In the wild, budgerigars (Melopsittacus undulatus) are nomadic, flying thousands of miles during the Australian summer following thunderstorms and seeking out standing water. Every few years this desperate search climaxes in a vivid spectacle, as tens of thousands of budgies flock around a shrinking water hole.

For the BBC Two series Wonders of the Monsoon, a BBC production crew headed to Australia to find and film one of the continent's greatest natural spectacles.

A moving target

Sometimes the flocks can form and disperse in a matter of days. Paul Williams appealed on national radio and in the press for reports of flocks anywhere in the country. Eventually, the crew’s search led them to Alice Springs in central Australia.

“Truck drivers travelling along remote desert roads had reported seeing budgies in the early mornings,” explained Paul. “At this time of day it’s light enough for budgies to spot potential predators, but they can avoid the sun’s most intense heat.”

Rising early, the team patrolled the featureless roads of the Australian outback scanning for signs of the budgies, until eventually they spotted small flocks in the distance.

Using satellite imagery the crew pinpointed a potential waterhole and headed straight there at first light the following morning.

They found a small circular waterhole, probably created over a century ago by the pioneering cattle herders who drove giant augers into the ground to bring water up from reservoirs deep beneath the desert.

As the sky warmed up so too did the team’s anticipation.

Small, amorphous black clouds formed and disappeared on the horizon. As the sun rose higher the black clouds grew larger, twisting and contorting, advancing towards the waterhole. This is what the crew had been waiting for.

Air-borne drama

Within minutes the air was electric with the beats of more than 80,000 tiny pairs of wings. It was a budgie tornado and it wasn’t long before the raptors arrived – brown falcons, black falcons, hobbies and kites.

The budgies circled around the waterhole – a strategy used to confuse the raptors, which were trying to lock on to individual birds. Falcons dived through the flock, separating individuals before chasing and striking. Hobbies followed, picking off stragglers.

The tornado descended en masse to drink. The budgies were so panicked by the threat of predators and their desperation for water, that some were pushed under the water by the weight of more birds landing on them.

As the flock took off again, half-drowned budgies were left behind, vulnerable and unable to fly, frantically flapping to get to shore. This was the opportunity the kites were waiting for – they effortlessly plucked the budgies out of the water.

After an hour the budgies flew off, diving into the long grasses to feed on spinifex seeds. The raptors, having had their fill for the day, also departed the water hole.

Curiously, with the predators now gone and the chaos over, this is when flocks of other birds like galahs and cockatiels arrived to drink. “Maybe the raptors just preferred the taste of budgies to anything else,” observed Paul.

For seven mornings the crew witnessed the incredible budgie tornado until one day a freak rainstorm drenched the desert. With standing water everywhere the budgies dispersed and the great event was over.

Watch Wonders of the Monsoon on Sunday at 20:00hrs on BBC Two, or catch up on BBC iPlayer.