Predator odor can reduce acorn removal by granivorous rodents in mixed oak forest stands

Developing better practices for rodent pest control is of high importance to reduce damage during forest restoration and in crop production. For example, during direct seeding with large and highly attractive seeds such as acorns, most seeds will disappear due to consumption or dispersal if not protected. An unexplored concept in reducing rodent damage is the use of repellents derived from predators. We tested the efficiency of three volatile compounds (2-propylthietane, 2-phenylethylamine and indole) associated with predators as rodent repellent candidates and scored the reduction of acorn (Quercus petraea) removal at two field sites in southern Sweden. We further investigated at what distance (5 cm, 10 cm, and 15 cm) from the odor source the odors were efficient in lowering the removal of acorns. Removal was lowest with 2-propylthietane (25-45 % of acorn removal), followed by 2-phenylethylamine (75-95% acorn removal) at 5 cm. Indole failed to decrease acorn removal and did not differ significantly from the control treatments. In the control treatments, almost all acorns (95-100%) were removed from the plots during the 48-hour sessions at both sites, and the acorns were removed faster than in the other treatments. Removal increased with distance from the 2-propylthietane odor dispenser at both field sites. Here, the lowest acorn removal occurred at 5 cm from the odor disperser. Our short time experiment shows for the first time the potential of using 2-propylthietane for short-term protection of acorns from foraging by granivorous rodents in oak woodlands. To help increase the reliability of direct seeding as a method for regenerating and restoring forests, future studies should investigate whether the range and longevity in the field of predator odor formulations can be improved.