I have a theory that many bird names are the result of drinking games among scientists. What else would explain how the merganser got its name? Perhaps it was a drinking game among Romans, because the name actually means diving goose in Latin. The “merg” part comes from the same Latin root that gives us submerge. “Anser” is the Latin word for goose. In Europe, the connection is easier to see because they call our common merganser the goosander.

Mergansers are diving ducks that dine exclusively on aquatic critters. They have thin, saw-toothed bills that allow them to grasp slippery fish underwater. There are six merganser species around the world. Three species breed in Maine. As luck would have it, now is the perfect time to see all three.

Common mergansers prefer the freshwater shallows of lakes and streams. They are perfectly comfortable on raging rivers, floating effortlessly through the whitewater. They nest in hollow trees. When they emerge, they frequently combine families to form bigger flocks. It’s not unusual to see flotillas of 20 or more chicks tended by multiple hens. Most Mainers residing on freshwater shorelines are familiar with common mergansers, often watching them swim by the dock or sitting on rocks.

Red-breasted mergansers prefer saltwater in winter. I’ve seen them as far south as The Everglades. They resemble common mergansers, but they are smaller, with a more ragged crest on the head, and the males sport a colorful breast that gives them their name. Red-breasted mergansers nest in the subarctic, using depressions on the ground adjacent to freshwater. A few nest in Maine, but these stay close to the coast.

Hooded mergansers are smaller than the other two and known for their oversized crests. The males raise it as a big white display to attract females and discourage competitors. Although they do it mostly in spring, it can happen anytime. Hooded mergansers prefer small shallow wetlands and nest in cavities, frequently making use of wood duck boxes. While the other two species are found across the globe, the hooded merganser is confined to North America.

Someday, I’ll write more about each of these intriguing ducks, but time’s a-wasting. They’re out there right now, waiting for you. Odd things happen just before our lakes freeze up. For instance, Sebasticook Lake inspired today’s column.

I stopped by the boat landing in Newport last week and was delighted to find dozens of hooded mergansers floating idly nearby. Certain lakes in Maine are at risk of algae blooms in summer if there is too much phosphorus in the water. A common reduction strategy is to lower the water level in autumn, draining out much of the old water and replacing it with fresh snowmelt in the spring. Sebasticook Lake is one of these. Sabattus Pond near Lewiston is another.

One consequence of drawing down lakes is that it concentrates the fish in shallower areas. Diving ducks love it. These include some of our own breeding ducks and arctic-nesting ducks that are heading south for the winter. Greater and lesser scaup, ruddy ducks, ring-necked ducks and goldeneyes can congregate in big rafts. Often, dabbling ducks also gather, foraging for underwater vegetation in the now-shallow water that was out of reach all summer. These lakes are popular among birders this time of year.

Even on lakes that are not drawn down, common mergansers are apt to form large flocks. I’ve seen gatherings of more than 300 on Pushaw Lake in Old Town just before Thanksgiving. They are likely to gather on large rivers, too. As the lakes freeze, some collect in the unfrozen sections below dams and rapids or wherever tidal flow breaks up ice.

Meanwhile, red-breasted mergansers are arriving in Maine after a summer in the far north. Most are back now. They’ll winter on the coast, feeding along the shoreline just outside of the surf. You should be able to find them just about anywhere through April.

All those mergansers are moving around at the moment, preparing for winter. Soon, another funny thing will happen. Once the lakes are frozen, some of our common and hooded mergansers will migrate to freshwater farther south. But some stay put, giving up on freshwater and tolerating brackish water throughout the winter. Some of the red-breasted mergansers may move up the Kennebec and Penobscot or float with the tide into brackish estuaries. Suddenly, all three mergansers, normally intolerant of each other’s preferred habitat, collect together. It’s a family reunion of distant cousins.

Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at mainebirdingtrail.com. He can be reached at duchesne@midmaine.com.