Glazer |0SCN3615 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
Glazer |1 IndexIntroduction 2Literature Review Background 2 Habitat & Ecology 3 Movement & Feeding 4 Communication 4 Sexual Behavior, Reproduction & Parental Care 5 Social, Territorial & Anti-Predator Behavior 6 Aggression 7Discussion 8Conclusion 11
Glazer |2Introduction The hippopotamus amphibious, also known as just the hippo, is an African mammalliving only on the continent of Africa with many unique behaviors. Hippopotamusderives from the Greek word, “river horse” which can be attributed to the large mass oftheir bodies similar to a horse and also their days spent in the water(NationalGeographic Online). The hippo is the third largest animal, behind elephants and whiterhinos (African Wildlife). I chose to take a deep dive in to the behavior of this animalafter a friend of mine shared a story about how she was on safari in South Africa when aherd of hippos stampeded their vehicle. This was a surprise to me, as I originallythought hippos were calm creatures. After my research and hearing this personalaccount, I have come to find they are if not actually the most aggressive, among the mostaggressive species in the animal kingdom.. This analysis will cover a general backgroundof 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 willbe investigated, particular attention will be focused on their aggression which is anunderlying theme through many behaviors.Literature Review The hippopotamus amphibious, a part of the hippopotamide family, has evolvedfrom 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 hasbeen found that pigmy hippos have common ancestors with pigs (Estes, 1991). Over
Glazer |3time, the pigmy hippo developed new attributes, such as complete aquatic abilities. Thisis a perfect example of evolution as animals will adapt to their environment in order tosurvive. Being able to function in the water has come to be very important to the hippofor examples such as feeding, mating, etc. While looking at both the pigmy hippo andthe (water) hippo, they do appear physically similar in some ways. The hippo ischaracterized by their barrel-shaped, massive, brown or grayish purple smooth andnaked skin, with short legs (Estes 1999). The head’s features include an enormousmuzzle, eyes, nostrils and small ears at the top of the head. In addition, hippos haveshort, muscular paddle shaped tails that play a large role in aggression that will befurther explained later. Hippos are so large that males can be as heavy as 7,040 lbs and66” tall. Typically, males weigh between 3,529-7,040 pounds while females rangebetween 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 ofAfrica, from the South of the Sahara from Guinea to the Ivory Coast (Estes, 1999). Thisis also an example of evolution because at an earlier time, hippos were more dispersedon multiple continents (Estes, 1999). Within these specific regions, hippos will findhabitats where water is plentiful and grazing can be accommodated. This usually meansedges of swamps or rivers where the water is deep enough to cover a good portion oftheir bodies when submerged (Estes, 1999). Hippo days are spent in the water for a veryspecific purpose; to avoid dehydration. There is a myth that hippos “sweat blood” whichderived 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
Glazer |4temperature, thus overheating very easily and needing the water’s benefits. Anotherreason that living part time in the water is so crucial is because it is much easier for amother to nurse and protect their child. For this reason they seek out bodies of waterwith gently sloping, firm bottoms.Movement& Feeding Hippos are in the rhythm of feeding on land at night, then returning to the waterto digest and rest during the daytime (Estes 1991). Though the hippo spends theentirety 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 andlarge body of this animal fool you, research has shown that hippos have been trackedmoving as fast as 30 mph, which is faster than an Olympic sprinter (NationalGeographic). On average, hippos will gallop up to 18 mph when threatened and half thespeed on a more normal basis. At night when feeding, the average hippo will travel 6-10miles to maximize grazing (National Geographic). With the exception of dependentcalves on their mothers, feeding is an independent practice for the hippo. They areprimarily herbivores and will consume about 88 pounds of grass every evening with themuscular lips, around 50 cm wide (Estes, 1991). In water, the hippo will also gallop, yetmostly stationary among groups for the majority of the day. Adult hippos can stayunderwater for up to 5 minutes if necessary(Estes, 1999). The animal has also adaptedto rise in her sleep involuntarily when needed (Estes, 1999).Communication In line with aggressive nature of the hippopotamus, it would make sense if theyadministered loud noises, generally associated with anger in society. In fact, the hippo
Glazer |5has been recorded evoking sounds as loud as 113 or more decibels which are comparableto a jet engine or standing at the stage of a loud rock concert (San Diego Zoo). Researchshows that hippos do the lion’s share of their communication in water as opposed to onland. Specifically these sounds are referred to as grunts, chuffs and honks (Out ofAfrica). Another technique that the hippo is known to do is to have their jaw submergedin water while calling out a sound that has the ability to travel through both water and toland (Out of Africa). While a deeper significance to the purpose of these sounds is stillunknown, researchers speculate they are used to warn off predators like most otheranimals do.Sexual Behavior, Reproduction& Parental Care The next portion of the essay will touch on sexual behavior, which leads toreproduction 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 showhis interest, he will sniff their backside and be sure to move carefully and showsubmission if the herd appears disturbed (Estes, 1991). In some cases, female hipposwill yawn to threaten the males (see Aggression). Courtship is not apparent from themale as he will immediately bring his new mate to the water where the entirety of sexualbehavior is executed. From there, the hippos will first clash jaws before the bull forcesthe female face down underwater and mounts his partner; this aggression is one ofmany examples of how hippos establish dominance. The male will become quiteaggressive and snap if the female resists from being underwater, thus forcing her backdown.
