Using measurements from ESA's Earth Explorer Swarm mission, scientists have developed a new tool that links the strength and direction of the magnetic field to the flight paths of migrating birds.

Migrating animals have for a long time been tracked by recapturing tagged individuals. More recently, radio-telemetry, which requires an observer to physically follow the tagged animal, has been used.

Cities like New York are obviously not known for their wildlife. You won’t find wolves or jaguars or other charismatic megafauna strolling the streets or hunting in big city parks. But if you know ...