Thursday, April 28, 2011

Bitterns – “kings of the wetland’

Bitterns – “kings of the wetland’
Peter Langlands
29 April 2011

Duck shooters are advised to take care not to accidentally shot a bittern during the upcoming season. These large birds are an endangered species and listed by DOC has “Nationally Threatened” and are fully protected.
Bitterns have evolved a streaked brown and black plumage to camouflage in with reed beds. The birds are about a kilogram in weight, half way in size between a mallard and Canada goose, but have a large pointed bill. Bittern often startle you as these large birds will flush out of the reeds at short range.
Bittern (or as they are known Matuku) have benefited from waterfowl wetland enhancement work done by Fish and Game and private individuals. But with over 90% of our wetlands drained the bittern have over all declined. Bittern are very much a bird of our larger wilderness wetlands, but are often sighted in drains and on farmland from March to June.
Although common at the Whangamarino wetland are bittern are quite scare and spread out though much of the country with a nationwide population of around 750 birds. If any shooters sight bittern or have photographs of bittern I would be keen to hear from you as I am collecting bittern records for a national database to assist with the conservation of the species (email –

Photograph shows a bittern in flight at Te Waihora (c. Peter Langlands- Bittern researcher).

Thursday, April 14, 2011

As another season ‘Bitterning’ at Whangamarino wetland comes to an end- by Emma Williams

How do you monitor a bird that is adamant it’s a blade of grass?!
Emma Williams
As another season ‘Bitterning’ at Whangamarino wetland comes to an end, it’s time to wash the mud off the waders, empty the water out of the gumboots, and go back to the desk to work out what on earth was going on.
This was our second season of research out in Whangamarino. Our objectives were to develop a monitoring method for bittern and it’s not easy trying to monitor a bird that spends the majority of its time impersonating grass in inaccessible bogs. Yet, as only 10% of their original habitat remains today, it’s never been more important to know what’s happening with the bittern population in New Zealand.
Thankfully, male bittern make a distinct, deep ‘booming’ call during the breeding season, which we are hoping will prove useful as part of a survey method. Unfortunately, the calling-rate of bittern seems to vary greatly over time and between stations. This makes it tricky to detect trends in bittern populations using call counts alone. For example, this season at Whangamarino wetland, 234 ‘booms’ (per 1.5 hours) were recorded at one station in October. Yet, only one month later, no bittern were recorded from that same listening post. Did the bittern move or do they just have fewer reasons to call?
Hopefully we’ve got enough data this season to get some idea. In 2009, Lynette Plenderleith and I went hard out trying to see if bittern really are as crepuscular as everyone suggests. The evenings looked good, with a beautiful peak in calling-rates appearing about half an hour after sunset. Mornings were not so clear cut, with lots of sub-peaks leading up to sunrise. After several mornings of dragging ourselves out of bed at 2am, only to discover that bittern were already up and booming, we concluded that something else was going on. One morning we both came back adamant it was the moon. This has been proposed before by others, such as Philip Teal and Jono More. Teal suggested that the moon was somehow linked to bittern food sources, like the movement of whitebait. Who knows though, may be it is just easier to advertise yourself to the opposite sex when you can see the female, she can see you, and most importantly, you know where her mate is lurking.
So this year (2010) we were back out there again, trying to get more information. Unfortunately, Lynette couldn’t make it - she decided frogs were her passion, and the temptation of a full scholarship and PhD in Australia was just too she passed her waders onto Elise Verschoor, and the swamp fever continued.
The objectives of this season were slightly different. We wanted to know more about the extent and cause of variability in calling-rates. We also needed to get around some of the issues that were limiting our sampling regime. Fundamentally, that we couldn’t sample more than two sites at once, and large sections of the inner wetland remained un-sampled (some places just took us too long to get to without a boat, and others you wouldn’t come back from, especially in the dark!). To solve this, Graeme Elliot and Stuart Cockburn lent us some of their bird recorders and we were able to directly compare MONO and STEREO recordings with results collected from an observer in the field.
The results so far
Its early days and there are still recordings to process, but things look promising. Recorders appear to be as reliable for detecting ‘booming’ bittern as a person physically in the wetland. In fact more reliable - at least with recordings you can ‘pause’ to write when multiple bittern boom at once.
It will take us a little longer to process the data regarding the variability in calling-rates though. What we do know already is that bittern call-rates peaked in October as predicted. Also, contrary to expectations, we detected a second peak in one small area of the wetland (the causeway). Although not common, this second peak has been observed before with the Eurasian bittern (Botaurus stellaris) and is thought to be associated with males advertising feeding areas to fledglings or females becoming available again after nest failure . So, is it a coincidence that most of the ferrets the Department of Conservation caught during their ‘mark-recapture’ trials were along the causeway this year? Who knows? The research continues, and we still have a long way to go...but we will keep you posted...

