– by Emma Williams, DOC Ranger
Today is World Wetlands Day, so we’re taking a look at the matuku/Australasian bittern which is a potential indicator of wetland health. These birds are dependent on the presence of high quality and ecologically diverse habitats and rich food supplies.
In the early hours of the morning in late September, a matuku/Australasian Bittern circles above Blenheim, follows the Opawa river towards the Cook Strait, and then drops down into the mouth of the Wairau river.
In all reality, this was a typical day, and the bird was just coming to the end of a long flight it’s made many times before.
However, for Arawai Kākāriki’s bittern researchers this was an exciting result!
To understand the importance of this result, we have to go back a few years. DOC’s Arawai Kākāriki restoration programme started studying bitterns in 2009. At that time DOC had good reason to be concerned about bittern populations here in New Zealand.
The matuku/Australasian Bittern was known to rely on wetlands for feeding and breeding, and 90% of these habitats had been lost. Those wetlands that remained were degraded and under threat. Based on this alone, bittern populations were always likely to be in trouble.
However, as the species is difficult to find due to its evasive behaviours and camouflaged plumage, we still had a lot to learn about bittern’s requirements and behaviours.
Early monitoring of male bitterns implied the population has under gone a substantial range reduction and this knowledge led to the species being reclassified as Nationally Critical in 2016.
Since then, Arawai Kākāriki started a five-year research programme to help identify sites of importance and causes of declines, and determine the species’ conservation needs.
This work relies on a network of organisations and partners, including Environment Canterbury, Bay of Plenty Regional Council, BirdsNZ, Ducks Unlimited NZ, Hawkes Bay Forest & Bird, and involves numerous volunteers.
A national radio-tracking study, which involved tagging 24 male matuku/bitterns with radio-tags at four sites has so far told us that male matuku/bitterns regularly move between sites within a 15 km radius of their breeding site. It appears, that in general, bitterns return to the same territories to breed each year and consistently hold the same territories throughout the breeding season.
Despite this, some of our tagged birds periodically disappeared and the short range of the radio-tags, and difficulty of the terrain, limit our ability to tell whether a missing bird has truly left the site. To solve this, we decided to trial a few GPS tags on bitterns this season to see where missing birds were going.
So, while that bittern was circling over Blenheim in the early hours of the morning in late September, its GPS tag was silently telling researchers that this bittern was the same bird that had been caught at Lake Ellesmere – 330 kms south of this location. It also confirmed that to get here, this bird had visited a much larger network of wetlands, drains, farm ponds, springs and dams than we originally thought.
Basically, these birds rely heavily on a mosaic of tiny wetlands scattered across the landscape, each acting as a tiny oasis amongst what is now a desert compared to what New Zealand once was.
It also confirmed that although this bird was recently counted in our Canterbury census, it was probably a Marlborough bird. Perhaps this is not an issue if this bird is an anomolie, but four of the five bitterns that currently carry GPS tags show the same behaviour, each moving distances > 100 km during the breeding season (a time when they were thought to have stable territories).
So now it looks like many of our Waikato matuku/bitterns may also be Bay of Plenty/Northland birds, and our Canterbury bitterns are also Marlborough birds. It’s still early days, but already this somewhat concerning given that New Zealand’s current population estimate is < 1000 bitterns – based on the recently tracked bitterns without boundaries, this could be an overestimate.
We will keep you updated on the programme as we learn more about what these bitterns get up to over the longer term. In the meantime, as it’s World Wetlands day tomorrow, we ask everyone to take a moment to consider those little pockets of wetland/freshwater habitat in your region – did you realise their importance for one of our most endangered birds? And is there anything else you could do to afford these sites greater protection?