Scatter-hoarding behavior in Siberian chipmunks (Tamias sibiricus): An examination of four hypotheses

Abstract

To store food items, animals employ scatter-hoarding, larder-hoarding, or a combination of both. However, little is known about the factors that drive animals to use different strategies. In the present study, we used seed placement experiments, both in the field and in semi-natural enclosures, in order to test four hypotheses related to the scatter-hoarding behavior of the Siberian chipmunk Tamias sibiricus. To investigate whether scatter-hoarding is a vestigial non-adaptive behavior (non-adaptive hypothesis), we provided each of 23 Siberian chipmunks with 30 tagged intact Quercus mongolica acorns, which were placed at the center of their enclosures, and then observed their behavior. To test whether scatter-hoarding behavior is a response to insufficient larder space (lack-of-space hypothesis), we provided each of 14 Siberian chipmunks with 30 tagged intact acorns, with open artificial burrows and then closed artificial burrows. To determine whether scatter-hoarding was used as a means to rapidly sequester food items from food patches (rapid-sequestering hypothesis) and whether the distance between food patches and burrows affects hoarding behavior, 10 chipmunks were randomly selected, and 30 marked acorns were introduced to their enclosures at 3.5, 0.5, and 7m from their burrows, over a period of 3days. To test whether scatter-hoarding represents a behavioral strategy to avoid the pilferage of food resources by competitors (pilfering-avoidance hypothesis), 10 randomly selected chipmunks were released into the enclosures immediately following acorn placement, and over the next few days, the other 10 rodents as potential pilferer were caged and put in the corner of the enclosures before acorn placement, with one individual in each enclosure. This deployment was expected to invoke anti-pilferage behavior in the focal caching animals. The results of the present study indicated that Siberian chipmunks exhibit scatter-hoarding behavior more often than larder-hoarding, regardless of age and sex. Scatter-hoarding behavior was common in Siberian chipmunks, thus failing to support the non-adaptive hypothesis. Meanwhile, the availability of larder space (open or closed burrows) had no significant effect on the intensities of either larder- or scatter-hoarding, thereby failing to support the lack-of-space hypothesis. In addition, the distance between seed sources and burrows also failed to influence the seed-hoarding behavior of the chipmunks, either in the field or in the semi-natural enclosures; and the chipmunks did not transfer scatter-hoarded acorns into dens. Therefore, we argue that the primary function of scatter-hoarding is not to ensure the rapid harvesting of Q. mongolica acorns, thereby failing to support the rapid-sequestering hypothesis. In contrast, Siberian chipmunks did increase scatter-hoarding behavior when faced with a risk of pilferage by superior competitors, which suggests that the scatter-hoarding strategy adopted by Siberian chipmunks can be explained by the pilfering-avoidance hypothesis, and the observation that the chipmunks intentionally moved seeds from their artificial burrows to scatter-hoard them further supports this hypothesis.