Already hurt by habitat loss and climate change, the number of butterflies migrating through California has fallen to a nearly 40-year low as populations encountered a cold, wet spring, researchers said.

The change was particularly dramatic for the red and black painted ladies, which last year enjoyed a possibly record-breaking migration after feeding on the vegetation nurtured by abundant rain in Southern California’s deserts.

Last spring, millions of them migrated through the state and into Oregon, passing Shapiro’s Sacramento site at a rate of four per second. This spring, he had reports of four painted ladies a month in the same area.

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