Displaying items by tag: Transmitters

Sunday, 20 January 2019 03:35

Hunt for the puweto

The spotless crake or puweto is only half the size of a blackbird and extremely shy but Dr Emma Williams and DOC ranger Rose Graham are experts at getting them to reveal themselves. Emma and Rose teamed up this year on a project to monitor spotless crakes in Waikato’s peat lakes Rotomanuka, Ruatuna and Areare where restoration work is being carried out by DOC and Fonterra’s partnership, Living Water.

DOC’s Arawai kakariki restoration programme has been investigating whether the species is a suitable indicator species for wetland restoration. Spotless crakes are thought to be suitable because they have large clutch sizes of up to five eggs – sometimes producing two clutches per season. They’re also very vulnerable, with nests and chicks being easy prey for a range of wetland predators.

The crakes need specific plants and good water quality for their habitat and food to survive. Theoretically, these specific requirements suggest crake numbers will increase quickly (within a few generations) at any sites that have good predator/weed control and have been restored with the right plantings. As long as wetland restoration efforts cover their home ranges adequately, more crakes should tell you that your restoration efforts have been a success.

Monitoring so far suggests this is true. To date, all three Waikato peat lakes have had three years of management and crake monitoring. During this time, the number of birds detected at listening stations (areas where puweto calls are played) have increased from 11 per cent to 42 per cent of the time. Crakes also rely on habitat that is important for other endangered species, such as the nationally critical Australasian bittern (matuku), suggesting their presence can indicate conditions are good for these species too.

Spotless crakes are a challenge to work with though. Many crake and rail species are difficult to sex as males and females often look similar – puweto are no exception. So little is known about the species, even attempts to sex them using their DNA is a challenge. This is because there is no baseline information to confirm which DNA testing methods are most appropriate to use. Unless you have a known male and female to test your DNA methods on, then you can’t tell whether the results you get are true or not.

To help with this, Arawai kakariki and Massey University are taking DNA samples from dead crakes found in museums or DOC freezers. The sex of these samples is known because internally the reproductive organs of male and female birds are distinct, and this information is recorded during the autopsy. The DNA test results from these samples can then be used to interpret DNA results taken from the live crakes captured in 2017 and 2018.

To monitor crakes, observers sit out and listened for 10 minutes at each station, three times each summer, in the morning or early evening. Each observer plays local puweto calls intermittently and records any sightings or sounds heard. They are shy so are rarely seen during surveys but are often heard calling back in response to calls.

To radio-track the crakes, Emma and Rose first had to catch them. To do this they trialled cage traps and a hinaki-type net (also known as a fyke net).

The net is usually suspended in water to catch fish. It has a series of funnelshaped openings, which makes it hard for fish or birds to escape.

However, to catch puweto on land, the net must be properly suspended above the water by using twisty ties, string, and stakes. Placed in naturally occurring tunnels among the raupo, and channelled with weed matting, this style of trap has proven the most successful to date, having caught four so far.

Once a bird has been caught, Emma bands it and attaches a transmitter to the bird’s back. They are so small that only tiny transmitters (the size of a jelly-bean) can be used – each lasting been four to seven weeks, and weighing less than a gram. Once the transmitter is attached, the bird can be released.

After that, Rose and Mark Lammas use the signal from the transmitter to refind birds. They follow each bird carefully for three hours a day in all weather conditions every day until the battery life on the transmitter has expired. To refind birds, Rose and Mark listen to the signal produced by the transmitter using a hand-held radio antenna.

Often the tracker gets within 10 to 15 metres of the bird, which usually stays out of sight in the dense lakeside vegetation. “It would appear one of the survival techniques of crake is that you can be right next to them and never know they are there. They can sneak across small open spaces without you seeing them at all,” says Rose.

The project was funded by the Living Water partnership (DOCFonterra).

Transmitters were purchased by DOC’s Arawai kakariki restoration fund.

Published in Issue 175

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The secret life of male bitterns

Typical male: Elvis Presley in cage trap looking at his own reflection.

Finally revealed by DU transmitters

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.

Published in Issue 163

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Habitat te Henga

Mutterings from the Marsh

Nearly nine months since the release date on January 22, and things are looking good for the first trial cohort of 20 pateke at Habitat te Henga.

Although rarely seen, their radio transmitters give the show away and let us know they have tended to take up residence in separate parts of the wetland. Many are clustered within a few hundred metres of the release site, while others have shunned their companions and are contentedly at the extremes of the wetland, west or east.

Required by the Pateke Recovery group to monitor the birds intensively for the fist six months, but only at monthly intervals beyond, we have been able to have volunteers maintain a weekly survey. With spring upon us and with certain pairs sticking close to each other we hope the more frequent monitoring will give us an indication if nesting is occurring.

Another more sombre reason though is that if a mortality signal is generated, we might be aware sooner and be able to recover a body to possibly determine cause of death. Three times we have had the mortality tone, and two carcasses were found while in the third case the transmitter was accurately tracked to almost 2-metre deep water. Was this a death or a case of harness failure? With that possibility and with an analysis of one carcass that showed no signs of predation but rather a tarsus fracture indicating a probable duck vs. vehicle incident, we have been fairly pleased with our predator control measures.

With no mortality tones in almost five months the population of 16 remaining birds seems nicely stable. But hang on you say, 16 plus three is 19 –what about the 20th? Well you might ask, as pateke channel 54 disappeared after five days and its signal could not be detected near or far at any of three local water reservoirs or along the extensive west coast beaches. Until it returned after 154 days! The prodigal’s return was welcomed but she obviously had other ideas and went again after a couple of weeks.

Maintaining predator control has been a large group of volunteers who check traps- some on their own properties, others checking traps on private or public land. Almost half of the traps though, are tended by our contractor who walks two 12 -14 km trap lines on a regular two weekly schedule. This large number of traps has allowed us to conduct an experiment which is ongoing.Alternate traps are baited with salted rabbit meat or a commercial dried rabbit product. The Statistics Department of Auckland University is analysing the results and by next year will be able to tell us if one is more efficient a lure than the other.

A contentious topic recently, but one I’ve been promoting is the use of UAV not for the casual model aircraft enthusiast, but as a genuine conservation tool. Chancing upon a local UAV manufacturer I was able to get him to look into using a UAV [drone] as an aerial radio receiver.

Drones with cameras used for conservation purposes are commonplace but the use of a drone to be able to track multiple radio frequencies could be a first and for a secretive species such as pateke [or kiwi] might greatly enhance monitoring. Test flights have taken place and for an idea of what the UAV looks like, a short video is on the facebook.com/habitattehenga site.

Other activities include a recent extensive survey of fernbird at three sites comparing the Forest & Bird reserve where predator control has been maintained for 15 years to two new sites only trapped over the past 18 months. This will give baseline date to use when we are able to add rodent control to some of the new sites. Spotless crake were to come in for a similar survey using sound playback in early October.

Meanwhile bittern are being seen more and more frequently. Nice to think it is due to our pest management, but it’s as likely to be due to more observations by interested persons. As with most conservation though, the hardest task is fundraising and a second translocation next year is dependant on successful applications. I’ll tell you how that went in a future update.

John Summich.

Published in Issue 165

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