We’ve all heard the old African proverb, “It takes a village to raise a child,” but it turns out the same applies to common mergansers. That’s right, these large diving ducks, which are found regularly on larger North Country lakes, engage in an unusual strategy for child-rearing known as “creching.”
It would be easy to believe that mergansers have insanely large numbers of offspring, since a single female can often be seen with more than a dozen little ones in tow. One female merganser was documented near Bemidji leading an entourage that included an astonishing 75 ducklings.
Such numbers are possible because female mergansers take turns caring for each other’s young ones. The ducklings of several females are routinely grouped together under the watchful eye of a single adult, giving the other females the opportunity to feed, groom, or simply rest.
The advantages of this are obvious to most human moms, who have deployed similar strategies with other moms in their neighborhoods for years. But the practice probably has other benefits as well. There’s advantage in numbers, which is why fish assemble in schools and birds gather in flocks. The large numbers of individuals can make it hard for a predator to focus on any one individual.
This also helps young mergansers overcome the loss of their mother, since they are readily adopted into the group. Mergansers not only readily adopt other young mergansers, females will often lay their eggs in the nests of other mergansers, further helping to increase the likelihood some of their offspring will survive. And since a female merganser may very well help raise the ducklings from nearby nests, it matters less which nest they come from.
After a roughly month-long incubation period, mergansers are precocious when they hatch, which means they are able to feed themselves almost immediately. To do so, of course, means getting to water and that’s the first challenge for a young merganser. Despite being large bodied, common mergansers nest most often in tree cavities, which means the first step in life for a young merganser can be a doozy. Shortly after hatching, the young birds must launch themselves from their nest and fall as much as 50 feet or more in some cases until they hit the ground. Then, the adult female leads them on a march to water, where the young birds can swim and dive, and start feeding themselves right away.
The adult females still have a role to play, fighting off some smaller predators, warning of others, and leading the young birds to productive feeding areas. The adult male mergansers, meanwhile, play little to no role in the raising of the young. They spend the summer living a life of leisure, typically hanging out with the other guys.
Mergansers are primarily fish eaters, although they also eat many other things, from aquatic insects to frogs. They can often be seen working shorelines in groups, occasionally looking under the water for things to eat. When they spot something, they dive and can stay underwater for up to a couple minutes. They have a long, narrow, serrated bill that helps them catch and hold the fish that are their primary prey.
In part because they eat fish, some people don’t like mergansers and they have occasionally been persecuted for that, although not with the intensity suffered by cormorants over the years.
Common mergansers breed primarily in the boreal forests of Canada, including northeastern Minnesota. They head south from our area in winter but they don’t move far. They’re hardy birds and can winter anywhere there’s consistently open water, so they can be found as far north as southern Minnesota during the winter months.