Before removing any large tree in WA, look for a hollow. A black cockatoo nest hollow takes about 200 years to form and 20 minutes to destroy. A 15-minute check from the ground tells you whether your tree holds one, and cutting between February and June avoids nesting season entirely.

Why one hole matters more than the whole tree

WA has plenty of trees. It does not have many holes.

Black cockatoos cannot dig their own nest. They need a cavity that formed slowly, through a broken limb, decay, and decades of termite work, in a tree that was already big when your suburb was still bush. Consultant surveys prepared for WA councils note that these hollows usually sit in trees more than 200 years old.

So the question before you book a removal is not "Is this tree important?"

It is narrower: does this tree contain something that cannot be rebuilt?

Most of the time, the answer is no. But you have to look.

Which birds are we talking about?

Three black cockatoo species live in the south-west, and all three are listed as threatened:

• Carnaby's black cockatoo
• Baudin's cockatoo
• Forest red-tailed black cockatoo

BirdLife Australia estimates the Carnaby's population across the Perth–Peel area has dropped by around half in the past 50 years, with its range shrinking by up to a third.

Here is the part people miss. These birds live a long time, which hides the damage. A flock in a Yanchep paddock can look healthy for a decade while containing almost no young birds. The adults are fine. They just have nowhere to breed.

Every hollow removed is a breeding pair that stops breeding. Not just this year. The sapling you plant as a replacement will not hold a cockatoo until the 2200s.

How do you check a tree for a nest hollow?

Walk out with a coffee and look up. Slowly. Most people scan a tree in four seconds and see leaves.

Look for these, in order of reliability:

• A dead or broken limb with an opening roughly the width of a dinner plate, usually high on the trunk or at a major fork
• Pale, chewed timber around the rim, where birds have widened the entrance
• White droppings, feathers or chewed nuts under one specific limb, not spread evenly under the canopy
• Cobwebs, dust or leaf litter across the opening. Good news. Hollow surveyors use this as a sign the cavity has not been used recently
• Birds arriving at dusk and staying, seen over two or three evenings

Does the season change anything?

Yes, more than anything else on this list.

Carnaby's nesting season runs roughly from July to February. Cut a hollow tree in October, and you are not removing a nest site. You are removing a nest with a chick in it that cannot fly and cannot be moved.

If the tree is genuinely dangerous, that is a different conversation. But "I've been meaning to deal with it" is not an emergency, and February to June exists.

What size tree does the law care about?

WA and Commonwealth rules use a measurement, not a judgement call. That makes it easy to check yourself.

A tree counts as potential black cockatoo breeding habitat once it reaches:

Take a tape measure to the trunk at about chest height. A 500 mm diameter is roughly a 1.57 metre circumference.

Under that? Almost certainly not a nesting tree.

Over it? Worth a proper look.

What happens if you get it wrong?

Under the Biodiversity Conservation Act 2016, taking, possessing or disturbing threatened fauna without authorisation carries penalties of up to $500,000 for an individual and $2.5 million for a company, according to the Department of Biodiversity, Conservation and Attractions.

Nobody is fining a retiree in Gosnells over an honest mistake. But builders, developers and landholders clearing at scale sit in a very different position, and "I didn't check" is a weak place to start from.

What does a ground check miss?

Quite a lot. Here is what each level of inspection actually catches.

The gap between the second and third rows is where the real mistakes happen.

A hollow can look perfect from below and be only a hand's width deep, which is useless to a bird. Another can show as a thin scar and open into a chamber a metre deep. This is why WA development assessments often involve drone resurveys of hollows already recorded from the ground.

A crew inspecting a storm-damaged marri in Kalamunda found exactly that split. Two openings. One is obvious from the driveway and barely deep enough to fit a hand into. One tucked behind a fork, easy to walk past, and deep enough to matter.

The visible one was decoration. The hidden one was the reason the tree stayed.

Reading that difference takes arborists who understand black cockatoo habitat, not just someone with a saw and a truck.

What if the tree has to come down anyway?

Sometimes it is failing, sitting over the house, and no amount of goodwill changes the physics. There are still better ways to do it.

Reduce instead of remove. Cut the tree back hard and keep it standing as a stag with the hollow limb intact. You lose the risk and keep the hollow. Perth Hills Councils do this in reserves regularly.

Delay past February. Costs nothing. Changes everything for a nesting pair.

Salvage the hollow. A hollow limb can be cut out as an intact section and remounted on a nearby tree. This is a standard condition on WA clearing permits.

Or install an artificial hollow. The specification is fussier than most people expect: at least 380 mm internal diameter, around 1.2 m deep, built to survive 20 years outdoors.

One catch. That decision has to be made before the day. A crew like AB Trees in Perth will section a hollow limb carefully if you ask, and chip it if you don't.

Ask on the phone. Not when the crane is already booked.

Takeaway

Perth will keep growing, and every tree holding one of these hollows is old, structurally compromised, and on borrowed time. That compromise is exactly what makes it valuable.

Which means the future of these birds is not being decided in Parliament. It is being decided one backyard at a time, by people holding a quote for a tree they have never really looked at.

Look at it. Fifteen minutes.

The thing you are looking for has been there since before the Swan River Colony.

FAQ

How long does a black cockatoo nest hollow take to form?

Roughly 200 years. Hollows form through limb failure, fungal decay, and termite activity over decades, which is why they only appear in very old trees. They cannot be replaced within a human lifetime.

When is black cockatoo nesting season in WA?

Roughly July to February for Carnaby's cockatoo. Scheduling tree work between February and June avoids the risk of destroying an active nest.

Do I need approval to remove a tree with a hollow in it?

Possibly. If the tree meets the habitat size threshold and contains a suitable hollow, removal may need authorisation, and local council rules may apply on top of state law. Get a qualified assessment before you commit.

How do I tell if a hollow is currently in use?

Cobwebs, dust, or leaf litter across the entrance suggest it is not. Fresh chewing around the rim, droppings or feathers directly below, and birds returning at dusk suggest it is.

Can I just put up a nest box instead?

Only if it is built to specification. Black cockatoos need at least 380 mm internal diameter and around 1.2 m of depth. Standard garden nest boxes are far too small.