Endangered Species Law & Policy

On December 10, 2024, the U.S. Fish and Wildlife Service (Service) released its long-anticipated listing proposal for the monarch butterfly (Danaus plexippus), along with a proposed critical habitat designation and species-specific 4(d) rule (Proposed Rule). The Proposed Rule indicates the public comment period closes on March 12, 2025.

The Service has proposed listing the monarch as threatened primarily as a result of threats from past and ongoing loss and degradation of breeding, migratory, and overwintering habitat, exposure to insecticides, and the effects of climate change. While the Proposed Rule acknowledges multiple broad-scale efforts to conserve the monarch, the Service indicates that these efforts have not ameliorated threats faced by the species.

The Proposed Rule establishes seven units of critical habitat, comprising 4,395 acres across seven counties in California: Alameda, Marin, Monterey, San Luis Obispo, Santa Barbara, Santa Cruz and Ventura. To determine critical habitat for the species, the Service looked at maximum occupancy rates of overwintering butterflies in California observed during the Western Monarch Count from 2013-2022. Areas selected for critical habitat were overwintering sites containing 1,000 butterflies or more during at least three years in the last ten-year period, 5,000 or more butterflies in one year of the last ten-year period, of 1,000 or more butterflies during at least two years if the sites were discovered less than ten years ago. The Service then identified “core” and “shelter” zones for each site. The agency considers “core zones” to be the general area within an overwintering site containing the trees where monarchs cluster and the “shelter zones” to include a 152-meter buffer constituting the approximate location of the support zone surrounding each overwintering site.

Under current Service regulations, the “take” prohibition of Endangered Species Act (ESA) section 9 applies to all species listed as threatened unless the agency issues a species-specific 4(d) rule providing exemptions from the broader “take” prohibition. Under the Proposed Rule, the following activities would be exempt from “take”:

• Activities that may maintain, establish, enhance, or remove milkweed and nectar plants within the breeding and migratory range and that do not result in conversion of native or naturalized grassland, shrubland, or forested habitats. Such activities include:
  • Certain habitat restoration and management activities
  • Livestock grazing and “routine” ranching activities
  • “Routine” agricultural activities
  • Fire management activities
  • Silviculture practices and forest management activities using state-approved best management practices
  • Maintenance, enhancement, removal, and establishment of milkweed and nectar plants on residential and other developed properties
  • Vegetation management activities that remove milkweed and/or nectar plants when conducted at times of year when monarchs are not likely present
• Implementation of comprehensive conservation plans and programs
• Maintenance or improvement of overwintering habitat
• Vehicle strikes
• Non-lethal collection, possession, captive-rearing, and release of a limited number of monarchs
• Non-lethal scientific research and educational activities involving a limited number of monarchs
• Possession of dead monarchs
• Sale of captive reared monarchs

In addition to the exemptions above, the Service is seeking public feedback on how to address pesticide use in any 4(d) rule for the species, including which pesticide uses and application methods result in exposure and adverse effects, and whether the exception for those uses should include measures to mitigate effects of pesticides on monarchs.

The monarch has been a candidate for listing under the ESA since December 2020, when the Service published a positive 12-month finding that listing the monarch as a threatened species was warranted but precluded by other, higher-priority species. The Center for Biological Diversity challenged the 12-month finding in the U.S. District Court for the District of Columbia, which resulted in a settlement agreement requiring the agency to submit a proposed listing determination to the Federal Register by December 4, 2024.