Ducks Unlimited
Monday, 26 November 2018 08:15

Predator Free New Zealand

Maybe - but not just yet

 

Counting every rat, mouse or mustelid trapped may be satisfying, but it is irrelevant in the war against predators and may be lulling us into a false sense of security, guest speaker Professor Carolyn (Kim) King told DU members at the conference.
 
In her speech, Maximising the Duck Harvest, Prof King, from the School of Science at Waikato University, thanked Ducks Unlimited, which like many hunting clubs around the world, had turned itself into a conservation group, supportive of conservation research organisations and with members who were observant naturalists contributing to conservation efforts.
 
She said a good harvest operation:
  • aims for a sustainable yield
  • never takes more individuals than the population can replace
  • can be like the constant harvest by rabbit trappers, deer cullers, and predators
  • a population can’t be affected if the yield is not declining.
 
As an example, she said, the winning team in the Great Otago Bunny Hunt in 2012 bagged 1035 rabbits as its contribution to the 10,424 tally from the 24-hour event. During the 21 years of the event, 253,735 rabbits have been killed (mean: 12,082 a year) but it has made no difference to rabbit numbers.
 
Harvesting is a dynamic target-habitatpeople system in which:
  • protection of a valued resource can be ineffective unless broader ecological/ sociological context is understood
  • the interaction of resource/habitat/ people defines the outcome
  • solutions require strategic organisation, stakeholders agreement and effective methods
  • the biology and strategic organisation determine effective policy (which DU does very well).
 
Using an example from Wiltshire in the UK she demonstrated how a predator control experiment produced a surprising result. In two areas of farmland, 1km apart and with similar habitat, predators were controlled in one area for three years and then in the other area for three years.
 
The study had been based on the assumption that habitat on UK game estates was the only important factor but the results clearly showed a big increased harvestable yield of grey partridges in whichever area was subject to predator control.
 A computer model developed from the study predicted that the highest populations would be found where nesting cover for the partridges was increased and predators were removed, even if shooting was permitted as well. Key is the interaction of habitat (controls productivity) and shooting mortality. If nests are protected, more young survive, so shooting can substitute for nest mortality caused by predators.
 
Using a NZ example to highlight the relationship between habitat and mortality, Prof King referred to wetlands in the Upper Waitaki area. In 1850, wetlands and swamps covered 71,000 hectares, but the effects of human activities has been devastating with 7300 ha swamps converted to pasture, more fragmented; 22,300 inundated by hydro electric schemes; 4200 ha braided riverbed dewatered (9% loss); 22,300 ha new open water habitat + 300 km more shoreline which doesn’t suit riverbed birds; predation is heavy and breeding rate low on the remaining 41, 700 ha wetlands (40% loss).
 
Food supply has the greatest effect on bird populations. The braided riverbeds were dewatered or turned into open water habitat, which did not suit the birds adapted to feeding on the riverbed, exposing them to predation and a drop-off in breeding.
 
Prof King said the deadliest predators for ducks were egg-loving hedgehogs, ferrets, stoats, rats, mice and cats. An Upper Waitaki Basin study of predation on the nests of dotterels, terns and stilts showed that cats, ferrets and hedgehogs did the most harm to nesting birds in that area.
 
She said, “We know we can kill predators, so what’s the problem?” Counting a pile of dead pests can be enormously satisfying but it does not tell us what we want to know, which is how many are still there, how to account for those that replace those dead ones, and how to know if we have taken out enough predators to benefit the birds we want to protect. That boils down to what actually determines the numbers of animals – both the predators and the birds.
 
Ferret numbers are controlled by rabbits (their main food source), not trappers. The rabbit yield is not declining: rabbits and ferrets are co-evolved prey.
 
A pilot trial in 2005 presented another serious problem – trap avoidance. Radio-collared ferrets in a study near Tokoroa were tracked by an aircraft which flew over the area during the day.
Nine of the 15 ferrets were located. Monitoring sites showed that six of the ferrets made 22 approaches to 2 experimental recording sites, which could have been traps, but only three entered the tunnels. On the final extensive trap-out, four of the 15 eluded capture, although their radio signals confirmed they were still there.
 
The following year collars were put on 30 ferrets west of Lake Taupo and a new toxic bait dispenser was used. Over five weeks, only 12 visited the bait stations and only eight took the bait. The monitoring regulations said every ferret had to be accounted for but of the 13 known survivors, only two could be caught.
 
