The latest winter survey of western monarch butterflies has delivered a mixed picture for conservationists. Annual counts carried out across California’s coast and nearby inland sites found a small increase compared with the previous season, but the overall population remains alarmingly low by historical standards. According to Monarch Joint Venture, volunteers recorded just over 12,000 butterflies during the 2025 overwintering season, making it the third-lowest total since organised monitoring began nearly three decades ago. Once numbering in the millions, the western monarch migration has declined dramatically, raising continued concerns about its long-term future.Scientists say the latest figures highlight that isolated year-to-year improvements should not be mistaken for recovery. Habitat loss, changing weather patterns and other environmental pressures continue to shape the fortunes of one of North America’s most recognisable migratory insects.
Western monarch butterfly count reaches 12,260 in 2025 winter survey
Reportedly, the annual survey covering the winter of 2025 recorded 12,260 western monarch butterflies across known overwintering locations. Volunteers visited 249 sites stretching from California’s Mendocino County south towards northern Baja California in Mexico, along with recognised inland locations in California and Arizona.Although that total exceeded the previous winter’s count of 9,119 butterflies, it still ranked among the weakest results since organised monitoring began in the late 1990s. It was the third-lowest population recorded during nearly three decades of annual surveys.The count represents the highest number of monarchs seen during the late November to early December survey period, when butterflies have settled into their winter refuges.
Western monarch butterfly population has collapsed since the 1980s
The western monarch migration once unfolded on a very different scale. Estimates suggest that during the 1980s, well over four million butterflies gathered each winter along California’s coast. Those enormous colonies have steadily diminished over the decades, leaving many traditional overwintering sites with only scattered groups or none at all.Scientists still cannot identify an exact population size that guarantees the long-term survival of the western migration. Previous research has suggested that somewhere around 30,000 butterflies may be needed to give the migratory population a reasonable chance of persisting from year to year. Recent counts have repeatedly fallen well below that level.The annual surveys provide only a snapshot of overwintering numbers, but when viewed alongside earlier records they reveal how persistent the decline has become.
PC: PBS
Why western monarch butterfly numbers change each winter
The number of monarchs arriving at overwintering sites is influenced by far more than a single season’s weather. The amount and quality of available habitat throughout the butterfly’s range affect breeding success long before winter begins.Conditions during migration also matter. Temperature patterns, rainfall and the availability of suitable shelter can all influence where butterflies settle and how many survive until the annual count takes place. These shifting environmental factors help explain why numbers can fluctuate from one winter to the next without necessarily indicating a long-term recovery or collapse.That means modest year-to-year increases need to be viewed alongside the much longer historical trend.
Habitat remains at the centre of conservation work
Efforts to support western monarchs continue to focus heavily on restoring suitable habitat across different stages of the butterfly’s life cycle. Flower-rich landscapes provide nectar needed by adult butterflies, while native milkweed species remain essential because monarch caterpillars feed exclusively on these plants.Conservation organisations advise that habitat restoration should be carefully planned rather than simply planting milkweed everywhere. In parts of California, especially close to coastal overwintering sites or in places where milkweed did not naturally occur, introducing the plant may not always be appropriate. Instead, locally native flowering plants that provide nectar through much of the year are often encouraged as part of broader habitat restoration.
How volunteers help monitor western monarch butterfly populations
The western monarch count depends almost entirely on volunteers working alongside conservation organisations. Hundreds of people spend time each winter visiting known butterfly roosts, recording colony sizes and reporting their observations.These long-running community science projects have created one of the most valuable datasets available for tracking the western monarch population over time. Consistent monitoring allows conservationists to compare changing numbers from year to year while identifying sites that may require additional protection or restoration.People interested in participating are encouraged to check local regulations before handling butterflies. Scientific collection permits are required in several jurisdictions, including California and Washington, while other regions may have their own restrictions covering the collection or rearing of monarchs.
Western monarch butterfly recovery depends on long-term conservation
Conservation groups continue to encourage simple measures that reduce pressure on pollinating insects. Limiting pesticide use where possible, planting suitable native flowers and sharing reliable information about pollinator conservation all contribute to healthier landscapes for monarchs and many other insect species.These individual actions are unlikely to transform the population within a single season, but they form part of wider restoration efforts taking place across the western United States. Programmes led by conservation organisations also support research, habitat restoration and partnerships with local communities.
