If you look to the heavens much to watch birds you have probably seen them the last week or so — big flocks of Canada geese winging north.

If you weren’t thinking much about it you might say, hey, birds fly north to nest in the spring — big deal.

But in fact, most Canada geese already winged north into the area two months ago to nest. Now, pairs of mated geese are raising little yellow puff-ball goslings in wetlands across the region. They aren’t going anywhere until those little guys can fly later this summer.

So who’s flying north now?

Those would be young, reproductively immature geese that have not yet found a mate. They came this far north with their families from southern wintering grounds. But now, their parents are nesting and raising new young, so these unmated geese have a built-in directive to head north.

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hey’re like grown kids being kicked out of the house. It gets them out of the hair of the new families and provides space for the new members of the species.

It’s occurring just before geese molt, or lose their old feathers to grow new ones — a time when, for several days each summer, they are unable to fly. So it’s called the molt migration.

Michael Furtman, a Duluth outdoor photographer who writes a regular waterfowl science feature for Ducks Unlimited magazine, described the molt migration.

“Canada geese don’t breed until they’re 3 years old (usually) and if all of those non-breeding birds spent the summer with the breeding population, they’d put stress on the resources needed to raise the next generation. They also need a secure area to undergo the molt ... since they will be flightless for several weeks,’’ Furtman told the News Tribune last week, saying there’s also probably a historic reason why the unmated birds head north in big groups rather than on their own.

“It’s my guess that being in a large flock while undergoing the molt provides much the same advantage enjoyed by herd animals — many eyes to spot predators, and you only have to be faster than your neighbor’’ to get away.

So now you know. This second, northward migration of Canada geese (and some ducks, too) each year is called the molt migration of birds too young to mate.

Amazingly, most of these birds have never made this flight before and, once they mate for life, will never make it again. Nature’s way of keeping things right.