COS 100-6 - Squirrels just wanna eat crumbs: Littered food waste removal by animals in urban green spaces

Background/Question/Methods

Urban animals have the potential to provide many under appreciated ecosystem services. Discarded food refuse is a widespread problem in cities that creates unsightly and unhealthy public spaces, but there is evidence that wild animals can mitigate these effects. In this study, we explore the drivers and dynamics of the removal of littered food waste by birds and squirrels in urban green spaces. Our goal was to understand how the supply of litter removal services varies depending on the composition of the animal community, type of green space, and interactions between species. We conducted experimental feeding sessions where we video recorded organisms removing food from feeding stations in green spaces across Philadelphia, Pennsylvania. We first examined how species abundances related to both the total amount of food removed and rate of removal and how these relationships were affected by weather and habitat. We then explored how interactions between species influenced the discovery and removal of food.

Results/Conclusions

We found that total amount of food removed increased significantly with eastern gray squirrel (Sciurus carolinensis) abundance and that city parks and picnic areas had higher total removal than forest preserves. Weather had little effect on removal. The rate of food removal increased significantly with the total abundance of birds as well as the abundance of Blue Jays (Cyanocitta cristata), which were highly efficient removers. We also found that where squirrels were abundant, the food was discovered more rapidly, and feeding by birds began shortly afterwards. This suggests that squirrels may facilitate bird feeding activity, though squirrel and bird feeding activity rarely overlapped, indicating competition dynamics may also be present. Overall, squirrels appear to be the main drivers of this ecosystem service, with bird diversity and abundance playing a lesser role. Beyond providing key insights into a poorly understood ecosystem service, these results also show that some ecosystem services in urban environments depend more on the abundance of common species than overall biodiversity. Management of green spaces to bolster populations of abundant urban species may sometimes have a greater effect on ecosystem services than will conservation of rare organisms.