Getting rid of toxic, foul-smelling trash dumps might seem like a good idea. That is, unless you are an endangered vulture.
A European Union environmental initiative to phase out landfills and shift towards a more “circular economy” in which material is re-used could have an unwanted side effect by depriving Egyptian vultures of a key food source.
The birds’ “food networks were vulnerable to the elimination of the main feeding areas in landfills, which are highly predictable resources,” warned Catuxa Cerecedo-Iglesias, a researcher at the University of Barcelona in Spain.
The findings by Cerecedo-Iglesias and colleagues illustrate how human infrastructure in the Anthropocene has become so entangled with the lives of animals that even well-meaning actions can send surprise ripples through the natural world.
In this case, the EU has a plan to cut the amount of municipal trash sent to landfills to 10% by 2035, down from 25% in 2016. The goal is to reduce landfill-related problems, including leaking toxic chemicals and emissions of planet-warming methane from rotting material such as food.
While these landfills are an environmental headache, they are a boon for airborne scavengers. Vultures flock to what is the equivalent of all-you-can-eat buffets. The dumps have taken on even more importance with the loss of other meals. European wildlife on whose carcasses the birds once dined has dwindled with centuries of intensive human development (though there is evidence that some animal numbers are now on the rise). More recently, declines in farming means fewer livestock carcasses on which the birds can feast.
The continent’s vultures have suffered along with the rest of its wildlife. Bearded vultures were wiped out from the Alps in the early 20th century, amid the mistaken belief that they killed sheep. Egyptian vultures, which are globally endangered, have had European numbers cut in half in recent decades.
One bright spot is northern Spain, where the number of Egyptian vultures has increased in recent years. But the new research suggests those gains could be in peril.
To understand how the landfill crackdown might affect these birds, Cerecedo-Iglesias tracked the movements of 16 birds tagged with GPS units during the summers of 2018 and 2019. The results revealed a string of 44 interconnected places where the birds gathered in northeast Spain, stretching from the outskirts of Barcelona into the Pyrenees. Those hotspots included areas with more intensive farming and managed “vulture restaurants,” where carcasses are intentionally left out for the birds. But the landfills loomed largest in the birds’ movements. They acted as central hubs to which the birds return again and again, the scientists reported in the journal Movement Ecology.
The movements differed depending on whether the birds were breeding or not. Breeding vultures generally roamed shorter distances presumably confining their travels to areas close to their nests. But either way, landfills were central.
If the food supply from landfills shrinks or disappears, the birds’ flight patterns suggest that livestock farms would become more critical.
Encouraging farmers to leave the carcasses of dead livestock out where vultures can find them could help replace the calories that would be lost if a landfill closes. But such livestock operations are confined to only some parts of the region and in mountainous areas above 1,400 meters in elevation.
If landfills close, those farming restrictions would leave “the vast majority of areas where Egyptian vultures are distributed devoid of food,” the authors warned. “So it is key to increase the surface of these areas at lower altitudes and other regions.”
Cerecedo‑Iglesias, et. al. “Resource predictability modulates spatial‑use networks in an endangered scavenger species.” Movement Ecology. April 20, 2023.