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Conservation
Without recent conservation efforts it is likely that very few mohua would remain – the species may even be extinct! Mohua conservation relies on research, monitoring, predator control and translocations. Establishment of new mohua populations on predator-free islands has helped to provide greater security for the species. Raising mohua in captivity was trialled at Orana Park in Christchurch but has not been able to contribute any significant results to the conservation program. Monitoring and research is critical to ensure that predator control methods and translocations are successful. But the most important component critical to the conservation of mohua is controlling introduced predators of which the mohua have no natural responses. The current focus of conservation efforts for mohua are maintaining large mainland populations and securing the species on large predator-free islands.
For a threatened species, mohua have a relatively high reproductive rate. Each year they can lay up to four eggs and if the conditions are right once these have hatched and fledged the pair can raise another brood. Therefore, if the factors that have caused its decline can be eliminated or significantly reduced, the mohua has a good potential for recovery. Bring on predator control!
Mohua monitoring & research
Colour banding mohua (demonstrated here by Maddie Charlton) is important for researching mohua so that the survival and breeding success of individuals can be followed. (Photo: Jason van der Wetering)
Scientists Peter Dilks (right) and Colin O’Donnell (left) remove a mohua from a mist-net in the Eglinton Valley. The mohua were colour-banded so that individuals could be identified for research purposes (Photo: DOC images)
Mohua research is a way of finding out detailed information about mohua behaviour, breeding, size of territories and tolerance to different predator control regimes or the success of translocations. The Eglinton Valley on the road to Milford Sound is one site where mohua have been studied in detail by the Department of Conservation scientists for the past decade. This in-depth monitoring requires birds to be caught in mist-nets and then colour-banded so they can be individually identified. Scientists can then map their territories, identify pairs and closely follow an individual’s survival and breeding success relative to different predator control regimes or following translocations.
Mohua research is also undertaken on Ulva Island, Stewart Island by Otago University. In past years research has also been undertaken in the Hurunui and Hawden Valleys in Canterbury.
Do you have a head for heights? Researching mohua involves much more than chasing after them through the forest with your binoculars, as conservation ranger Jason van der Wetering knows too well. Jason has worked for the Department of Conservation in the Eglinton Valley for three summers researching mohua. A favourite part of his work was climbing the large red beech trees to check on the mohua nests.
Predator monitoring & control
To be able to protect mohua from introduced predators it is important to understand the rodent and mustelid dynamics of each site. In New Zealand beech forests - the home of the mohua - predator abundance varies each year relative to the amount of food available. Food supply is greatest in the autumn after a year when the beech trees have flowered – an event that only happens once every few years. Once the beech seed has fallen, rat numbers increase followed by a build-up of stoats. If there is no predator control at these sites then rats and stoats form plague proportions and have a devastating impact on small bird populations, preying on native species such as mohua. Between 1983 and 1993 mohua population crashes occurred at six sites after heavy beech seeding and the subsequent stoat and rat plagues – events that we can’t afford to repeat if mohua are to survive!
Web: watch this video where scientist – and Mohua Charitable Trust representative – Graeme Elliott explains how suppressing rats in our forests protects mohua
www.doc.govt.nz
Seed-fall a useful predictor – To estimate when rodent and mustelid numbers are likely to increase to plague proportions, conservation rangers use seed-fall traps to collect beech seed. With “ladies stockings” surreptitiously hidden in their daypacks, rangers walk to their seed-fall tray sites and attach a stocking to the bottom of each of the seed-fall tray funnels. The stockings are left out for several months, collected and the seeds counted to provide an index of seed-fall for the area and an indication of if and when predator numbers are likely to increase.
Web: read about how seedfall and rodent monitoring in the Catlins Forest has helped the Department of Conservation to protect the mohua population from a rodent plague
www.odt.co.nz
Tracked by the ink – Monitoring the abundance of rodents and mustelids using tracking tunnels provides an important indicator of predator numbers and information on when predator control is required. The three key ingredients required for monitoring using tracking tunnels is peanut butter (to attract rodents), meat (to attract stoats) and ink - to record their footprints on cardboard as they walk through the tunnel. Monitoring usually requires ten transects of ten tunnels that are each spaced 50 m apart. The results provide a relative index of rat and stoat numbers that can be repeated several times during the year to detect any increases. In the Catlins Forest a tracking index of 10 – 20% is within the range that Catlins mohua can cope with, but if rat numbers reach above 30% then DOC staff begin to instigate predator control.
Did you know? In the red beech forests of the Eglinton Valley, Fiordland, a double beech mast event (two seeding years in a row) caused the near extinction of a once healthy mohua population. Tracking tunnel results showed that from 1999 to 2001 an unusually high number of ship rats erupted in the forests and were the likely cause of the loss of mohua, rather than stoats that were being controlled in the valley. Since then the Department of Conservation has implemented an intensive predator-control regime in the valley including bait-stations that are filled to time with any potential rat explosion.
The Mohua Charitable Trust helped return mohua to the Eglinton Valley through a transfer of 69 birds from Chalky Island in 2010. During the 2010-2011 summer 62 new mohua fledged and by March 2011 the Eglinton Valley mohua population was back up to at least 114 birds – a remarkable story of how good conservation techniques and help from the community can return mohua to our forests.
Time to fight back – Once predator numbers start to increase and a plague looks likely, it is important that swift action is taken to reduce rat and stoat numbers before mohua populations are decimated. There are several different methods available for predator control in beech forests. The most common method of stoat control is kill-traps (DOC 150s or 200s) in a wooden tunnel baited with a hen’s egg and meat. This trapping method also kills some rats but they tend to fill up the traps rather than have any significant impact on the rat population, especially during plague years. Stoat trapping is carried out in many areas throughout the year, without any complimentary rat control.
