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Approximately one-third of vertebrate scavenger species may be facing population decline

A small team of biologists at Stanford University has found evidence that approximately one-third of all vertebrate scavengers are threatened or decreasing in abundance. In their study, in the Proceedings of the National Academy of Sciences, the group made a list of all known vertebrate scavengers and compared it with published listings of species.

Prior research has shown that scavengers serve a vital role in many ecosystems—by removing dead carcasses, they remove the threat of disease and water contamination. Prior research has also shown that in places like North and South America, and Europe, scavengers clear approximately 75% of all carrion. In Africa, such services are even more important—hyenas clear more than 200 tons of dead waste each year.

In this new effort, the research team wondered how scavengers, particularly vertebrates, are faring in the face of a drastically changing world. To find out, they extracted the names of all known marine, freshwater and terrestrial vertebrate species from multiple sources—the total came to 1,376 species.

They then looked them up in the IUCN Red List, a global reference source of conservation information, to determine their status and found that approximately one-third of them were under threat or declining.

During their study, the researchers also found vertebrate scavengers live in a wide variety of places and are phylogenetically diverse—they found more than 200 family taxonomies. They also noted that larger scavengers, such as whitetip sharks, hyenas and vultures, have seen larger population drops than smaller scavengers, such as rats. Many of the smaller representatives were actually growing in number.

The researchers suggest this is likely due to both a reduction in competition from the larger scavengers and an ability to adapt to living in a changing world, particularly as it applies to living in the vicinity of humans.

Smaller scavengers such as rats, mice and other rodents may carry more diseases than larger scavengers, and because they live so close to human population centers, they are likely to present a growing health threat.