An increase of just 0.6°C in temperature can deteriorate the quality of nectar in key flowers for the monarch butterfly, putting at risk its ability to migrate and survive during the winter. This is revealed by research from the University of Ottawa, published in Global Change Biology Communications, which warns about the indirect impacts of global warming on this migratory species.
The study in Ottawa
The research, led by associate professor Heather Kharouba, was conducted at the Fletcher Wildlife Garden during the summer of 2023, with the collaboration of Environment and Climate Change Canada and the University of Western.
The team analyzed how a moderate increase in temperature affects the floral supply and nutritional content of nectar in species visited by monarchs.
The results were clear:
- An increase of 0.57°C reduced the number of flowers per stem by 12.9%.
- The concentration of sucrose in nectar fell by about 24%.
- Butterflies fed with lower quality nectar showed 25.9% less fat mass than those in the control group.
Physiological and ecological consequences
The reduction in fat mass is critical, as these energy reserves allow monarchs to make their annual 3,000 km migration from Canada and the United States to the forests of Mexico, as well as survive during the cold months.
The study emphasizes that neither lean mass nor water mass showed relevant differences, confirming that the effect of warming is concentrated on the butterflies’ ability to store energy as fat. In other words, the quality of nectar matters more than quantity when it comes to sustaining migration.
Population risks
The implications go beyond individual physiology. A reduction in the nutritional quality of floral resources at the end of the season could translate into:
- Lower migration rates.
- Decreased winter survival.
- Intensification of the population decline of the monarch butterfly, already classified as an endangered species in Canada and the United States.
Researchers’ recommendations
The University of Ottawa team warns that habitat restoration should focus not only on the abundance but also on the quality of floral resources. They propose:
- Incorporating species resistant to higher temperatures.
- Evaluating the thermal response of different nectar plants.
- Designing adaptive management strategies to protect migratory pollinators.
- Expanding future research to more intense climate scenarios and with greater species diversity.
The study demonstrates that even a moderate increase in temperature can have devastating effects on the nutrition and migration of the monarch butterfly.
Ensuring its survival requires identifying plants capable of maintaining nectar quality under warmer conditions and designing habitat restoration policies that prioritize resilience to climate change.
