LOS ANGELES — The number of Western monarch butterflies overwintering in California rebounded to more than 247,000 a year after fewer than 2,000 appeared, but the tally remained far below the millions that were seen in the 1980s, leaders of an annual count said Tuesday.
The Western Monarch Thanksgiving Count revealed the highest number of butterflies in five years but it is still less than 5 percent of the 1980s population, said Emma Pelton, senior endangered species biologist with the Xerces Society for Invertebrate Conservation.
Pelton said she was ecstatic about the turnabout but cautioned that it did not indicate a recovery of the species.
“It will take multiple more years to understand if this is the beginning of a trend or just a blip,” she said in an online news conference.
Western monarchs, the population found west of the Rockies, overwinter in groves along the Pacific Coast from Northern California’s Mendocino County south to the northern edge of Baja California, as well as in a few inland locations. Monarchs east of the Rockies migrate deep into Mexico for winter.
The Western monarch count is conducted by trained volunteers over several weeks around the Thanksgiving holiday.
The count released a year ago was the smallest ever seen, and the reasons for the turnabout are elusive, according to Pelton. Not only was there the largest one-year increase ever seen, but the butterflies were found at 283 sites, the most ever.
“The question of the day that we’re getting is really, why are we having this uptick? And we don’t have a single definitive answer for you,” Pelton said.
Factors could include good weather, the amount of milkweed the monarchs rely on and some interchange between the Western and Eastern populations, but the monarchs have a complex migratory cycle with multiple generations over a complex landscape, she said.
