POPULATION
STATUS & THREATS
STATUS
Western Monarch Populations
The monarch butterflies in Monterey County are part of the Western monarch population, which includes monarchs that overwinter in coastal California and, during the spring, summer, and autumn, live and breed in inland areas west of the Rocky Mountains.
The Western Monarch population is one of the best-studied butterfly populations in the world. Informal community science projects have monitored it since the 1980s, and scientists have been officially tracking it since 1997 with the Xerces Western Monarch Count. Because the Western monarch overwinters in coastal California, residents have many historical reports of what monarch populations used to be like.
Residents of Pacific Grove report that, historically, the air was so thick with monarchs, that it was like a "fluttering orange veil." As late as the 1980's, residents would open their door and their entire garden would burst with thousands of monarchs on lawns taking to the air at once. However, even the town that hails itself as "Butterfly Town, USA" has the same problems that threaten monarch butterflies across the United States: habitat loss, continued pesticide use, and climate change.
Since monitoring began in 1997, the number of western monarchs has declined by over 99%. If no action is taken to protect them, the US Fish & Wildlife Service estimates a 95% chance of extinction for this population by 2080.
When monitoring began in the 1980s, an estimated tens of millions of monarch butterflies overwintered in coastal California. By 1997, over 1,200,000 monarchs were counted in California. That number dropped to an all-time low in 2020 with less than 2,000 monarchs in California and none clustering at the Pacific Grove Monarch Sanctuary.
From 2021 to 2023, western monarchs slightly rebounded. In 2022, there were nearly 16,000 monarchs in Pacific Grove and over 300,000 across California—the highest number in 20 years! However, with extreme heat and drought from climate change, the 2024 population plummeted to less than 250 monarchs in Pacific Grove and just over 9,100 monarchs in California.
The recent rebound and fall show that monarch butterfly populations are, like many insects, “bouncy.” They can fluctuate widely from year to year. When conditions are suitable for monarchs, the population can recover quickly due to high reproduction rates. However, extreme weather conditions and events can wipe out large numbers of butterflies. Small populations are especially vulnerable to catastrophic events, making recent declines very concerning.
Status in Monterey County
Monterey County is an essential place for monarchs, with overwintering sites scattered along the coast. Twenty overwintering sites have been monitored in Monterey County since 1997, though not all are monitored yearly.
The Pacific Grove Monarch Butterfly Sanctuary is one of the largest publicly accessible overwintering sites in California, alongside Natural Bridges State Park in Santa Cruz and the Pismo Beach Monarch Butterfly Grove. It has the highest number of monarch butterflies that overwinter in Monterey County.
Volunteers with the Pacific Grove Museum of Natural History count the number of monarch butterflies at the Pacific Grove Monarch Sanctuary during the overwintering season (October - February). The latest count and other updates are available at https://www.pgmuseum.org/monarchs.
The following graphs show yearly mid-season and late-season monarch counts conducted by the Xerces Society in Monterey County.
THREATS
Monarch butterflies face significant challenges threatening their survival. The loss of essential breeding and overwintering habitats across North America has taken a toll on their populations. As these crucial spaces shrink, monarchs struggle to find places to rest and reproduce.
In addition to habitat loss, the widespread use of pesticides intended for pest control poses a serious risk to monarchs and other beneficial pollinators. These chemicals can have damaging effects on their health and well-being. Climate change adds another layer of difficulty, forcing monarchs to adapt to shifting conditions that impact their migratory routes and breeding areas.
Moreover, natural enemies such as predators and diseases pose constant threats throughout their life stages. It's vital that we adopt wise management practices and conservation efforts to provide ongoing support for monarchs and the ecosystems they inhabit. By committing to habitat protection and responsible land use, we can help ensure a sustainable future for these remarkable butterflies.
