The telltale V-formations of migrating Canada geese each spring are usually welcome harbingers of warmer weather. They are also a visible warning that your chances of stepping in something unpleasant at a local park, sports field or greenspace have dramatically increased. The iconic migratory birds are big poopers, and their waste is not just off-putting, but can seriously damage local ecosystems.
However, all that goose poop may have benefits. As a new Concordia study shows, goose feces — abundant in the urban environment and rich in nutrients — can play an important role up and down the food chain. This is especially true when processed by the black soldier fly, an insect commonly used in agricultural production.
"We wanted to see if the black soldier fly, a non-native species that is already industrially harvested widely, could be used to transform goose waste into valuable goods like protein and fertilizer," says Rassim Khelifa , an assistant professor in the Department of Biology . "The answer is yes; it can."
The study was published in the Journal of Environmental Management .
Mixed diets show best results
The researchers began by establishing a positive correlation between Canada goose flock size at 11 urban sites in southern Quebec and Ontario and the amount of feces the birds left behind. This established that these populations can quickly contaminate public spaces.
Next, the researchers conducted laboratory experiments that exposed black soldier fly larvae to three different kinds of diets: a standard mixture of wheat bran, alfalfa and corn meal, known as the Gainesville diet; a 50-50 split of Gainesville and feces; and feces alone.
The results revealed that the flies could survive and develop on all three diets, but with noteworthy differences, depending on their source of nutrition.
Larvae fed a mixed diet performed best, showing faster growth, higher survival rates and more efficient waste reduction. Those fed only goose feces developed more slowly, had lower survival rates and produced smaller adults. Even so, these flies managed to consume over half of the available waste, demonstrating that goose droppings alone can sustain the process, albeit less efficiently.
The trials also compared black soldier fly performance between those fed on a diet of raw feces compared to those that had been fed on droppings that had been autoclaved — a treatment that uses heat and pressure to eliminate fecal bacteria.
Flies raised on autoclaved diets consumed less material and grew to be smaller adults on the feces-only diet. They were also slower to develop, with lower adult body mass and shorter adult lifespans. These outcomes suggest that the microbiota in goose feces may contain beneficial microorganisms that support larval development.
Big boost to aquatic plants
Finally, the researchers tested to see if the insects' waste, known as frass, could be used as a fertilizer for duckweed. A fast-growing aquatic plant, duckweed is commonly used in animal feed, bioenergy and wastewater treatment and has previously been shown to interact well with goose waste.
Duckweed thrived when fertilized with goose-derived frass. Yield was 32 per cent higher relative to the samples fed on a standard formula (Hoagland medium), and frass-fertilized duckweed outperformed samples fertilized with both fresh feces and nutrient-rich controls. It also had shorter root systems, which is associated with access to abundant and accessible nutrients.
This circular, upcycling approach to urban waste management has multiple benefits, according to the researchers. First, it removes goose feces from public areas, improving sanitation and protecting habitats from processes like eutrophication. At the same time, it produces valuable insect and plant biomass that can be used as affordable alternatives for composting, livestock feed and organic fertilizer.
While much more study is required before this process can be implemented on an industrial scale, the researchers say this practice could be a low-cost benefit to managers of urban parks, farms and remote areas where conventional treatment is difficult or costly.
The study's first author is Carlos López-Manzano, a Concordia master's student in Biology. Additional research was provided by Hayat Mahdjou, PhD candidate, and Luis Rodrigo Arce-Valdés, a postdoctoral fellow.
This study was funded by the Natural Sciences and Engineering Research Council of Canada.
Read the cited paper: " Using an insect for sustainable waste management of a superabundant bird "
