A female wrybill bird nesting on the Ashley River, one of just eight pairs of the unique bird found there.

Conservationists are urging people to take greater care at the Ashley River after the nest of a rare bird was destroyed by a vehicle.

A dead wrybill chick and broken egg were found on the gravel bed of the North Canterbury river last week, apparently crushed by a four-wheel-drive.

Wrybills are unique to New Zealand and are the only birds in the world with a beak that curves to the side, used for prising insects from underneath stones.

GRANT DAVEY Conservationists are urging care after a wrybill nest was destroyed, apparently by a four-wheel drive vehicle

But numbers are in decline nationwide and the bird is regarded as nationally vulnerable. Just nine birds have been spotted on the river this year, the lowest number in 10 years, according to the Ashley-Rakahuri Rivercare Group.

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It comes after researchers expressed grave fears for another endangered species, the banded dotterel, after poor numbers were recently found at Kaikōura.

GRANT DAVEY The chicks were just days from leaving their nest when they were killed, with one already hatched.

With the wrybill breeding season under way until the end of January, the Ashley conservationists are calling on people not to drive on riverbeds and to be aware of nests, as all braided river birds nest on the ground.

Group chairman Nick Ledgard said access ways to the river had been temporarily blocked off to help protect the birds, with signs put up warning people of the presence of nests.

"This time of year places increased pressure on the river environment from people going there for recreation.

GRANT DAVEY A conservation group is now asking people to take greater care, urging them not to drive on the Ashley's riverbeds.

"In this particular case we are not sure how a vehicle got onto the river. It is extremely rare for a vehicle to run over a nest, as they only occupy a few small square centimetres.

"The birds were within a couple of days of evacuating the nest – one had hatched and the other was in the process of hatching."

Ledgard said the damage – discovered on Friday – was a major setback for the population of wrybills on the river, as pairs produce only one or two eggs a season.

Owners of 4WD vehicles are being urged to take care around nesting river birds.

The birds whose eggs were destroyed lost their first nest in floods in September and had to spend a month building a new one, about 5 kilometres upriver from where the Ashley crosses State Highway 1.

"These birds are very special, they are unique, with people coming from all over the world to see them. We just want to keep them for future generations," Ledgard said.

"During the breeding season when they are down here and vulnerable to disturbance on the riverbed we would urge people to keep out of the river and give them their space.

"If you are going to the river, please obey signs and don't use vehicles. Just be aware of the birds at the river."

Wrybills breed only in the braided rivers of Canterbury, though there are also a few pairs in inland Otago, and the riverbed habitat where the bird breeds has shrunk dramatically over the last 100 years.

They always return to breed where they were hatched – meaning once they are lost from a river, they are gone forever.