Conservationists and biodiversity managers have suspected for a while the karoro/southern black-backed gull was behaving as a predator to different native birds.
Now hen counts in Hurunui and Kaikōura present the karoro is a predator to threatened floor nesting birds for a supply of meals, Environment Canterbury senior biodiversity advisor Heath Melville says.
The karoro are “an enormous, lovely hen”, however have been monitored attacking nesting colonies till full failure by destroying eggs and taking young chicks for meals.
They are additionally recognized to attack new child lambs and calves, and different vulnerable livestock.
“We can actually see the black-backed gulls are relentless,” he mentioned.
“We have been performing some controls, however they’re nonetheless returning to those websites to breed.”
Environment Canterbury not too long ago accomplished hen counts on the Waiau Uwha and Hurunui rivers within the Hurunui district, and the Clarence Waiau Toa and Charwell rivers and alongside the Kaikōura shoreline.
This was coordinated with hen counts performed by the Department of Conservation (DOC) and different councils from throughout the South Island, to be taught extra in regards to the karora and threatened native species nesting in colonies, primarily in braided riverbeds.
The Waiau Uwha braided river hen surveys have been accomplished eight instances since 2008.
The latest rely produced the same end result to earlier years, with native hen numbers trending down, whereas karoro and unique species had been trending upwards.
In all, 45 hen species had been recognized within the Waiau Uwha survey, together with native wrybill, white and black-fronted tern, and banded dotterel.
The birds had been additionally threatened by animals and people, in addition to local weather change, habitat loss and weed infestations in riverbeds, leaving birds to nest in areas vulnerable to excessive river flows.
The Kaikōura websites had been added to the hen survey final yr, after the Kaikōura Zone Committee agreed to fund management work of the karoro, supplied employees interact with mana whenua.
A Te Rūnanga o Kaikōura spokesperson mentioned karoro eggs had been historically collected as mahinga kai, however there was no must handle the inhabitants previous to colonisation.
The birds have expanded into areas the place land use offers elevated meals sources, notably braided rivers surrounded by farmland, and close to landfills or refuse centres.
The Rūnanga was supportive of taking management measures, supplied selections had been primarily based on good knowledge, the spokesperson mentioned.
“The largest concern for Ngāti Kurī is having a transparent understanding of what’s going on.
“If the karoro is predating different native species in decline then we have to handle it.
“But what if we’ve got a cull after which we’ve got a illness undergo the inhabitants, then we’ve got contributed to wiping them out.”
Kaikōura had the biggest crimson billed gull colonies in New Zealand, whereas black-billed gulls, shags, terns, oystercatchers and dotterels had been additionally surveyed breeding within the space.
Bird counts had been new in Kaikōura, except for a 52-year research by native resident James Mills of crimson billed gulls on the Kaikōura Peninsula.
This research has proven the crimson billed gull was in regular decline, regardless of predator management measures carried out by DOC.
The endangered crimson billed gulls had been usually thought-about an issue to out of doors diners, which has been exacerbated by declining meals sources at sea, Melville mentioned.
“They get in individuals’s faces, take their eggs benny or their fish ‘n chips as a result of in lots of cases they’re actually ravenous, whereas the karoro do not are likely to get so shut, and are higher tailored at foraging a extra various eating regimen in extremely modified environments.”
Melville mentioned council employees will proceed partaking with the Rūnanga, DOC, LINZ, Clarence River Rafting (which have been helping in surveying nesting websites), researchers, and different councils and biodiversity managers to observe the inhabitants and develop methods to handle hen populations.
The karoro are proving to be a pest in different components of the South Island.
In Geraldine, DOC biodiversity senior ranger Ian Fraser mentioned his workplace has been working to manage karoro on native rivers over the past eight years.
“We have been speaking with [Te Rūnanga o] Arowhenua they usually have been working with Environment Canterbury, figuring out the potential of karoro eggs as mahinga kai and the Rūnanga has carried out some management work as effectively.”
Fraser mentioned land use adjustments over the past 1000 years had favoured karoro over different native birds.
The clearing of forests have created open plains, whereas immediately’s farms supplied loads of meals sources — “to not point out our waste amenities”.
“We have altered the stability, so we have to attempt to meddle in good methods.”
By David Hill, Local Democracy Reporter
Local Democracy Reporting is native physique journalism co-funded by RNZ and NZ On Air
