Is a Montreal field of weeds a lost dream for endangered monarchs?

The monarch butterflies fluttering across eastern Canada to lay their eggs this summer may have lost one of their most important pit stops after milkweed plants were mowed down on a parcel of land in Montreal.

Milkweed is indispensable for the endangered monarchs: adult butterflies lay their eggs on the plants and its nectar is the only food the caterpillars eat.

Conservationists say the loss of milkweed plants in late June from a 19-hectare parcel of land north of the airport could further jeopardize the species classified as endangered by the International Union for the Conservation of Nature last month.

“We were devastated for the loss to our pollinators on the Island of Montreal,” said Katherine Collin, a co-organizer at citizen conservation group Technoparc Oiseaux.

The monarch butterfly cannot complete its life cycle without that plant, added Alessandro Dieni, who manages the Mission Monarch program at Montreal’s Insectarium. Dieni fears monarch eggs or caterpillars could have been destroyed by the mowers and that some flowers, which serve as food for adults, might not have time to grow back this season.

Now local politicians, including NDP MP Alexandre Boulerice, as well as a petition with more than 22,000 signatures are calling for the federal government to protect the area.

The land where the milkweed once stood is part of a 200-hectare area owned by Transport Canada and leased by the Aéroports de Montréal (ADM). The maintenance mowing was done to get rid of “nuisance” plants like ragweed and tall grass, ADM spokesperson Eric Forest said in an emailed statement.

“There are no ‘monarch fields’ at this particular location,” the statement went on to say.

“The geographic location of the site, its history, and the low presence of milkweed do not have any critical habitat attributes,” he wrote.

Technoparc Oiseaux insists it has tagged 125 butterflies over three years in the area it calls the Monarch Fields as part of an international effort to learn more about the insect’s migratory patterns. Monarch butterflies travel as far north as Winnipeg and northeast to Newfoundland in search of milkweed over three or four generations before a “super generation” flies the entire 5,000 kilometres south to overwintering sites in Mexico.

By documenting a portion of the field and extrapolating it to the rest of the area using transect mapping, the group estimates as many as 4,000 milkweed plants were in the area that was mowed.

Collin, who campaigned successfully against a Medicom development project on a portion of the same land last year, said Technoparc Oiseaux “categorically reject[s] the notion that this is a site that is just filled with ragweed and has no ecological value.”

Monarchs are currently classified as at risk in Canada. Even so, there are no legal tools that prohibit cutting milkweed. It is prohibited to destroy migratory bird nests, which Technoparc Oiseaux says were found left behind in the field.

“We found destroyed nests, we found destroyed birds. The birds do nest in small, low-lying shrubs,” said Collin. “It is clear that this is not standard practice for maintenance; it is a mowing-down of a field during a protected migratory and nesting period.”

After receiving a complaint, an inspector from Environment and Climate Change Canada (ECCC) visited the site on July 5 and opened a file about a possible violation of the 1994 Migratory Birds Convention Act. When contacted by Canada’s National Observer, a spokesperson for ECCC wouldn’t comment on the specifics of the ongoing investigation.

The ADM did not say whether it destroyed any nests, adding it is “legally bound to maintain its facilities, including its green spaces … in accordance with the applicable rules and to avoid the presence of nuisances.”

Forest also said that if the ADM eventually develops the area that was mowed, it would be done with a “vision of sustainability” — an idea that Collin at Technoparc Oiseaux does not believe possible.

Back at the fields, milkweed is growing back and a monarch was spotted fluttering around the area as recently as July 22, according to the citizen-reporting app iNaturalist.

“If you leave a space alone, it's quite amazing what nature can accomplish in terms of its own resilience,” Collin said, “so we're confident that this will remain an important feeding site for the monarch butterfly and all the other pollinators.”