By Bryce Buckland (Birdlife on Grampians, Nelson).
Trapping groups like to know that their efforts achieve the best results protecting native birdlife. For smaller pests like rats, most groups use the standard box trap with a Victor Professional trap inside. You know what you catch, but tracking tunnels are the popular way to check what is still in the area. But how do you get accurate results from these?
Tunnels measure animal activity so aren’t a true indicator of pest numbers. You cannot be sure a pest hasn’t run back and forth and spread ink all over the indicator pad and you can’t be sure a rat hasn’t got an aversion to go near the tunnel. You possibly get false results. A guess at best.
DOC use tracking tunnels to obtain rat information before 1080 drops and this may be okay, but I believe the method is flawed, especially if it’s not where the rats actually live. Rats (and mice) are a “trigger species” for stoats and weasels. More of these rodents encourages more breeding activity for mustelids, so we need to take every opportunity to reduce rodent numbers.
In bush, (where most groups trap) the best food for rats is up trees. It’s where all fresh shoots, nuts, seeds and flowers are and tracking tunnels get no results from rats living in trees. Rats never need to come onto the ground so never go near a tunnel.
For rats, trees are a far safer place to live. Up there they are much safer from weka, hawks, falcons, hedgehogs, cats, dogs and (especially) humans with scary ground based traps. Many trees also have cosy, dry entrance holes in their trunks just right for raising young in highrise living.
Humans wouldn’t risk living on the street for food if we could live at the supermarket, untroubled and rent free! Unfortunately, trees are where small birds, their eggs and other species such as geckos live. These provide a tasty snack for invading rats so no wonder birds such as robin, tomtit, brown creeper and fantail get decimated by rats.
I could see rats living in a tree at a local reserve that never got caught in the traps we had placed at its base.
I manage a community trapping group on Grampians Hills at the backdrop to Nelson City and I decided to experiment with traps placed up among the branches in some trees. I modified a few Victor traps and nailed them directly above box ground traps.
In spite of them being quite unstable I started catching lots of rats. Encouraged, I looked around for a more stable trap and in August 2014 started using the SnapE rat trap made by Kness of USA. (Victor make a similar one.)
I purchased 20 of these and when compared with our 200 ground based traps, were caught over 30% of our rat totals from trees. From December 2014 to June 2015 our box traps caught 178 rats and we caught 151 rats in the trees (from just 20 traps).
Traps are best nailed in a reclined position, about a “rat’s body length” above the fork of a tree. Laying the trap back stops the peanut butter running out and encourages the rat to lean onto the trigger plate. Nailing the trap loosely with a galvanized clout allows the tree to grow without pushing the trap off and a floppy trap lessens the chance of a rat leveraging itself free.
We use smooth peanut butter (PICs of course) and apply it with a 50mm syringe. This dramatically speeds the job and is less messy.
I have now added an extra 60 of the SnapE traps.
Despite rat numbers currently being quite low, since 1st Feb 2016 to 31st August 2016, catches have shown 142 rats on the ground and 63 in the trees. In winter I would have expected more food on the ground such as fallen seeds etc , but over the last two winters, 60% of rat kills are in the trees.
We now have 97 traps in trees. Several tree traps are put directly above the possum trap and its possible to get a possum in one and a rat in the other. I have also put SnapE Mouse traps above both to stop mice.
Are rats all that cunning? Possibly not. One week I caught a rat’s tail in a tree trap and next week caught the same rat (minus tail of course). In another trap we caught a rat’s hind leg and next week caught the (now) three-legged rat. Apart from these two exceptions, rats are caught cleanly and struck right on the head.
Non-target catches have been low. In two years we have caught one blackbird, a sparrow and two waxeyes.
We don’t have robins. I’m concerned that a robin may be inquisitive enough to get caught in a tree trap.
What I like about tree traps:
• You will catch more rats.
• Less prone to interference from weka, cats and the public.
• They are easy to set.
• Very easy to clear kills. Just lift the lever.
• No handling of contaminated traps.
• Easy to re-bait. (Get yourself a 50mm syringe)
• No need to bend down to a box trap.
• Checking is far simpler. You can see the result from meters away. (Less human scent is good.)
• Even squeamish people don’t mind checking them.
• No boxes to build or maintain. Just nail on tree.
• You can carry dozens to your project in one pack load.
• The raised strike bar encourages the rat to approach in the best direction.
• Not too expensive. (Talk to Farmlands)
• Less bait theft by ground based invertebrates (ants, slaters, cockroaches etc and mice).
• Not blown away in storms
• Seem to last in the bush ok.
• Despite only having a few traps to start with, over two years we have had 46% of rat kills in the trees – rats we may never have caught.
Some downsides about tree traps:
• You need to select trees with a possible food source (seeds, flowers, nuts, etc).
• Not all trees have a good fork to put the trap on. (I nail up metal right angle brackets to fix this.)
• Birds like robins may get caught.
• Still some loss of peanut butter just as with ground based traps. Culprits never obvious.
• Storms and strong wind may set them off.
• Don’t catch mice. (Can use a mouse version.)
• Don’t catch weasels like a box trap will.
• Possums will interfere with them. (Install above possum traps.)
• Too much peanut butter can jam the trigger plate.
Tree traps may not be the total answer but my advice to trapping groups is that, if they want to ramp up rat kills (the objective after all) and don’t have robins to worry about, tree traps are a very worthwhile addition to their arsenal.
Good hunting: Bryce Buckland, Nelson.
You may email me at: www.Birdlifeongrampians.org.nz