Annual counts of Western monarch butterflies in California and northern Baja California by volunteers during Thanksgiving 2020 and New Year's 2021 found that a population decline has accelerated in recent years. The Thanksgiving count—1,914 monarchs—reflected a 99.9% decrease from the 1980s. Counts at specific sites where thousands of monarchs spent the winters past in found only a few hundred, or, in the case of some sites like Pacific Grove, California, none.
The Xerces Society for Invertebrate Conservation, a nonprofit that coordinates the counts, cites habitat loss and degradation, warming and other climate changes, pesticides, and loss of milkweed and other flowering plants as compounding factors in the Western monarch's endangerment.
The U.S. Fish and Wildlife Service and a California state court recently denied monarchs protection under national and state endangered species laws.