Monarch butterfly migration depends on a continuous chain of milkweed and nectar plant habitat across North America that has been severely fragmented by agriculture and development.
The welfare of individual migrating monarchs depends directly on habitat quality at each stopover. Monarchs that cannot find adequate nectar sources experience energy depletion that reduces survival probability and reproductive success. While insect welfare science is developing, the scale of monarch population decline - from billions to hundreds of millions - represents a potential welfare concern of enormous magnitude alongside its ecological significance.