Animal Diversity Web

Ge­o­graphic Range

Hip­popota­musi (Hip­popota­mus am­phibius) are found ex­clu­sively in the Ethiopian re­gion of the world. Hip­pos occur in rivers through­out the sa­vanna of Africa and the main rivers of Cen­tral Africa. Known pop­u­la­tions are found in coun­tries in­clud­ing: An­gola, Benin, north­ern Botswana, Burk­ina Faso, Bu­rundi, Cameroon, Cen­tral African Re­pub­lic, south­ern Chad, Côte d’Ivoire, north­ern Er­itrea, Ethiopia, Equa­to­r­ial Guinea, Gabon, Gam­bia, Ghana, Guinea, Guinea Bis­sau, Kenya, Liberia, Malawi, Mozam­bique, Namibia, Niger, Nige­ria, Re­pub­lic of Congo, Rwanda, Sene­gal, Sierra Leone, So­ma­lia, South Africa (only in north­ern and east­ern Limpopo Province, east­ern Mpumalanga Province, and north­ern KwaZulu-Na­tal), Sudan, Swazi­land, Tan­za­nia, Togo, Uganda, Zam­bia, and Zim­babwe. (Estes, 1992; Lewi­son and Oliver, 2008; Pushk­ina, 2007; Steven­son-Hamil­ton, 1912)

• Biogeographic Regions
• ethiopian
  • native

Habi­tat

Hip­pos are a semi-aquatic mam­mal, usu­ally in­hab­it­ing shal­low lakes, rivers, and swamps. The water must be deep enough for the hippo to sub­merge its en­tire body in; usu­ally water about 2 me­ters deep is pre­ferred. Dur­ing the day­time, herds pre­fer to sleep in shal­low water, or oc­ca­sion­ally on a mud bank, grouped closely to­gether. It is in these wa­ters that mat­ing and child­birth oc­curs. When shal­low wa­ters are not pre­sent hip­pos re­side in deeper water, leav­ing only their nos­trils above the sur­face to breathe. Hip­pos emerge from water at dusk and go ashore to feed, and travel in­di­vid­u­ally down fa­mil­iar paths usu­ally less than 1.6 km to dense, grassy graz­ing areas along the banks of the water. ("Hip­popota­mus", 2011; Estes, 1992; Lewi­son and Oliver, 2008; Roomer, 1872; Steven­son-Hamil­ton, 1912)

• Habitat Regions
• temperate
• tropical
• freshwater

• Aquatic Biomes
• lakes and ponds
• rivers and streams
• temporary pools

• Wetlands
• swamp

• Average elevation

  2000 m

  6561.68 ft

• Range depth

  1.5 to 14 m

  4.92 to 45.93 ft

• Average depth

  2 m

  6.56 ft

Phys­i­cal De­scrip­tion

Weigh­ing be­tween 1,300 and 3,200 kg, hip­popota­musi mea­sure be­tween 209 and 505 cm in length, in­clud­ing a tail of about 35 cm in length. They stand be­tween 150 and 165 cm tall. Hip­popotami have skin tones of a pur­ple gray or slate color, with brown­ish pink col­or­ing around their eyes and ears. Their bod­ies are cov­ered with a scarce amount of thin hair, ex­cept for thick bris­tle like hair on their heads and tails. Outer epi­der­mal skin lay­ers are ex­tremely thin, mak­ing them vul­ner­a­ble to wounds from fight­ing. ("Hip­popota­mus", 2011; Cough­lin and Fish, 2009; Nott, 1886; Roomer, 1872; Steven­son-Hamil­ton, 1912)

Hip­pos lack scent and sweat glands. In­stead, mu­cous glands se­crete a thick oily layer of red pig­mented fluid. For years this fluid was thought to be a mix­ture of blood and sweat, giv­ing it the nick­name “blood sweat.” It is now known that this fluid is a com­bi­na­tion of hip­po­su­doric acid and norhip­po­su­doric acid. These com­pounds cre­ate a sun­screen ef­fect by ab­sorb­ing ultra vi­o­let rays from the sun and pre­vent the growth of dis­ease caus­ing bac­te­ria. The se­cre­tion orig­i­nates col­or­less and turns an or­ange-red within min­utes of being ex­posed to the sun. ("Hip­popota­mus", 2011; Cough­lin and Fish, 2009; Nott, 1886; Roomer, 1872; Steven­son-Hamil­ton, 1912)

