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On the Scent - Bittern

It’s a beautiful morning on Lake Whatumā. As the last of the fog lifts and disperses,
leaving the lake’s clear water exposed, Kimi and I float along the edge of the western
shore quietly in our kayak. We’re looking for bittern nests and listening for the
tell-tale bubbling call of chicks.

Local landowner Andy,
tracking a bittern with the
use of an aerial
   

Nearby, peering out of two separate maimais are the heads of Finn McCool and Bernie Kelly. They’re watching careful for any signs of movement within the Raupo – an important job. Kimi and I can’t see more than a few metres in front of us as we move through the Raupo so we always need ‘spotters’ to detect the birds that are present but try to sneak away from us.

Suddenly, Kimi’s black Labrador nose begins to twitch. She’s picked up some scent. Her tail flicks up and begins to bounce from side to side as she reaches forward across the kayak. I slip off the kayak giving her permission to do the same. It is at this moment that we transform into our swamp alter egos. Kimi becomes an elegant torpedo - her otter-like tail propelling her beautifully through the water, until she silently disappears into the Raupo.

And me? Not so much.

My transformation is somewhat less fortuitous. Knee deep in mud, one foot already stuck and water up to my waist - my movements are best described as cloddish and ungainly. I slosh awkwardly after her trying my best not to sound like a heffalump bombing in a swimming pool. As I enter the Raupo, my radio crackles and Bernie announces that a bittern has flushed south of our location. We can never be sure of the sex of a bittern when we see one, but there are a few tell-tale signs that give us a clue.

Firstly, females are noticeably smaller than males, and secondly, in the case of Lake Whatuma, we know that none of the females are wearing radio-transmitters (yet!). Both Bernie and Finn carry radio-receivers. These devices detect the pulse-like signals emitted from any bird that’s been caught and
still carries a Ducks Unlimited transmitter. If a radio-signal is detected, Finn and Bernie can identify the bird and follow its movements even if they can’t see it in the thick Raupo – so when a relatively small
bittern flushes and they don’t get a signal on their receivers they know it’s likely to be a female.

The excitement in Bernie’s voice tells me this bird fits this criteria even before his words confirm it. Another female is great news. We’ve been searching bittern territories at Lake Whatuma for females and nests for a while now. We started unobtrusively by watching over known territories in October for something known as a ‘female foraging flight’. These flights are supposedly undertaken by females when they leave the nest to find food, a behaviour they have to do regularly because the males don’t feed them or the chicks. Such flights are noticeable and have enabled researchers to find nests overseas. By November, we have only witnessed a handful of these flights, and after investigating them further none suggested the presence of a nest. This surprised us. In previous years we’ve found nests by accident and all of them were (or would have been) at chick stage by November.

It was time to up the ante…and go in with the dog. Since November we’ve swept every known territory on foot looking for evidence of nesting. Up till now, and with the help of spotters like Bernie and Finn, we’ve been able to find at least four small unmarked birds (females), but none of them appear to show any interest in breeding. This latest bird would be the fifth. Bitterns are polygynous, meaning males often have more than one female. So it’s reasonable to expect up to five females to every male. To only find five on the whole lake – a site with at least twelve booming males – is somewhat concerning. If not down-right depressing.

To add to our concerns – the five males that still carry Ducks Unlimited transmitters at Lake Whatuma have been very unstable in their territories. They started off well, with all five returning to the lake in August to boom as usual and fight over the usual patches of real estate. Yet by October only two appeared to have claimed a Raupo patch. The others had spent all their time interfering with their neighbours before leaving to try elsewhere. Why are they not finding what they need at L. Whatuma?

So when Bernie confirms a fifth female. I think we can be forgiven for thinking we’d won the lottery. He immediately directs me southwards towards where the bird came up...but Kimi has different plans and starts heading northwards into the breeze. I pause for a second. On one hand I have a confirmed sighting to the south. A rare opportunity to reward the dog on fresh scent and a possibility that there was a nest nearby. On the other hand my dog clearly thinks she’s onto something better, and as I can’t be sure what the dog nose knows and John Cheyne is always telling me to ‘always trust your dog’…I decided to abandon the sterling advice of the spotter and follow Kimi’s lead.

I wasn’t disappointed. It took us awhile to find the four perfectly formed olive eggs that were tucked away on a carefully constructed platform in the thick Raupo. We think the nest belonged to the same bird that the spotter saw. Kimi has been trained on feathers and the live bird’s scent, and in this case the wind would have been wrong for her to detect the flushed female. Instead we suspect that the female moved south to evade us as we entered the Raupo. Kimi hit its scent track and was able to follow it back through the vegetation. It was definitely a team effort requiring all parties - the spotters,
dog and handler.

There are several reasons why we’re particularly interested in finding nests this season. We have little knowledge of how successful bitterns are in breeding and whether chicks survive to adulthood. Nests are notoriously difficult to find and this is part of our problem. To date we’ve had great success in developing methods for monitoring male bitterns (through their conspicuous booming call) but have no means for detecting females and chicks. Yet it’s the females and chicks that are our capacity to save the species. Just like money in the bank, the more we start with, the greater the capacity to grow our fund (or bittern population). One male can fertilise several females, so it’s the females that limit the size of our deposit. The more eggs she lays the higher the interest rate, and the more chicks that survive the greater the deposit in the following year.

…and of course to achieve this you have to prevent your significant other from hammering your credit card (prevent threats) in the meantime – this is tricky for bitterns as we’re still working out how many we’ve got, who’s hammering the bittern credit card and how much they’re spending…and there are so many potential spenders out there i.e. predators, poor water clarity, fluctuating water levels, poor food availability. We have many reasons to believe our bittern credit card is out of balance. In the last 12 months five starving nestlings have been found by members of the public right in the heart of urban areas – two females in Christchurch, and two males and a female in Tauranga - unusual behaviours for a secretive wetland specialist species. What happened to the parent that caused these birds to wander? Why were they nesting near to such accessible, high-disturbance areas in the first place? All five birds went into captive care and four survived to be released later in the year with healthy weights. We followed these birds post-release using Ducks Unlimited transmitters. To date two have died of starvation, one is missing – leaving a lone female surviving in Tauranga as our starting deposit.

As recently as 2010, surveyors at Whangamarino wetland – a site touted to be the national stronghold for bitterns – regularly recorded 50 + bittern calls within 15 minute long surveys. The number of birds calling could be as many as 12 individual birds per listening post and there were 40
listening posts – that was a lot of noise and a lot of birds. So many that observers regularly complained that they couldn’t keep track of them all.

Sadly these days are gone. Now the same locations are eerily silent, and observers are lucky to find seven birds across the whole wetland. The Australasian bittern is no longer Nationally Endangered. It is now Nationally Critical - the same threat classification as Kakapo – and the last threat classification
before Extinction. The clock ticks…all year around multiple threats hammered away at the bittern credit card…and once a year there’s a short opportunity for bitterns to make their
deposits. …how much longer before the balance turns red?

Emma Williams

 
 
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