Diario del proyecto Butterflies of California

Two years ago, when volunteers counted only 27,212 monarch butterflies in the Xerces Society’s annual Western Monarch Thanksgiving Count, it meant the butterflies had crossed a threshold identified by scientists as the point past which western migratory monarchs were likely to become extinct.

https://baynature.org/2020/12/04/with-fewer-than-2000-butterflies-counted-western-monarch-takes-an-astonishing-step-closer-to-extinction/