A new study by the Monarch Conservation Science Partnership reveals there is a substantial probability of “quasi-extinction” of the Eastern monarch butterfly migratory population within 20 years if ambitious habitat restoration and conservation goals are not achieved. Quasi-extinction means that the population reaches levels that are so low that it would be unlikely to recover. The authors tested the risks that the population could reach thresholds they thought were dangerously low: 0.01, 0.05, 0.15 and 0.25 hectares of occupied area in Mexico (note that the lowest level reached to date is 0.67 ha). The risk of quasi-extinction is between 16% (for reaching 0.01 ha) and 62% (for reaching 0.25 ha) during the next 20 years. Factors such as a declining numbers, small current population size, and high variability in population from year to year contribute to this risk.
Knowing the extent of the vulnerability of the monarch population is essential for selecting a target population size and conservation planning. Reaching that target population size will be vital for maintaining the monarch migration despite extreme weather events and resulting variability in the size of the population. The current target population set by the White House is 6 hectares of overwintering monarchs by 2020. Achieving that goal would dramatically reduce the risk of extinction. If the population starts at 6 ha, it has only a 3% risk of reaching 0.01 and a 25% chance of reaching 0.25 ha in the next 20 years.
While many factors (including habitat loss, climate change, pesticide use, and invasive species) are probably contributing to the current small monarch population, loss of milkweed on the landscape is a strong driver and “highly correlated with the adoption of herbicide-tolerant genetically modified corn and soybeans” (Semmens et al. 2016. pg 2). Due to this decline of breeding habitat, the authors of the study argue that conservation efforts to achieve the goal of 6 ha. should focus on habitat creation and restoration.
This report, in the wake of a serious winter storm at the monarch overwintering sites this winter that almost certainly killed many monarchs, shows the importance of the ongoing monarch conservation efforts across North America to bolster the monarch population. Monarch Joint Venture partners are working across the U.S to create and restore monarch habitat. Our partners are also educating the public about how they can participate in habitat creation, and conducting research on the best conservation implementation strategies. Truly everyone can take part in the effort to restore the monarch butterfly population, from young to old and urban to rural. With an all hands on deck approach, we can reach this ambitious goal to preserve the monarch migration for generations to come. Learn what you can do to create monarch habitat near you, and get involved today.
Several of the study authors work for organizations that are part of the MJV partnership: Wayne Thogmartin, Darius Semmens and Jay Diffendorfer (USGS), Karen Oberhauser (U of M Monarch Lab), and Chip Taylor (Monarch Watch).
Semmens BX, DJ Semmens, WE Thogmartin, R Wiederholt, L López-Hoffman, JE Diffendorfer, JM Pleasants, KS Oberhauser, OR Taylor. 2016. Quasi-extinction risk and population targets for the Eastern, migratory population of monarch butterflies (Danaus plexippus). Sci. Rep. 6, 23265; doi: 10.1038/srep23265.
The Monarch Joint Venture is a national partnership of federal and state agencies, non-governmental organizations, and academic programs working together to conserve the monarch butterfly migration. The content in this article does not necessarily reflect the positions of all Monarch Joint Venture partners. Header photo of migrating fall monarchs taken by Karen Oberhauser near Saltillo in 2008.