Yellow-bellied marmot hiding time is sensitive to variation in costs

Many species use refugia to avoid predators, but remaining in a refuge is costly because foraging and engaging in other beneficial activities are curtailed while in a refuge. Thus, we expect that the duration of refuge use will be optimized. We tested a key prediction of this optimization hypothesis in yellow-bellied marmots, Marmota flaviventris (Audubon and Bachman, 1841), by providing supplemental food next to their burrows to manipulate the costs of remaining in a refuge. We then systematically walked towards a subject that was foraging on supplementary food or a subject that was not foraging on supplementary food until the individual disappeared into its burrow. We found a significant effect of our feeding treatment; subjects with supplementary food emerged from their burrows sooner than those without it. We also found a complex interaction between our feeding treatment and immergence distance (i.e., the distance subjects were at when they disappeared into their burrows). Individuals that tolerated close approaches emerged sooner when food was present, while those that were intolerant of approaching humans took longer to emerge and emerged sooner when food was not present. Juveniles emerged significantly sooner than adults, while there was no detectable difference between emergence times for adults and yearlings. This is the first demonstration in a mammal that hiding time is sensitive to the cost of remaining in the burrow. A number of previous studies on hiding times have focused on ectothermic species. More generally, our results suggest that endotherms are also likely to optimize the time that they remain in a refuge.