Boars that encounter a wolf carcass will try to flee or fight the corpse, suggesting that sometimes dead predators can still influence their prey’s behaviour

Wild boars can still be scared by a dead wolf. Not only are apex predators scary to prey animals, but their carcasses seem to be able to produce a scare that other dead animals can’t.

Prey species behave differently depending on the presence or absence of predators in their environment, carefully navigating their world to reduce the risk of being eaten. Dead animals can also signal that a predator could be nearby, so some prey animals avoid carcasses. But little is known about how prey animals regard carcasses of predators, and if they could be mistaken for a live threat.

Daniel Redondo-Gómez of the University of Grenada in Spain and his colleagues have now tested this in the Susa valley in the Italian Alps. They placed the carcasses of 10 road-killed wolves (Canis lupus) and nine red foxes (Vulpes vulpes) in the mountain forests, monitoring them with motion-activated video cameras.

Twenty-six wild boars (Sus scrofa) ended up approaching the dead wolves. In nearly a quarter of these encounters, the boars would go into an abrupt fight-or-flight response, fleeing or even attempting to fight the wolf carcass, ramming and biting it. But in the 14 encounters with the red foxes – which only very rarely prey on boars – the probing pigs had no such fearful reaction.

The findings may mean that the “ecology of fear”, where predators influence their ecosystem by changing the behaviour of the prey, can persist into death. Carrion may have a bigger role shaping prey species’ lives than previously thought.

“That prey recognise their predators even when [those predators] are no longer lethal points to how powerful fear can be,” says Liana Zanette at the University of Western Ontario in Canada.

On the other hand, the boars correctly identified the carcasses as non-lethal most of the time, says Zanette.

The upside in enhanced caution through fearfulness is that it can keep an animal alive. “The downside is that spending time worrying about predators shaves off time spent looking for food, which is why scared prey typically eat less,” says Zanette.

Journal reference: Ecology and EvolutionDOI: 10.1002/ece3.9911