It is one of Australia's rarest birds, but conservationists say habitat crucial to the breeding and survival of the regent honeyeater is currently zoned for industrial development and urgently needs protecting.

Key points: Only 350–400 mature regent honeyeaters remain in the wild

Only 350–400 mature regent honeyeaters remain in the wild Nesting birds and chicks were observed in a Hunter Valley area zoned for industrial development

Nesting birds and chicks were observed in a Hunter Valley area zoned for industrial development Wildlife groups are calling on the Federal and NSW State Governments to intervene

There are only about 350 to 400 mature regent honeyeaters left in the wild, largely due to urban development and the loss of woodland habitat, and the critically endangered species is seen as being on the brink of extinction.

It is no longer found in South Australia and western Victoria, but is distributed across south-east Queensland, New South Wales, and eastern Victoria.

A pair of regent honeyeaters. ( Supplied: Dean Ingwersen )

Birdlife Australia's NSW woodland bird program manager, Mick Roderick, said during the last breeding season, field studies done in conjunction with the Australian National University, covering hundreds of locations across the species' breeding range, only found evidence of regent honeyeaters breeding in one NSW site.

Nesting birds and chicks were observed within the Tomalpin Woodlands, which are located within the Hunter Economic Zone (HEZ), a parcel of land in the NSW Hunter Valley, currently zoned for industrial development.

A regent honeyeater feeds its fledgling in woodland within the Hunter Economic Zone during the last breeding season. ( Supplied: Mick Roderick )

Mr Roderick said the importance of the site could not be overstated and the organisation was calling on the NSW Government and the Federal Government to step in to ensure the area was protected.

"The Tomalpin Woodlands are one of the most important patches of woodland habitat left in south-eastern temperate Australia; it was the only place where regent honeyeaters bred in the season just gone," he said.

"If that doesn't make the site important, then I honestly don't know what would. It's one of the single most important sites for that species.

"The biggest threat to regent honeyeaters is their critically low population. This is a species that is literally on the brink of extinction and we need to protect breeding sites for this species."

Hunter coal plant proposal raises alarm bells

A regent honeyeater released as part of a rehabilitation program spotted in a grevillea bush. ( Supplied: Dean Ingwersen )

Mr Roderick said concern about habitat loss in the HEZ had elevated recently with the site flagged for a coal-fired power plant proposal.

"Recently there has been a proposal to put a couple of new coal-fired power stations there, so Birdlife Australia is calling for the immediate protection of the site, because it is vitally important to a number of threatened species," he said.

"We are almost relying on the Federal Government to step in and use the national threatened species legislation to protect this site.

"How that happens, and whether it's added to the national park estate, we need to work out, but it certainly can't sit there as land zoned for industrial development and things like new-coal fired power plants to be thought of as potential land uses for this area, it's a crazy idea."

Birdlife Australia CEO Paul Sullivan said the organisation had started a petition asking for the HEZ to be rezoned.

"Allowing this critical piece of habitat to be zoned for industrial development is akin to endorsing the extinction of the critically endangered regent honeyeater," he said.

A wild female regent honeyeater feeds her chick. ( Supplied: Glen Johnson )

"Regent honeyeaters are one of Australia's most threatened species.

"Their population has declined by over 80 per cent in the last 30 years and without urgent government action, this bird will become extinct within the next 20 years."

Habitat also crucial to critically endangered swift parrot and other species

The Swift Parrot is listed as critically endangered and is often sighted in the Hunter Valley. ( Supplied: Liam Murphy )

Mr Roderick said apart from the regent honeyeater, the Tomalpin Woodlands were also crucial to many other species.

"It's not just about regent honeyeaters, another critically endangered bird, the swift parrot, which breeds in Tasmania, has been seen in the Hunter Economic Zone just about every year since 2002, making it one of that species' most important mainland sites," he said.

"So this is a critically important site for two nationally critically endangered species.

"The area is also home to an unprecedented number of threatened species — the total count of threatened flora and fauna, and threatened ecological communities, is up into the mid-40s.

Swift parrots migrate from Tasmania to the mainland each year and rely on flowering trees, including Forest Red Gums. ( Supplied: Bronwyn Ellis )

"It's a remarkable site, a biodiversity hotspot, that's how we refer to it.

"It has an incredible diversity of eucalypts, about 30 species, including two species new to science that haven't been described yet, so it literally is an amazing patch of bush, which really should be national park."

A fledging regent honeyeater in the Hunter Valley. ( Supplied: Mick Roderick )

The ABC has contacted Federal Environment Minister Melissa Price for comment.