Carnivory in Hippos

7 08 2007

Hippo Skull
Replica of the skull of the Hippopotamus, Hippopotamus amphibius, at Disney’s Animal Kingdom Park (via Wikipedia)

Hippos are one of those animals that are sometimes used to drive home the point that appearances can be deceiving; despite their fearsome dentition, they’re really herbivores. They may have bad attitudes and be a terror along African waterways, but at least they’re not carnivorous. At least, that’s the story.

Hippo
It’s easy to see why the hippopotamus got it’s name, meaning “River Horse.” Taken at the Philadelphia Zoo, August 2006.

While the vast majority of the hippo’s food intake is short grass that grows along river banks, this doesn’t exempt them from eating meat every now and then. In 1996, J.P. Dudley published the paper “Record of carnivory, scavenging and predation for Hippopotamus amphibius in Hwange National Park, Zimbabwe,” followed two years later by “Reports of carnivory by the common hippo Hippopotamus amphibius.” I do not have access to either of these papers, but as far as I understand it, they are the best scientific accounts that we have that hippos do sometimes eat meat. A pdf file announcing the Dudley’s work, states that not only was carnivory witnessed among the hippos, but even cannibalism, the strange habits of the studied group perhaps contributing to an anthrax outbreak that ended up killing 300 hippos in the area.

Mouth
Taken at the Philadelphia Zoo, August 2006.

More clues are offered up by a short summary from a 1999 issue of Natural History;

Although the hippopotamus’s usual fare is this habitual vegetarian can occasionally turn carnivore. Field biologist Joseph P. Dudley, formerly at Hwange National Park in Zimbabwe, observed a male hippo killing an impala ram that had swum through a pond to evade a wild dog. After eating some of the meat, the hippo returned to his herd.

A few minutes Later, ten more individuals from the group gathered at the floating carcass for a communal feast. Later a few of them climbed the pond’s banks to wrest another dead impala from wild dogs. “It seems almost incredible,” writes Dudley, “that carnivorous feeding behavior by hippos, even if of very infrequent occurrence, could have gone unreported for so long.” Perhaps, he opines, the behavior may have been attributable to “nutritional stress caused by severe drought conditions.”

Mouth
Taken at the Philadelphia Zoo, August 2006.

Even last night I caught a few moments of a nature documentary showing hippos mouthing/playing with bloated carcasses of wildebeest that drowned in an attempt to cross a river during their annual migration between the Serengeti National Park and Masai Mara National Park. The segment was short, but overall it didn’t seem that the hippos were very interested in consuming the dead antelope as much as mouthing it a bit before moving on. Likewise, hippos in captivity have been known to “play” with/harass other animals in their enclosures, especially birds. At Adventure Aquarium in New Jersey, many Turacos ended up dying of stress when they would fall into the hippo enclosure, the mammals taking the birds into their mouths and lashing them about, keepers frantically trying to rescue the birds with a dip net. Darren Naish has also posted anecdotal evidence of carnivory in captive hippos before, as well.

As I said before, I don’t have access to the scientific papers, but it seems that many of the hippo predation/scavenging events occur in years of drought, where large groups of the animals are brought together in one area when grasses and other “normal” foods are scarce. This could be why hippos in the documentary I mentioned above only “mouthed” the carasses of the wildebeest; they may have had plenty of food so there was no need to eat something that’s not a regular part of their diet. Still, as has been mentioned by Dudley, hippos often eat at night, and their nocturnal eating habits have generally kept us in the dark as to what they might be munching on other than grass.

But what about cannibalism and anthrax? A 2004 article in NewScientist suggests that the spread of anthrax in hippos was actually helped by a particularly harsh year where carnivory and cannibalism came apparent. The problem probably started in water contaminated with anthrax or grass containing anthrax spores. The problem with the hypothesis that hippos were initially infected by anthrax-contaminated water, however, is that the park in which the outbreak occurred is said to have plenty of flowing water, not the stagnant pools typical of an environment that harbors anthrax.

Regardless of how it got into the local ecology and transmitted to hippos, however, a particularly harsh or lean year could have easily caused rapid transmission in a population, even if only a small group were infected. If resources were scarce and hippos (known for their aggressiveness) were pushed closer together in the remaining areas of water and food, there would be much more fighting, and hippos leave tremendous gashes (prone to infections) on each other during these fights. This would make the animals more susceptible to infection, and because hippos appear to eat meat more when other food is scarce, the infected hippos would be more likely to be consumed, infecting even more hippos and leading to a runaway outbreak.