Glazer |6 Female hippos do not conceive until 9 years of age. Unlike many other animalswhose breeding period aligns with the abundance of resources, hippos have a relativelystable 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 gestationand thus rainy season with the most births (Estes 1991).Once fertile, females may calveat 2 years intervals with 8 month gestation periods (Estes 1991). One way that femalescan show they are in heat is from a ritual called urine testing. (Estes 1991). Females canshow their reproductive status by urinating on command for bulls, and the males aretrained to identify the urine accordingly. Once the hippo endures the 8 month gestation period, they prepare to give birthto one baby hippo (Estes 1991). The female will isolate herself during the birth periodeither on land or in shallow water. Within 10-14 days, the mother and newborn willrejoin their herd to proceed with normal behavior (Estes 1991). The mother is the soleparticipant in parental care, and has a very strong affinity with the calf. Theirrelationship 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 islacking information that is still continuing to be researched. Hippos are solitary at nightwhen foraging, though very social during the day when in water. There is very closecontact among pods of hippos, often resting on one another they are so close. During dryseason, there is heavier crowding where packs increase drastically in size. Male hippos are very territorial over their claim to land and water. Mature bullswill control large section of river and lakes with exclusive mating rights where no other
Glazer |7males may copulate, for extended periods of time: 8 years for lakes and 4 years forrivers(Estes 1999). Bulls will allow other bachelors to enter as long as they pose nothreat and agree to no sexual activity in the alpha male’s domain. One example ofterritorial behavior that the hippo will exhibit is called dung showering (Estes, 1991).This aggressive behavior consists of the hippo extracting their feces then proceeding toshower them over territory with help of the muscular tale for power. This tells others tostray from this region unless they are ready for a fight. Conversely, cow (female) herdshave 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 forcertain in terms of female behavior; a mother will protect her young. Females withoffspring 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 angryhippo are not something a predator would want to come in contact with; they areactually strong enough to snap a crocodile in two with one chomp if in the right positionto do so. For this reason, predators will attack from the back and stray from approachinganywhere near the jaw. Predators can only do so much from the rear, so these fights canoften lead to a prolonged standstill while they compete for the upper hand. Hippos maynot be as agile on land, thus intentionally will attempt to redirect the fight to water togain advantage.Aggression Arguably the most aggressive mammal of the animal kingdom, the hippopotamushas many ways of demonstrating aggression both among their kind and also to ward offpredators. Oddly enough, hippos are primarily herbivores and do not actually use their
Glazer |8jaws to hunt, they are solely for threat and dominance. Already discussed have beenexamples of aggression in communication with roaring and grunting, dominant sexualbehavior as well as dung showering for territorial advertisement. Furtherdemonstrations of aggression are exhibited through rearing, lunging, waterscooping/head shaking, infanticide, yawning and tusk clashing (Estes 1991). Tuskclashing is the act when two hippos will open their jaws for jaw to jaw contact, andcompete for who has their larger and stronger gape (Estes 1999). Yawning is anothersign of aggression which is when a hippo will tilt their head back and open their jaws aswide as possible exposing the maximum span, implying their strength and intending topose a threat; females will often do this when defending their offspring (Estes1999).With canines up to 20 inches, hippos have been held responsible for more humandeaths than any other large animal because they are threatened so easily and respondwith such aggression to small disturbances (Estes 1999).Discussion After extensive research on the different behavior of the hippopotamus, includingcommunication, feeding, sexual behavior, reproduction, parental care,social/territorial/anti-predator behavior and aggression, it is clear that aggression isapparent in many contexts of the day to day life for the hippo. The personal account Ihave of the previously mentioned safari story is completely supported by all of thesources I have used. I do not believe that any source could make an argument for whyhippos could be seen as tranquil creatures, with perhaps the exception of the nurturingactions of the mother-child relationship. Whether or not aggression is warranted will beuncovered in this discussion. Similar to many societies, it appears that males tend to
