Monarch butterflies shift to winter breeding for survival

Monarch butterflies in Northern California are adapting to climate change by shifting their breeding season to winter, according to a new study published in the Journal of the Lepidopterists’ Society.

This adaptation, observed particularly in the urban San Francisco Bay Area, could be crucial for the species’ survival. 

The study, led by David James, an associate professor of entomology at Washington State University, found that monarch pupae developing in the winter of 2021/2022 had a survival rate of about 50 percent. 

This finding builds on previous research documenting winter breeding in the region during 2020/2021, a phenomenon likely driven by warmer winters.

Monarchs evolving for survival

“We are witnessing monarchs evolving and adapting to new environmental circumstances,” James stated. “We can learn a lot from what they are doing, and this will inform our strategies for providing the resources they need to be successful.” 

This observation is crucial as it indicates the monarchs’ potential to adapt to changing climatic conditions, ensuring their continued survival.

Monarch pupae viability 

Over the past five years, the population of overwintering monarchs along the California coast has fluctuated dramatically, dropping from 192,624 in 2017 to an all-time low of 1,899 in 2020. However, numbers rebounded to 247,246 in 2021 and 335,479 in 2022. 

Concurrently, there has been a noticeable rise in winter-breeding monarchs feeding on non-native milkweeds in urban areas. The recent study is the first to assess the viability of monarch pupae during winter, providing vital data for understanding this new breeding behavior.

The research involved monitoring more than 100 wild monarch pupae at the Googleplex campus near Palo Alto during the winter of 2021/2022. Citizen scientist Maria Schaefer, who has collaborated with Professor James since 2020, led the monitoring efforts. 

Monarch survival rates in winter

Despite some losses due to landscaping activities, the study found a 49.4% success rate in pupal eclosion – the process of emerging as adult butterflies. 

Notably, the researchers observed that winter pupae can survive and produce adults over a period of up to seven weeks, compared to just 10 days in summer conditions. “Given that winter is a sub-optimal environment for breeding, these results are promising,” James noted.

Parasites and winter breeding

The study also examined the prevalence of the parasite Ophryocystis elektroscirrha in the winter-breeding population, using the shed-skin of the pupae (exuviae) for detection. 

The analysis suggested that approximately 70% of the population was likely infected with the parasite, highlighting the need for further research into its impact on the monarchs, particularly in the context of their new winter breeding behavior.

Modifying monarch conservation strategies

The emergence of winter-breeding monarchs presents an adaptation to warmer winters, providing an alternative to the traditional overwintering in non-breeding colonies at sites like Pacific Grove, Santa Cruz, and Pismo Beach. To support this new behavior, conservation practices may need to be updated. 

“Currently, conservation guidelines dictate that ornamental milkweeds, the ones that winter-breeding monarchs primarily use, should be cut down during winter to minimize parasite infection,” noted Professor James. 

“This is clearly bad for winter-breeding. We suggest that these guidelines should be modified to have milkweed cut back during late summer instead of late fall which should still minimize parasite infection while ensuring availability of plants for monarch winter-breeding.”

Broader implications of the study

The researchers plan to continue monitoring the winter-breeding monarch populations in the South Bay Area to gather more data. 

Their ongoing research aims to understand the role these winter-breeding monarchs may play in sustaining the overall population of western monarchs, which face numerous challenges due to climate change and habitat loss. 

The findings from this study not only provide valuable insights into the adaptability of monarch butterflies but also underscore the need for flexible and updated conservation strategies to support their survival in a changing world.

“The developing importance of winter breeding in western monarch ecology necessitates modifications to conservation guidelines that enhance the survival of immature stages, acknowledging the role of non-native milkweeds while minimizing parasite infection,” the authors concluded.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–