-diving ducks. For purposes of comparison, many diving ducks do well to reach 10 feet; mergansers can get to 40 feet and eiders, the diving champions of the duck world, to a bit over 60 feet. 

Once underwater, a loon can remain submerged for more than five minutes before resurfacing – often at a considerable distance from where it went under, to the frustration of birders trying to observe it.

Flight style     

As described earlier, loons are built for diving, with legs set far back on heavy bodies. That physical structure makes taking off in flight almost comically awkward; to get airborne, loons must “run” along the surface of the water over an extended distance. While many species of ducks also need a runway, some dabbling ducks can launch directly up into the air from a stationary position.

Once in the air, loons are powerful flyers, with deep, slow wingbeats. They don’t wheel about in flight the way some ducks do, and typically fly solo or in small groups. You are unlikely to see them in a “V” formation, or in the massive, stretched-out “skeins” formed by some species of ducks.

Social behavior     

Ducks tend to be social birds, often seen in flocks. Some species even engage in cooperative feeding; think of Northern Shovelers moving in a tight circle to stir up bits of aquatic vegetation.

Loons, in contrast, don’t form flocks. In the summer, they’re typically seen alone or in family groups. A pair of loons will often return to the same lake year after year – a phenomenon known as “territory fidelity” – and will aggressively defend their breeding territory against intruders. That “aggressively” is no joke. According to Cornell University’s “Understanding Loons” series, about 30 percent of territorial battles between male loons are fatal.

In the winter, it’s typical to see individual loons widely dispersed across an expanse of open water. Migration can bring increased numbers, as birds rest and feed in favored staging areas, but migrating loons continue to keep one another at a distance. You won’t observe loons forming tight clusters or engaging in the social behavior that migrating ducks often display.

Loon and duck vocalizations 

We’ve already established that ducks don’t just quack. Their vocalizations are as varied as their appearance, habitat and behavior, ranging from the classic "quack" of a Mallard to the whistles, squeals, bleats and coos of other species.

Loons also have a range of vocalizations, but the most iconic is the call of the Common Loon to its mate. “Eerie” and “haunting” are adjectives often used to describe it. It’s part shriek, part wail, part yodel, wholly unforgettable.

Check out this video from Cornell University – with the sound on, of course.

Your best chance to hear loons is on their breeding territory. During the winter, when more U.S. birders are likely to see them, loons are mostly silent. On occasion, though, a migrating loon will let loose one of its distinctive yodels or maniacal laughs while flying overhead.

Should you hear one, consider yourself very fortunate.