Emlynn Bethina

Monarch Butterfly Migration California 2024 Dates. Reports along the california coast are decreasing as monarchs begin their annual spring migration. Beginning in october, populations of monarchs that live west of the rocky mountains start arriving in california to breed and wait out the winter, and then head back inland in the early spring.

The 233,394 monarch butterflies observed in the 2023 count — which ran from november 11 to december 3 — represent butterflies west of the rocky mountains. Beginning in october, populations of monarchs that live west of the rocky mountains start arriving in california to breed and wait out the winter, and then head back inland in the early spring.