Peripheral obstructions influence marmot vigilance: integrating observational and experimental results

Animals generally allocate some time during foraging to detecting predators. We used a combination of observations and an experiment to examine how vegetation height and peripheral obstructions influence vigilance by foraging yellow-bellied marmots (Marmota flaviventris). First, we analyzed a large sample of observations of marmots foraging in nature. Marmots increased vigilance with vegetation height and reared on their hind legs when in tall vegetation. Second, we observed that marmots foraged in locations with lower vegetation than randomly selected sites in the same meadow. These observations suggest that marmots account for what they can see while foraging but do not rule out the influence of other factors correlated with vegetation height. Therefore, we experimentally blocked the view for 3 sides for marmots feeding on a controlled food source. When the apparatus blocked their vigilance, marmots were less vigilant when foraging, often moved outside the apparatus, and showed heightened vigilance while outside the apparatus. Peripheral obstructions explained more of the variance in our experimental than in our observational results. Together, our results demonstrate that marmots employ antipredator behavior to compensate for peripheral obstructions. Long-term studies show that marmots go locally extinct more often in areas with more obstructions to vigilance. Thus, marmots likely face greater predation risk in those areas, despite the behavioral responses documented in this study. Copyright 2009, Oxford University Press.