Faithful to instinct, the monarchs have hit the road for Mexico. The autumn migration is a great adventure, but one that only an estimated half of the butterflies survive. And with climate change, the challenge they face is even greater…
Surviving the chill
Every year for millennia, monarchs have been leaving us and heading south. Don’t take it personally: they simply can’t put up with our winters! In the forests of sacred fir (Abies religiosa) where the butterflies take refuge while waiting for spring, temperatures slightly above freezing are ideal for their survival. They keep them from freezing themselves while slowing down their metabolism, which allows them to conserve energy. But the road to their wintering area is filled with obstacles.
Risk of fuel exhaustion
First of all, to pull off this migration of over 4,000 kilometers, it takes fuel. The fuel for butterflies is nectar from flowers. To avoid breakdown, they have to gas up before taking off! However, where flowering meadows were once plentiful, now there are mostly fields with crops growing that produce little or no nectar. The habitat loss resulting from intensive agriculture is a hurdle to the monarchs’ autumn migration.
Drought and hurricanes
Another considerable challenge is that of climate change, the impacts of which on the monarch’s migration we’re only beginning to understand. For example, precipitation is less evenly distributed, which results in periods of drought alternating with heavy rains. In a period of drought, the growth rate of plants slows, and they produce a nectar of lesser quality.
In addition to drought, climate change increases the frequency of extreme weather events such as hurricanes and tornadoes. When those storms take place during the migration, and that’s the case in the fall, monarchs die off in much greater numbers. For example, this year the first migrants ran into hurricane Florence, which struck the American east coast in mid-September. What was the impact on the monarchs’ survival? We’ll only know when the results of the annual inventory drawn up in the Mexican wintering sites are available.
Protection still necessary
Even though monarchs were very abundant this summer in their breeding grounds in Canada and the northeastern U.S., that doesn’t mean that their decline has been halted for good. It just takes one difficult migration to reduce the population drastically. Meaning, to see how the number of monarchs evolves year after year, it’s vitally important to continue taking part in Mission Monarch!