Identification
Birds that look like ducks (but are not ducks)
Stand at a city pond and count the ducks. About half of them will not be ducks. The American Coots are rails. The Pied-billed Grebes are grebes (a lineage all of their own). The Common Loons are loons (also their own thing). The Double-crested Cormorants are cormorants. None of them is a duck, and none of them is closely related to a duck.
The reason they all swim and the reason they all look the same is convergent evolution. Eat in water, paddle with feet, evolve waterproof feathers, and you end up shaped like a duck whether you started as a rail, a grebe, or a loon. The bill and the feet are where the cousinship ends.
The two-second sort
| Feature | Duck | Not a duck |
|---|---|---|
| Bill | Flat, wide, with a soft tip for filtering | Pointed (grebe, loon, cormorant) or chicken-like (coot, gallinule) |
| Feet | Webbed (all four toes joined by skin) | Lobed (each toe has its own paddle - grebes, coots) or unwebbed (gallinules) |
| Diving style | Either tip forward (dabbler) or submerge with a small jump (diver) | Often a smooth slip below the surface without a splash (grebe) |
| Takeoff | Most spring straight up | Long running start across water (grebe, loon) |
| Tail | Short | Almost absent (loon, grebe) |
If you cannot see the feet, look at the bill. If you cannot see the bill, watch how it dives.
The eleven most commonly mistaken
| Species | Size | What gives it away |
|---|---|---|
| American Coot | 33 to 43 cm | White bill, head-bobbing swim, lobed toes |
| Common Gallinule | 30 to 38 cm | Red bill with yellow tip, walks on lily pads |
| Pied-billed Grebe | 30 to 38 cm | Sinks slowly without splash, banded bill |
| Horned Grebe | 31 to 38 cm | Golden ear tufts in breeding plumage |
| Western Grebe | 55 to 75 cm | Long black-and-white neck, famous rushing courtship |
| Common Loon | 66 to 91 cm | Checkerboard back, dagger bill, that wail |
| Double-crested Cormorant | 70 to 90 cm | Holds wings out to dry on rocks |
| Anhinga | 75 to 95 cm | Swims with only the neck above water, “snakebird” |
| Mute Swan | 125 to 160 cm | Not a duck. Obviously not a duck. People still ask. |
| Common Moorhen | 30 to 38 cm | The Old World gallinule |
| Purple Gallinule | 26 to 37 cm | Brilliant purple-blue, exaggerated long toes |
The American Coot deserves a paragraph. It is the bird most often mistaken for a duck in North America. It belongs to the rail family (Rallidae) and is, evolutionarily, closer to a marsh wren than to a mallard. The bill is bone white, chicken-shaped. The toes are not webbed - they are lobed, with separate paddle-shaped flaps on each toe. It bobs its head forward and back when it swims, which no duck does. It is also one of the most numerous water birds in the United States and the only one most people will see at every park pond.
Why the loon is not a duck either
The Common Loon is the bird whose wail across a Maine lake at dusk has done more for the tourist industry of New England than any chamber of commerce. It is not a duck. Loons (family Gaviidae) are one of the oldest lineages of birds still alive, with fossils dating back at least 35 million years. Their bones are unusually solid - most bird bones are hollow for flight, but loon bones are dense, which lets the bird dive to 60 metres after fish.
The price of solid bones is that loons cannot launch straight up out of water. They need a long running takeoff, typically more than 30 metres of open lake. A loon caught on a small pond or a road surface that resembles water cannot take off at all. Wildlife rehabilitators in northern states get several “stranded loon” rescue calls every spring.
Why the grebe is also not a duck
Grebes are unrelated to loons and unrelated to ducks. They are their own tiny order, the Podicipediformes, and recent genetic work suggests their closest living relatives are flamingos. Yes, flamingos. The two families share an extinct common ancestor from around 30 million years ago and share an unusual feeding apparatus involving filtering with a fine-toothed bill or filtering with a curved one.
The Pied-billed Grebe is the small chunky waterbird that disappears every time you raise your binoculars. It does not splash. It compresses its feathers, expels the trapped air, and sinks straight down with the dignity of a punctured raft. This trick, the “controlled sink”, is a grebe trademark.
What this changes
Almost everything that looks like a duck on a pond is something else. The pond’s apparent uniformity is a trick of plumage and habitat. Underneath, you are looking at four to five different orders of birds that arrived at the same body plan from different starting points.
The next time you see a city-park “duck pond”, count what is actually there. The coots, the grebes, the cormorant in the dead snag, the moorhens, the swans, the heron at the edge - everything except the Mallards and the Wood Ducks - is on the list above.
