Animals that feed on the corpses of other animals are generically defined as “scavengers”, an umbrella term that includes representatives of fish, reptiles, birds and amphibians. From hyenas to storks passing through carp, necrophagia is widespread in the animal kingdom, yet so far we have focused very little on the “what”: even scavengers have preferences in choosing corpses, and a study published in Ecology Letters reveals that they are more refined than one might think, and even have phylogenetic bases.
Hunting for corpses
The study was conducted by four Spanish researchers from different universities, who collaborated for more than a year in the swamps of the El Fondo natural park, near the city of Elche. It is a wetland area rich in biodiversity despite its small size, and is therefore rich in both corpses and scavengers. What is missing are the large predators and the necrophagous birds par excellence, the vultures: all ideal conditions for studying how a great variety of scavenger species feed.
The team then monitored the area between February 2020 and May 2021, using photo- and video traps and facilitating operations by disseminating additional carcasses in selected places in the park. Obviously not chosen at random: the researchers placed “the right corpses in the right place”, placing them where they could have died naturally, further favoring the work of the scavengers. The video material was then analyzed to discover how certain animals choose which corpse to eat and which to ignore.
Dog not eat dog (literally)
The videos captured by the traps show an extraordinary variety of species involved in the work of scavengers: the main protagonists are birds, ranging from the stork to the sacred ibis, from the magpie to the greenfinch. Among the mammals the red fox stands out but also the wild boar, among the scavengers there is also a fish, the carp. The characteristic common to all these animals? They never eat the corpses of their species.
Better said, scavengers choose their meal based on phylogenetic distance from the carcass. For example, birds almost never eat the corpses of other birds, with the sole exception of the southern shrike; mammals stay away from other mammals (with the exception of the fox), and so on. The reason is sanitary: corpses carry pathogens, and the corpses of a member of your own species carry pathogens that can affect you.
In addition to revealing this secret of the scavengers’ trade, the study also highlights how important these animals are in food webs: a sensational example comes from India, where three years ago the decline in the vulture population was linked to the death of half a million people, affected by diseases linked to corpses that the few scavengers were unable to remove.
