Sarah Lloyd AO, with keen sight and a trained ear, quickly jotted down the birds she could find. The field naturalist's list grew longer and longer - more than 20 species after an initial inspection.

As we headed deeper into the block, the song of the striated pardalote was clearest of all.

"When you hear so many pardalotes, you know there's a lot of trees with hollows," Ms Lloyd said.

"You can see them nesting there. They'll be nesting all through here. Sometimes they just nest in splits in the trunks, too.

"In that flora report relied upon by the government, they said there were few if any hollow bearing trees in this area - in the prison footprint. But from where we've just walked to here, there were a dozen at least. You can see them!"

The call of a yellow wattlebird was clear and distinct. Brown thornbills and starlings quickly came and went through the canopy, as they do. A black-faced cuckoo shrike perched overhead for a while.

Walking just 100 metres from Birralee Road and into the woodland block, the sound of birdsong even drowned out the road.

Listen: Birdsong on a spring morning in the woodland proposed to be cleared for a prison:

We stopped and watched a scarlet robin busily building its nest in a silver banksia.

It was a bittersweet moment though, knowing that - on Monday - a drilling rig and other heavy equipment will arrive on the site and eight core investigation holes will be drilled through the dolarite rock. The Northern Regional Prison project team informed 10 nearby property owners on Tuesday.

It's the first in a long line of proposed disturbances that will change the face of the woodland block forever culminating in, the government hopes, a 270-bed maximum security prison covering 16 hectares.

The scarlet robin - and all of the other birds building their nests overhead and all around - will have to stop their work. The white gums, swamp gums and black peppermints that have emerged variously over the last decades since the area was last selectively logged will be cut down.

Can't the birds just find somewhere else, though?

"Well, no," Ms Lloyd said.

"'Somewhere else' is disappearing rapidly as well, and it's already full of birds. It's like erasing a suburb and saying people can just go to the next suburb. It doesn't work for very long.

Related: Northern Prison: plan to set aside Brushy Rivulet land for conservation never eventuates

"If all of the nesting hollows are already occupied, birds don't just go somewhere else. They just decline more and more, which is what is already happening."

We stop to inspect blue pincushion getting ready to flower for spring. The plant was the main reason why the previous owner was unable to clear the land for a timber plantation in the late-1990s - like the Forico operation across the road. The government's botanist instead wanted it included in the CAR Reserve System, and the government purchased it.

Since then, the blue pincushion's status changed from vulnerable to rare. It was the same for the handsome hook sedge.

This change in status cleared the way for the government to use the southern corner of the land as it pleased, provided it did not come within 500 metres of a wedge-tailed eagle's nest in a young tree in the bush on neighbouring land, discovered by Ms Lloyd.

But Ms Lloyd said the conservation value of woodland was more than just words on a piece of paper. She points to the Midlands where generations of land clearing have left the region fragmented, and where song birds rarely return.

Related: Why songbirds are leaving the Midlands and how the music can return once again

"There's this notion that if it's only rare, if it's not Commonwealth-listed, then it doesn't really matter that much and we can just dismiss everything," Ms Lloyd said.

"They don't really take much notice of 'threatened' or 'endangered' either, really, which is why things are getting so much worse."

What about the wedge-tailed eagle? If they have multiple nests, can't it also just use one of the others if it becomes disturbed by the blasting, construction work and 24-hour operations of a maximum security prison?

"Some of the other nests are in really old trees. This one is in a young, healthy tree," Ms Lloyd said.

"They are so particular about where they nest. They like to be really sheltered, so it's usually on a south-east-facing gully where they're protected from the westerly winds.

"This tree is in a good location."

We make our way down to Brushy Rivulet itself, which was rising rapidly after the weekend's heavy rainfall. Wallabies hurry away, sulphur-crested cockatoos move from tree to tree and a pair of kookaburras make themselves known in the canopy. While not native, Ms Lloyd says the kookaburras are further evidence of hollow-bearing trees.

The terrain is hilly, heavily populated with dolerite rock.

It becomes obvious that to level the southern corner for the prison, extensive blasting will be needed.

"If it's anything like our place, the dolerite would be surface rocks, but then there'd be really big substrate rock," Ms Lloyd said.

With drilling imminent, Tuesday morning was one of the last peaceful moments for the birds of the Brushy Rivulet woodland to enjoy, on one of the last remaining substantial bush blocks between Westbury and Launceston.

In the area proposed to be cleared and blasted in preparation for the Northern Regional Prison:

- pallid cuckoo

- shining bronze-cuckoo

- striated pardalote

- brown thornbill

- grey currawong

- mountain duck

- yellow-throated honeyeater

- grey fantail

- eastern spinebill

- fan-tailed cuckoo

- European starling

- yellow wattlebird

- superb fairywren

- spotted pardalote

- silvereye

- scarlet robin

- sulphur-crested cockatoo

- black-faced cuckoo-shrike

- forest raven

- green rosella

- grey butcherbird

- brown falcon

- golden whistler

- galah

- dusky woodswallow

- kookaburra