Simulated Owl Predation Risk to Voles Modifies Browsing Effects on Tree Seedling Growth

Browsing effects of voles on plants can be mitigated by means of non-lethal predation, i.e. by subjecting voles to predator cues. Earlier studies largely focused on mammalian olfactory cues, whereas here we exposed Microtus voles to owl calls to examine whether the introduced predation risk reduces browsing on tree seedlings (silver birch, Scots pine, Norway spruce). We found that owl risk was associated with higher growth rate of birch seedlings, but only late in the growing season, while there was no obvious effect in case of pine and spruce. Early in the season, in the absence of predation risk, voles were able to move freely and search for their preferred food, grasses. Late in the season, when grasses were less palatable, voles likely targeted birch seedlings to a higher degree. Our results suggest that owl calls could alleviate vole herbivory on birches but, at least on a short temporal scale, will not protect seedlings of conifers.