Displaying items by tag: Bittern

Ducks Unlimited recently received a substantial donation to put towards its restoration work at Wairio Wetland.

Janet and Patrick Velvin, who live in South Wairarapa, are passionate about conservation, particularly water conservation, and contacted The Gift Trust, a philanthropic advisory service, to identify suitable causes they could support.

Cheryl Spain, executive director of The Gift Trust, said they had been impressed with the research on Wairio and DU’s partnerships with the Department of Conservation, Greater Wellington Regional Council and Victoria University, particularly its links with the student research projects at Wairio, and had chosen Wairio as a suitable recipient.

The Velvins visited the wetland for the first time and took part in a planting day with Victoria Uni students in early July.

After helping with the planting, they were given a guided side-by-side tour by Ross Cottle, who identified a suitable site on a promontory for a viewing hide, which could be constructed with some of the funds donated by the Velvins.

During the tour, Patrick asked if there were bitterns in the wetland, and as if on cue, a bittern obliged and flew in front of the them.

Janet became aware of the work at Wairio Wetland through the book Wairarapa Moana: The Lake and its People.

Janet said after the tour they were impressed with Ducks Unlimited and happy to give a donation towards the work at Wairio.

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.

Bittern Workshop

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.

John Cheyne

Steve Playle, Hugh Robertson and Nikki McArthur took advantage of excellent weather conditions on June 20 to carry out a winter shorebird census at Lake Wairarapa. The water level was relatively high (10.3 metres above datum), so most of the mudflats were under water and in turn that influenced some of the 
species counts.

 

By the end of the day they had counted 22 species of shorebirds and waterfowl, totalling 5647 birds. Highlights of the day included four Australasian bittern, two white herons and a little egret (the latter a relatively rare Australian vagrant). Hugh encountered a flock of 122 red-billed gulls at the Oporua Floodway, which 
is exceedingly unusual for this site. Red-billed gulls are extremely rare visitors to Lake Wairarapa, having been reported only a handful of times previously (11 birds in February 1948, “irregularly” between 1982-1983, 2 birds in April 1992 and 1 bird in February 2012).

 

A full summary of the species counted during June 20 census follows. For anyone who wishes to test their bird ID skills, or read background about any of the species recorded go to New Zealand (NZ) Birds Online website (http://nzbirdsonline.org.nz/).

 

 

This is the third winter survey since initiating this work in 2011, so it’s now possible tobegin comparing average species counts from June 2011-2014 surveys with those from Hugh Robertson and Barrie Heather’s earlier set of surveys carried out between 1985 and 1994, for the section of shoreline between the Tauherenikau Delta and the Oporua Floodway. These comparisons give an early indication of some of the changes that appear to have occurred to the relative abundance of various bird species at the lake over the past 30
years. A number of species appear to have increased in abundance over the intervening time, among them NZ dabchick, black shag, little black shag, little shag, black-fronted dotterel and black billed gull. A smaller number of species appeared to have declined in abundance over the same period, including SI pied oystercatcher, pied stilt and spur-winged plover.

 

 

Nikki explained the original aims of this survey work were relatively simple (i.e. to give the ability to describe changes that have occurredin the lake’s bird fauna over the past 30 years;

to allow them to detect future changes and to re-examine the relationship between shorebird abundance and water levels). You might be interested to know the data from these surveys have recently been put to a variety of other
uses, including:

• To provide quantitative evidence in support of an application to have the Wairarapa Moana wetlands recognised as a “wetland of international importance” under the Ramsar Convention.

• To provide evidence to support the Wairarapa Moana Wetlands (together with
the Ruamahanga River) being listed as an “Important Bird Area” under Birdlife 
International’s global IBA programme.

• To form part of our flood protection department’s programme for monitoring
the health of riverbed-dependent bird populations on rivers affected by flood 
protection activities (large proportions of the regional populations of several riverbed-dependent bird species overwinter at Lake Wairarapa).

• To provide regional population estimates for a number of shorebird species used for the development of a regional threat classification system for birds of the Wellington Region.

• And lastly, data collected during these surveys are combined with data compiled from other key shorebird sites around NZ to provide estimates of the national population sizes of a number of NZ’s shorebird species. These national 
population estimates are in turn put to a variety of uses, including a regular review of national threat classification rankings and ongoing monitoring of the population health of Arctic-breeding migrants using the East Asian/Australasian Flyway, a major avian migration route stretching from Alaska and Siberia in the north to NZ and Australia in the south.

 

Thanks go to Ian Gunn, Tony Silbery and Bob Green for assistance preparing for this survey, and to Bob Green, Grant McGhie, Graham Field and Tim Loe for permission to access various points of the shoreline. The next scheduled shorebird survey at Lake Wairarapa is for November 2014.

Nikki McArthur
Environmental Scientist
Greater Wellington Regional Council

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

Last issue I introduced Australasian bitterns, a rare, secretive wetland bird that often lives within a stones’ throw of people’s houses – yet only the lucky few who spend time in wetlands know this species exists!

As our  bittern is the rarest in the world, we have  several reasons to be concerned about the population here in New Zealand.