Bulky and bar­rel-shaped, it would seem hip­pos would be clumsy on both land and water. How­ever, adap­ta­tions to their semi-aquatic en­vi­ron­ments have al­lowed them to move swiftly on both water and land. On land, they are able to move at speeds up to 30 km per hour and can main­tain these speeds for sev­eral hun­dred me­ters. In shal­low wa­ters their short legs pro­vide pow­er­ful propul­sion through water, while their webbed feet allow them to nav­i­gate on shal­low river bot­toms. Place­ment of eyes, ears, and nos­trils high on their head al­lows them to re­main mostly sub­merged while still being able to breathe and stay aware of their sur­round­ings. When com­pletely sub­merg­ing, the nos­trils close and ears fold to pre­vent water from en­ter­ing them. The jaws of hip­popota­musi are ca­pa­ble of open­ing up to 150 de­grees, show­ing enor­mous, sharp, in­cisors and ca­nine tusks. Ca­nines grow to 50 cm and in­cisors grow to 40 cm, sharp­en­ing them­selves as they grind their mouths to­gether dur­ing graz­ing. ("Hip­popota­mus", 2011; Cough­lin and Fish, 2009; Nott, 1886; Roomer, 1872; Steven­son-Hamil­ton, 1912)

Sex­ual di­mor­phism is pre­sent in hip­popotami. Males tend to be about 200 kg larger than fe­males at ma­tu­rity, but can grow to be al­most sev­eral thou­sand kg larger with age. Males ap­pear to con­tinue grow­ing through­out their life, while fe­males reach their max­i­mum weight around age 25. Males reach a max­i­mum length of about 505 cm long, while fe­males usu­ally only reach around 345 cm. The largest hippo ever recorded was a cap­tive male hippo in Mu­nich, Ger­many, weigh­ing 4,500 kg. Aside from size, male muz­zles are larger and have a more de­vel­oped jowl area than fe­males. Tusks are also twice as long in males than in fe­males. ("Hip­popota­mus", 2011; Cough­lin and Fish, 2009; Nott, 1886; Roomer, 1872; Steven­son-Hamil­ton, 1912)

• Other Physical Features
• endothermic
• bilateral symmetry

• Sexual Dimorphism
• male larger

• Range mass

  1300 to 4500 kg

  2863.44 to 9911.89 lb

• Range length

  290 to 505 cm

  114.17 to 198.82 in

Re­pro­duc­tion

Hip­popotami are polyg­y­nous, mean­ing that one bull mates with sev­eral fe­males in the so­cial group. Al­though breed­ing is not strictly sea­sonal, con­cep­tion usu­ally oc­curs dur­ing the dry sea­son, be­tween Feb­ru­ary and Au­gust, and births usu­ally occur dur­ing the rainy sea­son, be­tween Oc­to­ber and April. (Estes, 1992; Roomer, 1872; Steven­son-Hamil­ton, 1912; de Ma­g­a­l­haes and Costa, 2009)

• Mating System
• polygynous

When search­ing for a mate, the dom­i­nant male wan­ders through a rest­ing or graz­ing herd, smelling each fe­male’s pos­te­rior end. He acts un­usu­ally sub­mis­sive to­wards the fe­males as to avoid being at­tacked by the herd. The goal of the sub­mis­sive male is to find a fe­male in heat. Once a mate has been found the courtship be­gins. The male taunts the fe­male, by push­ing her out of the herd. He pur­sues her into deeper wa­ters, until she be­comes frus­trated and lashes out and clash­ing jaws with him. He forces her into sub­mis­sion and mounts her, forc­ing her head under the water. It is un­clear why her head must be under the water. If the fe­male tries to raise her head to breathe, the male will usu­ally snap at her and force her head back down. Dur­ing mat­ing the males re­lease a wheezy honk­ing to an­nounce that mat­ing has oc­curred. Hip­popotami usu­ally mate every other year, due cost of parental in­vest­ment into the young. Al­though breed­ing can occur year round, it is most com­mon be­tween Feb­ru­ary and Au­gust. Ges­ta­tion lasts nearly a year, 324 days, and yields just one off­spring. The young are not weaned for nearly an­other year, and ma­tu­rity is achieved at 3.5 years. (Estes, 1992; Roomer, 1872; Steven­son-Hamil­ton, 1912; de Ma­g­a­l­haes and Costa, 2009)

• Key Reproductive Features
• iteroparous
• seasonal breeding
• year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• viviparous

• Breeding interval

  Hippopotami mate every other year.

