Note: some of the videos embedded in this article show predators eating animal carcasses.
To describe what kleptoparasitism is, I’m going to use a Pixar film.
Yes, Pixar’s 1998 film A Bug’s Life, while incorrectly making worker ant Flik a male*, provides a very excellent example of kleptoparasitsm. Poor Flik’s ant colony is forced to gather extra food every year in order to offset the losses from the larger and more aggressive grasshoppers, who regularly come and steal the ants’ food.
While real grasshoppers aren’t known for pilfering from ant food stores (they would find themselves very quickly dismembered and tossed on the pile), this type of interaction is very common between types of species that share the same food source, or need the same types of resources, such as nest-building material. Generally, it is the larger, more powerful species that nabs the resource from the smaller one. Hence the term ‘kleptoparasitism’: parasitic theft.
Most kleptoparasitism takes place opportunistically- few species have evolved to be thieves one hundred percent of the time because it’s simply not practical. The only exceptions to this occur if you consider brood parasitism a kind of kleptoparasitism. For example, common cuckoos exclusively make use of the nests built by other birds and have lost the ability to care for their own young. Conversely, slave-making ant species actually steal the young of other ants to do all the work in their colony. Et tu, Flik?
Kleptoparasitisitic relationships can also occur between members of the same species- one could consider the nabbing of prime territory or mates a form of kleptoparasitism. In fact, many species that have kleptoparasitic relationships with one another are very closely related, particularly in insects. This makes sense- the more similar you are, the more you compete for the same resources.
The relationships I want to talk about the most today, however, are the ones between species that are not closely related, but share the same ecological niches. And I want to discuss an interesting hypothesis, one that was also explored in A Bug’s Life. If you’ve seen the film, you’ll remember the ending:
Yep, Flik saves the day and helps his colony defeat the grasshoppers by reminding them that they vastly outnumber their parasites and, additionally, are equipped with limb-severing pincers. The ants are then able to overwhelm the grasshoppers with sheer numbers and presumably feast upon their remains offscreen.
So: how effective are numbers as a defense against kleptoparasitism?
Kleptoparasitic Relationships Between Large African Predators
Kleptoparasitism is a major problem for mammal species of a particular kind: small, lightweight, and specialized predators. On the African savannah, two species are notable targets for kleptoparasitism: the cheetah and the African wild dog.
Of the large mammalian predators on the savannah- the lion, leopard, cheetah, hyena, and wild dog- it is the cheetah and the dog who have the highest hunting success rates, of about 50 and 80 percent, respectively. Comparatively, hyenas and lions have closer to 30% success rates when they attempt to make a kill.**
Hyenas and lions, while not as speedy or efficient as the dogs and cheetahs, certainly know how to use their greater weight to their advantage- hyenas weigh about twice as much as both species, while lions have nearly four times their bulk. It is estimated that about 50% of all cheetah kills are parasitized by lions or hyenas, a rather grim statistic for an endangered species.
Unfortunately, there is very little a single cheetah can do against a hyena. Aside from the differences in weight and power, the specialized hunting style of the cheetah means that any injury could be fatal. Cheetahs (and wild dogs) are cursorial hunters, which means that they chase their prey over long distances. This requires a lightweight body and excellent stamina. A lion might be able to stalk and ambush its prey with minor injuries, and even with major ones it still has a chance of using its weight to steal prey from smaller creatures. But cheetahs and wild dogs hunt nearly exclusively for their own food.
The lion is the heaviest predator on the savannah, and they know it: as many as half of the kills a lion eats might be stolen from other predators. They kleptoparasitize even more than the much-maligned hyena, which in some studies hunts for as much as 95% of its own food.
However, hyenas can also kleptoparasitize the larger and more powerful lions. Their secret? Just as with the ants, it lies in numbers. If a group of hyenas outnumbers the lions feeding at a kill by a factor of four, they may challenge them. It’s a toss-up to whether or not they will succeed, though the presence of much larger male lions can make things much more dangerous. One study found that 71% of all hyena mortality was due to lions.
In fact, lions are a major cause of death for all of their competitors. African wild dogs and cheetahs also have much to fear from lions: lions will seek out and kill their cubs without even bothering to eat them afterwards. For this reason, while these species can forge a rough coexistence with hyenas, they actively avoid spaces that lions frequent.
You’ve been lied to, folks: Lions ain’t majestic beasts with flowing hair. Lions are gigantic assholes that make up for their crappy hunting skills by stealing meat from smaller animals. You say lion king, I say lion tyrant.
So on the savannah, killing your prey may be the simple part: the harder part is keeping it. Leopards, at least, have solved this issue by dragging their prey up into trees to eat at their leisure, though this doesn’t always work. Other species with less of an inclination for tree-climbing will make their kills in tall grass or dense foliage to avoid detection, though inevitably small scavengers like jackals and vultures will give them away. In fact, at times the scavengers can oust the killers themselves.
Much of the behavior of these smaller hunters, in fact, is heavily influenced by kleptoparasitism- more than you might think. After all, evolution doesn’t work in a vacuum, and if there’s someone out there making it, there’s always someone else ready to try and steal that success.
