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SCN3615 HIPPOPOTAMUS BEHAVIOR
12/4/2012
An analysis of the behavior of the Hippopotamus while taking a
closer look at the underlying theme of aggression in all aspects of
hippo life.
Ecology of Animal Behavior | Alexandra Glazer
December 5, 2012

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Index
Introduction 2
Literature Review
Background 2
Habitat & Ecology 3
Movement & Feeding 4
Communication 4
Sexual Behavior, Reproduction & Parental Care 5
Social, Territorial & Anti-Predator Behavior 6
Aggression 7
Discussion 8
Conclusion 11

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Introduction
The hippopotamus amphibious, also known as just the hippo, is an African mammal
living only on the continent of Africa with many unique behaviors. Hippopotamus
derives from the Greek word, “river horse” which can be attributed to the large mass of
their bodies similar to a horse and also their days spent in the water(National
Geographic Online). The hippo is the third largest animal, behind elephants and white
rhinos (African Wildlife). I chose to take a deep dive in to the behavior of this animal
after a friend of mine shared a story about how she was on safari in South Africa when a
herd of hippos stampeded their vehicle. This was a surprise to me, as I originally
thought hippos were calm creatures. After my research and hearing this personal
account, I have come to find they are if not actually the most aggressive, among the most
aggressive species in the animal kingdom.. This analysis will cover a general background
of the origin species, physical characteristics, habitat & ecology, movement, feeding,
communication, reproduction, sexual behavior, social behavior, territorial behavior,
aggression & anti-predator behavior. While all facets of the hippopotamus lifestyle will
be investigated, particular attention will be focused on their aggression which is an
underlying theme through many behaviors.
Literature Review
The hippopotamus amphibious, a part of the hippopotamide family, has evolved
from the still existing choeropsisliberiensis, otherwise known as the pigmy hippo (Estes,
1999). The pigmy hippo is a forest dwelling creature that only resides on land; it has
been found that pigmy hippos have common ancestors with pigs (Estes, 1991). Over

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time, the pigmy hippo developed new attributes, such as complete aquatic abilities. This
is a perfect example of evolution as animals will adapt to their environment in order to
survive. Being able to function in the water has come to be very important to the hippo
for examples such as feeding, mating, etc. While looking at both the pigmy hippo and
the (water) hippo, they do appear physically similar in some ways. The hippo is
characterized by their barrel-shaped, massive, brown or grayish purple smooth and
naked skin, with short legs (Estes 1999). The head’s features include an enormous
muzzle, eyes, nostrils and small ears at the top of the head. In addition, hippos have
short, muscular paddle shaped tails that play a large role in aggression that will be
further explained later. Hippos are so large that males can be as heavy as 7,040 lbs and
66” tall. Typically, males weigh between 3,529-7,040 pounds while females range
between 1,440 and 5,157 pounds (Estes 1999).
Habitat & Ecology
In the wild, the hippo is only found in very specific regions on the continent of
Africa, from the South of the Sahara from Guinea to the Ivory Coast (Estes, 1999). This
is also an example of evolution because at an earlier time, hippos were more dispersed
on multiple continents (Estes, 1999). Within these specific regions, hippos will find
habitats where water is plentiful and grazing can be accommodated. This usually means
edges of swamps or rivers where the water is deep enough to cover a good portion of
their bodies when submerged (Estes, 1999). Hippo days are spent in the water for a very
specific purpose; to avoid dehydration. There is a myth that hippos “sweat blood” which
derived from the red liquid that secretes itself from glands on the body (Out of Africa).
Though hippos release this fluid, they do not have sweatglands to monitor their body