• Breeding season

  Breeding occurs year round, but peaks between February and August.

• Average number of offspring

  1

• Average number of offspring

  1

  AnAge

• Average gestation period

  324 days

• Average gestation period

  234 days

  AnAge

• Average weaning age

  341 days

• Average age at sexual or reproductive maturity (female)

  1,279 days

• Average age at sexual or reproductive maturity (female)
  Sex: female

  1279 days

  AnAge

• Average age at sexual or reproductive maturity (male)

  1,279 days

• Average age at sexual or reproductive maturity (male)
  Sex: male

  1279 days

  AnAge

Prior to birth, preg­nant fe­males be­come very pro­tec­tive and ag­gres­sive to those who en­counter her. Preg­nant hip­pos iso­late them­selves on land or in shal­low water and do not re­join the herd until 14 days after giv­ing birth. At birth, calves weigh be­tween 22 and 55 kg. Mother and calf have a very close re­la­tion­ship. They are often seen clean­ing, cud­dling, and pre­sum­ably show­ing af­fec­tion to each other. Most at­tacks on hu­mans and other an­i­mals are by fe­males prior to birthing or when pro­tect­ing their calves. Calves are adapted for un­der­wa­ter nurs­ing; their ears fold back and their nos­trils close dur­ing suck­ing, grip­ping the nip­ple be­tween the tongue and roof of the mouth. Be­cause hip­pos live in a so­cial fam­ily en­vi­ron­ment, males are very pro­tec­tive over both the fe­males and calves in the herd and will often at­tack any­thing that poses a threat. (Estes, 1992; Roomer, 1872; Steven­son-Hamil­ton, 1912; de Ma­g­a­l­haes and Costa, 2009)

• Parental Investment
• precocial
• male parental care
• female parental care
• pre-weaning/fledging
  • protecting
    • male
    • female
• pre-independence
  • protecting
    • male
    • female
• post-independence association with parents
• inherits maternal/paternal territory

Lifes­pan/Longevity

Hip­popotami have av­er­age life ex­pectan­cies around 55 years in both cap­tiv­ity and the wild. The longest liv­ing hip­popota­mus ex­ceeded 61 years in cap­tiv­ity. In­fant mor­tal­ity rates are low, 0.01 deaths per year. (de Ma­g­a­l­haes and Costa, 2009)

• Average lifespan
  Status: captivity

  61 years

• Average lifespan
  Status: wild

  55 years

• Average lifespan
  Status: captivity

  55 years

• Average lifespan
  Status: wild

  45.0 years

  Max Planck Institute for Demographic Research

• Average lifespan
  Status: captivity

  49.0 years

  Max Planck Institute for Demographic Research

• Average lifespan
  Status: wild

  50.0 years

  Max Planck Institute for Demographic Research

• Average lifespan
  Status: captivity

  40.0 years

  Max Planck Institute for Demographic Research

• Average lifespan
  Status: captivity

  54.3 years

  Max Planck Institute for Demographic Research

• Average lifespan
  Status: wild

  54.5 years

  Max Planck Institute for Demographic Research

Be­hav­ior

Hip­popotami are a very so­cial species, liv­ing in groups of about 20 to 100 in­di­vid­u­als. They lead very seden­tary lives, rest­ing most of the day and leav­ing their rest­ing pools at dusk to feed. Most of their ac­tiv­ity is noc­tur­nal. Fe­males are the lead­ers of the herd, con­trol­ling the cen­ters of the rest­ing pools. Males rest along the outer banks of the pools, pro­tect­ing the fe­males and calves. By age 7, males com­pete for dom­i­nance. Dom­i­nance is usu­ally dis­played with yawn­ing, roar­ing, dung show­er­ing, and jaw clash­ing. Dom­i­nant males are usu­ally very in­tol­er­ant of ju­ve­niles at­tempt­ing to chal­lenge them. Larger males have a ten­dency to harm or kill the young males dur­ing these dis­plays. Ter­ri­to­r­ial be­hav­ior con­sists of wheez­ing, honk­ing, and dung show­er­ing. When ap­proach­ing new ter­ri­tory they stop and turn their back­side to­wards the area, lift their rear in the air and re­lease dung and urine. Their tails swing back and forth scat­ter­ing the exc­reta around the un­fa­mil­iar bound­ary. Male hip­pos often emerge from the water to spread dung along the shore­line and their graz­ing paths. Ju­ve­nile hip­pos can often be found fol­low­ing dom­i­nant males around smelling and lick­ing their rears. Fight­ing and de­fen­sive dis­plays are usu­ally most in­tense dur­ing the dry sea­son, when liv­ing con­di­tions are more crowded and re­sources are scarce. De­fen­sive dis­plays such as yawn­ing, jaw and tusk clash­ing, bit­ing, and re­treat­ing to rest­ing ponds are com­mon in fight­ing be­tween males as well as pro­tec­tion of the herd against preda­tors. (Bark­low, 2004; Blow­ers, et al., 2010; Estes, 1992; Lewi­son and Carter, 2004; Nott, 1886; Roomer, 1872; Steven­son-Hamil­ton, 1912)

