Effectiveness of trapping

I have been doing the math on a hypothetical situation where there is a population of 20 rats, 10 female and 10 male. If one of those rats is trapped every week (I trap an annual average of 3.75 rats a week over an area of 15ha and I check my traps every couple of days if weather permits) by week 20 when all the original rats have been trapped there could be at least 36 pups reaching sexual maturity! This is based on the female rats each having a litter of 6 pups which can be independent after 3 weeks.
I can only conclude that trapping alone will never suppress the rat population as the rate of breeding is greater than the rate of death by trap. This is especially relevant if traps are only being checked weekly or monthly.
Hopefully someone can prove me wrong?

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You’re not wrong, but any outcome will depend on variables within your model. Worst case scenario: if all your female rats start off pregnant and you trap mostly males (which most studies support) you could have many more rats than when you start. Alternatively, trapping could disrupt social structures and mating success and combine with natural mortality to reduce the rat population.

In general for rodents, most modeling and field trials have shown that widely distributed toxin is far more effective (and cost effective) than even the most intensive trapping.

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Yes I realised there are lots of variables but thought I would keep it basic. I have not recorded sex of my catches but will do from now on - I have a gut feeling though that the majority are males and may have only noticed one obviously lactating female.
I trap in a DOC reserve so there are hurdles with using toxins but I think they are worth jumping.

Just some thoughts. I have developed a technique of placing bait stations within in 2 - 5 metres of every DOC and possum trap to defend their baits from mice. Hazing for those traps brings mice and it is easier servicing 2 devices at once. As one expert said to me ‘a mouse dying of brodi poisoning is a mobile bait station’. Dealing with Dept of Cons is well worth while. Have you tried suggesting to them the use of Double Tap bait which I understand was specificslly developed by and for them.

What kind of bait is used? I have a lot of weka here and don’t want to poison them. They are good at pulling out dead rats and mice from trap boxes - I don’t use poison just traps so finding this an interesting topic. Never realised that mostly male rats are caught - but this does make sense.

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I use mainly peanut butter. I do try other bait at times (especially when the PB is eaten without the trap being triggered) but I find PB the most successful. I have in the past used blue Smooth but haven’t replenished my stocks for a while.

I have been using peanut butter and nutella in my victor traps. Put half and half the trap. When I started using nutella the rats had brown teeth when I got them out of the traps.
I have been using Difethialone rodent baits. It’s a lot nicer on the environment than Brofaldicom. Brofaldicom can last in soil for over 300 days. Difethialone only last for a few days.

How many traps do you have on your section? I think you would also need to add a re-invasion factor, this is significant and seasonal. There is is also the natural death rate. I imagine DOC has done very detailed calculations of this type. Might be worth asking the scientists. My own experience is that although the catch rate seasonally fluctuates, the general trend of annual catch rate lowers over time.

It is near impossible to control rats in the bush with traps alone. Toxin is required. You will also notice a diminishing return with traps only, same will occur if you don’t rotate toxins too.

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This is what I suspected for a long time. So why do we continue trapping at all? Just have a cup of tea!

I wish I could! That’s scary stuff but the reality I guess. I remember one of the first trapping workshops I attended the speaker described trapping rats as “just mowing the lawn” which is a good description. It’s a shame that spreading a toxin is the only practical remedy. Maybe AI or GE will provide an answer.


No I don’t think that doing nothing is the answer!


I have about 20 traps in a 15ha scenic reserve. There is a mix of single and double set DOC 200s, tunnel, D and Snap E traps. Monthly catches of rats have been fairly consistent over the 2.5 years I have been trapping with a yearly average of about 3.75 a week.

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My meandering thoughts. I wonder if the density of traps is just not sufficiently high. There are no absolutes in this game, but I have heard the retort “the more traps the better”. I have around 40 traps (a mixture of Victor tunnel, DOC, GN, D trap and one AT220) over 4.5 ha. This seems to give me pretty good control (as verified by tracking tunnels). My monthly rat catch rate is as low as three in Winter, and as high as 30 in late March/April. I attribute the peaks to seasonal rat re-invasions. I do use poison from time-to-time, particularly when targeting mouse populations, and as an early indicator of possum activity. I like trapping because I feel it gives me a much better handle on what is happening than I get using bait stations. When I use bait, I often find it will go mouldy before it gets eaten. This happens even when I am still trapping rats. This may be because I have far fewer bait stations than traps, but I think it may also indicate how effective Victor tunnel traps are.

Wow. It takes me 2-3 hours getting around my patch so if I increased the density it would stretch out that time. But interesting thought - maybe I should concentrate all my traps in one area to see what happens!

I sympathize. My section is steep so it takes me about 2 hours too. I guess the question is whether most of that time is taken re-luring or checking. If it is re-luring then I have made some suggestions previously that I find considerably reduces my time spent re-luring. Apologies for referencing my own stuff: 1.Terracotta lures for Victor traps 2.Update - Terracotta lures for Victor Traps 3.Mould-resistant Nutella lure aka “rat truffles” I know some people use coloured tape on the traps to indicate a trigger. The other (obvious) suggestion is to increase the number of traps at the same time as recruiting a couple of volunteers. Sounds like you have a lot on your hands!

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When I find a good site, I place more tunnels there to take advantage of the traffic. If a tunnel at a site has low interaction-rates, there isn’t much point in keeping it there. In theory, doubling the number of tunnels at one of your best sites should double the potential number of kills. By concentrating your tunnels at your best sites, you’d also have fewer stops to make, so it should take you less time to check your patch.


I have tried the connotation terracotta lures (all 4 flavours - chocolate, peanut, vanilla and salmon) without much success. The benefit was they didn’t generally go missing although I did loose a couple from the traps (I don’t know how). I only left them out about 6 weeks so maybe I should give them another go.
I will try the Nutella balls - would that recipe work with PB? - I have tried cocoa in PB and straight chocolate but find PB works best though it does go missing I presume by mice.

Not sure about the Connovation version, I haven’t tried them. The way the terracotta absorbs/releases seems quite important. I only use the chocolate lure. Unfortunately the rat truffle method does not with PB, the chemistry is a bit different for PB. The key purpose of the cocoa is to protect the ball from water and mould, rather than as a lure. Best of luck!!