The number of western monarch butterflies overwintering in California dropped by 30% last year, likely due to how wet it was, researchers said Tuesday.

Volunteers who visited sites in California and Arizona around Thanksgiving tallied more than 230,000 butterflies, compared to 330,000 in 2022, according to the Xerces Society, an environmental nonprofit that focuses on the conservation of invertebrates.

The population of orange and black insects has rebounded in recent years to the hundreds of thousands after it plummeted in 2020 to just 2,000 butterflies, which was a record low. But even though the butterfly bounced back, its numbers are still well below what they were in the 1980s, when monarchs numbered in the millions.