A distinctive, globally-endangered bird was spotted in the Whanganui River estuary over New Year.

Birds New Zealand Whanganui regional representative Peter Frost said local photographer and author Paul Gibson saw the eastern curlew on the estuary on New Year's Day.

"The bird was present the following day but appears now to have moved on elsewhere, which is a pity as it deserved to be seen by more people," Frost said.

"Standing a bit taller than an average ruler, this species is the largest shorebird in the world. The astounding thing about it, however, is its enormous curved bill, which at 17 centimetres is around half that of the bird's height.

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"This allows it to probe deeply into the mud to catch worms, or to reach out and quickly pick up fleeing crabs, as the bird on the Whanganui estuary was doing.

"As far as we know, this is the first time an eastern curlew has been recorded on the Whanganui estuary, perhaps a reflection of the paucity of observers rather than it never having visited previously. Nonetheless, it was a notable visit by a striking and increasingly rare species that, once seen, isn't easily forgotten."

The eastern curlew catching and eating a crab on the Whanganui estuary.
The eastern curlew catching and eating a crab on the Whanganui estuary.

Eastern curlew breed in mainly in wet moorland and boggy marshes from eastern Mongolia and northeastern China through to eastern Siberia and the Kamchatka Peninsula in Russia.

The species migrates down through the Yellow Sea and coastal Southeast Asia to spend the southern summer in estuaries and coastal marshes of Australia, mostly in the north, with a few spread through Indonesia, Papua New Guinea and New Zealand.

The declining global population of the species is currently assessed at around 32,000.

Citizen scientists and conservationists in Australia and New Zealand have been monitoring shorebird populations for many years.

Their data suggest that the species is currently declining at about 5.8 per cent per year, Frost said. If sustained, it would mean the population would halve in around 12 years. Because of this, the species is classed internationally as endangered and critically endangered in Australia.

In New Zealand, the eastern curlew is considered as a vagrant (meaning it strays far outside its expected breeding, wintering or migrating range), with the qualification that it is threatened overseas.

Counts made each summer by members of the NZ Wader Study Group, an affiliate of Birds New Zealand, showed a marked decline in the numbers of curlew, Frost said. In the mid-1980s, an average of 42 birds were counted annually at New Zealand's main estuaries and harbours. However, in the past few years this has decreased to around seven birds per year.

"Although there is some disturbance of birds on their non-breeding grounds, most of the decline is attributed to loss of habitat in the Yellow Sea," Frost said.

"This is a crucial stop-over area where migrating birds rest and rebuild their fat reserves on the 10,000–13,000km journey between their northern breeding grounds and their southern wintering areas. An estimated 65 percent of intertidal mudflats has been lost in the Yellow Sea over the past 50 years, mainly to land reclamation, harbour development and the expansion of aquaculture."

Frost said other migratory shorebirds had also been affected by the loss of habitat. They include prominent migrants to New Zealand such as bar-tailed godwit (kūaka), small numbers of which spend the summer on the Whanganui estuary, and the lesser or red knot (huahou), now seldom seen here.

Anyone with an interest in birds, or who would like to become involved in studies to help conserve them, is invited to join Birds New Zealand. For more information, contact Peter Frost by emailing birds.wanganui@osnz.org.nz