Ō Tū Wharekai wetlands – an important high country refuge for the nationally endangered Australasian Bittern.

Ō Tū Wharekai wetlands – an important high country refuge for the nationally endangered Australasian Bittern.

Peter Langlands

Wilderness

19 July 2010

The Ō Tū Wharekai wetlands, otherwise known as the Ashburton lakes, are one of three large scale wetland restoration projects undertaken by DOC in New Zealand (the other two being Awarua Bay and Whangamarino swamp.) Yet Ō Tū Wharekai is the only high country site. The wetlands in a large basin area between the Rangitata and Rakaia River catchments are one of the best examples of high country wetlands in the South Island, with a good representation of tussock, sedge and rare wetland plant communities. Amongst these diverse wetland communities, adjoining scenic high country lakes, the wetlands form the last stronghold (outside of the Mackenzie basin) for the Australasian bittern or Matuku in the central South Island high country. In the last six months birds have been sighted at Lakes Heron and Emma, in addition to the bird’s distinctive booming call, heard at the Maori Lakes. These lakes form an important network upon which this high country bittern population depends. The most recent sighting in July 2010 confirms that bitterns stay in these high country lakes throughout the year – even when most wetlands are frozen over in the region! Small inflowing creeks are likely to provide a foraging area for the birds.

The bittern is one of our rarer birds and is listed in the second highest threat ranking as being a nationally endangered bird. Bitterns once thrived in New Zealand but their numbers have rapidly declined since the 1950’s as the vast majority of New Zealand’s wetlands were drained. It is estimated that now only 750 birds remain in New Zealand (with most birds in the Northland and Waikato regions- where large wilderness wetlands remain). Now bitterns are scattered in very low numbers throughout the South Island. With only around 50 birds remaining in Canterbury. The Ashburton Lakes form one of three known important populations of bittern within the Canterbury Region, the other two being at Te Waihora (Lake Ellesmere) and in wetlands scattered throughout the Mackenzie Country. In addition a few birds are also found along smaller wetlands along Canterbury’s coast from Wainono Lagoon in the south to the Amberley wetlands in the North.

The bitterns are very much a bird of our wilderness wetlands preferring undisturbed and remote wetlands. They are large birds with a striking pointed bill, used for feeding on a wide range of prey items from small eels, fish to frogs and small birds. Yet most strikingly bitterns have brown and buff stripes on their breast to camouflage in amongst reed beds, and in particular- raupō (or bullrush) – a much favoured habitat of bitterns in the South Island. Bitterns are in the heron family and are the only group of birds having evolved to merge in with reed beds. From August until March bitterns have a distinctive booming call, similar to that of the endangered kakapo, which resonates eerily across our wilderness wetlands. Like the kakapo the bittern is sadly an endangered species and habitat enhancement and creation combined with predator trapping may be required to save this enigmatic bird.

Photograph caption- Bittern, or Matuku ( as they are known as in Maori culture) photographed at Ō Tū Wharekai wetlands in winter 2010 - in the Ashburton Lakes- one of few high country strongholds left for these birds (and now protected under the Arawai Käkäriki Wetland Restoration Program-DOC).

Key words –

Arawai Käkäriki Wetland Restoration Programme.

Ō Tū Wharekai (Ashburton lakes/Upper Rangitata river, Canterbury).

Australasian bittern - Botaurus poiciloptilus – Matuku

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