The effect of distance on the foraging patterns of the Eastern Chipmunk, Tamias striatus.

Abstract

A key factor relating to the survival and long-term fitness of an animal is its ability to forage efficiently. The concept of optimal foraging theorizes that an animal will modify its foraging time to maximize the amount of food attained. This model has been used to predict patterns of animal foraging. The eastern chipmunk (Tamias striatus) has unique foraging patterns because it hoards food collected during the summer months to sustain itself during the winter. Eastern chipmunks are territorial and must constantly be prepared for the risk of intra- and inter-specific competition during foraging. In this study, previously marked chipmunks were presented with 150 sunflower seeds on trays placed 3 m and 10 m from their burrow. Three trials were run at each distance for 15 individuals (n=45). The time that the chipmunk spent on the tray and traveling were recorded separately and the number of seeds gathered for each trial was recorded. The averages for foraging efficiency (measured in seeds/total time), seeds taken, travel time, time on tray, and feeding efficiency (measured in seeds/time on tray) were computed for both the near (3m) and far (12) distances. There was no significant difference in average foraging efficiency, number of seeds taken, or travel time. However, the time spent on the far tray was significantly less than the near tray, but the feeding efficiency was significantly greater at 12 m. This is not consistent with the theory of optimal foraging, which states the time spent at a far distance should be greater to allow the animal more time to gather food to keep the foraging efficiency constant. The chipmunks in our study were able to maintain a relatively constant foraging rate by altering their feeding efficiency, and not by changing the time spent foraging. The method employed by Tamias striatus in a natural setting to keep foraging efficiencies constant is modeled more realistically by our results than what is suggested by the optimal foraging theory.