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temperature, thus overheating very easily and needing the water’s benefits. Another
reason that living part time in the water is so crucial is because it is much easier for a
mother to nurse and protect their child. For this reason they seek out bodies of water
with gently sloping, firm bottoms.
Movement& Feeding
Hippos are in the rhythm of feeding on land at night, then returning to the water
to digest and rest during the daytime (Estes 1991). Though the hippo spends the
entirety of their day in the water, the species is still classified as a land animal. On land,
the mammal tends to travel in herds from 10-15 at a time. Don’t let the short limbs and
large body of this animal fool you, research has shown that hippos have been tracked
moving as fast as 30 mph, which is faster than an Olympic sprinter (National
Geographic). On average, hippos will gallop up to 18 mph when threatened and half the
speed on a more normal basis. At night when feeding, the average hippo will travel 6-10
miles to maximize grazing (National Geographic). With the exception of dependent
calves on their mothers, feeding is an independent practice for the hippo. They are
primarily herbivores and will consume about 88 pounds of grass every evening with the
muscular lips, around 50 cm wide (Estes, 1991). In water, the hippo will also gallop, yet
mostly stationary among groups for the majority of the day. Adult hippos can stay
underwater for up to 5 minutes if necessary(Estes, 1999). The animal has also adapted
to rise in her sleep involuntarily when needed (Estes, 1999).
Communication
In line with aggressive nature of the hippopotamus, it would make sense if they
administered loud noises, generally associated with anger in society. In fact, the hippo

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has been recorded evoking sounds as loud as 113 or more decibels which are comparable
to a jet engine or standing at the stage of a loud rock concert (San Diego Zoo). Research
shows that hippos do the lion’s share of their communication in water as opposed to on
land. Specifically these sounds are referred to as grunts, chuffs and honks (Out of
Africa). Another technique that the hippo is known to do is to have their jaw submerged
in water while calling out a sound that has the ability to travel through both water and to
land (Out of Africa). While a deeper significance to the purpose of these sounds is still
unknown, researchers speculate they are used to warn off predators like most other
animals do.
Sexual Behavior, Reproduction& Parental Care
The next portion of the essay will touch on sexual behavior, which leads to
reproduction and ultimately the need for parental care. The process begins when a bull,
male hippo, will wander through a herd of females in search of a mate. In order to show
his interest, he will sniff their backside and be sure to move carefully and show
submission if the herd appears disturbed (Estes, 1991). In some cases, female hippos
will yawn to threaten the males (see Aggression). Courtship is not apparent from the
male as he will immediately bring his new mate to the water where the entirety of sexual
behavior is executed. From there, the hippos will first clash jaws before the bull forces
the female face down underwater and mounts his partner; this aggression is one of
many examples of how hippos establish dominance. The male will become quite
aggressive and snap if the female resists from being underwater, thus forcing her back
down.

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Female hippos do not conceive until 9 years of age. Unlike many other animals
whose breeding period aligns with the abundance of resources, hippos have a relatively
stable environment. For this reason, seasons do not dictate their mating schedule,
though there is a natural tendency for dry season to be the primary period of gestation
and thus rainy season with the most births (Estes 1991).Once fertile, females may calve
at 2 years intervals with 8 month gestation periods (Estes 1991). One way that females
can show they are in heat is from a ritual called urine testing. (Estes 1991). Females can
show their reproductive status by urinating on command for bulls, and the males are
trained to identify the urine accordingly.
Once the hippo endures the 8 month gestation period, they prepare to give birth
to one baby hippo (Estes 1991). The female will isolate herself during the birth period
either on land or in shallow water. Within 10-14 days, the mother and newborn will
rejoin their herd to proceed with normal behavior (Estes 1991). The mother is the sole
participant in parental care, and has a very strong affinity with the calf. Their
relationship is externally visible through licks, nuzzles and other nurturing behavior.
Social, Territorial & Anti-Predator Behavior
The social and territorial behavior will be explored next. Much of this subject is
lacking information that is still continuing to be researched. Hippos are solitary at night
when foraging, though very social during the day when in water. There is very close
contact among pods of hippos, often resting on one another they are so close. During dry
season, there is heavier crowding where packs increase drastically in size.
Male hippos are very territorial over their claim to land and water. Mature bulls
will control large section of river and lakes with exclusive mating rights where no other