• Key Behaviors
• natatorial
• diurnal
• nocturnal
• motile
• sedentary
• territorial
• social
• colonial
• dominance hierarchies

Home Range

There is no pub­lished data on spe­cific ter­ri­tory size of hip­pos. Ter­ri­tory size de­pends greatly on the num­ber of in­di­vid­u­als in the herd and avail­abil­ity of water and veg­e­ta­tion. They often rest closely to­gether, rest­ing their heads on each other’s backs. (Nott, 1886)

Com­mu­ni­ca­tion and Per­cep­tion

Hip­pos are ex­tremely so­cial and have a large reper­toire of sur­face and un­der­wa­ter sounds. The honk­ing call made by sub­merged hip­pos is the most com­mon type of com­mu­ni­ca­tion, using ex­haled breath to alarm their herd of threats. This honk­ing can reach up to 115 deci­bels, equiv­a­lent to a loud thun­der, and when con­ducted by the lead male can cre­ate a cho­rus from other males up to a 1.6 km away. Vo­cal­iza­tions can be made on land or in water and are trans­mit­ted si­mul­ta­ne­ously through both. This is the only known case of am­phibi­ous calls in mam­mals. Sound heard above the sur­face comes from the hip­pos nos­trils, but is made in the lar­ynx un­der­wa­ter. Hip­pos have a large fat layer across the lar­ynx that vi­brates when the vo­cal­iza­tion is made, send­ing sound through­out the water. Un­der­wa­ter vi­bra­tions shake jaw tis­sues con­nected the skull and ear of other hip­popotami, trans­mit­ting the sound. (Bark­low, 2004; Estes, 1992)

Vi­sual dis­plays such as wheez­ing, yawn­ing, honk­ing, and dung show­er­ing are com­mon ter­ri­to­r­ial dis­plays. Male hip­pos often emerge from the water to spread dung along the shore­line or along their graz­ing paths to mark their ter­ri­tory. Be­sides smell re­cep­tion of urine and dung show­er­ing, hip­pos also use the vomeron­sal organ, op­er­at­ing like an un­der­wa­ter sy­ringe to draw in urine, to com­mu­ni­cate the re­pro­duc­tive sta­tus of a male or fe­male (Bark­low, 2004; Estes, 1992)

• Communication Channels
• visual
• tactile
• acoustic
• chemical

• Other Communication Modes
• choruses
• pheromones
• vibrations

• Perception Channels
• visual
• tactile
• acoustic
• vibrations
• chemical

Food Habits

Hip­popotami leave their rest­ing wa­ters at dusk, mov­ing down fa­mil­iar paths, "hippo paths," to grassy areas sur­round­ing their wa­terbeds. Hip­pos pre­fer to re­main close to water beds, how­ever they will travel sev­eral kilo­me­ters when food is scarce. Graz­ing lasts be­tween four and five hours each night, cov­er­ing be­tween 3 and 4 km in cir­cu­lar pat­terns. Their mainly fo­liv­o­rous diet con­sists of small shoots, grasses, and reeds. They do not dig for roots or fruits. How­ever, they will con­sume many other types of plants if they are pre­sent. Mus­cu­lar lips, 50 cm wide, are ideal to pull up grasses. Hip­pos do not use their teeth to chew their meals, and in­stead they tear and soften the grasses to pre­vent any nu­tri­tive loss. While their seden­tary lifestyle al­lows for a sim­ple diet, they are known to con­sume an enor­mous amount of food each night, 1-1.5% of their body weight (usu­ally around 40 kg of food). Hip­pos enter and exit their water pools at the same spot, re­turn­ing from graz­ing be­fore dawn. Oc­ca­sion­ally, if the hippo has trav­eled too far it will seek a nearby pool to rest in until the fol­low­ing night­fall. Hip­pos have been ob­served, on a few oc­ca­sions, con­sum­ing dead an­i­mals near their rest­ing pools. How­ever, their stom­achs are not suited to di­gest meat. It is pos­si­ble that this car­niv­o­rous be­hav­ior is in­duced by ill­ness or nu­tri­tional de­fi­cien­cies. (Estes, 1992; Lewi­son and Carter, 2004; Roomer, 1872; Steven­son-Hamil­ton, 1912)

