A spotted hyena carries a skeletonized wildebeest carcass.
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Photo by Marcel Oosterwijk, distributed under a Creative Commons Attribution-Share Alike 2.0 Generic license.
A spotted hyena carries a skeletonized wildebeest carcass.

Looking Nature in the Mouth

Spotted hyenas seem to be the perfect archetypes of dirty scavengers. They’re smelly, not quite so charismatic as the big cats they compete with, and, most importantly, have bone-crunching jaws capable of dismantling most any carcass left to rot among the African grasslands. In the impression of savanna dominance that persists in many of our imaginations, lions are regal predators while hyenas are a dedicated clean-up crew, assisting the economy of nature by horfing down pungent gore. This is not at all true.

While these carnivores feed on carrion when they can, long-term studies of spotted hyena populations have shown that they hardly rely on kills made by other carnivores. Scavenging accounted for about 33% of the diet of the Serengeti’s spotted hyenas in classic observations made by Hans Kruuk, while a 1999 paper by Susan Cooper and colleagues reported that the “Talek clan” of spotted hyenas in Kenya’s Masai Mara got all but 5% of their meat from hunting, making them among the most predatory hyenas ever seen. And after reviewing the scientific reports of hyena feeding behavior, Matt Hayward found that hyenas are generalist hunters. They usually don’t bother with some of Africa’s largest herbivores – buffalo, giraffe, and plains zebra – but otherwise they literally take what they can get.

Spotted hyenas are not loathsome carrion chasers. They remain among Africa’s apex carnivores through their ability to hunt, either alone or in packs. Not all their kills remains theirs, however. Lions are their chief competition, and, based on observations by Kruuk, spotted hyenas lose anywhere from 5 to 20% of their kills to kleptoparasite lions. The “king of the beasts” has no honor when it comes to meals, and they have been tussling with hyenas over kills since the last Ice Age, at least.

None of this will surprise zoologists. Experts on Africa’s fauna have known about the predatory prowess of spotted hyenas since the 1960s. Yet the myth hangs on. The way we think about and categorize nature obscures variation and flexibility for simplified, distilled factoids. Animals are labeled as herbivore, carnivore, or omnivore, or, as with the spotted hyena, categorized as a hunter or scavenger, as if these titles lock the actual animals into patterns of behavior they cannot violate.

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Tyrannosaurus rex stands over a kill at the Carnegie Museum of Natural History. Photo by Brian Switek.

The same problem extends to the fossil record. For years, news pieces and documentaries have breathlessly forwarded the question of whether the great Tyrannosaurus rex was a consummate hunter or a grubby scavenger. Setting up such a dichotomy, where the carnivorous tyrant must have done only one or the other, was nonsense. T. rex certainly chased down prey and scoffed rotting flesh, a conclusion backed up by tooth-scored bones and injuries on the tails of at least two hadrosaurs. More than that, dinosaurs taken as the ultimate in predatory hypercarnivores likely scavenged when they had the chance. The turkey-sized, sickle-clawed Velociraptor was certainly well-equipped for tearing into prey, but, as bitten and ingested bones suggest, this wouldn’t have stopped the dinosaur from taking easy meals left out in the open.

Then there are the animals whose dietary exploration takes us entirely by surprise. Whether a spotted hyena or a tyrannosaur is hunting or scavenging, they’re still eating meat. But there are animals that we think of as dedicated carnivores that scarf plants now and then. Alligators and crocodiles, for example, eat fruit often enough that they might actually help disperse seeds. And primarily herbivorous animals vary their meals, too. As Darren Naish has pointed out, “‘pure herbivory’ is apparently much rarer than we used to think” – deer and cows will often eat small birds and other animals if they can. Would a cow eat you and everyone you care about? If you’re a little bird, maybe.

Hippos go one step further. The tubby, tusked mammals are imposing enough that they sometimes try to snatch kills from predators. In an incident reported by Joseph Dudley, a hippo in Zimbabwe’s Hwange National Park killed an impala that had the bright idea of trying to escape a wild dog by swimming across a small pool. The hippo presumably killed the herbivore for straying into the wrong territory, but that didn’t stop another hippo from inspecting and consuming some of the impala. And while this was going on, Dudley wrote, wild dogs took down another impala near the water’s edge. A group of hippos ran the dogs off from the kill for some unknown motive, and once the dogs were gone the hippos scooped up whatever loose bits of meat were left on the ground.

Deer and hippos are primarily herbivores, but it isn’t aberrant when they go carnivore. We simply weren’t looking when they did so, or didn’t acknowledge the behavior. There are likely plenty of other examples of such dietary flexibility that pay no mind to our preconceptions about what certain animals eat. Nature is far stranger and more varied than we could expect. To see apparent rapacity or docility is one matter. To truly look nature in the mouth is another.

References:

Dudley, J. 1998. Reports of carnivory by the common hippo Hippopotamus amphibius. South African Journal of Wildlife Research. 98, 28: 58-59

Holtz, T.R. 2008. “A critical reappraisal of the obligate scavenging hypothesis for Tyrannosaurus rex and other tyrant sinosaurs.” in Larson, P. and Carpenter, K. (eds) Tyrannosaurus rex: The Tyrant King. Bloomington: Indiana University Press.

Hone, D., Tsuihiji, T., Watabe, M., Tsogtbaatr, K. 2012. Pterosaurs as a food source for small dromaeosaurs. Palaeogeography, Palaeoclimatology, Palaeoecology. 331-332: 27-30

Margalida, A., Campión, D., Donázar, J. 2011. Scavenger turned predator: European vultures’ altered behavior. Nature. 480: 457