How do migrating birds know exactly when, and where, to go?

by David Catchpoole

Imagine if, when you were very young and were utterly dependent on your parents for protection and food, they had abandoned you suddenly to go overseas? Without any written instructions as to where they’d gone, would you have been able to follow their path once you’d grown strong enough to try?

Sound impossible? Not for the Bristle-thighed Curlew! When the chicks are just five weeks old, the parents depart, heading for the tropics.1 Left behind in the marshes of the Alaska Peninsula, the chicks gorge themselves on berries and insects. As their little bodies become stronger, accumulating the all-important reserves of fat—fuel for the long journey ahead—they frequently take to the air for short flights, as if in premigratory practice.

Then one day, the birds launch themselves into the sky, and, finding the right winds, head off on the long nonstop flight south to their ancestral wintering grounds. As with most migratory bird species, the curlew novices are on their own, without a guide. Their parents and experienced elders have departed weeks earlier. Yet most2 of these first-year curlew pilots will unerringly navigate the vast Pacific Ocean, descending with pinpoint accuracy onto the mudflats and sandy beaches of islands in Fiji, Tonga and French Polynesia—their new home.3

The chicks of another famous migratory species, the Short-tailed Shearwater (‘muttonbird’),4,5 must also navigate on their first flight without the assistance of experienced guides.6 Breeding in burrows on islands off southeastern Australia, the parents suddenly desert the chicks at the end of summer. The parents head north, riding the prevailing winds that will take them around the western Pacific Ocean past Japan and Siberia, east around Alaska, and south down the western United States, before they return across the Pacific for the next start of the Australian summer breeding season….

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