Australasian bittern may be in more trouble than we thought

The australasian bittern's numbers may have been miscounted in recent years, researchers say, making them even more endangered than previously thought.

There are fewer than 1000 bittern remaining in New Zealand, and their wetland habitat is increasingly coming under pressure from agriculture and urbanisation.

Emma Williams says research is showing that bitterns travel between wetlands, criss-crossing the country to find the perfect nest in the reeds and the rushes.

This means that there's a considerable risk that some birds have been counted more than once.

"So if there's only half of that ... if we've been double counting them we're in big trouble here," she said.