• Primary Diet
• herbivore
  • folivore

• Animal Foods
• carrion

• Plant Foods
• leaves
• wood, bark, or stems
• flowers

Pre­da­tion

Oc­ca­sion­ally lions, hye­nas, and croc­o­diles will prey on young hip­popotami. Be­sides hu­mans, adult hip­popotami have no known preda­tors. (Lewi­son and Oliver, 2008)

• Anti-predator Adaptations
• aposematic

• Known Predators

  • lions (Panthera leo)
  • hyenas (Hyaenidae)
  • crocodiles (Crocodylidae)
  • humans (Homo sapiens)

Ecosys­tem Roles

Be­cause of their mas­sive size, hip­pos play an im­por­tant role in their ecosys­tems. Daily ac­tiv­i­ties both in and out of water cre­ate habi­tats for smaller or­gan­isms. The for­ma­tion of hippo paths from water to land clears av­enues that water can flow through dur­ing wet sea­sons. Flood­ing of these paths cre­ates most of the la­goons and side pools that small fish re­treat to dur­ing droughts. (El­tring­ham, 1999; Mose­pele, et al., 2009)

As with all mam­mals, sev­eral forms of par­a­sites af­fect hip­popotami on both the in­side and out­side of their body. Ec­topar­a­sites are par­a­sites found feed­ing out­side of the hippo’s body. Ocu­lotrema hip­popotami, mono­gene flukes, live on the outer sur­face of a hip­popotami’s eye. They at­tach to the inner edge of the nic­ti­ta­tine mem­brane and under they eye­lid of hip­popotami. Al­though the fluke does not cause se­ri­ous harm to the eye, the areas af­fected be­come ex­tremely ir­ri­tated. Leeches and ticks are com­monly found around the anal re­gion of the hippo. This is not un­usual due to their aquatic lifestyle. Other than the loss of blood and ir­ri­ta­tion around the at­tach­ment site, there is no se­ri­ous dam­age caused by these par­a­sites. En­dopar­a­sites are many. Flat­worms and Bux­ifrons bux­ifrons are com­monly found in the stom­ach and first 1.5 me­ters of the small in­tes­tine. A tape­worm par­a­sitizes the gut as adults, but occur as cysts in the mus­cles when in the lar­val phases. Liver flukes are most com­monly found in the liv­ers of young hip­popotami, sug­gest­ing hip­pos ac­quire im­mu­nity to the par­a­site with age. Mem­bers of the blood fluke fam­ily in­habit the he­patic por­tal sys­tem and the pelvic veins of hip­popotami. These flukes lay their eggs in cap­il­lar­ies, which then mi­grate to the in­tes­tine or blad­der to be passed out­side of the body. Once hatched, the "miracid­ium" larva pen­e­trates mul­ti­ple species of fresh­wa­ter snails and trans­form into "cer­caria" larva. These larva are then re­leased back into the water, where they are then able to pen­e­trate the skin of the hippo. (El­tring­ham, 1999; Mose­pele, et al., 2009)

• Ecosystem Impact
• creates habitat
• keystone species

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

Hip­popotami are ex­tremely valu­able to na­tive hunters, pro­vid­ing a sub­stan­tial amount of meat and valu­able tusks and hide. Their thick hide is used in mak­ing shields and elas­tic whips. Ca­nine tusks con­tain ivory, and is il­le­gally sold on the black mar­ket. (Lewi­son and Oliver, 2008; Roomer, 1872; Wil­son, 1882)

• Positive Impacts
• food
• body parts are source of valuable material

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

Hip­popotami are usu­ally very docile an­i­mals. How­ever, when threat­ened, es­pe­cially dur­ing drought-bur­dened sea­sons, at­tacks on hu­mans oc­ca­sion­ally occur. Ac­ci­den­tal en­coun­ters with hunters, boaters, and de­vel­op­ers oc­curs usu­ally be­cause the in­di­vid­u­als are un­aware of a pop­u­la­tion's pres­ence and can leads to human fa­tal­ity. ("Hip­popota­mus", 2011; Estes, 1992; Lewi­son and Oliver, 2008; Wil­son, 1882)

