Bitterns are an iconic wetland bird which is becoming increasingly rare through wetland loss and predation by mammalian predators.
They are the apex avian predator in many wetlands and their presence gives an indication of overall wetland condition and health.
I was fortunate that Greater Wellington Regional Council engaged me last year through my small wetland consultancy WetlandWorks to carry out wetland bird surveys on a number of wetlands on the eastern side of Lake Wairarapa. This included Boggy Pond, Mathews Lagoon, Wairio wetland, JK Donald Block and Bartons Lagoon.
Each trip was 8-10 days duration and we based ourselves at Kilmore Lodge, a great home away from home owned by Wellington Fish and Game. One of my recommendations to the Council was the need to carry out a bittern survey of all wetlands around the lake to get a good handle on the population and what threats each site was subject to.
The survey, carried out over two weeks in October and November 2013, focused on locating male bittern who in spring advertise their presence by making a booming call much like a fog horn. They establish territories in mainly dense raupo and use this call to advertise their presence to available females and make other males aware not to come near. The main calling periods are one hour either side of sunrise and sunset. Occasionally they boom all night and all day when there is plenty of action on. This requires regular early starts and late finishes for the bittern counters.
During the survey 20 male bittern were recorded booming and their territories plotted on a map. Seventeen of the booming birds were calling from patches of raupo and the other three from scattered wet patches of oioi (jointed rush), closer to the eastern lake edge.
The main concentrations were around five key sites: Boggy/Mathews/Wairio, Ponui Lagoon, Barrage Gates, south Donald/Mangatete Stream and Bartons/Tauherenikau River mouth.
While bittern are polygamous and males can attract more than one female to their territory, some males are unsuccessful at attracting any. Other studies indicate the sex ratio is about 1:1 so the total population for Wairarapa Moana and associated wetlands is around 40 birds. A report is currently being prepared for Greater Wellington Regional Council that will discuss how these wetlands can be better managed for bittern.
A “meeting of the minds” for people working on bittern was held at Kilmore Lodge, Boggy Pond, Wairarapa on November 2 last year. This was attended by the DOC bittern scientist from Christchurch, other DOC staff, a university student doing a doctorate on bittern, and Greater Wellington Regional Council staff.
This was followed by a get together of local people and landowners interested in bittern around Wairarapa Moana. About 25 people overall.
The presentations and discussions that followed focused on the biology of bittern, habitat use and threats from plant and animal pests and was followed by a short trip to the Boggy Pond car park where everyone heard three of the local male bittern booming and advertising their wares.
A great opportunity for everyone to share information on this threatened but still keystone wetland bird.
Australian wildlife ecologist and bittern expert Matt Herring visited last year and took the time to catch up with his New Zealand counterparts.
“The best thing we can do for nature is simply spend more time in it. From there, reverence grows and action flows.” M Herring, 2013
What a wonderful trip. It was as if we spent a week compiling precious pieces of a rare, incomplete jigsaw puzzle called “Australasian Bittern Ecology and Conservation”.
After several years of being in touch via email and phone, it was so nice to finally get together with the New Zealand bittern crew and see some of their sites first hand.
There is some great work happening across the ditch and a strong sense of being united in working towards reversing the decline of this iconic waterbird that we share. It is affectionately known as matuku hūrepo in Māori, or matuku for short.
The knowledge exchange began with the biennial National Wetland Restoration Symposium in Napier where I was honoured to be a keynote speaker, focusing on the importance of community engagement, novel habitats and active management.
We then had a day visiting wetlands around Hawke’s Bay, including Pekapeka Swamp, followed by a successful bittern workshop day organised by Matt Brady from DOC. It was now crystal clear to me that there’s a lot of love for matuku in New Zealand.
With much discussion about wetland restoration targeting bitterns, it was astounding for many folk to learn about bitterns in rice and how bare, ploughed paddocks ready for sowing are able to support nesting bitterns less than three months later. There was a range of inspiring case studies from around New Zealand at the workshop, and we got to visit some local work in Hawke’s Bay with Hans Rook.
After that, it was time to begin a broader tour of bittern sites across the North Island. First stop was Lake Whatuma, and thanks to John Cheyne and Bernie Kelly, we were able to track some bitterns while kayaking.
We discussed key issues like willow control, raupo (cumbungi) harriers as bittern nest predators.
This wetland has up to nine booming males, but far fewer females, perhaps only three. The apparent shortage of female bitterns across New Zealand is something DOC’s Emma Williams is very concerned about. We may well have the same problem in Australia.
males in rice fields have up to three nesting females in a single territory, there is emerging evidence that would support a general shortage of females here too. It’s definitely something we should consider: a booming male may not be a sufficient indicator of breeding
or site quality.