Ground-based bait stations are a good option for rat control in terrain that allows easy access and management. Bait stations are spread on a 100m grid throughout the forest and a toxin such as Pindone is placed in bait stations to prevent predator plagues. Ground-based predator control is now implemented across 4800 hectares of the Eglinton Valley, Fiordland to avoid rat and stoat plagues.
Aerial toxin operations are the best option for rat and stoat control in remote and large areas that are hard to reach with ground control. The main toxin used for aerial control is 1080. Trials have shown that almost 100% of rats are killed when aerial operations are pre-feed with non-toxic bait. Mast driven aerial operations are the main tool used to protect mohua in the Catlins Forest, Landsborough Valley and Blue Mountains Forests.
Web: click on the link below to watch a short video on predator control methods used to protect mohua from stoats and rats in South Westland
www.doc.govt.nz
Web: visit the following link to find out more about the benefits of 1080 poison for pest control
www.doc.govt.nz
Removing the top predator – What impact does removing stoats from the ecosystem have on the rat and mice populations, and subsequently the mohua? The food web in a beech forest is now a complex system with both native and introduced animals to consider – who eats who? Stoats are currently the top predator in our modified beech forest ecosystems and prey on rats and mice, as well as native flora and fauna. If stoats are removed from beech forests – as is now often the case through stoat trapping programs – there are fewer predators to keep the rodent numbers in check. By removing the stoats, are we allowing rat numbers to increase to levels where they can have more impact on mohua populations than the stoats we have removed? Is each situation unique to the year and site? Ecology is a complex business, but important to consider when implementing predator control regimes.
Translocations – a vital tool
The technique of moving threatened species from one site to another – known as translocations or transfers – is now a well-developed and essential tool for the conservation of many of New Zealand’s bird species including mohua. Translocations provide the opportunity for new populations to be re-established at sites where mohua have become locally extinct. Release sites will often be islands where introduced predators have been all but eliminated or mohua can be transferred back to mainland sites that now have predator control. Translocations also allow for mohua from more vulnerable mainland populations to be harvested and more secure populations to be established from these birds on islands.
The first transfers of mohua occurred in the late 1980s. By 2012 at least 16 mohua translocations had taken place moving birds from one place to another for conservation benefit. The Latest Known Status of Mohua Populations Table contains information on the source sites, release locations, number of birds transferred and the year of transfer for each of these translocations. New transfers are continually being planned to ensure the future survival of the species and to restore local ecosystems.
Did you know? The most recent and historic mohua transfer occurred in October 2011 when 60 mohua were moved from the Landsborough Valley, South Westland to Resolution Island, Fiordland. This is the first step in establishing a large, secure population on the 20,860 hectare predator controlled island. Step two is a second transfer of 30 – 40 mohua from the Catlins Forest to Resolution Island that was scheduled for October 2012 and supported by the Mohua Charitable Trust. Unfortunately poor weather meant the transfer had to be post-poned and rescheduled for 2013.
The next large, secure site for mohua is to be on Resolution Island, in Dusky Sound, Fiordland where 60 birds have already been transferred and more will join them in 2013 (Photo: DOC images)
As mohua transfers require skilled catchers (sometimes up to 20 people), many resources and time to organise usually only one or two can be carried out each year. The Department of Conservation’s Mohua Recovery Group – a group of experts on mohua conservation – help to decide which transfers are of highest priority at their annual meetings.
Preparing a mist-net site in the Landsborough Valley to catch mohua for a translocation (Photo: Jo Whitehead)
Transfers are historical moments in mohua conservation. Here avid conservationists Murray Willans (left) and Barry Lawrence (right) from DOC release mohua onto Chalky Island in 2001.
Genetic considerations
Considering genetics is now a key component of species conservation, including for mohua. The more genetic variation that can be maintained in a species the higher its egg fertility, hatching success rate and general resistance to disease. As mohua distribution and population sizes shrink so does the size of the genetic pool available. Some populations have already been through significant genetic bottlenecks – where a founding population is established from only a limited number of individuals. When establishing new populations of mohua through translocations it is very important to consider the genetic variation of the source population – has the source population already suffered from a genetic bottle neck?
Genetics is a topic that is increasingly being studied and practical applications for conservation management being applied. The latest research on mohua genetics was by Lisa Hegg from Otago University. One of her significant findings and recommendations relevant to conservation efforts was that 60 individuals is the minimum number of mohua that should be transferred to establish a genetically robust founding population. In the case of large islands such as Resolution Island she recommended transferring a minimum of 80 individuals to retain sufficient genetic diversity from the source population. Establishing large populations from multiple source sites can also be another way of increasing genetic diversity of new populations. This research was supported by a grant from the Mohua Charitable Trust.
Did you know? In 1995 the first population of mohua was established on a predator-free off-shore island in Fiordland - Breaksea Island. The mohua were sourced from the Blue Mountains for the transfer. Since then the mohua population on Breaksea Island has taken-off and nearing carrying-capacity. Birds have since been transferred from Breaksea Island to five other islands to establish new populations. These islands (and the year of transfer) include Anchor Island (2002), Chalky Island (2002), Codfish Island (2003), Pigeon Island (2007) and Pomona Island (2010). Chalky Island has also been used to source birds for a transfer back to the Eglinton Valley in 2010. And what do these island mohua populations and the Eglinton Valley now all share in common? The original genetic source of all the mohua is from the Blue Mountains and they have now been through two genetic bottlenecks!
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