Wednesday, April 13, 2011

Update from Colin O'Donnell- on bittern from DOC's work

Progress with developing monitoring techniques for cryptic swamp birds (bittern, fernbirds and rails)
The Department of Conservation has begun developing monitoring methods for swamp birds over the last year. We require robust methods to map distribution, identify critical habitats and monitor response of swamp birds to wetland management. Methods need to be sensitive enough to detect significant population changes within relatively short timeframes so that management can be adaptive. So far we have developed a national database for Australasian bittern, reviewed impacts of introduced mammalian predators on wetland birds and trialled automatic bird call recorders for recording bittern. Bittern usually call at night, with peaks at dawn and dusk and live in some deep swamps, so they are challenging to monitor using conventional means - so using auto recorders for inventory and/or monitoring is a promising possibility. In field trials at Whangamarino wetland in the Waikato region the recorders were excellent at recording bittern calls (up to 50 boom trains per 15 minutes) , with the recorders generally performing as well as human observers in our initial trials. Work is continuing on identifying the best time of year and night to monitor numbers and designing the sampling methods needed.

Contact: Colin O’Donnell (


Dr Colin O'Donnell
Ecosystems and Species Unit
Research and Development Group
Department of Conservation — Te Papa Atawhai
VPN: 254985 | M: +64 276602476

Conservation for prosperity Tiakina te taiao, kia puawai

Tuesday, April 12, 2011

Key bittern locations in the South Island

Hi all- the map attached some key sites (n=13) where bitterns currently occur within the South Island.
Click on map thumbnail to expand the image

If any one wants any detailed maps within each site then please email me
-Peter Langlands

Why do bitterns "freeze" on roads ?

From: Chris Gaskin
Sent: Tue, 12 April, 2011 7:33:11 PM
Subject: [BIRDING-NZ] Interesting encounter on the way ...

Hi all,
Heading to Tawharanui this morning for a meeting, came round a corner on the low flats area (just after Sandpiper Lodge and before the windy climb through the woods) and found a bittern standing in the middle of the road, beak skywards. Invisible - yeah right!
The bird rocketed off, flapped to the side of the road to land in the grassy verge. I stopped, great views. When I pointed the bird out to some people in the car behind, all I got was ...... Stunning bird. Check out the drainage ditches leading off from the road next time you're out there.
When I mentioned this at the meeting Maurice (one of the rangers) commented he'd see one the day before in the little tidal inlet beside the road (opposite the Lagoon). Good place for banded rail too.
Happy birding-

My reply to Chris's posting -
Hello Chris- thanks for your posting. Bitterns are vulnerable to being road-killed and suffer form collision events- which I suspect have increased as the bird's habitats have become increasingly fragmented. Also each year several birds are brought into bird rescue centres having been involved with car- over head power line collision events. I am working on analysing data from the National bittern database at the moment about causes of bittern mortality- with Colin O'Donnell. When they freeze on roads it doesn't help their cause- also with such a small population now ( 750 ?) it makes these records of collision events more important for this nationally threatened species. The birds visual fields may also may it vulnerable to collision events. While doing the National bittern database which I worked on for a year for DOC I recognised Northland and the Waikato as being NZ;'s two most important conservancies for bittern. If interested Chris I have a bittern blog -