In kiwi sanctuaries in Northland, stoats were refusing to go into the bait tunnels and it was only a brief 1080 operation that stopped the decline of kiwi chicks. Though it is awful stuff, we have to use the tools we have until we come up with something better, she said.
 
Predators are intelligent and quickly learn to avoid new devices presenting danger to them. In Britain, American mink, which escaped from fur farms in the 1950s, had become a serious threat to the native water vole (Ratty in Wind in the Willows). The mink, like rats, are good swimmers which means they can avoid land traps set on river banks. The problem was tackled by using traps placed on floating rafts, which might be appropriate to adapt as a control for Norway rats here, Prof King said.
 
 
New technologies are absolutely essential and can transform results. She said at a 1976 conference that she attended senior scientists said rat eradications on islands were impossible, but they were wrong. The invention of brodifacoum in the 1980s plus precise bait placement enabled Breaksea Island to be cleared of Norway rats in three weeks in 1988.
 
“That’s what we need – some kind of new technology that will break the mould, something different... One of the definitions of insanity is to keep on doing the same thing and expecting different outcomes,” Prof King said.
 
We can and must increase the intensity of predator control, but to be effective it must add to the natural mortality. Mustelids were introduced to control rabbits but rabbits were breeding at a faster rate and their numbers were unaffected. The mustelids were only substituting for natural mortality.
Only when rabbit breeding is reduced for other reasons (drought, 1080), can mustelids and/or trappers add to their normal losses, and achieve a real effect
Failures were usually due to some combination of:
 
Human attitudes
  • Forgetting that nature is on the predators’ side and ignoring the effects of natural selection
  • Counting numbers removed, not numbers remaining,
  • Lack of coordinated, agreed strategy
  • Lack of flexibility in response to experience
  • Insufficient stakeholder support.
 
Inadequate technology
  • Inefficient tools
  • Failing to deploy combination of methods
  • Having no effect on fertility, immigration.
 
Prof King said, on the other hand, some of the common features of successful predator control were a combination of:
 
Human attitudes
  • Operator confidence, meticulous preparation, sufficient funding
  • Never repeating mistakes, never giving up, so accumulating improvements, combining/switching strategies when necessary
  • Landscape scale coordination
  • Strong community support.

​New technology

  • Adds to natural mortality
  • Prevents immigration
  • Targets fertility
  • Confirms benefit to native species.
 
Prof King concluded by saying Predator Free NZ was still a long way away but “don’t despair, history is encouraging!”, and DUNZ would play an important role.
In the meantime we must keep using whatever tools we have so we still have native species surviving by the time we develop something better, protecting duck nesting sites is possible and needed now.
 
PFNZ is going to be much more difficult as it requires development of as-yet-unknown, 100 per cent acceptable methods to control predator replacement rates.
 

 

Published in Issue 175
Monday, 19 March 2018 07:22

Boggy Pond April rounds

Last April, I was able to complete the servicing round down at Boggy Pond, Mathews and the Wairio Restoration Block. The total predators trapped there for the month was :
 
1 cat, 5 ferrets, 1 weasel, 9 rats, 29 hedgehogs, 6 mice and 1 hawk.
 
While there I GPS’d another eight potential trapping sites on the new bund wall that was recently created.
 
A Timms trap was missing from the trap site by the Bridge to No Where and a Timms/ DOC 250 was missing past the second bridge  leading to the Viewing Hide. I suspect these  have been stolen as they were there when I serviced the gear in February. These missing traps will be replaced after duck shooting season. I am wary that more may disappear during that time with the influx of hunters to the area.
 
Steve Playle.
 
 

 

Published in Issue 164
Sunday, 25 February 2018 09:58

Ferret lured by sardine juice

This trapped ferret is located in a fenced area adjacent to part of the wetland, note the sprayed access to the trap.

The ferret must have liked the smell of the juice from the ‘Sardines in Springwater’. Note the colour of the ferret, mostly white.

Another hedgehog trap used, DO 200 (pic right). Blackbirds use the top of the trap to crack the snail shells on. It is awash of snail ‘juice’, for the want of a better word, and the trap is surrounded by empty snail shells, sometimes this activity sets the trap off.
Published in Issue 165
Wednesday, 07 February 2018 01:16

Protecting Whio

Keen predator hunter protecting Whio

The Ruahine Whio Protection Trust (RWPT) is a registered charity formed in late 2014 and functions though the efforts of a small group enthusiastically lead by chairwoman Janet Wilson. Its purpose is to raise funds to help protect and raise the number of Whio in the Ruahines and surrounds.

