Comparative foraging behavior of grey squirrels (Sciurus carolinensis) and eastern chipmunks (Tamis striatus)
Grey squirrels (Sciurus carolinensis) and eastern chipmunks (Tamias striatus) live in temperate forests and residential areas in eastern North America. The habitats and diets of the chipmunks and squirrels overlap broadly. Although both species cache hard mast for use in winter, squirrels scatter hoard seeds and chipmunks larder hoard them. We examined foraging in chipmunks and squirrels in artificial seed patches of 200 sunflower seeds mixed with 4.2 cm of sand in a tray 20-cm diameter base x 7 cm height. We measured giving-up density (GUD), the amount of seeds remaining after a foraging bout. We also characterized species-specific foraging patterns by analyzing video of the foraging bouts and tested for an effect of predator urine on the foraging behavior.
When squirrels and chipmunks encountered the seed patches, their foraging patterns were significantly different. Squirrels would sit in the patch, locate a seed, shell and consume it, and repeat this action until leaving the patch; squirrels’ overall GUD was 50.8 (±5.5 SE). The average amount of time spent in the patch was 15 minutes with periodic brief pauses (mean: 1 s/min) for vigilance behavior. When chipmunks encountered the seed patches, they ate 0-5 seeds in the patch, then larder hoarded the seeds in their burrows (mean 3.5 trips); chipmunks’ GUD was 6.3 (± 2.4 SE). The total time in the patch was longer, 25 minutes, with longer and more frequent pauses (mean: 20 s/min) for vigilance. Predator urine suspended on wicks next to the seed patches had no impact on the foraging of chipmunks (mean GUD (±SE) with no predator urine: 4.3 (± 4.4); with predator urine: 12.1 (± 7.9)) or squirrels (with no predator urine: 48.8 (±6.3); with predator urine: 51.6 (±12.6).