Happy new year! During the last days I have been trying a method for recording footprints. This is because we want to estimate small mustelid predation over vole populations by small mustelid visits to baited tracking tunnels. It works like this: The plastic tunnels have a wood plate inside. The surface of the wood plate is covered with Kraft paper and a sponge. An “ink” is placed in the sponge and in previous experiences I tried an ink of glycerin and carbon black but dries quickly. I tried this time with a more sophisticated method based on a chemical reaction! This ink is a solution of ferric nitrate, polyethylene glycol and water. In the paper I sprayed another solution of tannic acid, ethanol and water. And as a result, when the little animal step the sponge and after the paper… it leaves a nice footprint! In this case there are some footprints of rodents.
I am still improving it, maybe by placing another sponge in the middle of the plate, but it has been an exciting experience. Back to chemistry after finishing my degree! thanks by the way to the team of Gregorio Crini for giving me a hand with the chemistry part ;-P
You may find a deeper description of the methodology in these two articles:
King, C.M., Edgar, R.L., 1977. Techniques for trapping and tracking stoats (Mustela erminea); a review, and a new system. New Zeal. J. Zool. 4, 193–212.
Graham, I.M., 2002. Estimating weasel Mustela nivalis abundance from tunnel tracking indices at fluctuating field vole Microtus agrestis density. Wildlife Biol. 8(4) , 279–287.
There is also a lot of nice information of the method available in internet, for instance from New Zealand, where small mustelids where introduced and may produce strong predation pressure over native fauna. In this case, these tunnels have been then used as a cheap way to monitor small mustelid populations and provide information for management.
Thanks also to my supervisors and also my colleague Paco Diaz-Ruiz for the advices.