What is the main threat to migratory birds worldwide?

The story behind the answer

Habitat loss is the top global threat because migrants rely on three kinds of places—breeding grounds, stopover “gas stations,” and wintering sites. Deforestation, wetland drainage, intensive agriculture, and coastal development remove or fragment these habitats. If any link in that chain disappears, the journey fails, even if birds aren’t hunted and the climate is stable.

Think of a flyway as a highway with only a few fuel stops: lose one, and traffic stalls. Shorebirds in the East Asian–Australasian Flyway, for example, declined where Yellow Sea mudflats were reclaimed. Protecting and restoring wetlands, grasslands, and coasts along flyways is the most effective fix. Memory tip: migrants need to nest, rest, and refuel—habitat provides all three.