Carnaby's Black Cockatoos, how many do you count? Imge by Ken & NyettaBirds Australia is calling for volunteers across the state to take part in the 'Great Cocky Count' on April 7.

Previous counts have only been conducted in the greater Perth area, but organisers are widening the search to concentrate on collecting numbers of the endangered Carnaby's black cockatoo this year.

Volunteers will be assigned to bird roost sites between Esperance and Geraldton, and asked to be at the site 30 minutes before sunset and count the birds as they fly in, waiting until 30 minutes after sunset.

Co-ordinator Dr Xander Kabat says it's a surprisingly accurate way to get scientific data.

"The surveying technique is very straightforward and it's a very clean way to monitor any population."

"Being able to do it in one night gives us a snapshot throughout the state and avoids double counting of birds."

Volunteers don't need any special training, Dr Kabot says, and are provided with simple guidelines on how to spot and record bird numbers.

It's believed only 40,000 birds remaining in the wild across Western Australia, and the cockatoos are listed as endangered.

Last year the Esperance population was almost wiped out. 200 birds were found dead after a day when the temperature reached 48 degrees.

Investigations by the Department of Environment and Conservation have concluded that heat stress was the most likely cause of death.

Of a greater threat across the state is loss of habitat, Dr Kabot says.

"They live in older trees, so any time pine trees or old eucalypts are cut down that shrinks their roosting habitats."

Carnaby's cockatoos have black bodies with white tails and beak. People who sign up signing up for the cocky count will be assigned a roost to monitor.

"Because this year we are trying to spread the count, if anyone know of a roost we're thrilled to get that data as well."

To register, contact greatcockycount@birdsaustralia.com.au