Diet and Color Preferences of Eastern Grey Squirrels in Bellingham, Wa

Team Members: Sarah Hiedrich, Carlee Takizawa, Mackenzie Johnson, and Collin Neuhauser

Urban dwelling eastern grey squirrels are extremely adaptable to changes in their environment, which allows them to be successful in areas with strong anthropogenic influences. According to previous studies, squirrels living in urban areas exhibit different behaviors than their wild counterparts but still choose food based on the optimal foraging theory. Our experiment focused on how squirrels foraged using visual cues to optimize nutrition in food choice. 

Squirrels were given the option of Pirate's Booty and a blend of nuts, seeds, and grain. To determine if the squirrels responded to color, we also dyed the two food options and included them as additional options. The squirrels we studied were located on the Western Washington University campus and several local parks. Sites were chosen based on prior knowledge of Eastern Grey Squirrel habitation. Once at a site with squirrels present, the four food options were set out approximately 6 inches apart. Observers stayed for 30 minutes after setting out food making observations on squirrel behavior, interactions with food, and other confounding variables such as presence of crows, other humans, and motorized vehicles.

Figure 1. Simple histogram of squirrel first choice if given an option of 4 food types. Types included squirrel feed (SQF), colored squirrel feed (SQFC), processed food (PRC), and colored processed food (PRCC) (n=29).

Squirrels were found to prefer the uncolored corn puffs when presented with the 4 different food types. A total of 23 out of 29 squirrels chose this food type first (Figure 1). When we ran a statistical test though, we found no significant preference between the natural blend and the processed corn puffs.

 Although our data was not statistically significant, most squirrels did prefer the un-dyed puffed corn over the other three options. We determined that squirrels may chose the less energy profitable corn puffs due to the warmer season. When food is more abundant there is little pressure to be selective in food choice. Also, visual cues may have driven the squirrels to pick the un-dyed puffed corn since it was the brightest of the four options.

There are many factors that could have confounded the results. One of the most important limitations was the sample size collected, only 29 squirrels were observed. Another issue was the way data was collected. Instead of recording which food option the squirrel took first, it would have been better to base preference on proportions taken over a set period of time. In addition, without tagging or identification of each squirrel, there was no way to know if a squirrel had already been observed between collection days. Finally, the puffed corn was much larger than the seeds and the color treatment shriveled the corn puffs while hardly working with the seeds.