In 1997, about 100,000 monarch butterflies congregated at the Pismo Beach Monarch Butterfly Grove; in 2016, fewer than 20,000 were counted in the same location.
Huge fluttering hoards of monarch butterflies have long been a signature of the eucalyptus-lined tourist destination on Highway 1, but that statewide population has significantly declined in the past 20 years as habitat changes wreak havoc on the insects’ migration patterns.
Danielle Patterson, a State Parks interpreter who oversees the 85 interpretive docents working at the Monarch Grove, confirmed the park has seen a decline in its population in recent years — something that is concerning for one of the biggest aggregations of monarch butterflies in California.
“I don’t think we’ll ever get to the point where, you know, there aren’t any butterflies,” Patterson said. “It could be that we get to where it’s just significantly less. But that’s something we can’t predict. Fingers crossed it doesn’t happen.”
19,755 The number of monarch butterflies counted at Monarch Grove in Pismo Beach in 2016.
Patterson attributed the decline to a loss of habitat, namely native milkweed, displacing the butterflies’ normal migration habits as they journey west and south for the winter.
Monarch butterflies from all over the western United States congregate in San Luis Obispo County from November to late February, some coming as far as 2,000 miles to escape freezing winter weather. They gather here in sheltered groves, clustering tightly together at night to stay warm and then, during the day, creating clouds of fluttering orange warmed by the sun. Monarchs east of the Rocky Mountains spend the winter in Mexico.
During the summer, monarchs lay their eggs on milkweed plants, and the butterflies in their larval stage feed on the plant.
Patterson cautioned that other isolated incidents like weather can play a role in the butterfly numbers.
“A lot of different factors go into this,” she said, noting that a tree that had previously shielded the park and its sensitive flying residents from coastal winds fell this year and likely contributed to smaller numbers. “Again, it’s something we can’t really predict.”
That loss of habitat doesn’t just impact the grove — statewide experts continue to worry about the insect’s changing migration patterns.
The Western Monarch Thanksgiving Count records the number of monarchs at important overwintering sites across the California coast.
In 2016, the number of butterflies counted in the study increased slightly — but according to the U.S. Fish and Wildlife Service, the increase was likely caused by an increase in the number of volunteers and sites participating in the count in 2016, not an actual increase in butterflies.
Volunteers at 253 sites across the state recorded a total of 298,464 monarch butterflies, compared with the 1.2 million they recorded in 1997. That year there were 76 sites.
Numbers were down at many of the historically large sites in California year-over-year: Pismo Beach’s population fell by 29 percent compared with 2015, when 28,073 butterflies were counted at the grove. The Morro Bay Golf Course, the next largest site for butterflies in the county, recorded 12,189 butterflies in 2016, compared with 13,492 the year before.
100,000 The number of monarch butterflies counted at Monarch Grove in Pismo beach in 1997
There was some good news, however: Volunteers with the count located four new congregating sites in Southern California, and a private site in Monterey County had more than 39,000 recorded butterflies — the largest grouping of the insects recorded in the past 10 years, according to Fish and Wildlife.
The season has since ended at the butterfly grove. The butterflies typically take off by late February, Patterson said, though this year they left slightly earlier than usual, meaning you won’t be seeing the masses of orange and black until November.
For those who want to do their part to help the population rebound, Patterson has some suggestions.
She encourages people living in the San Joaquin Valley and further inland to plant native milkweed to help make up for some of the loss of habitat.
Locally, she said planting milkweed isn’t necessary, and could actually endanger the population because of a parasite called Ophryocystis elektroscirrha that is found in tropical milkweed and infects monarchs.
“I always like to tell people when they come into the park to do their research,” she said.