OOS 4-1 - The hidden ecology of urban garbage: Food waste may indirectly simplify urban bird communities

Urbanization is now a leading, but often unrecognized, cause of biodiversity loss, on par with agriculture and forestry. Yet, many of the processes and interactions that structure ecological communities in urban areas are poorly understood. Most urban ecological studies still focus on direct effects (e.g., predation, habitat destruction or fragmentation), even though ecologists have long recognized the importance of indirect effects (e.g., trophic cascades) in structuring communities in “wilder” spaces. Here, we explore direct and indirect mechanisms that determine bird community composition in a case study of Vancouver, BC, developed amidst ongoing conversations with municipal governments. We hypothesize that, by inadvertently augmenting populations of scavengers (e.g. American crows) via abundant food waste, people subsidize the nest predation of specialist songbirds and undermine Vancouver’s bird diversity.

To test this hypothesis, we conducted preliminary surveys of bird diversity, abundance, food waste availability, and microhabitat across 12 transects along an urban habitat gradient in Vancouver. We triangulated this primary data with high-resolution land cover data. We then fit Bayesian hierarchical models to infer the relative effects of food waste availability and other environmental variables (e.g., land cover, seasonality, weather) on bird diversity and abundance.

Preliminary results indicate that food waste availability is positively associated with crow abundance and negatively associated with bird species richness, and crow abundance is negatively associated with species richness.

Our findings indicate that complex interactions, including indirect effects, likely play significant roles in structuring urban communities, and warrant greater research attention. Our results also suggest that reducing the food waste available to wildlife (e.g., through modifications to public waste bins and pick-up schedules) is a viable social-ecological intervention to augment urban biodiversity and its benefits to people.