What it is
The monarch (Danaus plexippus) is a milkweed butterfly. The North American migratory subspecies plexippus is the famous multi-generation migrant. IUCN moved that subspecies from Endangered to Vulnerable in assessment 2023-1. The shift was a change in the assessment model, not evidence that the migration had recovered. A U.S. Fish and Wildlife Service listing process is still underway.
Range
The migratory subspecies breeds across much of North America and winters in Mexico and California. Other, mostly non-migratory, populations live on islands and in the American tropics. This card is about the migrant.
What happened
Overwintering clusters in Mexico and California shrank in the late twentieth and early twenty-first centuries as milkweed and winter forest were lost and weather extremes hit the roosts. The 2023 IUCN downlisting did not claim the flyway was healthy. It changed how a small, fluctuating count is scored. USFWS has not finished its own decision.
When / status
Migratory subspecies: IUCN Vulnerable (2023-1), formerly Endangered. USFWS listing still open.
Human role
Habitat loss, pesticides, and a changed climate on a migration that already depended on a few winter groves.
Sources
IUCN Red List (Danaus plexippus plexippus, VU 2023-1; species page); USFWS monarch species page.