Drone cameras help DOC find rare bittern nests in Canterbury

Fewer than 50 bittern are thought to remain in Canterbury, and the Department of Conservation (DOC) is now using drone thermal imagery to find their nests.

The birds have begun nesting in wetlands and lakeshores around the country. Estimates put the national population at fewer than 1000.

“The drone pictures have incredible detail,” said DOC Biodiversity ranger Allanah Purdie.

Bittern are very hard to monitor because of their camouflage, shy nature and wetland habitat, which is difficult to access. Past monitoring has focused on male calls, so little is known about the females and their nesting outcomes. DOC combines the thermal imagery with high resolution video to detect them.

In Canterbury, bittern nest mainly around Te Waihora/Lake Ellesmere and in coastal wetlands. Purdie said DOC needs to understand how many there are, their fledging success rate and the causes of failure.

The drone monitoring is part of a wider project funded by Environment Canterbury as part of Whakaora Te Waihora. That programme aims to restore and rejuvenate the mana, mauri and ecosystem of Te Waihora/Lake Ellesmere. The bittern project aims to halt the population’s decline around the lake through monitoring, habitat protection, predator control and advocacy.

Drone operator Daniel Manchester’s company, Proform, did the filming. “It’s like being able to find a needle in a haystack,” he said of the thermal imaging. The team works to protocols developed by DOC.

Why the birds are struggling

Purdie said habitats such as Te Waihora are not in great shape, and starving bittern fledglings often turn up in more urban areas searching for food. Bittern feed on small fish like bullies and tuna/eels, which are diminishing in numbers.

In summer, when the lake water is low and warm, those fish move away from the lake margin into cool deep streams. Bittern cannot hunt them there.

How to take part

People around Aotearoa are taking part in the Love Bittern Project’s Matuku Muster, which runs until the end of November. They monitor and record bittern calls at dawn and dusk. DOC’s release points readers to the Love Bittern Project page, The Great Matuku-hūrepo Muster, to get involved.