The Xerces Society New Year’s report shows a greater-than-average western monarch population decline, bringing the population to approximately 116,758 monarchs.
Seasonal mortality driven largely by winter weather and predation has remained between approximately 35-49% during the past six winters. The 2022-2023 estimate shows a 58% decline that exceeds the average but remains largely positive compared to the last two winters.
In the Thanksgiving 2020 measurement, the population dipped to the lowest of all time: 2,000 monarchs.
Abnormal winter weather in California is a large contributor to the population counts this year. Flooding and downed or damaged trees from storms caused a population decline. Paired with inaccessible roads hindering volunteers from observing sites, the condition of the population in some areas remains unknown.
“Small populations are particularly vulnerable to being snuffed out by extreme weather, so we are lucky these storms occurred in a relatively good year,” said Emma Pelton, a conservation biologist at the Xerces Society and western monarch lead.
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General monarch population decline is largely attributed to climate change, habitat loss and pesticide use. The population has declined by more than 80% in central Mexico since the 1980s and by more than 99% in Coastal California since the 1980s. Staggering statistics bring increased attention to conservation efforts and legal protections to safeguard the species.
The Western Monarch Count is collected by community science volunteers and partners at sites along the Pacific coast from Mendocino, California, to Northern Baja, Mexico. Additional locations have been added in recent years in the Saline Valley of Inyo County California and Arizona. This year, 169 sites were collected during both the Thanksgiving and New Year’s collections.
Butterflies were observed along the central coast with 49% reported in San Luis Obispo County, 28% in Santa Barbara County, 11% in Monterey County and 10% in Santa Cruz County.
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