National Geographic

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.

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

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:

Cooper, S., Holekamp, K., Smale, L. 1999. A seasonal feast: long-term analysis of feeding behavior in the spotted hyaena (Crocuta crocuta). African Journal of Ecology. 37, 2: 149-160

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

Hayward, M. 2006. Prey preferences of the spotted hyaena (Crocuta crocuta) and degree of dietary overlap with the lion (Panthera leo). Journal of Zoology. 270, 4: 606-614

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., Choiniere, J., Sullivan, C., Xu, X., Pittman, M., & Tan, Q. 2010. New evidence for a trophic relationship between the dinosaurs Velociraptor and Protoceratops. Palaeogeography, Palaeoclimatology, Palaeoecology. 291, 3-4: 488-492

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

Trinkel, M. 2010. Prey selection and prey preferences of spotted hyenas Crocuta crocuta in the Etosha National Park, Namibia. Ecological Research. 25, 2: 413-417

 

There are 8 Comments. Add Yours.

  1. Brian
    November 8, 2013

    very interesting that hippos, which everyone considers a vegetarian, will scavenge meat when the opportunity arises, should give us all something
    to think about.

  2. WA_side
    November 9, 2013

    Well that adds an interesting possibility to my thoughts regarding what ate a sheep on my Mother’s property in Southern region of Western Australia! As non-scientists (and non-farmers), we’ve assumed primarily wild dogs, or perhaps wild pigs, though the ground did not look roughed up enough for pigs.

    Also thought foxes may have eaten some later on, though presume they are not big enough to have dragged the carcass while it still had wool attached. I had noted that there was a reasonable amount of emu droppings near the sheep, but believed they only ate vegetation and small insects. Perhaps emus enjoy a little rare lamb?

    I don’t imagine I will see proof in either direction, but it does suggest the closeness of the droppings to the sheep MAY not have been coincidental as I had concluded. Equally of course, it proves no causality either.

    Either way, your article does suggest I should let go of my desire for nice, tidy demarcation in how the world works and embrace the murkiness.

  3. Em
    November 9, 2013

    “Either way, your article does suggest I should let go of my desire for nice, tidy demarcation in how the world works and embrace the murkiness.”

    A favourite in the comments section. . . Sums up my thoughts exactly.

  4. Brian Edwards
    November 10, 2013

    1) I remember a case of a sacred cow in India that was caught on film killing and eating the local chickens about 5 years ago.
    2) As a vegetarian I have friends who claim to be “carnivores” but since most meat is consumed away from the kill site and hours if not days after the kill I feel compelled to point out that they are scavengers eating carrion lol.

  5. Mitch
    November 11, 2013

    Really interesting article.
    This is the type of article I come to Nat Geo for!

  6. evodevo
    November 11, 2013

    A young, hungry hawk will eat roadkill – saw one doing that – no different from having mom and pop bring something to the nest, I guess. Chimpanzees hunting monkeys comes to mind, also, as a surprise to biologists. Protein-short diets will drive some interesting behaviors.

  7. Dan Peterson
    November 20, 2013

    Great article, Brian, and good to see you have a regular blog on Nat. Geo. though it will be difficult to prove it, I think it very probable that most of the so-called ‘herbivorous’ dinosaurs, were in fact omnivores, that took small prey at any opportunity, much like the bird eating deer and bovines. Every time I see that scene in Jurassic Park with the kids in the tree face to face with the Brachiosaurus, I imagine it gobbling them up despite Dr. Grant’s assurances that it was a harmless planteater.

  8. Troodon Roar
    August 15, 2014

    I couldn’t agree more with this article. I always find it really annoying when people continue to cling to unfounded and erroneous stereotypes about animals. To use another example, one of the most deeply-entrenched beliefs among scientists is that reptiles are not very intelligent. However, recent studies have pretty much completely shattered that notion. Anoles are capable of problem-solving. Iguanas can be trained to defecate in a specific location, like cats and dogs. Monitor lizards are capable of counting up to 6, and have also been observed playing. Tortoises can navigate mazes better than rats. The list goes on and on.

    Another example is the stereotype that birds are not capable of killing large prey. This myth was debunked in 1996, when a paper was published that confirmed that a Golden Eagle had once successfully managed to kill a juvenile cow that must have weighed at least 251 pounds. Beginning in 2006, Darren Naish began to spread the word about the ability of birds to kill large mammals on his Tetrapod Zoology blog, but even today, the idea is still seen as taboo.

    In nature, pure herbivores and pure carnivores are, indeed, rare, as are pure scavengers and pure hunters. In my opinion, the entire “debate” about whether tyrannosaurs were hunters or scavengers should never have even occurred at all. It is obvious that they were most likely both.

    Likewise, researchers began to hypothesize in the late 1990s that troodontids might have been omnivorous. Once this hypothesis gained traction, people instantly began to assume that troodontids could never have hunted large prey because they were omnivorous.
    In the late 2000s, further studies showed that this notion was false. It was revealed that Troodons in Alaska were twice as large as their more southern relatives, and that they were likely the apex predators in their environment. However, that doesn’t mean they couldn’t have also eaten plants. As an analogy, modern polar bears are the apex predators in the Arctic, but they still occasionally eat plants. There is no reason why troodontids in Alaska could not have done the same.

    Just like how it is a terrible idea to put people into a box and subject them to stereotypes, it is also an equally terrible idea to do so the natural world. Let’s stop trying to pigeonhole nature into our own preconceived notions, and let’s start appreciating the beauty and diversity of the natural world. People often say that diversity is the spice of life. However, I disagree with this analogy. Spices are unnecessary, and only exist to make food tastier. On the contrary, food is necessary for life. And so is diversity. Diversity is the food of life.

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