The monarch migration: A disappearing phenomenon?

The monarch (Danaus plexippus) is the most recognizable butterfly species in the world. Its annual migration is unique: at the end of the summer, individuals leave Canada and the northeastern United States for hibernation sites in the mountains of Mexico.

A migratory phenomenon in danger of disappearing

What is behind this trend? Reasons cited include the decline and loss of natural habitat and the eradication of milkweed by pesticides in industrial agriculture zones, but also the impact of climate change across the migration route and especially affecting the hibernation sites in Mexico. Most recently, climate change—particularly extremes such as droughts, record precipitation and a late frost this spring—has had a dramatic impact on both the monarch and milkweed.

Where have all the monarchs gone?

The first monarch butterflies generally arrive in Québec in mid-June. However, as of July 10, only three sightings of monarchs had been reported in the province, and less than 50 had been reported in all of eastern Canada. Very few people have been lucky enough to see them so far this year. At the time of writing this post, the number of observed monarch butterflies has dropped by about 90% from last year on the community science website eButterfly. Ninety percent! Scientists and butterfly enthusiasts across the continent are worried. The monarch population in eastern North America is at risk of disappearing altogether.

2013: The worst year on record for monarchs

While summer 2012 was an exceptionally good year for butterflies, including monarchs, so far 2013 is the worst year on record for monarchs on the eastern side of the continent. In order to properly understand this sudden absence of monarchs in Québec and the rest of Canada, it is important to take a continental view and consider the weather events of the past year.

Extreme weather conditions

First of all, in the summer of 2012, the United States experienced a record drought, in terms of both area and intensity; this resulted in poor-quality milkweed and flowers of other plants. These plants are essential to the monarchs, as they produce the nectar they need to replenish their energy when migrating. This had a huge negative impact on the monarchs’ reproductive success. The consequences of this drought were also felt in the fall as the migrating monarchs crossed this area, with its usual abundance of flowers nowhere to be found. The nectar of these plants also allows them to build up stores of energy for their hibernation period in Mexico. On top of that, spring 2013 was marked by unusually cold temperatures and a great deal of precipitation. The monarchs’ ability to reproduce as they headed back north was therefore greatly diminished. On the US website Journey North, thousands of people waiting to see their first monarchs of the season observed very few individuals and noted very late sightings.

Monarch population down by 59%

Over the winter, researchers take advantage of having the entire migrating population from eastern North America concentrated in Mexico to assess its size. This past winter, these experts reported that the population occupied just 1.19 ha—a drop of 59% from the previous year and more than 500% from the average of the past 20 years (6.7 ha of forest). This is unheard of.

Monarchs’ adaptation to climate change

Many factors may explain this drop in monarch populations. But extreme phenomena associated with climate change are increasingly clear, and species must adapt at breathtaking speed. Is the pace of change too fast for the monarchs to keep up? Will we have summers without seeing this magnificent butterfly, and will its epic migration be a thing of the past? Is the monarch’s situation an alarm bell warning us of what other animals and plants may be experiencing? Let’s not wait for time to tell—when it is too late for our children to appreciate this unique phenomenon.

What can I do to give butterflies a helping hand?

Create an attractive haven for these wonderful migratory insects by growing milkweed and nectar-producing plants. Your garden will become a place where you can observe these flamboyant Lepidoptera at your leisure. At the same time, you will help protect a migration phenomenon that is unique in the world and, unfortunately, in decline.