Behavioral response of captive marsh deer to an economic and easy-to-install repellent: a potential mitigation solution for conflict?

Abstract

Deer species can cause serious damages to trees through browsing and antler rubbing, and these impacts can generate significant economic losses. As a tool to minimize damages to trees by deer, repellents based on odor, visual and/or taste stimulus have been developed and tested. Repellents vary greatly in terms of costs, forms of use, duration, and/or the local context. Thus, selection of the most-effective repellent to each situation should consider the local environmental and socioeconomic contexts. Pyrazine analogs have been recognized to induce avoidance and fear-related behaviors in deer. These compounds are also found in ordinary and daily-use products, such as coffee, which can be easily obtained. The marsh deer (Blastocerus dichotomus) is the largest native deer of South America. The southernmost population of this species is found in the lower Delta of the Paraná River in Argentina, a large wetland highly modified due to commercial afforestation of Salicaceae. Local forestry producers usually report damage to plantations attributed to marsh deer, with a minor fraction of these producers perceiving high levels of damage and economic losses. We tested an easy-to-install repellent system based on coffee grounds by conducting trials focused on four captive marsh deer. The trials consisted in offering pellets of grain and fiber to deer, dividing the overall ration into two identical factions separated by 15 meters within the enclosure. In the “repellent site”, a subset of the regular food was placed on the ground and treated with the repellent, whereas the other subset, also located in the ground but not treated, was used as the “control site”. Whereas deer individuals presented alert behavior (50-100% of the times) after approaching the repellent site, this behavior was never observed at the control site. Significant differences were found among individuals probably due to a dominance interaction inside the group. The weight of food remains in the repellent site was significantly higher than in the control site at the end of the study. A repellency system based on coffee grounds could be an economic solution to be used by forestry producers of the Paraná River delta or by anyone interested in diminish damages to particular resources. In addition, it is a biodegradable option with insignificant environmental impact and could be especially useful to be applied at small spatial scales, since it requires domestic materials and a relatively limited installation cost in terms of time spent to set up the system.