This summer’s drought and record-breaking heat could affect the fall migration of the endangered monarch butterfly, according to researchers from the University of Ottawa.
They say the extreme weather may be prohibiting plants from producing enough of the nectar that monarchs need to fuel their fall migration to Mexico.
“We think that climate change is the key factor. Increasingly, it’s actually been prioritized as the main threat of facing monarchs, especially since 2005,” said associate professor Heather Kharouba.
“We know, especially looking at the numbers that we get from Mexico, that if there was a bad weather year, that it really does impact the monarchs.”
The monarch is a popular butterfly species that inhabits all of Canada’s provinces with the exception of Newfoundland and Labrador, according to the government of Canada’s profile of the pollinator.
Climate Change and Environment Canada has classified the butterfly as endangered since December 2023 under the federal Species at Risk Act .
The agency partnered with the university and Kharouba to research how the plants they need are affected by warming temperatures.
At a farm in Kinburn on Ottawa’s rural western edge, Kharouba’s team has placed roughly 40 netted cages in pairs around five different plant species.
One of each pair contains an open-top mini-greenhouse around the plant, increasing the temperature by a few degrees to mimic the effects of climate change.
“It’s really important to know how the flowers change, so if they flower earlier or if they flower later, that has important implications for the population,” said Jenna Boomhower, a master’s student at the University of Ottawa who’s leading the project under Kharouba’s supervision.
Boomhower said that during one of this year’s heat waves, temperatures in the mini-greenhouse rose to 50 C, compared to the control cage at around 45 C.
Throughout the summer, monarchs are placed in the netted cage where they can feed on the nectar from the plant, Boomhower explained.
Researchers then weigh the monarch over a five-day period and measure the amount of sugar in the plant using handheld instruments and capillary tubes to determine the nectar’s quality.
According to Boomhower, providing good-quality nectar should allow the Monarch to gain weight and build energy reserves.
While the researchers initially focused on the impact of warming temperatures on plants, this unanticipated dry summer has added an extra layer of complexity.
“The drought has caused the nectar to be thicker, and that can create problems for monarchs as they try to get the nectar out with their proboscis,” Boomhower said. “Have you ever tried to drink a milkshake with a small straw? It’s really difficult to get out.”
The lack of moisture also created problems for the plants, many of which dried out and died.
“It’s entirely killed off some of the plants that we’ve been considering. So in that sense, there is no food from those plants available, there are no flowers,” Kharouba said.
“Right now we’re looking to see how monarchs are going to respond to those flowers that have been under these drought conditions.”
The experiment runs until Sept. 15, when researchers will begin a detailed analysis of their findings.
While Kharouba’s team took five butterflies from the field, they bred over 300 monarchs, many of which will be analyzed further. The rest of the butterflies will be released for migration.
