A species status assessment (SSA)report contains the best scientific and commercial data available about the status of the species, including the impacts of past, present, and future factors (both negative and beneficial) affecting the species. A team of people composed of U.S. Fish and Wildlife Service biologists, in consultation with other species experts, prepared and updated an SSA for the monarch butterfly.

Changes to the updated Species Status Assessment 2023 (version 2.3) reflect the new data available about monarchs. The new data did not significantly change the analyses and future condition forecasts presented in the 2020 SSA report (version 2.1). However, we incorporated the new information and references into the updated SSA (version 2.3) which added to our current understanding of monarchs. Updates to the SSA (version 2.3) includes the following: 

1. Monarch populations survey numbers for both the eastern and western North American monarch populations were updated and reviewed. The extinction risk model for the monarch was not re-run with the new data because the relatively small change in population value would not change the outcome of the previously run model.
2. New relevant recent scientific literature papers were reviewed, and relevant resources were incorporated.
3. The restoration accomplishment reports provided to the Monarch Conservation Database were reviewed and added. 

We are seeking comments about species biology, taxonomy, range, population trends, threats, species status, including: 

•  Any new scientific or commercial information about alternative migratory pathways 
•  Population dynamics and contributions from the nonmigratory populations, specifically resident monarchs in southern Florida, the Gulf Coast, the southern Atlantic Coast, and the southern Pacific Coast

For full information about the types of public comment we are requesting, see our proposed rule. Please include sufficient information with your submission (such as scientific journal articles or other publications) to allow us to verify any scientific or commercial information you include.

The primary drivers affecting the health of the two North American migratory populations are: loss and degradation of breeding, migratory, and overwintering habitat; exposure to insecticides and effects of climate change climate change
Climate change includes both global warming driven by human-induced emissions of greenhouse gases and the resulting large-scale shifts in weather patterns. Though there have been previous periods of climatic change, since the mid-20th century humans have had an unprecedented impact on Earth's climate system and caused change on a global scale.

Learn more about climate change . Probability of extinction for the eastern migratory North American population ranges from 56 to 74% by 2080. And in the west, by 2080, probability of extinction is greater than 99%. Many other influences to monarchs were evaluated, including disease, parasitism, captive rearing, collection, impacts of tourism at overwintering sites, invasive swallow-wort plants, vehicle mortality, and natural catastrophes. However, these other potential influences were not determined to be key population drivers.

Eastern North American Monarch: The eastern monarch population declined as milkweed was historically removed from the landscape by land development and the widespread use of herbicides. Monarchs continue to be impacted by the ongoing effects of this past habitat loss and degradation. Monarch egg densities were higher on milkweed in agricultural fields and the loss of agricultural milkweeds has resulted in a decline in monarchs. Furthermore, declines in suitable overwintering habitat due to climate change and logging have also contributed to the overall decline in the eastern migratory monarch population.

Western North American Monarch: The western monarch population has declined due a number of factors, including habitat loss and degradation, pesticides, climate change and other pressures on the migratory cycle. The western monarch faces overwintering habitat loss from urban development, land conversion, loss and degradation of overwintering groves, disease, tree pests and wildfires.

The proposed rule was developed based on a comprehensive review of the best available scientific and commercial information about monarch butterflies. Our agency also incorporated the cumulative effects of climate change climate change
Climate change includes both global warming driven by human-induced emissions of greenhouse gases and the resulting large-scale shifts in weather patterns. Though there have been previous periods of climatic change, since the mid-20th century humans have had an unprecedented impact on Earth's climate system and caused change on a global scale.

Learn more about climate change when determining the current and future condition of the species. With a warming climate, drought and increasing temperatures are predicted to have larger impacts on both the eastern and western monarch populations. Climate change affects monarchs directly through increased temperatures and indirectly by impacting habitat availability, disease and predators.

The U.S. Fish and Wildlife Service uses the 3 R’s of conservation biology principles to understand species viability or ability to survive or live successfully. These three principles are resiliency, redundancy and representation. In this case, we analyzed the best available science to determine the resiliency, redundancy and representation of the monarch butterfly across its historical range.

Resiliency is the ability of the species to withstand and recover from random disturbances within its environment. Weather conditions such as wet or dry years or warm and cold years can cause shifts to population size. Population size and growth rate tend to increase or decrease together and may be influenced by connectivity among populations. Large effective population sizes and population connectivity also help increase resiliency.

Redundancy is the ability of the species to withstand catastrophic events such as droughts, wildfires or large pollution events. Redundancy is characterized by having multiple, resilient populations across the species range and its habitat. It can be measured by population size, geographic area of the habitat and degree of connectivity of populations.

Representation is the ability of the species to adapt to both short-term and long-term changes or stressors in its physical and biological environment such as changing climate conditions or diseases. Representation is characterized by the species’ genetic and environmental diversity within and among populations.

Monitoring at overwintering sites allows for the most practical and direct assessment of annual population levels. In addition, migratory populations are studied consistently and comprehensively, reflecting the full range of threats and population changes over the prior annual breeding and migration cycle.

Eastern monarchs: Migratory monarch populations are monitored annually through overwintering surveys in Mexico for the eastern migratory population. Because it is not possible to count individual monarchs at the overwintering sites in Mexico, the size of the eastern population is measured based on the area occupied by clustered monarchs. 

Western monarchs: Community scientists began monitoring the abundance of monarch butterflies at overwintering sites in California in the 1980s, but the concerted effort of the Western Monarch Count didn't begin until 1997. Today, western monarch numbers are gathered by volunteers who follow a specific protocol for counting clustered monarchs. The annual count helps us monitor the size of the population and trends.

Monarch populations fluctuate each year. Like many insects, monarchs are sensitive to environmental conditions such as temperature, precipitation and other factors. In response to these changing conditions, monarchs can experience large swings in population numbers from year to year. A single overwintering count cannot be used to assess the monarchs’ overall population or to determine endangered species status.