The matuku or Australasian bittern is so good at being undercover, that it is difficult to find and track. Photo / Imogen Warren
The matuku or Australasian bittern is so good at being undercover, that it is difficult to find and track. Photo / Imogen Warren
The trial of a drone equipped with thermal imaging has successfully located some of New Zealand's most elusive and cryptic native birds.
The Australasian bittern, or matuku, is a rare bird sometimes heard but rarely seen in wetlands across the country, including in Waikato. Bittern were common in New Zealand in pre-colonial times but are now classified as 'Threatened – Nationally Critical', numbering fewer than 1000. Introduced predators, native Australasian harriers (kāhu), and reduction in wetland habitats and water quality are their main threats.
The males are known for an unusual booming call to attract females. Listening for this distinctive sound helps estimate the birds' population within their preferred habitats, using audio recording devices or trained volunteers scattered around wetlands.
A rare photo of the secretive wetland bird caring for a clutch of eggs. Photo / Hawkes Bay Today
But those methods mean bittern population estimates are based on male numbers only. The use of a drone fitted with a thermal-imaging camera will give new insight into the species, allowing scientists to monitor female bittern and nesting success.
Harry Caley, DoC's wetland birds science adviser, says the drone trial flights were carried out at five sites around Bay of Plenty and Coromandel: Little Waihi Estuary, Kaituna Wetland, Waimapu Estuary, Pahoia Estuary and Whangapoua Harbour.
Researchers and volunteers, led by DoC's Tauranga-based biodiversity ranger Karl McCarthy, spent many hours locating male bittern to determine where their territories were. Then ecologists at Flightworks helped find females and their nests using a thermal-imaging drone.
The flights coincided with bitterns' peak breeding season activity. Each flight lasted about 20 minutes, covering 10 to 15 hectares. Across the 49 flights, researchers spotted at least 11 bitterns and two nests. The presence of the drone did not disturb the bitterns so their behaviours were also captured on video, including birds mating (thought to be the first time that this has been filmed).
"Thermal imagery works best with a high-temperature contrast between bittern and their environment," says Hamish Kendal of Flightworks. "Fieldwork began at 5.30 each morning to take advantage of the cool vegetation contrasting against the warm body temperatures of the bird," he says.
The young bittern that John and Jude Bowen found in their backyard in Cambridge last month. Photo / Jude Bowen
When nests were found, researchers would walk in on foot to position small camera systems which captured bittern activity that will be crucial to help determine why the bittern population is still falling. The drone also captured the amount of time females leave the nest, development and fledging of chicks, and their predation by other species.
The thermal-drone trial was successful in relatively short vegetation of rushes, but has yet to be proven effective at finding the birds and their nests in thicker vegetation such as tall raupō.
Nigel Binks, DoC senior ranger biodiversity, says the successful trial is an important step in the work to protect bittern.
"Detecting female matuku has historically been quite difficult; the only way to do it is with a trained detection dog walking through a wetland, which is really invasive and can scare females off the nest," he says. "Being able to identify female bittern will give a more accurate representation of the population, and teach us about the habitat requirements of these birds.
"We plan to use the drone to fly over known nesting habitat types to determine whether we have nesting bittern in Whangamarino, which is one of New Zealand's internationally recognised Ramsar wetlands. Finding their nests will help determine the main predators of bittern eggs and chicks, and the camera systems will help us do that.
"With this information, we will be better equipped than ever to plan appropriate management to increase the likelihood of successful fledging and, at the same time, add to the population gene pool."
The thermal-drone work was carried out as part of Arawai Kākāriki, DoC's national wetland restoration programme. The announcement of the successful trial coincided with World Wetland Day, which aims to strengthen and multiply action for protection and enhancement of wetlands.
