Activists are angered at the eggs of endangered tarapiroe, black-fronted terns being broken by Crate Day punters in Canterbury.

The Ashley Rakahuri Rivercare Group (ARRG) said approximately 150 4WD vehicles zoomed up and down the Ashley Rakahuri River, which threw stones, breaking the eggs of nesting birds.

It said Police and the Department of Conservation were at the river, where signage warned of restricted areas around three major colonies of the Bird of the Century contestants which, like other river birds, are in the midst of nesting and hatching chicks.

ARRG spokesperson Grant Davey said some of the participants expressed concern for the birds, but little or none was shown.

"They drove into nesting areas which were clearly signposted, and in one case past protestors. Black-fronted terns were wheeling around the vehicles and chicks were scurrying to get out of the way," he said.

Davey said the drivers "knew they were doing something wrong" because a lot of the vehicles were without number plates removed or they were taped over.

He said he found four of the nests with broken eggs or eggs thrown out of the nest, or a chick away from the nest.

The Ashley Rakahuri Rivercare Group said 4WD vehicles zoomed up and down the Ashley Rakahuri River, which threw stones, breaking the eggs of endangered tarapiroe, black-fronted terns. Photo: Supplied / Grant Davey

A driver stopped and Davey said to him 'do you know you people have been running over eggs?'.

"And he said, 'do you want to photograph?' And I said 'yes, please' and he stepped out of the car and he brown eyed me. I think that sums it up. Absolute disrespect."

Police said they were in attendance at Ashley River Gorge on Saturday and there were no incidents of note related to Crate Day there or at other locations.

The black-fronted tern are very threatened. The ARRG said in the last few years approximately one fledgling (a chick that gets to the flying stage) has been produced for every ten nests on the Ashley River.

"This year the outlook is much better," Davey said.

"But it is not helped by the actions of irresponsible people. Ashley Rakahuri Rivercare Group is angry that these rallies go ahead despite the fact it is peak breeding season on braided rivers".

Main Image: A protester from the Ashley Rakahuri Rivercare Group in Canterbury stands in front of 4WDs racing down the riverbed where endangered tarapiroe, black-fronted terns are nesting. Photo: Supplied / Grant Davey