Monarch butterflies undertake one of the most extraordinary animal migrations on Earth, traveling thousands of miles between summer breeding grounds and winter sanctuaries, but face population collapse from multiple threats.
Monarch welfare at the individual level involves the extraordinary physiological demands of multigenerational migration. The migratory generation that travels thousands of miles to overwintering sites does so in a state of reproductive diapause, channeling energy into fat accumulation for the journey. Individuals that encounter storms, pesticides, or habitat gaps during migration may fail to complete the journey. At overwintering sites, mass mortality events from extreme cold or disease can kill millions simultaneously. The scale of the historical decline — from billions to hundreds of millions — represents not just a conservation crisis but a welfare crisis for the billions of individual insects whose welfare trajectories were curtailed.