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males may copulate, for extended periods of time: 8 years for lakes and 4 years for
rivers(Estes 1999). Bulls will allow other bachelors to enter as long as they pose no
threat and agree to no sexual activity in the alpha male’s domain. One example of
territorial behavior that the hippo will exhibit is called dung showering (Estes, 1991).
This aggressive behavior consists of the hippo extracting their feces then proceeding to
shower them over territory with help of the muscular tale for power. This tells others to
stray from this region unless they are ready for a fight. Conversely, cow (female) herds
have been observed and have an entirely different dynamic that has yet to be explained.
Cow herds may not be as easily explained as bull herds, but one thing is for
certain in terms of female behavior; a mother will protect her young. Females with
offspring will fight to the death to keep predators, (primarily lions, crocodiles & hyenas),
sometimes even male hippos, away from their calves (Estes 1999). The jaws of an angry
hippo are not something a predator would want to come in contact with; they are
actually strong enough to snap a crocodile in two with one chomp if in the right position
to do so. For this reason, predators will attack from the back and stray from approaching
anywhere near the jaw. Predators can only do so much from the rear, so these fights can
often lead to a prolonged standstill while they compete for the upper hand. Hippos may
not be as agile on land, thus intentionally will attempt to redirect the fight to water to
gain advantage.
Aggression
Arguably the most aggressive mammal of the animal kingdom, the hippopotamus
has many ways of demonstrating aggression both among their kind and also to ward off
predators. Oddly enough, hippos are primarily herbivores and do not actually use their

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jaws to hunt, they are solely for threat and dominance. Already discussed have been
examples of aggression in communication with roaring and grunting, dominant sexual
behavior as well as dung showering for territorial advertisement. Further
demonstrations of aggression are exhibited through rearing, lunging, water
scooping/head shaking, infanticide, yawning and tusk clashing (Estes 1991). Tusk
clashing is the act when two hippos will open their jaws for jaw to jaw contact, and
compete for who has their larger and stronger gape (Estes 1999). Yawning is another
sign of aggression which is when a hippo will tilt their head back and open their jaws as
wide as possible exposing the maximum span, implying their strength and intending to
pose a threat; females will often do this when defending their offspring (Estes
1999).With canines up to 20 inches, hippos have been held responsible for more human
deaths than any other large animal because they are threatened so easily and respond
with such aggression to small disturbances (Estes 1999).
Discussion
After extensive research on the different behavior of the hippopotamus, including
communication, feeding, sexual behavior, reproduction, parental care,
social/territorial/anti-predator behavior and aggression, it is clear that aggression is
apparent in many contexts of the day to day life for the hippo. The personal account I
have of the previously mentioned safari story is completely supported by all of the
sources I have used. I do not believe that any source could make an argument for why
hippos could be seen as tranquil creatures, with perhaps the exception of the nurturing
actions of the mother-child relationship. Whether or not aggression is warranted will be
uncovered in this discussion. Similar to many societies, it appears that males tend to

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exhibit these dominant characteristics more through territorial advertisement, though
females are not far behind when it comes to defending the young. In reading many
articles, I found that majority of the public is unaware to the ferocious nature of these
animals. ABC Nightline’s article touched on this briefly saying not to mistake them for
“coach potatoes, docile, or harmless” despite their “bathtub” like structure (Harris,
2009). Reflecting on all of the research I have gathered, I cannot fully understand why
an herbivore would be so hostile with no reason. It makes me wonder, why are they
threatened so easily? Why do they exhibit these threat displays even among their kind?
Hippo on hippo kills not common that I question why they feel the need to have these
dominant displays. The fact that females will show threat displays to males when
approaching their young was interesting to me as this doesn’t seem cohesive with the
rest of the social structure. Though some research does show that hippos kill within
their own, the incidents are usually justified by disease or overpopulation as opposed to
violence with no justifiable reason attached.
On the same note relating to the concept of feeding, when the most prominent
feature of the hippo is their jaws which could kill with such ease, why and how do they
remain herbivores? I understand that some research has shown that a hippo stomach is
not necessarily designed for meat consumption, but I argue that if that was the only
source of food available, wouldn’t their stomachs adapt to being able to ingest this type
of food over time? From all the reading I have done on feeding, it seems as though
hippos are in no way considering the optimality theory, where animals will eat what
provides the greatest fitness benefits with the least amount of effort. Every night, hippos
spend hours and walk miles in order to consume 88+ pounds of grass which is

