Stanford University researchers have discovered a significant decline in populations of large scavengers worldwide, which could have implications for human health. These apex scavengers, such as vultures and hyenas, play an essential role in limiting pathogens by consuming carrion. However, their decrease has allowed smaller scavengers like rats and raccoons to proliferate, which can carry zoonotic diseases that may spread to humans.
The study, published in the Proceedings of the National Academies of Sciences, analyzed data from over 1,300 vertebrate scavenger populations and found that 36% were threatened or declining. This drop was more pronounced among larger scavengers. “The evidence we found is very clear,” said Rodolfo Dirzo, senior author and Bing Professor in Environmental Science at Stanford’s School of Humanities and Sciences. He emphasized that while large scavengers are declining, smaller ones are increasing but cannot consume as much carrion and pose disease risks.
Chinmay Sonawane, the study’s first author and a doctoral student in Dirzo’s lab, highlighted the importance of understanding these ecological connections: “I think as we become more aware of these connections, we’re going to be more inclined to protect these species because, in turn, we are ultimately protecting our health.”
The research points out three main factors contributing to this decline: habitat loss, intensive livestock production, and wildlife trade. These issues impact scavengers through habitat removal for grazing cattle or killing them due to perceived threats to livestock.
Dirzo called for policies supporting apex scavenger recovery by protecting habitats and reducing poaching while addressing prejudices against these animals. “There is this prejudice that these scavengers – vultures and hyenas and the like – are nasty animals…but they are important not only for the functioning of ecosystems but also for human well-being,” he stated.
The study received support from several Stanford institutions including the School of Humanities and Sciences and the Doerr School of Sustainability. Co-authors include Maya Xu and Natalie Ward along with Ariella Chichilnisky du Lac.
For further information on this research or other scientific studies from Stanford University contact Sara Zaske at (510) 872-0340 or via email at szaske@stanford.edu.