Hippo

Looking at the dentition of hippos, part of the reason why I wouldn’t necessarily expect carnivory to be common is that their teeth seem to be more adapted to be weapons than efficient cutting/slicing teeth. Hippos may have a good amount of power behind their bite, and the teeth in the front of their jaw are certainly powerful when it comes to puncturing, but it would seem to me that they would have to puncture carcasses with their massive front teeth and then try to rip off bits to then swallow whole; they lack the more efficient piercing and cutting teeth of carnivores like dogs and big cats. The apparently get by well enough without it when times get hard, but it doesn’t seem like they’re particularly well-adapted to carnivory. The following clip gives us a brief glimpse of a hippo scavenging from a buffalo carcass, although it doesn’t seem particularly interested in consuming much or fighting the lions for the carcass;

While it may be easy to write off such behaviors as aberrant or abnormal, they are very important to our understanding of ecology. Many people have a somewhat Disney-esque idea of what nature is like, with the “great Circle of Life” allowing each animal to have their own niche and live in harmony with each other; carnivores only eat other animals, herbivores only eat plants, and mammalian babies are cared for by both the “mommy and daddy” until they grow up. The truth of the matter is that ecological interactions are far more complex than we realize, sometimes revealing a “darker” side of nature than some people care to acknowledge (but again, this is putting a moral judgment on nature, which does not operate by a moral code or “Law of the Jungle”). There is cooperation in nature, but there is also fierce competition, and when ecologies start to become strained, whole new dimensions of behavior that are otherwise hidden or only barely visible come into play in an attempt to allow for the survival of the individual animal. Why should we expect otherwise?

Skeleton
Hippo Skeleton. Via Wikipedia.

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24 responses

7 08 2007
Neil

Fascinating, I had no clue! This is very interesting given the notion that hippos might be close to whales…and whales started out as carnivorous artiodactyls. Any evidence for carnivory in Anthracotheres? Also seems like a great case for some spec zoo: giant ambush hippos with nasty sharp teeth…I guess you’d end up with something like Ambulocetus on steroids!

7 08 2007
laelaps

Thanks Neil! As for Anthracotheres, I don’t know of any actual evidence for carnivory, although I wouldn’t put it past them. I’ll see what I can dig up, though (it makes me wonder if Smilodon ate grass every now and then like my cats like to do)

“giant ambush hippos with nasty sharp teeth”… At least now I know what will be in my nightmares this evening…

7 08 2007
Zach Miller

Hippos are perhaps my favorite African mammal. Their skulls are just so bizarre! I’d know about hippo canivory for some time, but this was an interesting post nonetheless. What are your thoughts on the proposed “Afrotheria,” Brian? It’s a supposed clade that includes hippos, elephants, and various other small abbarant African fauna, extinct and extant.

7 08 2007
TheBrummell

Hi Brian,

Nice post… I’d heard rumours of Hippo carnivory, but nothing solid. I’d also heard that diet aside, hippos are the most dangerous non-human animals in Africa, given the death toll (of humans) caused by them. Seems that getting between a hippo and the local waterway at night is a really bad idea.

Anyway, I tracked down those two papers by Dudley. The 1998 I was able to get as a HTML document, which I pasted into MS Word 2003 – I could email that to you if you want. The 1996 is available in hard-copy in the University of Guelph library, I could photocopy, scan, and email that to you if you say “please”. It’s only 3 pages long, so not a big deal.

30 10 2009
aartima

its fairly accurate but i thought the current thinking is that anthrax does not survive in water but it suvives in the bodily fluids, thats how it was spread from hippo to hippo when they were chowing on some hippo guts?

7 08 2007
laelaps

Thanks for checking up on the paper for me Martin! I had a look myself today, but they were behind a subscription wall. If you could please send them over to me I would be most grateful; I definitely would like to know the details of what Dudley saw. Thank you so much for helping me out!

As for the “most dangerous animal in Africa” business, I guess that depends who you ask. If you’re in or around the water, it’s hippos (and crocs, too), while I’ve heard that Cape Buffalo kill just as many, if not more, people every year. If you’re camping outside your tent at night, hyenas and ants are probably your main worry, and I probably don’t have to say much about malaria-carrying mosquitoes. Still, out of the big mammals, I’d venture to guess that Cape Buffalo are probably #1 with hippos coming in as a close second, although I haven’t seen any statistics to prove this (I wonder if any sort of file is kept…). I would agree with you that getting to close to a hippo is hazardous to one’s health, though; there are plenty of recorded attacks, perhaps some involving people being bitten in half, and given the discussion of carnivory I wonder if hippos consider us food in lean times too. It’d make for a good b-movie at least.

