(Disponible en français : Le déclin de la population de monarques : réponses gouvernementales)
Note: This publication was updated in May, 2017: Update – The Monarch Butterfly: An Icon Endangered
Many environmental issues in North America require continent-wide cooperation. Managing the monarch butterfly, the only butterfly known to make a two-way migration like birds do, is an example of this need.
Each year, monarch butterflies travel thousands of kilometres to and from their wintering grounds in Florida, the mountains of Mexico or southern California (see Figure 1). Recently, the first sightings of the season have occurred in Canada.
However, while the area occupied by this species was larger this winter than last, that area was the second smallest in more than 20 years, reflecting the decline in monarch butterfly populations over that period.
Figure 1 – Monarch Butterfly Migration Pattern in North America
Source: Map adapted from Environment Canada, Species at Risk Public Registry, Management Plan for the Monarch (Danaus plexippus) in Canada – 2014 [Proposed], Figure 3.
Monarch butterflies are divided into two populations, based on whether they live west or east of the Rocky Mountains. The western population hibernates in California, and the larger eastern population overwinters in Florida or the forests of Mexico.
Measurements of monarch butterfly populations are taken during the insects’ hibernation period. In Mexico, the area of forest occupied by monarch colonies during their hibernation is used as an indicator of the number of butterflies arriving from Canada and the United States each year.
As shown in Figure 2, this area can vary significantly but has generally decreased since the 1990s. Volunteer-reported data from California suggest that the western population has also declined, though it has been stable over the last four to five years.
Figure 2 – Area of Forest Occupied by the Eastern Population of Monarch Butterflies (hectares), Mexico, 1993–2014
Note: The measurement is taken in December of each year.
Source: Figure prepared by the authors using data obtained from Omar Vidal and Eduardo Rendón-Salinas, “Dynamics and trends of overwintering colonies of the monarch butterfly in Mexico,” Biological Conservation, Vol.180, December 2014; and E. Rendón-Salinas, A. Fajarsdo-Arroyo and G. Tavera-Alonso, Forest Surface Area Occupied by Monarch Butterfly Hibernation Colonies in December 2014, 27 January 2015.
Causes of the decline
The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) identifies a number of habitat-related issues that contribute to the declining monarch population. In particular, COSEWIC presents loss of habitat at overwintering sites – the result of forest degradation in Mexico and real estate development in California – as a key factor.
The loss of milkweed is also a factor that commonly affects monarch habitat across North America. Monarch butterflies breed only where milkweed is found, since their larvae feed exclusively on this plant.
Milkweed is often considered undesirable for agricultural purposes and is eliminated with herbicides. However, the butterflies need milkweed to complete their migration, because they undergo a generational turnover on their return journey.
COSEWIC also identifies other factors – such as pesticides, extreme weather and climate change – as potential monarch health stressors.
Government initiatives: Examples from Canada, the United States and Mexico
In Canada, the management of habitat critical to monarchs falls mostly under provincial jurisdiction. However, the federal government plays a role in monarch conservation through its responsibility for international affairs and its power to enter into international agreements.
The federal government also promotes coordination of conservation activities among the various levels of government, conducts scientific research and provides funding and technical expertise in support of monarch conservation.
Under Canada’s Species at Risk Act (SARA), the monarch butterfly is listed as a species of “special concern,” a category for species that are not yet threatened or endangered, but may become so. SARA requires management plans with goals for maintaining population levels of species.
In 2014, the government held consultations on a proposed management plan for the monarch. At Point Pelee National Park, Parks Canada restores monarch habitat and offers tours in September as the butterflies start their migration south.
The U.S. Fish and Wildlife Service announced in February 2015 a $2-million cooperative agreement with the National Fish and Wildlife Foundation to create the Monarch Conservation Fund, which will help finance conservation projects.
On 19 May 2015, the U.S. released its National Strategy to Promote the Health of Honey Bees and Other Pollinators. One of the overarching goals included in the strategy is to increase the eastern population of the monarch butterfly so that it occupies an area of approximately 6 hectares in the overwintering grounds in Mexico by 2020.
In Mexico, hibernation sites have been protected as various forms of wildlife reserves since the 1980s. The Monarch Butterfly Biosphere Reserve, created in 2000 and recognized as a world heritage site in 2008, covers more than 560 square kilometres.
Enforcement actions by the Mexican government have reduced illegal deforestation on the reserve, while multiple public and private efforts to create better economic conditions in the region have decreased local incentives to harvest the forest illegally.
As for trilateral initiatives, a North American Monarch Conservation Plan was released by the Commission for Environmental Cooperation in 2008. In March 2014, the Prime Minister of Canada and the presidents of the United States and Mexico issued a joint statement announcing the creation of a working group to ensure the conservation of the monarch butterfly.
Most recently, in April 2015, the three countries discussed monarch butterfly conservation at the annual meeting of the Trilateral Committee for Wildlife and Ecosystem Conservation and Management in San Diego, California. At the meeting, officials from each government, including a representative from the Canadian Wildlife Service, discussed initiatives under way in their home countries.
The meeting’s participants also visited the San Diego National Wildlife Refuge Complex, where they planted 90 native milkweed and other pollinator-friendly plants that will act as habitat for monarch butterflies.
Borders, Brianna, and Eric Lee-Mäder. Milkweeds: A Conservation Practitioner’s Guide – Plant Ecology, Seed Production Methods, and Habitat Restoration Opportunities. The Xerces Society for Invertebrate Conservation, 2014.
Commission for Environmental Cooperation. Conserving the Monarch Butterfly and Promoting Sustainable Livelihoods.
International Union for Conservation of Nature [IUCN]. World Heritage Nomination – IUCN Technical Evaluation: Monarch Butterfly Biosphere Reserve (Mexico) – ID No.1290, April 2007.
Jepsen, Sarina, et al. Conservation Status and Ecology of the Monarch Butterfly in the United States. NatureServe and The Xerces Society for Invertebrate Conservation, March 2015.
National Fish and Wildlife Foundation. Monarch Butterfly Conservation Fund.
Species at Risk Public Registry. Species Profile: Monarch.
Vidal, Omar, José López-García and Eduardo Rendón-Salinas. “Trends in Deforestation and Forest Degradation after a Decade of Monitoring in the Monarch Butterfly Biosphere Reserve in Mexico.” Conservation Biology. Vol.28, No.1, February 2014.
World Wildlife Fund Canada. Monarch Butterfly.
Authors: Penny Becklumb, Jed Chong and Tim Williams, Library of Parliament