On Martha’s Vineyard and across New England, 1973 turned out to be the perfect summer for the monarch butterfly.

The temperatures hovered two to three degrees above normal in Maine, a summer home for the monarch, and the season was fairly dry. That September, when the fall migration began, the monarchs came down the coastline and crossed Vineyard Sound in swirling clouds, feeding on the goldenrod and roosting in the trees at Squibnocket and Gay Head in numbers that no one had seen in more than a decade.

The monarchs were dancing and weaving their way to a winter home thousands of miles somewhere to the south — in 1973, scientists were still two years away from finding out precisely where.

Island naturalists who have been watching the monarchs for more than a generation say that the Vineyard hasn’t hosted an exodus to match it in the 41 years since. That moment was caught on film, though, in a 10-minute long movie shot on Super-8 film by a woman who’d never used a movie camera before, but who caught the journey so vividly that watching the scenes go by today, she can still feel herself breathing as she filmed.

“It was the most mystical thing, because it was so quiet, but you could hear ‘shhhhh’ from their wings, these thousands of butterflies,” said Shirley Mayhew, a writer, photographer and retired English teacher in West Tisbury. She shot the film at Squibnocket and what is now Aquinnah on the evening of Sept. 13, and the early morning of Sept. 14, 1973.

Today the Gazette released a clip from Mrs. Mayhew’s film as part of its Historic Movies of Martha’s Vineyard project. The movie — in which golden autumn leaves appear to burst away from the trees, transforming themselves into tornadoes of departing monarch butterflies — is the sixth Vineyard film presented by the paper in the last 16 months. It was converted to a digital file by Art Donahue of Motion Picture Transfer in Franklin and edited for presentation by John Wilson, a filmmaker and television producer and director from Edgartown.

The film appears as ecologists around the country raise a cry over the fate of the monarchs, whose numbers have fallen off perilously in the last few years because of the loss of habitat at their wintering grounds in the mountains of central Mexico, as well as the eradication in the United States of thousands of acres of milkweed on which monarch caterpillars must feed.

  —Shirley Mayhew 

When she shot her film in September 1973, Mrs. Mayhew was preparing to take her daughter Deborah to college in Ohio. The two went for a final late summer walk along the beach at Squibnocket.

“We just noticed lots and lots of butterflies on the milkweed and on the dirt roadways. I started thinking, ‘Where do they go at night?’ I found out, somehow, that they roosted in trees,” Mrs. Mayhew said. “I borrowed a camera from the Edgartown school. I had never taken a moving picture before. Then I went back about six the next morning. They didn’t leave until the sun hit them and warmed their wings up. So there would be maybe a dozen that would suddenly fly away.”

Mrs. Mayhew was interested in monarchs long before she shot the movie. That summer her book Seasons on a Vineyard Pond, based on her thesis for Goddard College, appeared in Island bookstores.

“Mom did a study of our pond for her thesis,” said her daughter Sarah, who watched a digital copy of the film with her mother. “And so we studied everything in and around the pond. So I suspect that we found caterpillars — monarch caterpillars — looked them up, found out they were monarchs and so we took some to hatch. We brought them into the house and they escaped and made a chrysalis right on my earring rack.”

When Mrs. Mayhew filmed the monarchs, it had been 11 years since the Island had seen a migration to rival it.

On Sept. 14, 1973 the Gazette reported that “All across the Vineyard in the past two weeks, grass and fields and sky have been aflutter with the orange and white and black of monarch butterfly wings.”

The migration of 1973 also surpasses anything that followed it, say Island naturalists who have seen Mrs. Mayhew’s film. Matt Pelikan, the regional ecologist for the Island office of The Nature Conservancy, recalled a historic flight in 1997.

“This is more impressive than I saw,” he said while watching the film. “That’s really a snowstorm. There must surely be many tens of thousands.”

—Shirley Mayhew

Suzan Bellincampi, director of the Felix Neck Wildlife Sanctuary, watched the movie with Marion Hammond, the office manager, and both agreed. “In my time, I’ve seen nothing like this,” Ms. Bellincampi said. “I’ve seen groups of them, but not that density. Never.”

