Field trip - Part 2

science

You might want to read Part 1 before you start this entry. Or perhaps you don't like linear narratives, in which case, read them in any order you like.

The other main activity on our field trip was small mammal trapping and radio-tracking. One of the best ways of estimating the population of animals that spend much of their time hiding, or being otherwise rather inaccessible, is a 'mark-recapture' scheme. The theory goes something like this:

  • you set out your traps on a grid of known area and check them regularly for animals (all the traps are filled with warm bedding and food so that the trapped animal has a pleasant stay in the trap hotel)
  • when you catch an animal, you mark it (in our case by carefully clipping an small patch of fur in a unique pattern)
  • at the end of your trapping period, you put the total number of animals trapped, the number of animals you marked, and the number of recaptures into a big, scary equation
  • what you should end up with is some estimate for the population size in that area

This is all well and good, but our grid of traps was laid out on a 45° slope. All we could use to grapple our way up this slope were the wild garlic plants growing there. I can't recommend wild garlic as a secure anchoring point, and if you add in the additional difficulty of holding on for dear life to the garlic with one hand, and holding a trap containing a small rodent with the other, it becomes very tricky indeed. We also had to go through this procedure very early in the morning, which meant that we went in for breakfast reeking of garlic. Then there was the 'Rodent Roulette'...

We caught four species of small rodents in our traps: wood mice, voles, shrews and yellow-necked mice. You had to carefully empty the contents of your trap into a polythene bag to see what you'd got. Then came the technically difficult bit--putting your hand into the bag[1], grasping the little squeaker gently but firmly by the scruff of the neck and taking it out of the bag, and finally working out what sex it was, weighing it, clipping it and so on, and letting it go about its rodenty business again.

The first three species weren't too much of a problem, but the yellow-necked mice were terrors. If you've seen Monty Python and the Holy Grail, you'll know what I mean when I say that they remind me of the ["killer rabbit(Cool! You can buy one -- an excellent Christmas present for easily frightened children)":http://www.wickedcoolstuff.com/monpytkilrab1.html]--they look cute and innocent, but it's all a show. Somehow they are able to turn around inside their skin and give you an almighty nip, where the pain is out of all proportion to the size of the critter. We took turns to do the trap emptying, so the remaining students looked on with glee at the hapless victim, chanting, "Yellow-neck! Yellow-neck!". And that was how 'Rodent Roulette' was born.

Radio tracking of mice was less physically hazardous (once you'd got the radio collar on them). All we had to do was wander around the woodland at night with an aerial, listening to the blip of the radio transmitter, and try to work out where our mouse was. My radio-tracking partner and I were doing fairly well until we started to get very strong blips from the transmitter. We thought we must be right on top of our quarry and shone our torch down at the source of the signal. There--perched on a log, and sporting a big collar--was our mouse, transfixed by our torch light. The idea was to track the animal unobtrusively--not to almost step on it--so we backed off a bit.

We did find that wandering round a wood for much of the night was unexpectedly creepy. Wildlife is much noisier than you might think. Badgers sound like tanks crashing through the undergrowth, snorting and snuffling, and we kept jumping out of our skin when the automated insect sampling trap switched itself on. But the whole experience was great, despite the hazards. I loved seeing and hearing animals close up, learning new techniques and exploring new intellectual territory. For better or worse, it was what convinced me that I wanted to spend my life doing research.

[1] Remembering the cardinal rule of the Biologist: always keep well clear of the biting, scratching, kicking or stinging end.

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