The bittern/matuku: A national wetland treasure

It’s World Wetlands Day. Jack van Hal takes us behind the scenes of a research programme underway to learn more about the conservation needs of the Australasian bittern/matuku. 

The Australasian bittern/matuku is an iconic wetland species, most of us have probably never seen. This is because they are very cryptic birds that like to blend into their surroundings – but also because there are fewer of them around these days. Bitterns have recently been classified as Nationally Critical due to a substantial range reduction (50% range reduction since the early distribution records prior to 1900) with populations now highly fragmented and no large flocks counted anywhere in the country.

Bittern chicks at Tiwai spit in 2017. Photo: Sarah Crump

Local Bay of Plenty volunteer and bittern tracker Bev Nairn holding bittern ready for transmitter attachment. Photo: Emma Williams

This is why the Arawai Kākāriki programme has recently embarked on a more intensive five-year national research programme on bitterns to identify causes of decline and determine their conservation needs. This work is in partnership with Environment Canterbury, Birdsnz, Ducks Unlimited, Hawkes Bay Forest & Bird and involves numerous volunteers. While bitterns have been actively monitored using automatic acoustic recording devices (ARDs), at a number of wetlands, capturing and tracking individual birds using transmitters only began more recently in 2014. Eleven bitterns (10 males and 1 female) are currently being monitored, in conjunction with a range of partners and volunteers, at four sites in Waikato, Bay of Plenty, Hawke’s Bay and Canterbury in order to understand more about their movements, behaviours and ecological requirements.

A bittern in the hand….

One of the challenges is capturing bitterns. Males are easiest to locate in breeding season, as we can use their booming to locate their territory. Sneaky capture methods are used. A cage is set up on a path he has been using in the wetland, and then a rival male’s booming and a mirror is used to entice him into the cage. Most male birds have been caught this way. We want to know where they go, what they do and if they have a mate with a nest in the area. The ultimate prize would be to catch the nearby females, so we can locate the nests, monitor the outcomes and figure out where bitterns go in the off season. The females are proving much more difficult to capture. Best practice for female bittern capture remains a work in progress!

Bittern in cage – caught by his own reflection. Photo: Emma Williams

What have we learnt………

While it is still early days in the study, we are starting to get good data from birds in different wetlands in different parts of the country. Data is revealing that there is more to the bitterns story than meets the eye. So far we know that there’s a difference in weights by region. Hawke’s Bay and Whangamarino male bitterns are approx 500 grams heavier than Canterbury and Bay of Plenty bitterns. Hawke’s Bay bitterns utilise a network of wetlands across the wider landscape throughout the year, moving as resources (particularly water levels) change. It looks like the Whangamarino and Canterbury bitterns do the same (Whangamarino bird moved 10.7 kms, Hawke’s Bay birds moved within 15 km of Lake Whatuma while a chick in Canterbury that later starved, had moved over 140 kms).

Bittern researcher Emma Williams setting up a cage trap. Photo: Sarah Crump

There’s plenty more to learn about bitterns as our research progresses!

Help us to protect our wetlands this World Wetlands Day. Visit our website for more information or attend an event near you.

Click here for more information on the Arawai Kākāriki Wetland Restoration Programme.