Inside the Outdoors: Another dimension to Canada goose migration
If a person did not know better, they might have thought the month is October or November. The chorus reverberating across the lake was immediately recognizable as an urgent conversation among Canada geese. Their formation was an exaggerated “V,” much longer on one leg than the other. Their direction was roughly northwest, their number about 50, give or take.
What were they doing way up there in migration formation, when most males and females of their kind had long since paired up and mated? Just the day before I had seen my first family group of Canadas, with downy, fuzz-ball goslings being watched over by both parents, goose and gander. This marital fidelity is not the rule with ducks, but it is so with geese—swans, too—which likely contributes to a high percentage of their young surviving to reach the juvenile stage. Having parents that are aggressive and are large enough to intimidate many predators does not hurt your chances, either.
So, at a time when other Canada geese are doing their part to raise the next generation of their kind, what is the explanation for this group of half a hundred or more that I saw so high above, joined in what had all the appearances of migratory flight? It’s highly probable that the group I saw, and others like it, are gathered in what has come to be called “molt migration.”
All birds, geese, ducks and swans included, will molt—shedding their feathers and replacing them with new ones—at least once each year. Some molt all their feathers in the same molt period. Others do not and may—for example—molt their flight feathers in one cycle, and their body feathers in another.
The molt cycle in birds is necessary to retain their flight capability and thermal protection. Birds’ feathers are dead; not alive, like skin and internal organs. They become worn over time and lose the qualities that enable birds to fly efficiently and protect their bodies from temperature fluctuations. In fact, feather wear is one way biologists can distinguish adults from young-of-the-year birds of some species, like ruffed grouse.
Feathers can also be lost in narrow escapes from predators. A classic depiction in wildlife art is a rooster pheasant losing tail feathers to a hunting dog that got too close before the bird took flight. Similar things may happen with songbirds in encounters with neighborhood cats, or so I can imagine. But unlike feathers that are shed and replaced in a molting cycle governed by a bird’s hormones—as normal molting is—if a feather is lost prematurely its replacement is likely to begin off-cycle, immediately.
But if many Canada goose and gander pairs are now raising their young, which are these geese that are participants in the molt migration? The best scientific evidence points to most being unmated birds, likely to be juveniles that either have not reached sexual maturity, or birds that were “unlucky in love,” as the expression goes. Also included in the molt migration may be adult pairs that by some twist of fate have lost their brood of young, perhaps too late for their hormonal regulators to prompt them to re-nest.
So why does the molt migration happen in the first place? Some scientists theorize that this behavior is—for lack of a better term—“hard-wired” into geese, dispersing the population and thereby contributing to a better chance of survival among those that migrate. That, as opposed to remaining where highly territorial mated pairs are raising their young, and having to compete with them for space and food.
So just where were those geese that I saw high overhead bound? And what portion of an area’s spring Canada goose population takes flight on a molt migration? The limited data suggest that these things can vary a great deal. One study in Wisconsin suggested that as many as half of spring arrivals on that state’s breeding grounds eventually migrate to new areas before molting. On the other hand, a similar study in New Jersey concluded that only about 20% to 30% of Canada geese there did so.
As for where Canada geese are bound on molt migrations, this could vary a great deal. Some early studies of the behavior found very short migrations. But more recent data has shown molt migrations as long as the distance from South Dakota into Canada.
Biologists and the general public care about such things because of the impact that these migrants can have at their destination. One reason is crop damage if the area to which they migrate is agricultural, as is probable when the creatures involved are Canada geese. Another is a potential for long-term damage to the birds’ natural, non-agricultural, habitat, as has happened with snow geese on their Arctic breeding grounds.
It is several months from fall, the hunting seasons, and the onset of general avian migration. But the sound of “wild goose music” and the sight of that familiar V formation high in the sky was a delight, if somewhat out of seasonal context!