This workshop was organised by Wildside, the trapping arm of the Banks Peninsula Conservation Trust. Around 30 people were present, those from furthest afield being a carload from the Ashley-Rakahuri Rivercare Group in Rangiora – Geoff Swailes, George Scott, Eddie Stancombe and Nick Ledgard.
The workshop started off with a welcome from the main organiser, Marie Haley of Wildside. Andy Cox from DOC then introduced some basic parameters of trapping:
- How habitat determines what predators do best, and therefore which are likely to be of most concern and should be targeted.
- The importance of targeting predator control in locations where it is most likely to make a difference (e.g., where endangered plants exist or birds are nesting).
- Picking winners, rather than setting traps everywhere.
- You could end up just ‘harvesting’ predators ie. keeping them at a constant level. But ‘harvesting’ can still reduce the level of predation.
- The ability to sustain effort long-term – or any gains made can be quickly lost.
- The advantages of ‘pulsing’ control efforts – undertaking periodic ‘hits’ rather than continuous trapping. Pulse at times of most likely success – such as winter when animals are most hungry.
DOC has a range of ‘best practice’ predator control documents. These aim at predator elimination and/or maximum control, and can therefore be too elaborate for amateur implementation. This is why they are not available to the public over the internet. However, they contain much useful information, are worth consulting, and can be obtained from DOC.
Andy then went on to talk about rat eradication.
Rats have the habit of sampling food, before returning to eat large amounts – hence the importance of pre-feeding, so that no early ill-effects bring about bait shyness. Using anticoagulant poisons such as brodifacoum, eradication is very attainable on islands (even very large ones), where a couple of well organised ‘hits’ can get all rats and there is little chance of reinvasion. But elimination is not possible on the mainland, due to ‘open’ boundaries allowing ready reinfestation, plus the need to avoid repeated use of certain poisons because of bioaccumulation. Too many repeated ‘hits’ also promotes resistance and bait shyness. There are two types of anticoagulants – first and second generation. First generation, such as warfarin, needs multiple feeds to be effective, but is less persistent in the ecosystem and leads to less bioaccumulation. Second generation is far quicker acting and often requires only one ‘hit’, but is more persistent in the environment and bioaccumulative. Therefore second generation poisons should not be used too often – the rule of thumb is not to use them more than twice over the lifetime period of the main species one is trying to protect. Bioaccumulation of poisons in animals further up the food chain is to be avoided, but to date there is no evidence of any harm to ‘accumulating’ animals.
Wayne Beggs of DOC spoke on cat and mustelid trapping.
Cats can have home ranges of 1-50ha, so trap density varies. In riverbeds, traps are often at 50m intervals. Main traps are Timms and Sentinals. Legholds can be more effective than kill-traps, but must be checked daily. Similarly with cage traps, which some people reckoned were more effective than kill-traps. Cats like to use open tracks. There are no good poisons for cats. Also cats can readily regurgitate any food which feels not right, so little time for poisons to take effect.
Mustelids. A stoat’s home range can be from 40-250ha. They do not store fat, so must eat regularly – reckoned to be 25-33% of body weight daily. Hence their storage of food in dens, which are visited as part of set routes around territories. Traps are often set at 100m intervals. Main trap is DOC 200 (250 for ferrets), which is approved as killing humanely. Fenn traps are probably better, but are not approved as humane . ‘Catch-em-alive’ treadle traps are said by some to be best of all, but need daily checking. Baits are eggs and fresh meat, with the latter the best. It is strongly recommended to vary baits used, animals get ‘bored’ with the same offerings all the time. Put small pieces of bait outside traps (prefeed), to ‘settle down’ animals and make them less nervous about entering traps.
There is recent evidence that double sets can be better than single. Two DOC 200s can be in one box (with bait in between), or two boxes can be set back-to-back. The possibility of putting a DOC 200 and a Timms at same location to create a food ‘hub’ was discussed. But would the smell of cats deter mustelids from visiting?
The recently developed gas-powered resetting traps are improving and gaining acceptance, particularly for rats and possums. There are still problems with artificial lures – not yet as effective as natural baits.
After tea and biscuits, we went outside to see trap demonstrations.
Some take-home messages for our Ashley trappers:
- Use a variety of bait types, changing them fairly frequently.
- In DOC 200s, use a board half-partition instead of central mesh baffle. Easier to make and install, plus simpler to extract trapped animals.
- Test DOC 200s for correct set-off weight – 85 gms for weasels.
- Predators do not like smell of freshly treated (CCA) timber, so will avoid such traps until well weathered. Not much we can do about that.
- As we make traps, we are ideally placed to make and test design variations. Evidence that boxes and tunnels with straight walls and floors better than those with deviations created by traps protruding above floors and out from walls.
- Keep records of which traps, and which trap locations, work best.
- Buy some Sentinals and try them out on cats.