How was the giant Canada goose rediscovered in Rochester after being declared extinct?

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Canada geese flying in their signature v-formation weren’t always such a common fall sight in Minnesota.

Hunting and habitat loss decimated the birds’ population a century ago. Numbers had dwindled so low that scientists believed the biggest type of Canada goose, the giant Branta canadensis maxima, was actually extinct.

It wasn’t. The city of Rochester unwittingly harbored a flock of giants for decades and had a key role in the birds’ comeback story. Now giant Canada geese are everywhere in the Midwest.

A reader who grew up in Rochester wanted to know more about how the giants survived. She asked Curious Minnesota, the Strib’s reader-powered reporting project: How was the giant Canada goose rediscovered after being declared extinct?

It’s a unique Minnesota tale that involves one of the Mayo Clinic’s founding brothers, a persistent biologist named Dr. Harold Hanson, and a visit to the grocery store.

“All reports of the demise of this magnificent goose, the largest in the world, have proved to be greatly exaggerated,” Hanson wrote in his 1965 book, “The Giant Canada Goose.”

The giant Branta canadensis maxima is one of seven recognized subspecies of Canada goose. While there are some other differences, it is largely its size that sets it apart.

Giants can weigh up to 24 pounds and have a wingspan of more than six feet. They also often stick around the Great Lakes area in the winter, instead of migrating farther south with their smaller cousins.

Otherwise, the giants have the same black face and white chin strap that distinguish all types of Canada goose.

Scientists were slow to see it as a separate kind of Branta canadensis in the first place. Some thought it was a myth, even though hunters reported bagging birds with staggering weights.

Documenting its existence initially involved “a degree of mystery, unreceptive officialdom and general disbelief at the technical level,” Hanson wrote. One expert even suggested specimens were likely so big because a zealous taxidermist had overstuffed them.

The big bird didn’t get its official writeup – and the name Branta canadensis maxima – until 1951. But just six years later, the American Ornithologists Checklist declared the giant was “believed to be extinct.”

The entire species of Canada goose was under threat at the time. Unregulated hunting in the early 1900s and the destruction of wetlands had taken a toll on population numbers.

The giants weren’t really all gone, however.

While ornithologists argued about whether they existed, a flock was growing in Rochester.

In the 1920s, Dr. Charles Mayo purchased 15 Canada geese in North Dakota. He brought them to Mayowood, his more than 3,000-acre family estate in Rochester. At least some — maybe all — were giants. The flock attracted wild birds and began to grow exponentially.

The birds got more help in the 1930s, when the city dammed the Zumbro River and created the 20-acre Silver Lake. For decades, a power plant discharged warm water into the lake, keeping it from freezing over in the winter. Canada geese started coming by the thousands to make their home in Rochester.

Because Canada geese pick out mates based on size (called assortative mating) and then stick together for life, the giants among them maintained their subspecies. They became the dominant type of Branta canadensis in Rochester.

Hanson, a bird expert who worked for the Illinois Natural History Survey, often came through Rochester during fall fishing trips. He was “perplexed” by their seemingly large size, he wrote, but could never be sure just how much bigger they were. Maybe he was misremembering what the Canada geese looked like in Illinois, he wrote.

Then the Minnesota Department of Conservation invited him to Rochester in January 1962 to band, weigh and measure some of the trapped flock.

“On that memorable day, the temperature held around zero and a strong wind blew. But this only added zest to the enterprise,” Hanson wrote.

Hanson, along with staff from the state conservation department and the U.S. Bureau of Sport Fisheries and Wildlife, got to work weighing the geese. At first, they thought the scale was broken, he wrote.

“They went to a grocery store just on the north side of Silver Lake, and they bought 10 pounds of flour and five pounds of sugar,” said retired Rochester Post-Bulletin outdoors writer John Weiss, who later interviewed one of the participants.

They weighed the dry goods at the store first to double check, and then tested the scales again.

“The impossible weights we had been getting were correct,” Hanson wrote.

The U.S. Department of the Interior soon put out a news release proclaiming the giant goose lived: “The giant goose is not only still around, but even appears to have a sizable population that is adapting to man’s changes of its environment.”

The city’s relationship with the striking but messy creatures has taken many tumultuous turns since those heady days of rediscovery.

For decades, Rochester celebrated their giant geese, naming their amateur baseball team the Honkers and installing goose statues around town. The population at Silver Lake grew to astonishingly high numbers.

Tens of thousands would winter there and Rochester became the “epicenter of goose hunting in Minnesota,” Weiss said. He recalled taking his father-in-law to Silver Lake after he first moved to Rochester in the 1970s. At first, they only spotted about 1,000 on the water. Then they looked to the east.

“I went, ‘Why is the sky moving?’” Weiss said. “The geese had been feeding, and they were coming in. It rained geese for a half hour. Just flock after flock after flock would come in.”

By the early 2000s, the city was home to about 40,000 geese — each one pooping as much as two pounds a day. Some residents complained about encounters with aggressive geese, who are especially protective of their young.

Rochester’s officials eventually stopped fostering the flocks’ exploding population and began working to manage it instead. They took away bins of goose food in 2007 and planted tall grasses and wetland plants around the lake to keep the geese from gathering on shore.

In 2021, they (controversially) decided to smother eggs with corn oil and put them back in nests. The geese wouldn’t lay more eggs, but the oil cut off oxygen and fewer goslings would hatch. The next year, workers and volunteers began instead collecting some eggs before embryos fully developed, destroying them and replacing them with ceramic ones.

The efforts — along with the power plant’s closing in 2008 — have had an effect.

Silver Lake now freezes over in the winter, eliminating what some described as their “hot tub.”

The birds scatter to find open water these days, Weiss said. And during last year’s Christmas bird count in Rochester, the Zumbro Valley Audubon Society tallied just 8,637 Canada geese.

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