When we talk about the monarch butterfly, we’re generally referring to the “eastern population,” which stretches, in Canada, from the eastern Rockies to the Maritime provinces. However, the other Canadian population, named the “western population,” migrates in late summer just like our Québec monarchs, but over a shorter distance. Unfortunately, that other Canadian population has been having some problems for a while as well...
Individuals different from our Québec monarchs?
In fact, according to recent genetic studies, western monarchs are no different from Québec monarchs. Nonetheless, the two groups are distinguished from each other by the place where the majority of individuals gather over the winter. In Québec (eastern population), the butterflies will travel more than 4,000 kilometers to get to the state of Michoacán, in central Mexico, in order to rest in the oyamel forests. The western monarchs, who live in southern British Columbia, will undertake a shorter journey – roughly 1,000 kilometers – down the California coast to find interesting sites. Most of the western butterflies will gather on stands of eucalyptus, an exotic tree from Australia. Native stands where butterflies would once settle have almost all been eliminated through the urbanization of the area.
Different populations, same problems
The western monarchs and those from Québec are affected by similar problems. In the 1980s, it was estimated that 4.5 million monarch butterflies would head down the California coast to winter. In the mid-2010s, the population plunged by around 97 percent, reaching a dramatic level of 27,218 monarchs in 2018, the lowest ever recorded to that date. The Xerces Society monitors that declining population by organizing butterfly counts during the winter months with the help of citizen volunteers (as with Mission Monarch). This past January they released the results, which are hardly encouraging, of their Thanksgiving count: a total of 29,418 monarchs. That may represent a slight increase compared to 2018, but more sites were visited in 2019. Which means that the western population finds itself at a critical level, just as it did in 2018. And that worries biologists, since they reckon that a population below 30,000 individuals is at great risk of collapsing.
What are the causes of such a decline?
The same causes are found there as in the east: mostly habitat loss. That translates to fewer wintering grounds for adult butterflies hoping to rest during the cold season and fewer sites suitable for breeding during the warmer season: therefore, less milkweed for the caterpillars, and fewer nectar-producing plants for the butterflies. Luckily, the western monarchs can count on the assistance of a certain number of citizen volunteers. These people help protect the habitats necessary to this population’s survival and rigorously monitor their condition while taking part in population counts at key moments.
It can never be repeated enough: your role is essential in protecting the monarch! Without you, it would simply be impossible. We hope we can count on your invaluable collaboration this summer when the monarchs are back with us.
As for the western population, let’s hope that it enjoys a mild winter, a prolific summer and a migration without severe weather disturbances.