Population Increase

Monarch Butterfly Populations Soar in California After Dramatic Losses

Population Increase

Monarch butterfly populations have rebounded in California after reaching historically low numbers in 2020. The Xerces Society for Invertebrate Conservation reported an increase from 2,000 monarchs in 2020 to nearly 250,000 in 2021 at overwintering sites in the state.

Factors Contributing to Population Decline

Scientists believe that habitat loss and pesticide use have played significant roles in the decline of monarch populations. The United States is home to two distinct monarch populations, with the western population overwintering in California.

Pacific Grove: Butterfly Town USA

Pacific Grove, California, has long celebrated the arrival of monarch butterflies each October with its annual Butterfly Parade. However, in 2020, the town’s two-acre sanctuary saw no monarchs. This sanctuary is one of California’s main overwintering sites.

Conservation Efforts

In 2014, the Xerces Society and other groups petitioned the U.S. Fish & Wildlife Service to protect monarchs as a threatened species. The USFW determined that listing monarchs under the Endangered Species Act was warranted but delayed due to higher priority actions.

Hypotheses for Population Increase

Scientists are still uncertain about the exact reasons for the monarch population increase in 2021. Some hypotheses include:

• Ideal weather conditions
• Reduced pesticide use during the COVID-19 pandemic
• Wildfires preparing the ground for wildflower growth
• New additions from the eastern monarch population
• Less competition

Spread Instead of Clustering

David James, an entomologist at Washington State University, suggests that the low monarch count in 2020 may have been due to the butterflies spreading out instead of clustering at traditional overwintering sites.

Threats Remain

While the increase in monarch numbers is encouraging, the Xerces Society emphasizes that the population is still dangerously low. Habitat loss, pesticide use, and other threats continue to pose challenges to monarch survival.

Importance of Conservation

Conservation efforts remain crucial to protect and recover monarch butterfly populations. Addressing the threats they face is essential for ensuring their future survival.

Factors Impacting Monarch Populations

Habitat Loss: Monarchs rely on milkweed plants for reproduction and feeding. Habitat loss due to urbanization, agriculture, and other development has reduced milkweed availability.

Pesticide Use: Pesticides, particularly herbicides, can harm monarch larvae and adults. Exposure to these chemicals can disrupt their life cycles and reduce their populations.

Climate Change: Changing weather patterns and extreme events can affect monarch migration, reproduction, and overwintering success.

Additional Threats: Other factors that can impact monarch populations include disease, parasites, and competition from other butterfly species.

Conservation Strategies

Habitat Restoration: Planting milkweed and other nectar-producing plants in gardens, parks, and roadsides provides essential resources for monarchs.

Pesticide Reduction: Reducing pesticide use, particularly during monarch migration and breeding seasons, can mitigate their negative impacts on butterfly populations.

Monarch Monitoring: Citizen science programs and professional surveys help track monarch populations and identify areas of concern.

Education and Outreach: Raising awareness about the importance of monarchs and the threats they face is crucial for fostering conservation efforts.