Weeding islands for river bird survival

19 September, 2022

River islands covered in weed on the Hurunui River come at the cost of river bird life.

Earlier this month, a group effort on the ground resulted in a weed-free NIWA Island, which lies just downstream from SH7 bridge.

The approximate 25 nesting river birds, including black-fronted terns, wrybill, black-billed gulls and banded dotterels, require a weed-free haven because they will only nest in places that are completely free of vegetation taller than themselves.

Hurunui District Council’s Water and Land Coordinator Rima Herber said this was the natural state of the braided rivers before introduced plants began to occupy these ecosystems.

She was one of the group members weeding the Island’s tree lupin, (not to be confused with the coloured Russel’s lupin found in the Tekapo Basin), and said maintaining a safe nesting habitat is essential for the survival and existence of these river birds.

“These birds use river islands such as NIWA Island to keep safe from predation by cats, rats, hedgehogs, stoats, ferrets and weasels.”

This ongoing project is managed by Environment Canterbury (Ecan), and partly funded through the Immediate Steps funding, previously administrated through the Hurunui/Waiua Uwha Zone Committee.

“The birds that nest on these braided rivers will not nest anywhere else,” said Herber.

ECan recently had a substantial channel dug between the island and the riverbank, as the original channel disappeared during the recent winter high-water events.

In addition to the weeding, an intensive trapping project on the island to catch any mammalian predators that find their way onto the island is also on the plan.

“This was a lesson learnt from a previous year when rats swam across to the island with the result that very few birds fledged that year.”

The tree lupin: is an invasive introduced plant, well adapted to the dry low-fertility environments of the riverbeds. It grows fast, is very deep rooting, has tough long-lived seeds and will grow to over two meters in a couple of seasons.

PHOTO:

• Environment Canterbury Biodiversity and River staff Zipporah Pleog (L) and James Sharp, (R) with Hurunui District Council’s Water and Land Coordinator Rima Herber, (Centre).