Do brown bears Ursus arctos avoid barbed wires deployed to obtain hair samples? A videographic assessment

Abstract

Studies of the movements and abundance of predators can reveal their ecological roles and facilitate their conservation. These studies rely increasingly on noninvasive methods such as hair collection and camera traps. Insights from hair sampling, however, may be compromised if collection devices elicit avoidance behavior. To determine the extent to which brown bears Ursus arctos avoided barbed wire deployed to collect hair samples, we paired two wires on each of six small streams with motion-activated video recorders in the Wood River system, southwestern Alaska, where bears prey on sockeye salmon Oncorhynchus nerka. Of 350 videos showing a bear approaching the wire with an unambiguous result, the bear contacted the wire in 80.9% and avoided it 19.1% of the approaches. Females more often avoided the wire than did males (39% versus 20%), and bears more frequently avoided the wire at night (23.6%) than during daytime (10.8%) and crepuscular (19.1%) periods. Other comparisons (bears in groups versus single bears, and adults versus cubs) were not significantly different. The high proportion of approaches that led to contact with the wire indicates that this hair-sampling method is generally successful. Our findings also suggest, however, that interpretation of data obtained from such sampling should consider the possibility of biases with respect to sex and time of day.