Effectiveness of predator odors as gray squirrel repellents Frank Rosell Abstract: The ability of gray squirrels (Sciurus carolinensis) to discriminate between different predator odors and the use of predator odors to deter gray squirrels from foraging on plants have not been previously investigated. To test the hypothesis that predator scent decreases foraging, I investigated the effect of such scent on consumption of butternuts (Juglans cinerea) in the field. Results showed that (i) red fox (Vulpes vulpes) scent was significantly more effective than either a control or human scent; (ii) raccoon (Procyon lotor) scent was significantly more effective than white- tailed deer (Odocoileus virginianus) scent (but only after 7–9 h); (iii) red fox scent was not significantly more effective than raccoon scent; and (iv) human scent was not significantly more effective than the control. The utility of predator odors in controlling damage by gray squirrels should be explored. Résumé : La capacité des Écureuils gris (Sciurus carolinensis) à reconnaître les odeurs de différents prédateurs et l’utilisation de ces odeurs pour éloigner les Écureuils gris et les empêcher de se nourrir d’espèces données de plantes n’ont jamais été étudiées. J’ai éprouvé l’hypothèse selon laquelle l’odeur d’un prédateur diminue l’activité alimentaire en examinant l’effet d’une telle odeur sur la consommation de noyers cendrés (Juglans cinerea) en nature. Les résultats indiquent (i) que l’odeur du Renard roux (Vulpes vulpes) est significativement plus efficace que l’odeur témoin ou que l’odeur humaine, (ii) que l’odeur du Raton-laveur (Procyon lotor) est significativement plus efficace que celle du Cerf de Virginie (Odocoileus virginianus) (mais seulement après 7–9 h, (iii) que l’odeur du Renard roux n’est pas plus effi- cace que celle du Raton-laveur et (iv) que l’odeur humaine n’est pas significativement plus efficace que l’odeur témoin. L’utilité des odeurs de prédateurs pour contrer les dommages causés par l’Écurueil gris vaut la peine d’être exploitée. [Traduit par la Rédaction] 1723 Notes Introduction Many prey species have the ability to assess their risk of being preyed upon. Predator avoidance is associated with costs such as a reduction in feeding rates and breeding op- portunities (Lima 1985; Lima and Dill 1990). Prey may re- duce these costs by assessing the risk of a predator being present from its odor. Avoidance of predator odor can be ei- ther species-specific (e.g., Swihart 1991) or general (e.g., Nolte et al. 1994). Furthermore, some prey learn to respond only to predators that are actively dangerous (Dickman 1992). Recognition of (and response to) predator odors by prey is of adaptive significance because it reduces predation risk. Mammalian pests such as rodents cause conflict with man by spreading disease to both humans and livestock, spoiling stored food, and damaging buildings, trees, and crops (Gurney et al. 1999). Tree squirrels gnaw ears of growing corn and the bark of trees (Kenward 1983). Western gray squirrels (Sciurus griseus) have caused serious losses to timber pro- duction in Jackson County, Oregon (Baldwin et al. 1986). Gray squirrel (Sciurus carolinensis) damage has also been reported to American chestnut (Castanea dentata) in West Virginia (Brooks 1922) and sugar maple (Acer saccharum) in Connecticut (Britton 1933), Michigan (Brenneman 1954), and Minnesota (Irving and Beer 1943). Gray squirrels have also been reported to pose a serious problem to commercial foresters in Britain (Rowe 1984; Rowe and Gill 1985; Gurnell 1987). Squirrels may also gnaw through the insulation on electricity cables, dig up bulbs, corms, and newly sown seeds, eat ripe fruit, and damage plastic bird netting (Gurnell 1987). Gray squirrels often annoy people by nesting in attics or be- tween walls and by raiding gardens and bird feeders (Nowak 1999). Chemical repellents such as Squirrel-Away™ are now be- ing marketed in stores for the general public’s use against squirrels. However, the above-mentioned conflicts could pos- sibly be reduced by using predator odors as repellents (e.g., Merkens et al. 1991). The use of predator odors to deter gray squirrels from eating butternuts (Juglans cinerea) has not been investigated, nor the ability of gray squirrels to dis- criminate between different predator odors. Three species known to prey on gray squirrels in United States are the red fox (Vulpes vulpes), the raccoon (Procyon lotor) (Whitaker 1996), and man by hunting (Nowak 1999). Gray squirrels should therefore avoid the scent of these three species. In this study I investigated 3 different predator odors (human, red fox, and raccoon) as repellents of gray squirrels. To test the hypothesis that predator scent decreases foraging, I designed a study to investigate the effect of such scent on butternut consumption in the field. I tested the following predictions: (i) red fox scent would be more effective than a Can. J. Zool. 79: 1719–1723 (2001) © 2001 NRC Canada 1719 DOI: 10.1139/cjz-79-9-1719 Received January 15, 2001. Accepted July 10, 2001. Published on the NRC Research Press Web site at http://cjfas.nrc.ca on September 12, 2001. F. Rosell. 1 Department of Zoology, Norwegian University of Science and Technology, N-7491 Trondheim, Norway. 1 Present address: Faculty of Arts and Sciences, Department of Environmental and Health Studies, Telemark University College, N-3800 Bø in Telemark, Norway (e-mail: Frank.Rosell@hit.no).