Tukuk-OSMigration is the decision to let someone else have the good season: animals chase summer’s long daylight and food abundance across the planet twice a year. The Arctic tern rides the spring from Arctic breeding grounds to the Antarctic and back each year — tens of thousands of kilometres annually, seeing two summers, and living a life that adds up to the equivalent of several round trips to the Moon over its lifetime. The bar-tailed godwit flies nonstop from Alaska to New Zealand — over 11,000 km and about eleven days without landing, food or sleep, shrinking its own organs to travel light, a feat no human aircraft could copy at that efficiency.
The navigation toolkit is genuinely multi-instrument: the sun by day with a body clock to correct for its movement; star patterns learned in youth (classic closed-sky experiments proved birds learn which stars circle the pole); evidence supports a magnetic sense tied to light-sensitive chemistry in the eye; plus landmarks, coastlines and inherited routes. Monarch butterflies solve the hardest version: individuals that have never made the trip migrate from Canada to a handful of Mexican groves their ancestors chose — the map is in the genes, corrected by selection each generation.
Why bother: the payoff is energy math. Temperate summers offer almost endless daytime feeding for chicks; the tropics are stable but crowded and poor per capita. Migration trades enormous risk — exhaustion, storms, predators at stopover wetlands, windows and towers — against the richest feeding grounds on Earth. Populations of migratory species collapse precisely because every stopover matters: losing one wetland drains a continent’s birds.