Date:  21 December 2020

The endangered tōrea/Chatham Island oystercatcher is a little smaller than the variable oystercatcher found around the coast of mainland New Zealand, but larger than the similar-looking South Island pied oystercatcher. Found only on islands in the Chathams, its population of 350 and limited access to suitable, safe habitat mean the species is at high risk of extinction.

A total of 13 chicks have hatched so far this year out of 24 nest sites, with 20 more eggs still in nests currently. All chicks in a season will normally hatch by the end of January, with the last chicks fledging in March.

However, DOC Technical Advisor Dave Houston says that in 2018 up to half the eggs from nests were vanishing.

Last year, efforts to better understand why the eggs were disappearing zoomed in on two beaches. Cameras were installed overlooking oystercatcher nests, which are simple scrapes made on the ground, often in the sand.

“The cameras let us see all interactions going on at the nests. It confirmed a high level of predation on eggs and chicks. We saw that feral cats were taking eggs, sometimes making repeat visits to see if more eggs were being laid,” Dave Houston says.

“We also saw a harrier drop down to pick up an egg and carry it away, returning over a period of an hour or two to take the rest. Weka, which are an introduced species to the Chathams, were also approaching nests.”

In response to this information, the trapping line in the area is now checked almost daily by a local DOC ranger during the breeding season. Harrier predation is being investigated further.

“We need to understand the harrier issue a bit more. It may just be individual harriers that have picked up a habit. The cameras will help us continue to learn.”

Footage also highlighted that nests on narrow beaches can be destroyed by weather.

“Introduced marram grass has changed the dune profile, making it steeper than dunes with a native grass like pingao. Oystercatchers end up nesting closer to the tideline to find a flat sandy area, and we’ve seen how easily nests can be washed away in a storm.

“We put some tyres out around nests last year and the birds have returned to the same location this year, so they obviously see this as improving the prospects of their chicks.”

DOC Rēkohu/Wharekauri/Chatham Ranger Nic Tuanui has been leading the work on the ground and says it is exciting to see eggs hatching this year.

“We’ve put in some hard yards to help protect these miheke/taonga species and we always feel a real sense of achievement when they do hatch. However, we’re very conscious of the challenges these chicks face to get to adulthood.

“These birds are unique to the Chathams and we’re lucky they’re still found on a few beaches around the island. Locals can help protect them by being really careful with vehicles, dogs, or livestock that might disturb nesting birds on beaches. Remember to walk or drive below the high tide line to avoid disturbing shorebird nests, control feral cats and have pet cats spayed.” 

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