Ship rats are smarter than Norway. Sometimes you get a little puzzled by traps being set off without catching anything. If that happens regularly, is is possible that a (smart) ship rat has discovered that they can set off the trap by pushing on the side of the strike plate until it trips. Some loose a leg by doing it, but often it just gives them only a fright, they run off, but are back not long after to collect the spoils of their effort.
One way (not sure if there are other) of dealing with this is putting the inside mesh upside down (MUD). This forces them to climb over the mesh and when they jump down, there is no way back.
It doesn’t appear to be a problem for other predators, maybe apart from older Norway or the not so smart ship rats. I have caught all sorts in that way, incl. a younger possum, rabbits, stoats, weasels and of course lots of rats. Once you caught the smart ones, you can turn it around again, if you like.
MUD will probably prevent Tuis taking their chances, if that is a risk in your area.
Photos of a stoat and a rabbit caught this way. (Ooops As a ‘new’ user only 1 photo allowed.)
Let us know how you get on. I’ve used it also where I use walnut as bait, where the DOC200 is in more open areas along a path/track and where finches etc. are foraging. They don’t seem to enter the trap with mesh set to MUD. The use of walnut crumbs to create a path to the trap and in the front of the DOC200 is a good way to make them feel safe inside the trap. With half a walnut on the strike plate clearly visible once they are inside the trap they will try to get to it and ship rats are smart enough.
Brown/Norway and ship rats are both intelligent species. Brown rats are, generally speaking, harder to trap than ship rats, because they are more neophobic/trap-shy. You can put a buffet of Grade-A edible lures inside a tunnel, and they’ll often eat a small sample at the entrance(s) but refuse to enter the tunnel. The browns that make burrows under our deck, sharpen their teeth on it, and attempt to gnaw their way into our pantry from below, are often very difficult to trap, for this reason.
The advantages that ship rats have, is that they’re smaller and lighter than brown rats, and are better climbers.
One way to trap more rats, especially the ones that are able to run across treadles, is to recalibrate your traps. Years ago, I’d wondered why one of my DOC 200’s was trapping so few predators, when the one 20m away was racking up kills. I discovered that its trigger weight was set at 220g, while the other trap set at 120g. If every trapper learned how to calibrate their DOC 150 and 200 traps, the number of kills nationwide would increase significantly. Since I recalibrated my traps to 80g, I’ve trapped way more predators than before, including female weasels, which are the hardest predator to kill with DOC traps.
I’m going to try MUD the next time I have trouble.
It might be hard to tell for a year or so, @willem, because we’ve just had an aerial bait drop, and rat and stoat numbers seem to be right down. Of course it doesn’t take long for them to come back.
ww: I carry half an old merino singlet to test traps - folded and rolled up and secured with a rubber band. It weighs 83 grams. I might cut three grams off…
I’ve only had two DOC200s/250s fail to fire so far, but after cleaning them, and operating the plate a couple of times, they were back to normal.