It was now October and time to visit the 7200-hectare Whangamarino Wetland, between Auckland and Hamilton. This Ramsar site was once the world’s most important wetland for the Australasian bittern, with more than 140 booming males in 1980.
Nowadays, there’s only about a dozen. I learnt about the many issues that are implicated in the decline, such as introduced species and water quality, but I think the huge water level fluctuations are central.
Near Tauranga, we visited the Lower Kaituna Wetland, and were lucky enough to spot a bittern feeding in the eleocharis. Part of the restoration work in the broader area is starting from scratch, essentially constructing new wetlands.
And on the edge of Tauranga itself, right on the coast, we visited a bittern breeding site that was tidal. This was quite perplexing. The vegetation is low and we wondered where they build their nests without being flooded.
Unfledged chicks have been found in land nearby, including a recreational park. We talked about how this site would be suitable for a thermal drone in locating nests and monitoring breeding success.
All in all, a wonderful trip, with special thanks to all who made it possible. I’m looking forward to returning the favour!
The love for matuku in New Zealand is admirable, and the conservation work being done is inspiring
New research highlights the importance of New Zealand’s wetlands for one of our most secretive native birds, the Australasian bittern or matuku, Conservation Minister Eugenie Sage said on World Wetlands Day, 2 February.
GPS tracking of matuku/bittern has, for the first time, revealed that it flies more than 300km between wetlands in the eastern South Island as well as large distances between North Island wetland sites.
Previously it was thought bittern ranged only small distances from their home wetlands.
DU is one of several partners in the Department of Conservation-led research, which shows that bittern rely on a network of wetlands to feed and breed in.
It also means matuku/bittern may be rarer than previously thought as birds have probably been double-counted in local counts in different parts of the country.
In the study, male bittern were tracked flying 330km from Te Waihora/Lake Ellesmere in Canterbury to wetlands near Blenheim during the breeding season last spring.
They also flew 117km from Whangamarino wetland in north Waikato to south Kaipara and from Whangamarino to Kaituna in the Bay of Plenty.
DU director and bittern expert Emma Williams’ workload has become a whole lot busier after she was appointed science advisor (wetland birds) for the Department of Conservation in October.
A fulltime job for four years, her main task is to deliver the national bittern research plan. The role also involves work with other wetland birds such as spotless crakes and marsh crakes with the aim of setting up new collaborations with organisations to try to fill some of the knowledge gaps about cryptic and native wetland birds.
Projects include working with Stephen Hartley and students at Victoria University in Wairarapa Moana. One of the current projects involves putting out artificial bittern nests in several study sites, including Wairio, to determine what predators are targeting bitterns.
Emma says new bittern monitoring projects in South Kaipara, Auckland region, Tauranga and Turangi are expanding DOC’s national monitoring reach. The goal is to identify where bittern strongholds and hot spots are and inform where new projects are needed to try to reverse bittern declines.
Bitterns are found throughout New Zealand - in the North Island they predominantly inhabit Northland, Waikato and East Coast wetlands; while in the South Island they mostly inhabit West Coast, Canterbury and Southland wetlands. The most important bittern site nationally is Whangamarino Wetland, a large and diverse wetland complex in the Waikato.
Bitterns are large, stocky birds, with streaky dark brown and beige plumage on their throat, breast, abdomen and thighs; and dark brown on the neck and back. The head is dark except for pale beige around the cheek, forming a pale eyebrow. Plumage can vary significantly and may be age related.
Bitterns are rarely sighted due to their exceptionally cryptic behaviour, inconspicuous plumage resulting in excellent camouflage and the inaccessibility of many wetlands. They are mostly active at dawn, dusk and throughout the night. Bitterns are occasionally spotted in the open along wetland edges, drains, flooded farmland and roadsides.
They are very sensitive to disturbance and will silently creep away to avoid detection, or adopt the infamous ‘freeze’ stance (with the bill pointing skyward) if approached. This allows bitterns to blend into many environments, whilst maintaining a close watch of surroundings. If an observer continues to advance on a bittern, then it will eventually take flight in a laborious manner.
Often the only sign of bittern presence in a wetland is the male’s distinctive booming call at the beginning of the breeding season. Each call sequence may consist of 1-10 individual booms, with an average of 3 booms. Boom sequences are repeated at regular intervals, and normally preceded with inhalations or gasps. Females are mostly silent, apart from producing an occasional ‘bubbling’ sound upon return to the nest, or a nasal ‘kau’ when alarmed. Bitterns in flight may produce a resonant ‘kau’ or ‘kau kau’.