 

In the last DU issue I discussed several threats known to limit bittern populations overseas - threats that are unfortunately also present in New Zealand. These threats include habitat loss (here in NZ this loss amounts to a shocking 90 percent!), introduced predators, modified water levels, poor water quality and inconsistent food availability. Unfortunately, despite knowing this, we still have little information about what’s happening with the bittern population here in New Zealand.

This is mainly because bitterns are almost impossible to find and study due to their camoflage plumage and elusive behaviour. Not being able to find this species also means conservationists can’t tell if their efforts to save the species are working.

 

To solve this problem we’ve been developing several monitoring methods that can be used to detect and count breeding male bitterns. This year we wanted to measure how well these methods work.

To do this we needed to catch and ‘mark’ as many male bitterns  as possible on Lake Whatuma, in Central Hawke’s Bay. We knew this would be tricky because to-date few bitterns have been caught.  However, as a team we collectively had several years of bird catching experience using a variety of methods…knowledge of two methods that had been used successfully to catch bitterns overseas…an ability to adapt as we went…and a ridiculous amount of dogged determination… And it worked!

Since September we’ve been able to catch six  male bitterns at Lake Whatuma. We caught all six birds by luring them into cage traps using a combination of calls and mirrors.

 

Playing bittern booming calls within a bird’s territory worked because it tricked the resident male into thinking that a rival male is challenging it. The resident male tries to creep up on this fake rival male intending to see it off. Eventually it sees its own reflection in the back of the cage trap, which it mistakes for the intruding bird, causing it to enter the trap. As soon as the resident male steps on the treadle plate inside the trap, it’s weight releases a catch, dropping the cage door shut, and capturing the bird.

 

Once caught, we banded each bittern with a metal M-band to make them uniquely identifiable in the hand. 

We also attached the radio transmitters provided by Ducks Unlimited sponsorship to help us locate and  identify the bird even when it was hidden from  us in the thick vegetation.

 

Before releasing the bird we weighed it, took a range of measurements (such as length of tarsus, bill, wing and tail), and some photos of its bill and feather patterns.

Photos and measurements can be used to crudely determine the health of the bird and as a general guide to help us confirm its age and sex. Each captured bittern was named in the honour of a deceased crooner – so by November we had caught Barry White, Bing Crosby, Tama Tomoana, Prince Tui Teka, Howard Morrison and Elvis Presley.

 

Once we’d finished processing each captured bird we released them back into their territories.

After that we regularly located birds using the signals emitted from their transmitters. Locations of marked bitterns were plotted to map their territories. We also checked where birds were located during our monitoring sessions and noted if a bird called during monitoring periods, and for those birds that did call we looked to see if observers had succeeded in detecting them. 

 

The results of our monitoring trial are still being analysed but preliminary results already show that breeding male bitterns have high site fidelity during the breeding season, meaning they always boom from the same area.

This is good news for our monitoring methods as it allows us to assume that booms heard at the same location at different times during the breeding season were produced by the same bird.

 

There was one exception. Bing Crosby, a bird caught in the northern end of the lake, permanently left his territory in October (midway through the breeding season). However, we have reason to believe that Bing was not as popular with the opposite sex as his namesake – and therefore does not count as a breeding male. Indeed we suspect he left the lake because he was single and  wanted to try his luck at wooing a female  elsewhere. There are several reasons why we suspect this. Firstly, the quality of Bing’s booming, something that’s associated with mate attraction, dropped steadily throughout the breeding season. This was not observed with the other marked males. Secondly, we had fewer observations of unmarked non-booming birds (females?) within Bing’s territory compared to some of the other booming males. This causes us to suspect that any visiting females were not staying for long. 

Thirdly, in the final days leading up to Bings disappearance he became more transient, often appearing in places that seemed well outside of his usual territory.

 

For example, two days before his disappearance he was found in the heart of his neighbour’s territory cavorting with two unmarked non-booming bitterns. His neighbour was booming within 100 metres of these liaisons - A final desperate attempt at securing a Lake Whatuma female perhaps??

 

Finally, after Bing’s disappearance we searched his territory for evidence of nest  attempts and were unable to find anything  to suggest he had attempted to mate with a female. We believe he was a single male trying his luck, but still can’t say this with certainty because many of the birds interacting with Bing were still unmarked and the sex of bitterns is difficult to determine from plumage alone.

Still, if we had not had the transmitter on him we would have never known that about these behaviours. Interestingly we observed similar transient behaviours with the other five marked bitterns. Although for them these observations occurred much later in the season and coincided with the time when we were expecting bittern chicks to fledge.

At this time of year (December/January), it makes sense for males to be more mobile, as chicks are supposed  to be relatively independent after fledging,  leaving few reasons for males to invest time and effort in maintaining their territories.

 

As you can see we still have much to learn about bitterns, their needs and behaviours. However, just in these last six months, through the use of the transmitters provided by Ducks Unlimited, we’ve been able to associate some of our observations with individual birds allowing us to put these observations into greater context.

 

All six of our marked bitterns have now left Lake Whatuma – again something we did not (and could not) have known would happen if our marked birds were not carrying transmitters.

We plan to continue following these six bitterns over the next six months. Hopefully the more we learn about them, their movements and habitat requirements, the more these observed behaviours will start to make sense.