this post was submitted on 31 May 2024
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Amazing that the tuatara burrowing is more of an issue than rabbits burrowing!
I just came across this document detailing the design of the fence, and was surprised to see it's not very deep at all!
I had expected a deep fence going down a metre or so underground, instead it seems they went out - with a mesh buried 10-20cm that comes out from the fence so that digging animals are overtop of the mesh when they think to dig, and can't dig through it. It makes sense now that burrowing tuatara could let animals in, as it would be much easier for an animal to dig out than for one to dig in.
Yes. What they found for rabbits, back in the day whilst figuring out how to design it, was that they'd always go right up to the fence and then try to dig. If they hit metal then they'd move sideways rather than backwards, so the skirt goes about 40cm outwards and that prevents all the rabbit incursions.
At the time I don't think they ever imagined the need to design for tuatara burrowing outwards, but probably good that it's only starting to become a question at about the time they've been planning for the fence to be replaced anyway. It'll be interesting to see if and how this affects all the other fenced sanctuaries that have sprung up later.
Another bonus of replacing the fence is that they'll be able to change the mesh, as the original one didn't have small enough holes to prevent baby mice getting through. I'm not sure how the mice inside will be properly eradicated after that's done. The original eradication was (I think) a brodifacoum drop which would no longer be practical unless everything important was somehow cleared out from inside the fence first.
Yeah I saw the mention of baby mice getting through. I'd guess having a fence that keeps them out is the first step, then they could probably reduce numbers with trapping, which may be able to wipe them out eventually. Not sure if there is an issue with say tuatara crawling into mouse traps?