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extremely time consuming and not remotely efficient. This is so time consuming that
they need to spend the whole day relatively stationary and digesting to recuperate from
the previous night’s forage. Considering the jaw meets all necessary hunting
qualifications and they are already experienced in aggression, I found it odd that they do
not seek game that would provide more fitness benefits; even smaller animals such as
fish. I ponder how they have evolved to stray from what seems to be the obvious choice
of choosing meat over grass.
Another topic the literature review skimmed the surface of was the evolution of
the aquatic abilities of the common hippo. From the older published research, circa
1990s, the only evolution of species mentioned was the pig and pigmy hippo. Newer
studies show that in fact the hippo may actually be in closest relation to the whale
(Feldhake 2005). In terms of the methodology that was used to arrive at this conclusion,
the author does a good job explaining the different stages of evolution used to arrive
here. For me, it still seems like a stretch to suggest they could have evolved from the
same animal, when this said common ancestor died out during the ice age and there is
no complete information (UC Berkley, 2005). At first glance I would say that the whale
and hippo are an example of divergent evolution, as they seem to become more and
more dissimilar. At closer analysis, because pieces are missing from the evolutional
lineage it is hard to make that conclusion, especially because hippos and whales do still
have some similar characteristics.
It is clear through my readings that the social structure and hierarchy of cow
herds are still very much left up for discussion. Much of the observations that are being
done are within captivity, which presents the challenge of whether or not observing non-

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wild hippos would provide different results. Why are they so hard to observe in the
wild? I find it particularly interesting that there is so much information on the males
and their territory but none on the females. I understand they have very different roles
in the hierarchy, but what are the cows doing that is so different that no conclusions can
be made? Most of the research I have found simply states female social structure is hard
to understand, but I did not find many follow up studies on anyone trying to delve
deeper or going forward. For one, I think an obvious behavior that female herds execute
is the dilution effect. The way that they congregate in the water pods during the day to
protect the young shows that they are trying to lessen their chances of being picked by
any predators, in this case most susceptible to a crocodile.
Conclusion
Hippopotamuses are clearly complex creatures that have very specific behaviors
that cannot be seen in any other species. This can be attributed to their unique physical
characteristics that allow them to do so (ie. tail /dung showering or jaw/tusk clashing).
Overall, within every category of behavior, aggression of some kind makes an
appearance. Though many would not expect it, the seemingly adorable creature is very
easily disturbed and will react accordingly. With more research on the concentration of
female social systems, maybe we will gain more insight as to why there is a distant
relationship between males and females and also more about how females operate in
general.

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References
Blowers, TE., J. Waterman, C. Kuhar and T. Bettinger, 2010. Social Behaviors within a
group of captive female Hippopotamus amphibious. Volume 28 Issue 2 pp 287-
294, Journal of Ethology <http://link.springer.com/article/10.1007%2Fs10164-
009-0184-6?LI=true>
Estes, R.D. 1991. Chapter 13 Hippopotamuses. Pages 222-226 in The Behavior Guide to
African Mammals: including hoofed mammals, carnivores, primates. University
of California Press, Berkeley and Los Angeles, California and University of
California Press, Ltd., Oxford England.
Estes, R.D. 1999. Chapter 17 Hippotamus.Pages 185-189 in The Safari Companion: A
Guide to Watching African Mammals. Chelsea Green Publishing Company, White
River Junction, Vermont.
Feldhake, Glenn, 2005. Hippos: Natural History & Conservation. Voyageur Press, Inc.
Harris, Dan. Up Close and Personal with the Hippos of Uganda. Aug 21, 2009. ABC
Nightline http://abcnews.go.com/Nightline/story?id=8376416#.UL7o-uQ1mSo
Hippo.Out of Africa<http://www.outtoafrica.nl/animals/enghippo.html>
Hippopotamus. National Geographic
Online<http://animals.nationalgeographic.com/animals/mammals/hippopotamus/>
Hippopotamus. African Wildlife Foundation
<http://www.awf.org/content/wildlife/detail/hippopotamus>
How Do Hippos Communicate with Each Other and What Type of Sounds Do They
Make?Big Site of Amazing Facts.<http://www.bigsiteofamazingfacts.com/how-
do-hippos-communicate-with-each-other-and-what-type-of-sounds-do-they-
make>
Mammals: Hippopotamus San Diego Zoo
<http://www.sandiegozoo.org/animalbytes/t-hippopotamus.html>
UC Berkeley,2005. Scientists find missing link between the whale and its closest
relative, the hippo. Phys Org. <http://phys.org/news2806.html>