India, July 23 -- More than half of Earth's 3,380 migratory bird species are in decline as habitat loss, invasive species, hunting, pesticides, building collisions and fishing nets erode the vast networks they rely on.

Scientists say new tracking tools and a full annual-cycle approach, backed by international cooperation and proactive policies, can still reverse these losses if governments and communities act quickly.

Every year, billions of migratory birds connect the world's continents, oceans and ecosystems as they undertake epic journeys between their foraging habitats and their breeding grounds.

A bobolink (Dolichonyx oryzivorus) leaves its breeding grasslands of North America for the Pampas of South America. A Newell's shearwater...