Indeed, what alarms her is that last summer she saw so few monarchs.

“Monarchs are the things you always see,” she said. “Kids relate to them. Everybody knows monarchs. It’s almost like we take them for granted, to be quite honest, because they’ve always been there. But this last year was unbelievable. I would say that we saw less than a dozen through the whole year. And we would see a dozen a day in past years. It was pretty shocking.”

In this country, the problem begins with the eradication of milkweed, the plant on which monarchs lay their eggs and the only one on which the hatching caterpillars can feed, said Chip Taylor, a professor in the department of ecology and evolutionary biology at the University of Kansas in Lawrence, as well the founder and director of Monarch Watch, a conservation group.

Growing genetically modified corn and soybeans and spraying them with insecticides kills off tracts of milkweed that grow near industrial farms, Professor Taylor said.

“We need to engage the gardeners all over the country to get involved not only in monarch conservation but pollenary conservation in general,” he said. “When we’re losing monarchs, we’re losing all the things that they share the same habitat with. So if you’re losing monarchs, you’re losing your pollenators, and the pollenators provide the fruits, nuts, berries and seeds and foliage that everything else feeds on, including the small mammals and the birds. It’s a cascade. You take these things out of the system and you’re having an effect on a whole lot of different organisms.”

Another worry is deforestation in the mountains of central Mexico where monarchs winter. Nobody knew where the butterflies were heading on their flight south until Fred and Nora Urquhart, biologists at the University of Toronto, discovered the wintering grounds in 1975, two years after Mrs. Mayhew shot her Super-8 film.

Impoverished loggers value the tall oyamel fir trees in which the butterflies roost, and despite a mixed effort at conservation by the Mexican government, Mr. Taylor said, the acreage available to the monarchs has fallen off drastically in the last decade. They roost in only 12 separate sites of a few acres each, high up in the cool, moist mountains, according to Monarch Watch.

Jan Pogue, the publisher of Vineyard Stories in Edgartown, has seen the butterflies with her son Christian in the mountains of Michoacán.

“You end up in a ravine,” Ms. Pogue said. “There’s a small stream. There is a log that has fallen across the stream. You climb across on rocks and you can sit down. You can go up into the forest a little bit. And you wait. You can’t quite comprehend what you are seeing until you stop. If you’re moving, there’s a swirling around you, but you don’t get it. Your mind can’t process what you’re seeing. As soon as you stop, what you’re seeing is the swarming of these butterflies. They love the water, so they’ll dip down and swirl. They’ll come and land on you. They sit on your hand. . . . Just waves of them.

“And as the light gets less and less, and it gets cooler and cooler, they go into these big cones, hanging from the trees. You could see them fluttering. They move in and out of this thing to keep themselves warm. And we were awed. You just want to hold your breath for a minute. You don’t want to lose that moment.”

Ms. Pogue added that their guide, a spry woman who might have been 80 years old, told the group that although there appeared to be many monarchs around them, “she is seeing less and less.’”

Suzan Bellincampi and Matt Pelikan said Islanders and others can help bring back the monarch butterfly (and other pollinators) by planting milkweed and other nectaring flowers. One can also join a monarch conservation group and register yards as monarch way stations, and monitor and report them to Monarch Watch and other groups.

“Maybe the most important thing about trying to raise monarchs in your yard is that it changes how you think, and how your actions are affecting the natural world, and how you’re interacting with wild species around you,” said Mr. Pelikan. “That’s really the Holy Grail for environmentalists.”

Mrs. Mayhew hoped that the presentation of her movie of the great monarch migration of 1973, two generations after she shot it, will help the cause. “I feel so privileged to have seen and filmed this,” she said. “It was an astonishing thing.”

Those who want to contribute old Island films to the Historic Movies of Martha’s Vineyard project, or who have questions or comments about it, may contact Tom Dunlop at tdunlop@mvgazette.com. To avoid damage, please do not run an old film through a projector. To see the collection of Island films presented to date, go to mvgazette.com/historicmoviesofmarthasvineyard.