The number of western monarch butterflies wintering in California has rebounded to more than 247,000 a year after fewer than 2,000 appeared, but the count remained well below the millions seen in the 1980s, officials said Tuesday. an annual statement.
The Western Monarch Thanksgiving Count has revealed the highest number of butterflies in five years, but it still represents less than 5% of the 1980s population, said Emma Pelton, senior endangered species biologist at the Xerces Society for Invertebrate Conservation.
Pelton said she was pleased with the turnaround, but cautioned it did not indicate a recovery for the species.
“It will take several more years to understand if this is the start of a trend or just a blow,” she told an online press conference.
Western monarchs, the population found west of the Rocky Mountains, winter in thickets along the Pacific Coast from Mendocino County in northern California south to the northern edge of Baja California, as well as a few inland locations. Monarchs east of the Rockies migrate deep into Mexico for the winter.
The counting of Western monarchs is carried out by trained volunteers over several weeks around the Thanksgiving holiday. It dates from 1997 and observed a loss of more than 95% of a population which, according to previous studies, once numbered a few million.
The tally released a year ago was the smallest ever, and the reasons for the turnaround are elusive, according to Pelton. Not only was there the largest one-year increase ever, but the butterflies were found at 283 sites, the most ever.
“The question of the day we get is really, why do we have this hike? And we don’t have one definitive answer for you,” Pelton said.
Factors could include good weather, the amount of milkweed monarchs depend on, and some exchange between western and eastern populations, but monarchs have a complex migratory cycle with multiple generations over a complex landscape, a she declared.
Pelton said she believes the numbers will continue to fluctuate until the underlying causes of the huge declines over the decade are addressed.
“And the root of those is habitat loss, both at overwintering sites in California and elsewhere, and then migratory breeding habitat,” she said.
Among the details of the data, the count showed that the wintering sites tended towards the south.
California’s central coast typically sees the most monarchs, and the San Francisco Bay Area also has significant numbers. In the last count, however, Bay Area sites had few or no monarchs.
Most of the monarchs — more than 95,000 — were found in Santa Barbara County, including a site on private property that had 25,000 butterflies.
Further south, Ventura County had nearly 19,500 butterflies and Los Angeles County more than 4,000 – numbers not seen since the early 2000s.