Wetenschap - 14 februari 2013

Playing hide-and-seek with mice

Acorns with chips make seed dispersal visible.
Wild pigs have no influence on hoarding behaviour field mice.

Animals play a major role in seed dispersal. To research this you need to map this dispersal. Various techniques are currently used for doing this. One is to hide  small magnets or transmitters in acorns. Another is to attach a tiny string to the acorn, like a flag. A big dis¬≠advantage of these measures is that they interfere with the natural process. The acorns become too heavy or too easily spotted by competitors.
PhD candidate Lennart Suselbeek at Resource Ecology has come up with a solution. He uses a simple chip to track the acorns. 'These are in fact the domestic animal identification chips used also for dogs and cats. So it's just a common-or-garden aid which can be bought for a few euros apiece.' The chips are small (about a centimetre long, a few millimetres thick), light (0.05 grams), re-usable and do not require any energy. The last point is a big plus: it means that theoretically, you could keep track of the fate of the acorns forever.
Wild pigs
Suselbeek spent two years gaining extensive experience with his method. He hid about 1200 'chipped' acorns in experimental grounds in the forests around Ede, Wageningen and Wolfheze. Not just in order to play hide-and-seek with field mice, though. He is researching whether the presence of wild pigs affects the way in which mice hoard their acorns. Do the mice give each acorn its own hiding place or do they create one big store?
Their strategy is critical for the dispersal of acorns in the forest. But Suselbeek could find no evidence to suggest any influence of this sort. Mice hoard their acorns piece by piece and pigs do not seem to be a decisive factor in this. Suselbeek thinks that risk-spreading is a major determinant in not having a single store. He will now investigate this further. Meanwhile, his new search technique has already generated an article in Methods in Ecology and Evolution.
The new method, according to Suselbeek, is especially suitable for animals which do not transport their food over long distances. He found most of his marked acorns within fifty metres of the feeding grounds. Searching from this is relatively time-consuming. Combing an area of forest 25 square metres big with an instrument like a metal detector easily takes an hour. 'That is the biggest limitation. However, for experiments in a clearly defined area it is a very promising new technique.'