This raises a rather interesting question: are some of our assumptions about the social nature of these hunters wrong? Recall that if they greatly outnumber lions, hyenas can steal their kills. Conversely, this means that even the lions need to be in large groups to resist losing their spoils. Do these predators group up specifically to reduce kleptoparasitism?
But wait, I hear you say. The reason why animals hunt in groups hunt in groups is because they need to work together as a team to kill much larger animals!
Well… yes and no. Animals that hunt together in groups are actually restricted to larger prey***, because they need to have enough food to feed everybody when they’re done. What feeds six lions more effectively: one impala or one Cape buffalo?
If you think about it this way, hunting larger prey is a handicap and not at all an advantage- especially when you consider the increased danger from things such as injuries. That cute little impala isn’t going to kick your head in with the same force that a Cape buffalo will. (Also, the impala is less likely to turn around and stomp on your remains to be sure the job is done.)
It’s a fact that most predatory animals- estimates range from 85-90%- hunt by themselves. So what led some animals to seek out big, dangerous prey that they couldn’t finish alone? Probably not the thrill of it all. Remember how dangerous injuries are for some predators? There has to be a big payoff for all that risk.
But perhaps we’re looking at it the wrong way- maybe the tendency to group up evolved before predators started attacking oversized prey. In that case, why did the hunters start working together?
Resource distribution may be a large factor: if prey animals are spread out evenly through the environment, predators will probably have the most success hunting alone. But if prey animals are clumped all together and tend to try to defend one another, a group may have a better chance of splitting somebody away from the herd than a solo hunter.
However, the distribution of resources doesn’t neatly tie up every loose end. While some species have a higher likelihood of making a kill in larger groups, many do not. In fact, most mammalian predators are quite capable of hunting smaller prey by themselves- single wild dogs can kill impala, and it is actually more common for hyenas to kill prey alone than when in a group. In a large study of species that either hunted in groups or alone, ecologists Packer and Rutton actually found that there tended to be no overall benefit in terms of hunting success when animals hunted in groups.
Additionally, most group hunters live in larger groups than the ones they hunt in- hunting parties tend to be cliques that split away from the main group. And the phrase ‘group hunting’ itself may be misleading. While African wild dogs statistically have increased hunting success in larger groups, individual dogs within a hunting party may all initially be pursuing different prey animals at first, then converge upon the first animal that becomes vulnerable. In this sense, they are hunting “alone” until the final moments.
I mentioned earlier that hyenas usually make their kills by themselves: however, they may be trailed by other members of their clan that attempt to take the meat for themselves once the hard work is done. So not only do group-living animals have to share their meat, they might have to share it with individuals that didn’t even help get it. How’s that for a raw deal!
So exactly what advantages do hunting in groups confer? Resistance to kleptoparasitism may actually be a big factor. A hyena may be able to steal from a lone wild dog. But what about ten?
(They may not be able to kill the hyena, but they sure can annoy the shit out of her.)
In this video, finally, the smaller hunters are able to drive off the larger ones and finish their meal. Just like Disney taught us in A Bug’s Life!
Now, I’m not going to suggest that this resistance to kleptoparasitism is the only reason some predators hunt in groups- there’s a whole host of other factors that I haven’t even touched on, like the ones that have nothing to do with eating- group living confers other benefits, especially for a little fellow who might become prey as easily as predator. But I do challenge you to reconsider what you thought you knew about why animals hunt in groups.
Let me close with cheetahs, since I discussed them a great deal earlier. Most cheetahs hunt alone. However, many male cheetahs hunt in groups of 2-3 related individuals known as ‘coalitions,’ some females hunt with their cubs, and some adolescents of either sex will hunt together.
Most studies of cheetahs conclude that while coalitions enable cheetahs to seek out larger prey, the amount each animal eats is no higher than it would if it hunted alone (and may even be less). Resistance to kleptoparasitism may provide benefits- though, surprisingly, one hyena is still capable of scaring three fully grown male cheetahs off a kill.
The answer this time, in fact, probably lies with social behavior and has nothing to do with hunting at all. Female cheetahs tend not to be territorial, and live in vast home ranges overlapping those of many other females. This makes it more difficult for male cheetahs to defend access to females- unless they have wingmen to back them up.
So in the end, cheetahs still kinda get screwed no matter what. Good luck, guys.
Read on: What about prey animals? Why do they form groups? Shatter your dreams learning why here (hint: lions aren’t the only assholes). If you want to learn about obligate brood parasitism, read about the lives of cuckoos and cowbirds here! And if you want to learn ab0ut an animal that kills its young for shits, try Coot Parenting Tips.
Or just return to the Nonfiction section to see a list of all articles I’ve written. Thanks for reading!
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*No, I will never get over this.
**Note that these percentages are extremely rough, and vary tremendously based on factors such as group composition, environment, and the experience of the animals involved.
***There are some circumstances where this does not hold true. Chimpanzees, for instance, hunt small prey in groups so that each hunter hopefully catches his own prey, and dolphins and other group-hunting marine predators usually hunt schools of smaller fish.