Assessing the sensitivity of foraging and vigilance to internal state and environmental variables in yellow-bellied marmots (Marmota flaviventris)

Both internal and environmental factors influence the trade-offs animals make between foraging and antipredator vigilance. However, few studies examine both internal and environmental factors simultaneously, preventing us from drawing inferences about their relative importance during foraging. We capitalized on a long-term study of yellow-bellied marmots (Marmota flaviventris) to compare the relative importance of internal state-based factors versus external environmental factors in explaining variation in marmot foraging and vigilance behavior. Results indicate that while internal factors such as baseline fecal glucocorticoid metabolites, parasite infection, and body condition influence the time allocated to both foraging and vigilance, environmental factors such as group size and habitat characteristics only explain variation in the time allocated to vigilance. Thus, our findings reveal not only the importance of considering effects of both internal and environmental factors in explaining behavioral trade-offs but also the value in evaluating the subtle ways in which factors explaining vigilance and foraging differ. Studies on foraging and vigilance typically focus either on internal or environmental factors that influence behavior. This paper makes contributions to the field by integrating both internal factors, such as parasite infection, body condition, and fecal glucocorticoid hormone levels, and external factors, such as group size and habitat characteristics, in evaluation of behavioral trade-offs. We find that foraging and vigilance are affected differently by internal and external factors. This highlights the fact that even though foraging and vigilance are closely related, they are unique behaviors and there are opportunities in understanding how the factors that influence them differ.