Science - September 11, 2014

A nose for truffles, not for acorns

Roelof Kleis

Wild boar have a good nose for truffles, but not for acorns, thinks PhD researcher Lennart Suselbeek. When they are looking for acorns they do so randomly, shows research on how wild boar track down hoards of acorns. Suselbeek came to this conclusion on the basis of experiments both in the lab and in the field.

The aim of the study was to find out whether wild boar have any impact on the way wood mice hide acorns. Wild boar are just as fond of acorns as mice are. So they are in competition and mice have to be smart. One way of doing that is to lay down a lot of little caches, spreading the risks. 

Sense of smell

Suselbeek studied the hoarding behaviour of the mice by equipping acorns with a tiny transmitter, with which he could keep track of each individual acorn. The results were striking. Boar seem to have no impact on the hoarding behaviour of mice as long as the acorns are not hidden too close to the tree. Suselbeek: ‘Boar look close to the tree, because they know there are acorns there.’

Boar seem to look for acorns in a fairly random, undirected way, showed experiments in a ‘lab environment’. According to Susel-beek, you can see this from their tracks in the forest. ‘You often see a whole patch of ground that has all been dug up at once. That suggests that boar are not capable of a focused search making use of their sense of smell.’ But, says Suselbeek, that does not mean wild boar have a poor sense of smell. ‘I think it is more that acorns have evolved by natural selection to give off only a very weak odour signal.’

Chances of survival 

So boar have no impact on the hoarding behaviour of mice. The mice themselves do, however. The more mice there are, the faster the acorns are stashed away, and the more spread out. ‘A question of competition,’ thinks Suselbeek. The oak benefits from this. The more spread out the acorns are, the bigger the species’ chances of survival. According to Suselbeek, his findings tie in with those of research elsewhere which points to the existence of some kind of optimal dispersal of seeds.

Lennart Suselbeek is due to graduate with a PhD on Wednesday 8 October with his thesis ‘Of mice and oaks’