The breeding season is extremely long, spread over a 10-month period. Females construct a reed platform nest amongst dense vegetation deep within wetlands.
A clutch of 3-6 eggs is produced between August and December (peaking in November), and then incubated solely by the female for 25 days. Chicks remain in the nest for 7 weeks and fledge from November to May. Bitterns are considered an indicator of wetland health, as they are dependent on the presence of high quality and ecologically diverse habitats, which are rich in food supplies (such as eels, fish, freshwater crayfish, aquatic insects, molluscs, worms, spiders, frogs and lizards).
Bittern numbers have declined drastically since the arrival of European settlers, with over 90 percent of freshwater wetlands now drained and cleared. Ongoing wetland degradation continues to be the chief threat, resulting in habitat modification and loss, reduced food availability and poor water quality. Other threats contributing to bittern declines include predation by introduced mammals (particularly cats, rats, dogs and mustelids), human disturbance of nesting bitterns, as well as power-line and vehicle collisions.
You can help bitterns by becoming involved in wetland conservation and reporting all sightings (or calls) to your local Department of Conservation office. Most importantly you can protect wetlands on your property by planting native vegitation to create riparian buffers and fencing waterways from livestock.
Wildlife Project Administrator
(supplied by The Isaac Conservation and Wildlife Trust)
Now, if I was to ask how many of you have seen a juvenile bittern or a bittern nest, I think it’d be safe to assume that most of you haven’t. And that’s saying a lot given that you are all wetland enthusiasts who regularly work and play in these kind of habitats.
So when we got a report that a female bittern chick had been found wandering along a road in Christchurch you can imagine our surprise. What was one of the most cryptic and secretive wetland birds doing on a road in the city? And the surprises didn’t end there – a few weeks later a second female bittern chick walked into a residential garage, only 500m from the location where the first bittern was found.
There had to be a nest nearby – but where?
Both bitterns were very skinny and clearly dehydrated. They were taken to bird rehabilitator Jackie Stevenson, who set about trying to fatten them up and get them feeding for themselves. In the meantime, local ornithologist Peter Langlands set about trying to find their nest.
Now this is no easy task. Bittern nests are tricky to find. A broody female bittern will build her nest by bending blades of raupo to form a floating platform that is perfectly hidden in the thick vegetation. And she’s not necessarily alone. Male bitterns can have multiple females, which all appear to nest within close proximity to each other.
Once a mother-to-be is happy with her nest she’ll lay between 3 and 5 eggs before starting to incubate. She hatches the eggs and rears the chicks alone, apparently chasing the male away if he tries to get too close. While incubating, she’s almost impossible to see as her streaked plumage blends perfectly in with the surrounding vegetation. Occasionally she’ll slip silently off the nest to feed, but only momentarily as this leaves her eggs vulnerable to predators.
After about 25 days, her eggs will hatch to produce little fluffy chicks with Albert Einstein inspired hairdo’s. These fuzz balls, emerge as masters of disguise straight from the eggs, and will adopt a perfect ‘freeze pose’ that looks similar to that of the adults if they are disturbed. Chicks fledge at about seven weeks old. However, there is some suggestion that they may start wandering from the nest as early as two weeks old - which is perhaps how one chick ended up on a city road and the other in a household garage.
Midway between the locations where these two birds were found lies Travis wetland, a 120 hectare swamp complex that has been restored over the last 15 years by the Travis wetland trust and the Christchurch council. It is the most likely place where these two birds came from. As it happens Travis is a noteworthy place, with an interesting history. In the 1960’s, this beautiful wetland was under threat from developers, who wanted to convert it to a residential area. Luckily, the locals had other ideas. They realised the importance of the site’s natural biodiversity, and argued long and hard for its protection. After a long battle that involved a petition signed by almost 7000 people, biodiversity won out, and in 1997 the site became a natural heritage park.
And lucky for bitterns that it did!
Since then, these two bitterns have done well in captivity and we were able to release them over the festive season - one along the Waimakariri river and the other at Harts Creeks. We attached radio transmitters to both bitterns, one of which was kindly funded by Ducks Unlimited. Both of these birds will be tracked regularly by local enthusiasts and, as female survival and breeding success is the secret to saving a species in decline, and these birds are the only females to carry transmitters at the moment - the information we gain will be essential for saving the species.
And thanks to Gill Lundie for organising the school visit.
Emma Williams has continued working on the bittern project assisted by me and other volunteers.
Key points are:
Coordinator Project Bittern (Matuku)