And Zach; admittedly I don’t know much about the Afrotheria as a clade, so I have to do some reading. From what I understand, however, it’s mainly based on molecular evidence from living animals, and fossil evidence seems to contradict the molecular evidence (i.e. some of the ancestors of elephant shrews and other animals have been found outside of Africa). In the end I think it’ll either be trimmed down and kept or cast off in time, but we really need to fossil evidence to work it out. I’m highly dubious of it at the moment, but then again I haven’t exactly given the evidence a fair look yet.

7 08 2007
Christopher Taylor

I’m not at all surprised by hippos eating meat at least opportunistically – meat eating is far from unknown in artiodactyls. I remember seeing footage on a nature doco (unfortunately, I can’t remember which one) of a giraffe gnawing on a buffalo carcasse. Duikers will apparently kill birds and small mammals. Pigs and peccaries, of course, eat damn near anything.

As for Afrotheria, I’m currently both for and against the idea. Recent morphological analyses (such as Wible et al., 2007) have actually recovered a “core Afrotheria” as monophyletic – all the modern taxa that the molecular data groups as monophyletic except for the Afrosoricida. The Afrosoricida still doesn’t want to join the Afrotheria on morphological grounds, remaining firmly attached to the Eulipotyphla. The molecular data, on the other hand, is quite adamant that afrosoricidans are afrotherians. We’re just waiting to see who gives first – analyses on both sides are still a little deficient. Wible et al., for instance, didn’t include perissodactyls in their analysis, which are one of the groups that might be most likely to break up the core Afrotheria. I feel I should point out, too, that even if Afrotheria is not actually African in origin that doesn’t say anything about its monophyly or otherwise.

7 08 2007
Neil

The high level clade shuffling within placentals is one of the most fascinating trends in biology, and for my money as Christopher notes, a ‘core afrotheria’ is well supported at this point by both morphological and molecular data. Cetioartiodactyls (including hippos) don’t seem fit into this group however.

Hippos as the ‘most dangerous african mammal’ has become something of truism now, almost certainly just because it’s a counterintuitive and surprising idea. Not to say that I would want to meet one in a dark alley, but yeah mosquitos, tsetse flies those are the dangerous African animals almost approaching humans in their destructive power.

8 08 2007
johannes

Neil,
a homeothermic metabolism seems to rule out lengthy croc-style ambushes. An Ambulocetus-like animal might mount an occassional, opportunistic ambush, but ambushing large land mammals could not be its only source of food. It would have to fall back to fishing, eating molluscs and/or herbivory for its daily maintenence. BTW, if we are talking about freshwater cetaceans:
I have heard that the Yangtze Dolphin has been officialy declared extinct. If this is true it would be really shocking. Does anybody knows more?

Zach,
Afrotheria as a clade includes hyraxes, aardvarks, proboscidans, , Arsinoetherium, the golden moles, the desmostylians and the Sirenia (manatees and dugongs).
Tenrecs (including otter shrews), elephant shrews and hyaenodonts might be members of Afrotheria, too, but this is controversial. The Bibymalagasy, Plesiorycteropus, might have been an afrothere, too, but in fact it is not even sure if it was a placental at all. It might have been a non-placental eutherian, a highly aberrant zhelestid or something.

Hippos, however, are members of the Cetartiodactyla, a clade that is firmly settled into Laurasitheria; they are definitely not afrotheres. This said, anthracotheres were present in Africa before there was a landbridge between Africa and Eurasia, but they were semiaquatic and probably good swimmers.

8 08 2007
laelaps

Johannes; thank you for once again lending your expertise to us! I think part of the croc-style hunting that was mentioned partially stems from this image, and I would certainly be interested to find out how creatures like Ambulocetus hunted.

As for the White Yangtze River Dolphin, it’s believed to be functionally extinct; none have been sighted recently, and even if there are some still alive it is too few to sustain the population (short of an ecological miracle). The last time I heard anything was via this article last fall.

Neil and Chris; thanks for your thoughts on Afrotheria. I think that evidence does support a “core group” as well, although it’s probably not as inclusive as might commonly thought. Some pruning might be in order, although more work will have to be done to determine this. I wasn’t suggesting that finding fossils of ancestors/members of Afrotheria would junk the clade either; just that a bigger picture should be embraced if we’re to figure this one out. As I’ve said before, I’m not up-to-snuff on my understanding of molecular studies, so I have plenty of catching up to do on this topic myself.

8 08 2007
Hoofnagle gets some things right, others wrong on Ecology « Laelaps

[…] While I’m not one of the Disney-fied, harmonious “Circle of Life” view of nature (hippo carnivory and cannibalism can show us that, at least), this passage is little more than a straw man argument. […]

9 08 2007
Mike

I have been fortunate enough to visit Kenya. Whilst in the Tsavo West National Park on our way to visit a site called Mzima Springs, we got talking to the local guides. I was there to examine the Nile crocs, but it was their stories of the large male hippos scavenging meat from carcasses in times of drought that I recall.

