Wood duck hen, United States

Nest stop: Mexico!. World Migratory Bird Day

Birds don't bother with passports, visas or luggage—they just spread their wings and go. Twice a year, billions of migratory birds crisscross the globe, flying thousands of miles between breeding and wintering grounds. That epic commute is exactly what World Migratory Bird Day highlights. From the Arctic tern, which logs about 44,000 miles a year, to the tiny ruby-throated hummingbird crossing the Gulf of Mexico in a single flight, these seasonal fliers show what endurance really looks like. Observed on the second Saturday in May and October, the day also draws attention to the challenges migratory birds face: habitat loss, climate change and light pollution can all disrupt their routes.

Among the travellers worth spotlighting is the wood duck, pictured here. This North American species has made quite a comeback after once facing steep population declines due to hunting and habitat loss. Thanks to conservation efforts and nest box programs, they are now a regular sight in wooded swamps, marshes and lakes. While some wood ducks stay put year-round in the southern United States, northern hens migrate south when the chill sets in, heading for milder regions stretching from the southern states to Mexico.