"The Arctic Tern is not the only bird that spends its breeding season in the Arctic. Billions of birds belonging to nearly 200 speciesfrom small sparrows such as the Smith's Longspur to large waterfowl such as the Greater White-fronted Goosemake their way to the far north every spring to reproduce and then make the return flight south for the winter."
"Migration is costly. Even under ideal conditions, such an epic journey requires huge amounts of energy and exposes the travelers to dangerous weather. The mortality risk is high. But undertaking these trips allows the birds to take advantage of the seasonal conditions in these environments. The endless summer sun supports lush plant growth, flourishing insect swarms, and plentiful fish populations nourished by zooplankton blooms. With 24 hours of light a day, the birds can more easily catch food such as slippery fish and tiny insects."
Golden autumn sunlight glints through sedges and shrubs of the tundra in northern Alaska as winter approaches and snow and ice soon will bury the region. For months the chatter of Arctic Tern colonies accompanies the summer breeding season, then daylight wanes and individuals fall silent in a behavior known as dread before the colony launches. Arctic Terns undertake roughly 25,000-mile migrations to Antarctica, the longest known animal migration. Billions of birds from nearly 200 species travel to Arctic breeding grounds each spring and later make perilous, energy-intensive return flights south for the winter. Migration exposes birds to dangerous weather and high mortality risk but permits exploitation of abundant summer food resources and continuous daylight that eases foraging and reduces nest predation.
Read at www.scientificamerican.com
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