30 08 2007
Waterlogged Weblog « Laelaps

[…] Carnivory in Hippos […]

13 11 2007
Trav

I recently travelled to the Chobe river (Chobe National Park, Botswana). Whilst there my group encountered a dead elephant lying in the river. Crocodiles were basking nearby though one was biting at the flesh near the tail. At the other end, a hippopotamus spent more than 20 minutes either chewing on the trunk of the elephant or tearing into flesh on the back of the head. We initially thought the hippo was just mouthing the trunk which was odd behaviour in itself, so joked it was performing mouth-to-mouth resuscitation on the elephant. It soon became clear that its intent was to consume the meat though, evidenced by the biting on the head and consumption of meat it tore off the carcass. Quite interesting to watch and the guide was rather surprised to have seen it also – he considered it very unusual behaviour.

28 12 2007
David Marjanović

On the dangerousness of hippos, the important thing to remember is that crocs will kill you when they’re hungry — hippos will kill you for trespassing.

On Afrotheria, I’m sure it’s real, firstly, because LINE insertions — a quasi-morphological character that is practically immune to homoplasy — support it, Afrosoricida included; and secondly, because there is no good morphological analysis of placental phylogeny — the Wible et al. (2007) paper was a good start, but its taxon sampling (at least) is still utterly pathetic. Let’s come back in ten years, then we’ll hopefully have something to compare!

The Bibymalagasy, Plesiorycteropus, might have been an afrothere, too, but in fact it is not even sure if it was a placental at all.

Correct.

It might have been a non-placental eutherian, a highly aberrant zhelestid or something.

I fear you merely remember what I made up for Spec. For Spec it would come in very handy if the bibymalagasy were a zhelestid, but, while there’s no evidence against this, there is none for it either!

17 05 2008
n

I have cared for hippos for many years in captivity. I have seen them kill and partially eat an Egyptian Goose which had shared their enclosure for over 10 years. We considered it such a fluke that we left the remaining goose in the yard, and it was killed as well, but not eaten. In all, they killed 3 geese but only consumed part of one. It’s been speculated that they kill and eat other mammals for the saline component in the blood/meat of their prey. We no longer house any birds with the hippos.

13 10 2008
Brad Drown

I’m leaving this posting as just more evidence that a hippo will kill and eat another living thing if the hunger or the desire is great enough. A close friend of mine recently returned from a trip to Africa where he was part of a group of teachers who went there to volunteer their time. He told me of a morning when a group of villagers and himself were walking along a dirt road. Trees or jungle were on one side and on the other side was a cleared area where a man had tied his prize beef calf so it could graze. The group was startled when a large hippo broke from the jungle and crossed the road in front of them. The hippo went straight to the large calf and attacked it violently. The calf was still alive when the hippo tore out the stomach area and began eating the calf alive. When the calf made some noises, the hippo began biting the head and neck of the calf. In a short time the head was torn from the body of the calf and it was now dead. The group of people were afraid to move so they all stood silently and watched. My friend told me that this hippo ate a good deal of this calf including most of the organs and both of the hind quarters. The hippo had no trouble crushing bones and getting to what it wanted on the calf. He told me this viewing went on for about forty minutes and when the hippo seemed to be finished, it looked at all the people standing in the road and took three or four steps toward them. Then, the hippo casually walked across the road and back into the jungle. One of the guides told him that such events were very common and that natives don’t recognize the behavior as strange or odd. The guides told him a great deal about other animals we would not think could behave this way and I guess they do so often.

22 10 2008
African Safari Stories

Wow! Great post filled with sooo much useful and interesting information.

13 10 2009
27 10 2009
william shannon

Awsome, but sick. Its the kind of thing that people need to know about animals. All animals! Some people dont know, or rejected it even thought its the true because they’ve never heard of it or they think that its wrong when every its life.

16 05 2010
eliupendo lobuku

Its grate website and most people should make a visit and learn more.
this website is also nice for the student who are study animals.

8 09 2010
tytyr

Wow! Great post filled with sooo much useful and interesting information. )))) not a libebel

4 12 2010
markgelbart

Have you seen the television special, “Hippos: The Darkside,” airing on National Geographic Wild? The showed footage of hippos eating meat.

This surprised me, so I googled “Hippos eat meat,” and found your blog. I’ll have to stick your blog as one of my favorites.

29 04 2013
Corazon

Very nice post. I just stumbled upon your weblog and wanted to say
that I’ve really enjoyed surfing around your blog posts. After all I’ll be subscribing to your
feed and I hope you write again very soon!

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