How much does social group size influence golden marmot vigilance?

A commonly cited benefit of group living is the ability for individuals to reduce the time devoted to scanning for predators with increasing group size - the 'group size effect'. Interestingly, most studies reporting a group size effect have focused on documenting a significant group size effect and did not discuss the relative 'importance' of group size. One way to study the relative importance of group size is to calculate the amount of variation in vigilance explained by group size. I studied effects of social group size on golden marmot (Marmota caudata aurea) vigilance in two ways. First, I estimated the overall amount of time marmots were vigilant during their morning active periods. Second, I estimated the amount of time marmots were vigilant specifically while foraging. Analyses statistically controlled for several factors that have been suggested to confound the study of group size effects. While marmots were active, only 14% of the variation in vigilance was explained by social group size. For foraging marmots, even less variation (about 6%) was explained by social group size. The amount of variation explained by social group size in golden marmots is considerably less that reported in several studies of other species where explained variation was reported or could be estimated from data. Some of the discrepancy between variation explained in this and other studies may stem from my focus on social group size which appears to explain less variation than the more commonly studied foraging aggregation size. However, species differ in the amount of time they devote to foraging and therefore vary in the magnitude of net benefit from group size effects. Future comparative work will be required to rigorously study the relationship between amount of time foraging and the magnitude of group size effects.