?Mesmerising?: a massive murmuration of budgies is turning central Australia green and gold

The humble budgerigar has transformed the red centre into a sea of green and gold.

A massive murmuration - the phenomenon of thousands of birds flocking together - has swarmed the Northern Territory.

Photographer Steve Pearce has captured the natural phenomenon, explaining the sheer quantity of the birds causes the air pressure to change.

After a tough couple of years due to drought and bushfires, some inland Australian bird species are now thriving after a buoyant wet season.

"You hear one budgie, that first fella comes in, he flies past, then another one, then it's like over a short time, maybe five minutes, they all just turn up and start arriving en masse.

"There's a critical mass that sweeps in. It's spectacular."

Pearce said this was the biggest murmuration he had ever seen.

"The photos are always only pointing in one direction. There could have been 100,000 of them.

"And it last for hours, there was no stopping them. Big groups would come in and get a drink, get some food, they would get full of seeds and come back for a second drink.

"It was hours and hours of budgie mayhem."

They were there to eat, drink and court each other. A budgie bush party - schoolies for the animal kingdom.

"They're just having fun, a bunch of kids riding motorbikes in the sky."

You can feel the pressure of the air shift, he said, as thousands of budgies fly in, swooping in intricate patterns.

"The visual stuff it's mesmerising, you can't look away, it's spectacular. It is a dynamic expression of nature," Pearce said.

A show this big is rare. The nomadic creatures need to drink water daily and as the smaller watering holes dry up they are forced to congregate together. They go where the rain goes - so it never lasts long.

Over the previous spring/summer period it had been perfect conditions for mating.

"The landscape facilitates the explosion," said Pearce.

"It all came down to climate conditions, rain, food availability, all those things crossed over to make the perfect breeding environment."

But the most important aspect to this explosion of life in outback Australia is old trees.

"All this birdsong exists because they have gnarly trees around them," Pearce said.

"Each one needs a tree hollow to nest in. Without old trees, trees that have hollows, dead branches, the classic river red gum, that take 100 years, this wouldn't happen.

"Our iconic birds, they need those crappy old trees to nest in."