Study: Climate change alters flower nectar quality and supply
Impacts pollinators, like monarch butterflies, by degrading their food source
University of Ottawa
image:
“Even though the butterflies could eat as much as they wanted, they couldn’t make up for the lower-quality nectar”
Heather Kharouba
— Associate Professor, Department of Biology & University Research Chair in Global Change Ecology
view moreCredit: University of Ottawa
Monarch butterflies have always been remarkably resilient. Every fall, these delicate orange-and-black travelers set out on a journey so improbable it borders on myth, flying some three thousand kilometers from Canadian fields all the way to Mexico’s mountain forests, their overwintering grounds. They’ve been weathering habitat loss, extreme weather and pesticides, but new research from the University of Ottawa suggests a new snag in their epic trek. The culprit? Nectar. Turns out, their main food source isn’t what it used to be.
Late last summer, a team of scientists led by Heather Kharouba, Associate Professor in the Department of Biology at the University of Ottawa and University Research Chair in Global Change Ecology, set up a simple but revealing experiment. Instead of focusing on the butterflies themselves, they looked at the plants the monarchs depend on during migration.
A subtle but serious threat to monarch survival
They observed that a tiny bump in temperature, just 0.6 degrees Celsius, was enough to lower the quality of the nectar these plants produced. Monarchs fed on these “warmed” blooms built up about a quarter less body fat than their counterparts.
“It’s not that the butterflies are being directly harmed by the heat,” says Professor Kharouba. “It’s that warming is making the nectar less nutritious. Even though the butterflies could eat as much as they wanted, they couldn’t make up for the lower-quality nectar.”
Climate change alters nectar quality
The experiment, carried out by Katherine Peel from Dr. Kharouba’s research lab, and collaborators from Environment and Climate Change Canada and Western University, took place at the Fletcher Wildlife Garden in Ottawa. The team ensured that only the plants were warmed and that the butterflies remained at regular outdoor temperatures. The results were clear: as the temperature crept up, late-season flowers produced less nectar, and what they did produce was lower in sugar.
Scientists have known for years that monarchs are in trouble, but this study uncovers a more subtle risk. “We’re seeing that climate change can hit pollinators indirectly, by degrading the resources they count on,” explains Professor Kharouba. “I believe the findings are a wakeup call for anyone working to protect these butterflies and, really, for anyone planting a garden or maintaining a park as the planet heats up.”
The research also inspired a unique blend of science and art. The study was the focus of visual artist Valérie Chartrand through an exhibition called Flutterings: Monarchs and Climate Change, hoping to spark new conversations about how we care for the creatures around us and to demonstrate how art-science collaborations can deepen public understanding of complex environmental issues.
The study, titled “Warming-mediated decreases in nectar quality translate into lower energy reserves of the monarch butterfly (Danaus plexippus)”, was published in Global Change Biology Communications.
Journal
Global Change Biology
Method of Research
Meta-analysis
Subject of Research
Animals
Article Title
Warming-Mediated Decreases in Nectar Quality Translate Into Lower Energy Reserves of the Monarch Butterfly (Danaus plexippus)
Article Publication Date
20-Jan-2026
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