Janet has tramped for years in the Ruahines as a member of the Palmerston North Tramping and Mountaineering Club (PNTMC), and whio are often spotted on the river. Although being a protector of whio was not Janet’s original ambition, she took the opportunity to become a protector of the whio living and trying to survive in the area. Janet took over the running of the Oroua Valley Blue Duck Protection project from the NZDA (Manawatu Branch) in 2011. This expanded in to the Pohangina River in 2012.

“Life hasn’t been the same since,” said Janet. Trapping began in the Ruahines in 2007.  Several groups now look after approx 1800 predator traps, predominantly DOC 200’s. These range from the Aorangi–Awarua Trust’s lands in the North to the Pohangina River in the South. In 2015 a Ruahine Whio Management Plan was developed by these groups with support from DOC, and along with the RWPT, they now make up what is known as the Ruahine Whio Protectors Collective.

Janet still coordinates the Oroua and Pohangina projects. Between July 2015 and June 2016, 110 stoats and weasels were caught, as well as 450 rats. She has a good team of willing volunteers but is always keen to hear from experienced trampers and hunters who might like to help out the whio. For many a tramp in the bush is no longer just a Sunday outing. It has become an ongoing war against the stoats, weasels, rats, and any other likely whio enemy.

Whio are the most endangered bird in the Manawatu and Janet is keen to raise the profile of our $10 duck locally. Janet said the Oroua and Pohangina rivers have the most southern population in the North Island. There are no known whio in the in the Tararua and Rimutaka ranges.

Published in Issue 169
Tuesday, 31 October 2017 02:37

The need for continual predator control

I run a yearly total as at November 30 each year as part of the excellent initiative of the ‘Swamp Comp’.

For the year ending November 2015 from 6 DoC 200 traps placed around the margins of my wetlands, the list was 11 Weasels, 1 Stoat, 2 Ferrets, 33 Hedgehogs and 7 Rats.

So for the 2016 year where 2 more traps were added in February, with the total of 4 Weasels, and Stoats, 1 Ferret, 12 Hedgehogs and 16 Rats it seemed that we were making a great inroad.

It may seem now that the inroad thought was rather premature, with just under 5 months of the current year run, the total sits at 20 Weasels, 3 Stoats, 7 Hedgehogs and 9 Rats.

The other point is that I have one trap [See photo, note there is an egg, I also bait with the juice from Sardines in spring-water] that is generally located in a central position, with the other traps generally outside of it.

That trap known as Cabbage Tree, has accounted for 15 of the Weasels, 2 Stoats, and 4 Rats, the last one as of April 25.

Possibly the high number may be attributed to the very wet Summer-Autumn where the wetland core which is generally only damp under the Harakeke, Coprosma and Toe Toe associations is this year very wet, so perhaps there is a concentration moving around the dryer margins, however that is only a possible theory as equally the food abundance could be another contributing factor.

Ian Jensen.

Published in Issue 172
Monday, 04 September 2017 00:16

Hard Work at Boggy Pond

Steve Playle of the Greater Wellington Regional Council (GWRC) was on the job in early January getting trapping work done around Boggy Pond in the Southern Wairarapa.  
“I started back at GW on the 9th and my first job was to get the trapping work done over 10/11 January.
 
“Predators caught were 5 ferrets, 1 weasel, 8 rats, 21 hedgehogs, 4 mice, 1 magpie, 1 rabbit and 1 thrush. Water levels were still very high in the Wairio Restoration Block and at the southern end there were a couple of big flocks of Pied Stilts in residence. At Boggy Pond the Royal Spoonbills were back in residence where Tony Silbery took his photos of breeding birds last year. I am assuming there may be breeding taking place again this season.
 
“The total major predators taken since the trapping commenced in July 2013 now stands at:
  • 62 cats,
  • 140 ferrets,
  • 8 stoats,
  • 53 weasels,
  • 652 hedgehogs and
  • 295 rats.
There was a period prior to Christmas where it went quiet on the ferret scene but obviously there has been some movement over the festive break. It is great to see the water levels so good in the Wairio Restoration Block,” said Steve.
Published in Issue 170