Endangered birds benefit from flood

Stripped clean . . ..Looking west along the Ashley/Rakahuri River which is now clear of weeds and vegetation following the recent flood. PHOTO: SUPPLIED


The populations of endangered braided river birds could increase thanks to the recent flood in the Ashley/Rakahuri River.

The force of the water has stripped all the weeds from the river bed, leaving gravel islands, where birds like to nest, free of cover for predators.

Birds such as the wrybill, black-fronted tern, and banded dotterel, require bare gravel to nest on.

The Ashley/Rakahuri Rivercare Group (ARRG) has found a correlation between bird numbers and the amount of bare gravel.

After several years of no large floods, the beds of smaller foot-hills fed rivers such as the Ashley, Opihi,and Orari have been overwhelmed by weeds.

Group member Grant Davey says where there were deep braid channels there is now high islands, and vice versa.

All signs of recent river extraction has also been erased, and the fairway widened, in some cases by 50 metres or more, he says.

river seems to have been lifted up and moved by flood waters resulting in a complete change in its morphology.”

Mr Davey says the islands are where the birds prefer to nest, and are safest from predators. Norway rats and stoats swim to the islands, but other predators such as hedgehogs and cats are much less likely to do so.

David Owen, Environment Canterbury’s principal biodiversity adviser, braided rivers, says, the floods have presented the opportunity to try to keep the river relatively weed-free.

“Left unchecked, the weeds will inevitably return.

ARRG, with regional council funding, had been about to mechanically clear 64 hectares of weedy islands. ARRG is now working on a strategy to stop the weeds growing again.

The floods did hit the group hard, however. It lost 100 predator traps, out of 400, during the floods. They were set along the berm of the river and around the estuary, mostly tied to trees or in scrub, and were swept away in the raging torrent.

A Givealittle page has been set up to raise funds to buy more traps before the breeding season starts in September. To date over $1800 has been raised. Traps cost about $50 to $70 each.

Over the past 16 years, ARRG has protected an 18km stretch of the river with traps to eliminate predators, allowing the braided river birds to breed and raise chicks safely.

Their work has helped the birds to hold their own on the Ashley and even increase slightly, compared with gradual to catastrophic decline (depending on the species) on unprotected rivers. To help go to: givealittle.co.nz/cause/flood-destroys-predator-traps-help-us-buy-more.