Glazer |9exhibit these dominant characteristics more through territorial advertisement, thoughfemales are not far behind when it comes to defending the young. In reading manyarticles, I found that majority of the public is unaware to the ferocious nature of theseanimals. 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 whyan herbivore would be so hostile with no reason. It makes me wonder, why are theythreatened 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 thesedominant displays. The fact that females will show threat displays to males whenapproaching their young was interesting to me as this doesn’t seem cohesive with therest of the social structure. Though some research does show that hippos kill withintheir own, the incidents are usually justified by disease or overpopulation as opposed toviolence with no justifiable reason attached. On the same note relating to the concept of feeding, when the most prominentfeature of the hippo is their jaws which could kill with such ease, why and how do theyremain herbivores? I understand that some research has shown that a hippo stomach isnot necessarily designed for meat consumption, but I argue that if that was the onlysource of food available, wouldn’t their stomachs adapt to being able to ingest this typeof food over time? From all the reading I have done on feeding, it seems as thoughhippos are in no way considering the optimality theory, where animals will eat whatprovides the greatest fitness benefits with the least amount of effort. Every night, hipposspend hours and walk miles in order to consume 88+ pounds of grass which is
G l a z e r | 10extremely time consuming and not remotely efficient. This is so time consuming thatthey need to spend the whole day relatively stationary and digesting to recuperate fromthe previous night’s forage. Considering the jaw meets all necessary huntingqualifications and they are already experienced in aggression, I found it odd that they donot seek game that would provide more fitness benefits; even smaller animals such asfish. I ponder how they have evolved to stray from what seems to be the obvious choiceof choosing meat over grass. Another topic the literature review skimmed the surface of was the evolution ofthe aquatic abilities of the common hippo. From the older published research, circa1990s, the only evolution of species mentioned was the pig and pigmy hippo. Newerstudies 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 arrivehere. For me, it still seems like a stretch to suggest they could have evolved from thesame animal, when this said common ancestor died out during the ice age and there isno complete information (UC Berkley, 2005). At first glance I would say that the whaleand hippo are an example of divergent evolution, as they seem to become more andmore dissimilar. At closer analysis, because pieces are missing from the evolutionallineage it is hard to make that conclusion, especially because hippos and whales do stillhave some similar characteristics. It is clear through my readings that the social structure and hierarchy of cowherds are still very much left up for discussion. Much of the observations that are beingdone are within captivity, which presents the challenge of whether or not observing non-
G l a z e r | 11wild hippos would provide different results. Why are they so hard to observe in thewild? I find it particularly interesting that there is so much information on the malesand their territory but none on the females. I understand they have very different rolesin the hierarchy, but what are the cows doing that is so different that no conclusions canbe made? Most of the research I have found simply states female social structure is hardto understand, but I did not find many follow up studies on anyone trying to delvedeeper or going forward. For one, I think an obvious behavior that female herds executeis the dilution effect. The way that they congregate in the water pods during the day toprotect the young shows that they are trying to lessen their chances of being picked byany predators, in this case most susceptible to a crocodile.Conclusion Hippopotamuses are clearly complex creatures that have very specific behaviorsthat cannot be seen in any other species. This can be attributed to their unique physicalcharacteristics 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 anappearance. Though many would not expect it, the seemingly adorable creature is veryeasily disturbed and will react accordingly. With more research on the concentration offemale social systems, maybe we will gain more insight as to why there is a distantrelationship between males and females and also more about how females operate ingeneral.
G l a z e r | 12 ReferencesBlowers, 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-uQ1mSoHippo.Out of Africa<http://www.outtoafrica.nl/animals/enghippo.html>Hippopotamus. National GeographicOnline<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>