Hey Kids, Don't Feed the Wildlife: The Dark Side of Biophilia

Editor's Note: This contribution is part of the Journalist for a Day program for the 2019 Aquatic Sciences Meeting. In his 1984 book Biophilia, E.O. Wilson posits that connections with natural biodiversity are essential to mental development. Modern research supports the notion that a personal relationship with the environment can provide benefits in human health and ground us in environmental responsibility. Our innate affinity for nature can take many forms, from shinrin-yoku (“forest bathing”) to bird watching. While our tech-centric society could use a dose of nature, some believe that certain biophilic activities could actually be doing more harm than good. Aquatic systems imbedded in the urban environment are considered “sentinels of change,” and may represent the future of aquatic environments that face increased pressures of urbanization. Therefore, urban lakes and ponds provide an excellent system to study the impacts of anthropogenic forces from both an ecological and sociological context. These systems conjure images of idyllic summer days spent practicing a common form of biophilia: feeding the ducks. During routine monitoring in a shallow, urban pond, Sven Teurlincx, a researcher at the Netherlands Institute of Ecology (NIOO-KNAW), noticed that waterfowl would flock to citizens. What did those people have in common? A pocket full of bread, and a desire to connect with their local landscape (Fig. 1). Excess nutrient loading, or eutrophication, is a primary driver of habitat degradation in aquatic systems across the globe. Impacts of eutrophication are biologically devastating, ultimately resulting in proliferation of algae, reduction in water clarity, and the creation of low-oxygen “dead” zones. Though we generally associate nutrient loading with surface runoff from agriculture, Teurlincx wondered if the seemingly harmless activity of feeding ducks could actually contribute to eutrophication of urban lakes. Upon further research, he found that the Canal and River Trust estimated that citizens in England and Wales feed up to 6 million loaves of bread per year to waterfowl in urban watersheds. Urban lakes are in a delicate balance between macrophyte dominance and algal blooms that depend on nutrient loading, flow, and depth. Teurlincx's work is best understood within the context of the aquatic community, where algal blooms develop in the absence of macrophytes that take up nutrients and impede light from penetrating the water column. However, ducks provide a top-down control on plant density through grazing. Consequently, supplementary feeding may promote duck biomass, which ultimately adds more herbivore grazers to a system. This can create a series of feedback loops that encourage well-meaning citizens to feed ducks, who will happily accept a snack. Teurlincx and his colleagues considered the consequences of feeding waterfowl using a variety of approaches. First, students in an aquatic ecology course at NIOO-KNAW undertook a field campaign to collect observations on bird density and quantify supplementary waterfowl feeding by humans. Next, measurements of dry weight and nutrient content were performed for the most common food items, particularly different types of bread and fruit. Teurlincx and his students also performed “hand experiments” to determine how much bread is provided per feeding. (In case you are curious, the average hand provides approximately 1 piece of bread.) The results were surprising because although only an average of 4–5 people were observed feeding ducks per day, calculations suggest that on occasion 8 kg/ha/day, or 16 loaves of bread, entered the urban pond. In other words, a small amount of people provide quite a bit of bread. To explore the fate of the food items, Teurlincx then conducted litter bag experiments to track decomposition and subsequent nutrient release. Whole wheat bread, a staple of the supplementary waterfowl diet, is richest in phosphorus. In addition, the group found that bread and other processed foods break down very quickly. Finally, results of the field experiment were combined with a modeling approach (PCLake) to quantify the impacts of supplementary feeding. After running the model, Teurlincx found that nutrient addition from supplementary feeding was enough to push the system to algal domination. For this approach, he considered birds as a feature of the lake. When bird biomass itself was considered, the critical boundary between macrophytes and algae was shifted toward bloom conditions. Let us not forget that though waterfowl may ingest human-offered food and macrophytes, they contribute to nutrient loading by defecation, “sloppy feeding,” and roosting behaviors. The bottom line is that Teurlincx's work demonstrates that a common biophilic practice, feeding waterfowl, may push urban systems beyond their carrying capacity. In extreme cases, the nutrient loading capacity is equivalent to that from agricultural runoff. Other researchers have also explored the impacts of “guanotrophication,” in which fecal deposits from large flocks of geese act as nutrient vectors in suburban and agricultural watersheds. One of the ecological consequences of feeding ducks may be an accelerated degradation of water quality and increased frequency of algal bloom events. What is the solution? Teurlincx cautions that citizens must accept the consequences of this social activity, and decide what role it fills in our society. He is currently working with a student in tourism and management to explore the reasons why we practice this form of biophilia. Until then, remember, scientists suggest that you should look, but not feed the ducks.