Urban scavengers like spotted hyenas are preventing over a thousand tonnes of carbon emissions annually in Ethiopia’s second-largest city, according to new research revealing the predators’ role as accidental eco-warriors.

By consuming organic waste that would otherwise rot, these predators are saving the city of Mekelle over $100,000 USD in waste management costs while reducing the significant sanitation risk associated with routine roadside dumping.

In Mekelle, a rapidly urbanising city with a population of over 660,000, over one million chickens, goats and sheep are slaughtered in people’s homes for food each year. The leftover parts of the animals not consumed by people are then discarded, with two thirds of the organic waste being dumped at roadsides or other open sites.

The University of Sheffield-led study reveals urban scavengers such as spotted hyenas, African wolves and vultures are providing a vital ecosystem service by consuming waste that, left to rot, releases greenhouse gases and spreads disease.

Research lead Dr Gidey Yirga, from the University of Sheffield’s School of Biosciences, said: “At a time when cities across the world are struggling with waste and climate goals, we’ve found that scavengers are providing essential ecosystem services while significantly reducing potentially catastrophic sanitation risks.

“Animals like spotted hyenas have adapted to a high-density, urban environment and have become an essential part of the city’s ecosystem.

“This demonstrates a mutually beneficial coexistence between people and large carnivores that, in most circumstances, require vast natural environments free of human intervention.”

To understand the scale of organic waste discarded across the city, researchers interviewed over 400 randomly selected households to understand their waste disposal habits. This data was extrapolated across the entire city, revealing that approximately 1,058,200 animals are slaughtered each year in people’s homes.

This generates 1,240.6 metric tonnes of meat waste - the equivalent to the total weight of roughly 31,000 live sheep. In a city with generally poor waste management and sanitation, this mountain of meat waste is dumped along roadsides and other open sites throughout the city.

The study found that by scavenging the meat waste, urban predators are preventing over 1,000 metric tonnes of carbon emissions entering the atmosphere and saving waste disposal services worth over $100,000 USD annually.

Dr Yirga added:“In our conversations with residents we found that they recognise and appreciate the benefits of living alongside these urban scavengers, highlighting the further potential of a peaceful coexistence between wildlife and humans in urban areas.

“This model could be applied to other Ethiopian cities and across many other African states where organic waste is routinely dumped at road sides.”

Having established hyenas and other scavengers' value to the city, the research team is now turning its attention to the animals themselves. The next phase of the research will investigate how their urban lifestyle could be physically changing the animals by comparing them to their wild counterparts.

Read the study in full.