The curlew sandpiper looks like it borrowed its bill design from a much larger bird. This small wader packs a long-distance migration into a body the size of a sparrow. It breeds in the Arctic and winters in the southern hemisphere, crossing the entire planet twice a year.
Breeding plumage is a rich chestnut red, unmistakable on the mudflats. The head, breast, and belly all turn the same rusty colour. It looks like a bird on fire. Outside the breeding season, the transformation is complete. The bird becomes pale grey above and white below, with a distinct white eyebrow. A different bird entirely.
Feeding happens by probing in soft mud. The curved bill reaches small worms, molluscs, and crustaceans below the surface. The bird sews the mud like a needle, head down and tail up, moving steadily. A curlew sandpiper feeding is focused. It does not look up. It does not stop. Day and night, it works the tidal flats.
The call is a soft, whistled "chirrip," often given in flight. Flocks call constantly as they move across the mudflats. This background chatter rises and falls with the tide. It is the sound of a group that has come a long way together.
In New Zealand, these birds are regular but uncommon visitors. They arrive in spring and leave in autumn. A few thousand birds each year scatter around the coast. They prefer the north: the Firth of Thames, Kaipara Harbour, and Manukau Harbour. A bird that has travelled far to find a quiet mudflat.
The migration route is extraordinary. Curlew sandpipers breed in Siberia and Alaska. They fly south across Asia, stopping over in the Yellow Sea to refuel. Then they continue to Australia and New Zealand. A one-way trip covers 15,000 kilometres. They do it twice a year. No one told them it was too far.
The population is declining. The Yellow Sea mudflats, critical for migration stopovers, have been reclaimed for industry and agriculture. The birds arrive. The mud is gone. They keep trying anyway. Climate change also affects Arctic breeding habitat, while wetland drainage in Australia reduces wintering grounds.
A curved bill distinguishes this species from the similar
red-necked stint. The stint has a straight bill. The curlew sandpiper has a decurved one. It is a small difference. It matters to the birds. It determines what they can eat and where they can survive. Evolution rarely revises the draft.