When Canada geese come to Maine, I go to Canada. As winter approaches, migrating Canada geese fill certain ponds and fields in the state, especially in Aroostook County. Ponds in Caribou, Mars Hill and Washburn fill up with honkers. By day, the geese feed in agricultural fields post-harvest. By night, they will often gather in towns where they are safe from hunters and predators. It’s quite a display.

As impressive as the numbers can be, the abundance of Canada geese pales in comparison to the snow goose invasion of Quebec City. Up to a hundred thousand geese can gather at one time. It’s a world class spectacle. So, over Columbus Day weekend, a small group of Maine Audubon members from the Penobscot Valley Chapter met at Fields Pond for a five hour expedition to Quebec.

Snow geese nest in the high arctic and winter in the southern United States. There are two races. The greater snow goose summers in northeastern Canada and winters along the mid-Atlantic coast from New Jersey to South Carolina. The lesser snow goose lives farther west, and winters in the southwestern states and Mexico. It’s the greater snow goose that gathers in such impressive numbers in Quebec.

There are between 800,000 and one million greater snow geese in the world. We know, because almost every single one of them passes through one spot on the planet: Cap Tourmente on the St. Lawrence River. It’s a Canadian National Wildlife Refuge located 25 miles northeast of Quebec City. Cap Tourmente was established as a refuge in order to protect the few remaining snow geese that still existed a century ago. Hunting pressure had reduced their numbers to only about 3000. In the United States, the hunting of snow geese was banned in 1916.

Today, their numbers have recovered, and hunting resumed in 1975. In fact, the population has increased rapidly over the last three decades, possibly because climate change has warmed the high arctic, lengthening the growing season. Snow geese are voracious vegetarians and will devour just about any arctic plant, consuming every part of it, even the root.

It is one plant in particular that draws the snow goose to the St. Lawrence River: the American bulrush. It grows in great quantities near Quebec City. The root is a starchy tuber, rich in energy, the ideal fuel for long migrations. The geese stop at Cap Tourmente in both directions as they fly to and from their seasonal territories, fattening up for several days before moving on.

Snow geese have a special adaptation that allows them to feed on tubers. Their bills are serrated, and they can clip off vegetation. In fact, upon arrival in the fall, the geese quickly snip off all of the bulrush stocks, which float away with the tide. The geese then plunge their heads into the mud to pull up the roots.

Cap Tourmente’s sediments are rich in iron. After a few days, the heads of snow geese are stained a rusty color. The color persists until they next molt, which isn’t until the following summer. That’s a long time to stay stained. It’s so distinctive that biologists can tell which birds have just arrived and which have been feeding for several days.

From early September through October, wave after wave of geese pass through Cap Tourmente. Those without offspring arrive first, taking less than a week to fly all the way down from the arctic. Those with families take up to five weeks, stopping along the way to nourish the kids. Favorable winds start the birds moving. Those that have had enough time to refuel continue south, replaced by newly arriving birds. Bad weather can bottle up the geese for a while, so numbers fluctuate.

During our visit to the refuge this year, unseasonably cold weather had reduced the flock to about 5000. Overnight, the weather warmed, the winds shifted, and by afternoon of our second day, refuge scientists estimated that the flock had suddenly grown to 23,000. Through late afternoon, we watched continuous V formations arriving from the north. The next morning, we watched a sky full of V formations heading south.

Most of these birds miss Maine. Their route tends to follow the Connecticut River, with stops in Vermont and Pennsylvania. However, small flocks do wander into Maine, and there are usually a few around somewhere. Be on the lookout. If you see flocks of large white birds out in a corn field, take a gander.

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.