29 Nov 2023

Our Changing World – Keeping an eye on the Makarora mohua

From Afternoons, 3:35 pm on 29 November 2023

In the 1800s, mohua were one of the most abundant of the forest birds, found in different forest types. Their bright yellow heads (hence their common English name, yellowhead) and yellow-feathered bellies led them to being dubbed the ‘bush canary’ by European settlers.  

A close-up of a small bright yellow bird being clutched in a person's hand.

Mohua. Photo: Claire Concannon / RNZ

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But – and you know this story – forest clearance and introduced predators reduced their population and range significantly. These little songbird insectivores nest in holes in trees, and so are vulnerable to stoats and ship rats. Some mohua have been transferred to predator-free offshore islands where they are doing well, but on mainland New Zealand there remains just a few small, scattered populations living in South Island beech forest.  

One of these can be found just north of Makarora, near Cameron Flat, in the silver beech forest that lines the west side of the Makarora River as it runs alongside State Highway 6 through the Haast Pass. Keeping an eye out for this little population is a Central Otago Lakes Branch of Forest & Bird volunteer team, and conservationists from the Southern Lakes Sanctuary.  

Three people in tramping gear and carrying backpacks stand in front of a gravel riverbed, with forest-cloaked mountains rising in the background to a cloudy grey sky.

Laura Molles, Grant Maslowski and Jo Tilson. Photo: Claire Concannon / RNZ

Cryptic in the canopy 

Despite their flashy yellow colour, and loud song, these birds are difficult to count. They spend most of their time high in the canopy, where they often fly with their cousins, pōpokotea whiteheads, and pīpipi brown creepers.  

To properly monitor them, this year the Southern Lakes Sanctuary is catching and banding all the birds they can. 

Plus, they are collaborating with Atarau Sanctuary, who are developing a new monitoring tool using machine learning to identify individual birds from acoustic recordings. To train the algorithm, Dr Laura Molles says, you must first provide it with labelled data, which is why she is spending her time following banded mohua through the forest with recording equipment to capture their song.  

The promise is a non-invasive monitoring tool that could let you know not just species presence and absence, but numbers and movements of individual birds.  

A man in a green fleece holds a pole while a woman in a grey merino and glasses ties the pole to a branch in the forest.

Grant Maslowski and Laura Molles set up the mist net. Photo: Claire Concannon / RNZ

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