• Negative Impacts
• injures humans

Con­ser­va­tion Sta­tus

Ac­cord­ing to the IUNC Redlist, there has been a 7 to 20% de­cline in hip­popota­mus pop­u­la­tions over the past 10 years. It was es­ti­mated that in the 29 coun­tries within its ge­o­graphic range, there are only be­tween 125,000 to 148,000 in­di­vid­u­als. Al­though hunt­ing and ex­ploita­tion of hip­popotami are il­le­gal, it re­mains the main rea­son for de­clines in pop­u­la­tions. This ex­ploita­tion is most com­monly found in areas where hippo pop­u­la­tions are on un­pro­tected land. Habi­tat loss is an­other rea­son for pop­u­la­tion de­clines. Hip­popotami rely heav­ily on fresh­wa­ter bod­ies, mak­ing them vul­ner­a­ble to drought, agri­cul­tural and in­dus­trial de­vel­op­ment, and rerout­ing of nat­ural water flows. There are few con­ser­va­tion ef­forts aimed at pro­tect­ing hippo habi­tat and pop­u­la­tions specif­i­cally. Coun­tries where hip­popotami are most com­mon have strict hunt­ing reg­u­la­tions and pro­tected habi­tats, in­clud­ing na­tional parks, re­serves, and con­ser­va­tion areas. (Lewi­son and Oliver, 2008)

• IUCN Red List

  Vulnerable
  More information

• IUCN Red List

  Vulnerable
  More information

• US Federal List

  No special status

• CITES

  No special status

• State of Michigan List

  No special status

Con­trib­u­tors

kas­san­dra mason (au­thor), Rad­ford Uni­ver­sity, Karen Pow­ers (ed­i­tor), Rad­ford Uni­ver­sity, Kier­sten Newtoff (ed­i­tor), Rad­ford Uni­ver­sity, Melissa Whistle­man (ed­i­tor), Rad­ford Uni­ver­sity, Laura Podzikowski (ed­i­tor), Spe­cial Pro­jects.

Ref­er­ences

2011. Hip­popota­mus. Pp. elec­tronic data­base in P La­gassé, ed. Co­lum­bia Elec­tronic En­cy­clo­pe­dia, Vol. 1, 6th Edi­tion. Co­lum­bia Uni­ver­sity: Co­lum­bia Uni­ver­sity Press. Ac­cessed Feb­ru­ary 09, 2012 at http://​www.​encyclopedia.​com/​topic/​hippopotamus.​aspx.

Bark­low, W. 2004. Am­phibi­ous com­mu­ni­ca­tion with sound in Hip­popota­mus am­phibius. An­i­mal Be­hav­iour, 68/5: 1125-1132.

Blow­ers, T., J. Wa­ter­man, C. Kuhar, T. Bet­tinger. 2010. So­cial be­hav­iors within a group of cap­tive fe­male Hip­popota­mus am­phibius. Jour­nal Of Ethol­ogy, 28/2: 287-294.

Cough­lin, B., F. Fish. 2009. Hip­popota­mus un­der­wa­ter lo­co­mo­tion: Re­duced grav­ity move­ments for a mas­sive mam­mal. Jour­nal Of Mam­mal­ogy, 90/3: 675-679.

El­tring­ham, S. 1999. The Hip­pos. Soho Square, Lon­don: T and A.D. Poyser Ltd.

Estes, R. 1992. The Be­hav­ior Guide to African Mam­mals: In­clud­ing Hoofed Mam­mals, Car­ni­vores, Pri­mates. Los An­ge­les, Cal­i­for­nia: Uni­ver­sity of Cal­i­for­nia Press.

Lewi­son, R., W. Oliver. 2008. "Hip­popota­mus am­phibius" (On-line). IUNC Red List of Threat­ened Species. Ac­cessed Feb­ru­ary 01, 2012 at http://​www.​iucnredlist.​org/​apps/​redlist/​details/​10103/​0.

Lewi­son, R., J. Carter. 2004. Ex­plor­ing be­hav­ior of an un­usual mega­her­bi­vore: a spa­tially ex­plicit for­ag­ing model of the hip­popota­mus. Eco­log­i­cal Mod­el­ing, 171/1–2: 127-138.

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