Floods threaten rare birdlife

The flooding of the Rangitata River and other parts of Canterbury is causing headaches for the Department of Conservation as it wrestles with the damage to native birdlife.

DOC’s Eastern South Island operations director, Nicola Toki, said severe flooding in the upper Rangitata, upper Rakaia, and Hakatere/Ashburton rivers would have significantly impacted the breeding success of threatened native birds such as ngutu pare/wrybill, tarapirohe/ black-fronted tern and tu¯ turiwhatu/dotterel, wiping out the vast majority of nests in the riverbed.

‘‘There were about 4000 blackbilled gulls in the area but they too will have been impacted.

‘‘Adults will have flown to safety to escape the rising flood waters, and some chicks may have survived if they were ready to fledge the nest.

‘‘Due to the flooding, biodiversity rangers won’t be able to complete braided river bird monitoring as the nesting season is nearly over.’’

The Rangitata River, which peaked at over 2300 cumecs on December 7, is now flowing about 230 cumecs, and Toki said extreme weather events such as last week’s heavy rain and flooding appear to be becoming more common.

‘‘When the breeding season of a braided river bird is disrupted they can attempt to re-nest, but if extreme weather events happen later in the breeding season, the birds run out of time to re-nest and successfully fledge chicks.

‘‘In combination with other threats to braided river birds, such as ongoing habitat loss and predation, an increase in damaging extreme weather events is likely to negatively affect the population trajectories of already declining species.’’

On a positive note, Toki said a black-fronted tern colony has already started nesting again near Geraldine.

‘‘They will attempt to breed and raise another round of chicks who will hopefully have more luck at fledging. We will survey the riverbeds this week to see if wrybill and dotterel pairs have begun re-nesting.’’

DOC’s predator control programmes in braided rivers will also be impacted by the recent flooding, Toki said, and rangers will be investigating the riverbed this week to reset the trap line and clean traps buried in silt or other flood debris.

‘‘While the birds are able to adapt, a smaller population will struggle to recover against general habitat loss and predators. It’s important the trap line is reestablished to ensure the birds have the best chance of a successful breeding season, despite the recent flooding,’’ she said.

At DOC’s Twizel office, there were concerns about the black stilt/kaki – one of the world’s rarest braided river birds.

‘‘Recent widespread flooding will have disrupted braided river birds breeding, and impacted on the team’s ability to recover kakı¯/black stilt eggs from the district’s braided river.

‘‘It can take several weeks following a flooding event before kakı¯ return to the riverbeds ... like other braided river birds, kakı¯ are used to braided rivers flooding.

‘‘However, ongoing or reoccurring flood events can impact kakı¯ in the wild by destroying nests and reducing the number of times kakı¯ attempt to breed in a season,’’ Toki said.

‘‘The Kakı¯ Recovery Programme may collect less eggs from wild kakı¯ than in previous years.’’

‘‘Adults will have flown to safety to escape the rising flood waters, and some chicks may have survived . . .’’ Nicola Toki