Waikato magpie wars

Forest and Bird, Issue 281, 1 August 1996, Page 32

Waikato magpie wars

While not in the league of possums and stoats; magpies and mynas are increasingly being recognised for their damaging impacts on many native bird populations. JACQUI BARRINGTON examines some ingenious methods being developed for controlling these introduced pests.

VER-FHE LAS? three years, a Waikato valley east of the Hakarimata Range near Ngaruawahia has seen some innovative environmental work. Graham and Diane McBride began a programme of integrated landcare on the farm they’ve owned for 12 years. The work has included improving the wetlands, weed and pest control, and tree planting.

They tackled possums, hares, rabbits, feral deer, ferrets, cats and wild pigs. They dealt to the willows in the wetland that were choking the kahikatea and cabbage trees. They created three lakes, planted woodlots of black walnut and Tasmanian blackwood, set up a native plant nursery raising kahikatea, rimu and tanekaha seedlings, and planted at least 100 trees each year including some specifically to provide more food to encourage native

birds. The trees thrived as did the wetlands. But no native birds returned. Graham, who was born locally and has lived in the area off and on for some 20 years, mulled things over with the manager of the adjoining farm, Greg Barlow, and they came to the conclusion — somewhat reluctantly — that maybe the local increase in magpie numbers was to blame. Greg, an Australian by birth, was uneasy at the idea that these icons from

his country of origin might be the problem, but came around to the need to control their numbers. It was Greg, using plans for a humane birdcage trap with two spring-loaded doors developed by a Danish gamekeeper in the 1950s, who knocked up a magpie trap. It was probably the first Larsen trap used in New Zealand. Over the next two years Graham, Greg and a third adjoining landowner, Padam

Malepati, trapped over 400 magpies between them. Graham advertised their work by stringing up the dead birds along his roadside fence. While some neighbours were disgusted and accused him of cruelty, the results speak for themselves. For the first time in many years native birds have returned, along with small exotic finches. It is thought the three adjoining properties lie along a flight corridor from nearby native forest which the magpies had blocked. With the removal of the magpies, the corridor has been reopened, bellbirds are once again singing in the valley, and the first kereru in seven years and the first juvenile tui in 16 years have been sighted. Some of those neighbours who criticised the programme have now thanked the trio and expressed their appreciation at hearing a dawn chorus of native birds once more. UT GRAHAM, Greg and Padam there was room for improvement. While Graham developed a lightweight version of the Larsen trap, Greg felt the Larsen was too small and obtained plans for a walk-in "letterbox" trap from the UK Game Conservancy. This trap is a free-standing structure, some 1.8 metres high and wide, and 2.5 metres long,

with a wooden frame covered with wire mesh. The roof is recessed downward in the centre where a letterbox-style entrance is positioned the length of the trap with a number of wooden perches placed across it. Once the magpies are caught, a quick blow to the head on a nearby fencepost stuns them. Then cervical dislocation (pulling their necks) or shooting in the back of the head with an air-rifle ensures a quick and humane death. The trap is particularly suited to rural situations. It is far less labour intensive than the Larsen which must be continually cleared and reset. Its record is 16 magpies in one day. The secret of success is positioning, preferably on a hilltop with some tall trees nearby already favoured by magpies. Ideally, traps should be cleared late in the day when no other magpies are around. By limiting the amount of human involvement with the traps, other magpies hopefully won’t associate them with people and will be less likely to get wise. For those who worry about the caging of a wild bird, these traps are so efficient that the "call" magpie used to attract others to the trap can usually be changed daily, as soon as more are caught, thereby cutting to a minimum the time a bird is held in captivity. The call bird has a perch, a roof over its head, water and food in the cage (bread and dogroll go down a treat), and the bird rarely exhibits any sign of stress unless the cage is being moved. Any trap should be firmly anchored to a fixed structure; on Waiheke Island two Larsen traps have been stolen, and in Hamilton call birds have been freed. Greg and Graham are now looking at modifying the letterbox trap — by making the access smaller — to see if they can tackle the huge numbers of resident mynas. The trick will be to exclude harriers that otherwise come into the trap for a free lunch. The harriers can of course be released, but their presence prevents the capture of any further mynas.

around the same time as Greg and Graham were developing their traps, engineer Philip Leyden was wondering what had hit the Owairaka valley near Te Awamutu, where he’s lived for 25 years. Magpie numbers had rocketed from five in 1994 to around 40 the following year. "Tt was like a scene out of Hitchcock’s The Birds," he says. "They took over the skies and the land. Overnight the dawn chorus, apart from their own, dried up." Using his engineering expertise he modified the Larsen trap to a lighter, all-metal Z N ANOTHER part of the Waikato, at

construction with four capture compartments instead of two, allowing two pairs to be caught at once. Over a six-week period he trapped some 70 magpies, before the native birds returned. His company, Leyden Fabrications, is now making traps to order, for sale at $350. Magpies, and also mynas — unlike native avian predators of chicks such as harriers — appear to perform a kind of ethnic cleansing in their immediate area, playing a pivotal role in excluding native

birds from mixed habitat like rural and urban areas with pockets of native forest. Both species are also increasingly moving into bush areas and colonising the margins, with former tui nesting sites in the Urewera, for example, deserted since magpie arrival. The adverse effects of magpies and mynas are most severe when native birds are at their most vulnerable — at nesting time. While the evidence that magpies impact on native birds is still largely

anecdotal, it is convincing enough for the Waikato, Auckland and Northland Regional Councils to have included magpies in each of their Regional Pest Management Strategies — Northland’s also includes mynas. In practice, however, the councils are only committed to handing out information to landowners on humane control methods, rather than to mounting control programmes themselves. Official control programmes are

unlikely until the level of effects of magpies and mynas on native birds can be quantified by hard scientific research. But this is the Catch-22. DoC, which has the statutory obligation to deal with threats to native fauna, has so far been unwilling to fund any research on the grounds that there is no "evidence" of the impacts. Forest and Bird looks forward to the development of more research projects such as David Tindall’s myna study (see box opposite). With a proliferation of threats now facing most native bird species, the contribution from magpies and mynas is one threat that should not be ignored. To those who argue that the magpies and mynas are "just defending their families and territory" and that it’s not their fault they were brought here, spare a

thought for the harassed and displaced native birds whose nesting attempts are thwarted by the intruders, and who increasingly have nowhere else to go. Note: Magpie/myna call tapes can be obtained from the Fish and Game Council, RD9, Hamilton for $10. Plans for the Larsen and the "letterbox" traps are available from Forest and Bird’s Auckland and Wellington offices (please send a SAE).

JACQUI BARRINGTON 15 Forest and Bird’s northern field officer and has led the campaign to have magpies and mynas recognised as significant pests of native birds.