Blog

The hippopotamus (Hippopotamus amphibius) (/ˌhɪpəˈpɒtəməs/; pl.: hippopotamuses; often shortened to hippo (pl.: hippos), further qualified as the common hippopotamus, Nile hippopotamus and river hippopotamus, is a large semiaquatic mammal native to sub-Saharan Africa. It is one of only two extant species in the family Hippopotamidae, the other being the pygmy hippopotamus (Choeropsis liberiensis or Hexaprotodon liberiensis). Its name comes from the ancient Greek for “river horse” (ἱπποπόταμος).

After elephants and rhinoceroses, the hippopotamus is the next largest land mammal. It is also the largest extant land artiodactyl. Despite their physical resemblance to pigs and other terrestrial even-toed ungulates, the closest living relatives of the hippopotamids are cetaceans (whales, dolphins, porpoises, etc.), from which they diverged about 55 million years ago. Hippos are recognisable for their barrel-shaped torsos, wide-opening mouths with large canine tusks, nearly hairless bodies, pillar-like legs, and large size: adults average 1,500 kg (3,300 lb) for bulls (males) and 1,300 kg (2,900 lb) for cows (females). Despite its stocky shape and short legs, it is capable of running 30 km/h (19 mph) over short distances.

Hippos inhabit rivers, lakes, and mangrove swamps. Territorial bulls each preside over a stretch of water and a group of five to thirty cows and calves. Mating and birth both occur in the water. During the day, hippos remain cool by staying in water or mud, emerging at dusk to graze on grasses. While hippos rest near each other in the water, grazing is a solitary activity and hippos typically do not display territorial behaviour on land. Hippos are among the most dangerous animals in the world due to their aggressive and unpredictable nature. They are threatened by habitat loss and poaching for their meat and ivory (canine teeth).

Etymology

The Latin word hippopotamus is derived from the ancient Greek ἱπποπόταμος (hippopótamos), from ἵππος (híppos) ‘horse’ and ποταμός (potamós) ‘river’, together meaning ‘horse of the river’.^[3][4][5] In English, the plural is “hippopotamuses”.^[6]

Taxonomy and origins

Classification

Head, skull and mandible of Hippopotamus amphibius

The modern hippopotamus and the pygmy hippopotamus are the only living members of the family Hippopotamidae. Some taxonomists place hippos and anthracotheres in the superfamily Anthracotheroidea. Hippopotamidae are classified along with other even-toed ungulates in the order Artiodactyla.^{[7]: 39–40}

Five subspecies of hippos have been described based on morphological differences in their skulls as well as differences in geographical range:^{[7]: 3 [8][9][10]}

• H. a. amphibius – (the nominate subspecies) ranges from Gambia east to Ethiopia and then south to Mozambique and historically ranged as far north as Egypt; its skull is distinguished by a moderately reduced preorbital region, a bulging dorsal surface, elongated mandibular symphysis and larger chewing teeth.
• H. a. kiboko – found in Kenya and Somalia; was noted to be smaller and more lightly coloured than other hippos with wider nostrils, somewhat longer snout and more rounded and relatively raised orbits with the space between them being incurved.
• H. a. capensis – found in Zambia and South Africa; distinguished by wider orbits.
• H. a. tschadensis – ranges between Chad and Niger; featured a slightly shorter but broader face, and pronounced, forward-facing orbits.
• H. a. constrictus – ranged from the southern Democratic Republic of Congo to Angola and Namibia; skull characterised by a thicker preorbital region, shorter snout, flatter dorsal surface, reduced mandibular symphysis and smaller chewing teeth.

The suggested subspecies above were never widely used or validated by field biologists; the described morphological differences were small enough that they could have resulted from simple variation in nonrepresentative samples.^[7]: 2 A study examining mitochondrial DNA from skin biopsies taken from 13 sampling locations found “low, but significant, genetic differentiation” among H. a. amphibius, H. a. capensis, and H. a. kiboko. Neither H. a. tschadensis nor H. a. constrictus have been tested.^[9]

Evolution

Until 1909, naturalists classified hippos together with pigs based on molar patterns. Several lines of evidence, first from blood proteins, then from molecular systematics,^[12] DNA^[13][14] and the fossil record, show their closest living relatives are cetaceans (whales, dolphins, and porpoises).^[15][16] The common ancestor of hippos and whales branched off from Ruminantia and the rest of the even-toed ungulates; the cetacean and hippo lineages split soon afterwards.^[13][16]

Artiodactyla	Tylopoda   Artiofabula    Suina       Cetruminantia    Ruminantia   Whippomorpha    Hippopotamidae Cetacea

The most recent theory of the origins of Hippopotamidae suggests hippos and whales shared a common semiaquatic ancestor that branched off from other artiodactyls around 60 million years ago.^[13][15] This hypothesised ancestral group likely split into two branches again around 54 million years ago.^[12]

One branch would evolve into cetaceans, possibly beginning about 52 million years ago, with the protowhale Pakicetus and other early whale ancestors collectively known as Archaeoceti. This group eventually underwent aquatic adaptation into the completely aquatic cetaceans.^[16] The other branch became the anthracotheres, a large family of four-legged beasts, the earliest of which in the late Eocene would have resembled skinny hippos with comparatively smaller, narrower heads. All branches of the anthracotheres, except that which evolved into Hippopotamidae, became extinct during the Pliocene, leaving no descendants.^[15][16]

A rough evolutionary lineage of the hippo can thus be traced from Eocene and Oligocene species: from Anthracotherium and Elomeryx to the Miocene species Merycopotamus and Libycosaurus and finally the very latest anthracotheres in the Pliocene.^[17] These groups lived across Eurasia and Africa. The discovery of Epirigenys in East Africa, which was likely a descent of Asian anthracotheres and a sister taxon to Hippopotamidae, suggests that hippo ancestors entered Africa from Asia around 35 million years ago.^[18][19] An early hippopotamid is the genus Kenyapotamus, which lived in Africa from 15 to 9 million years ago.^[17] Hippopotamid species would spread across Africa and Eurasia, including the modern pygmy hippo. From 7.5 to 1.8 million years ago, a possible ancestor to the modern hippo, Archaeopotamus, lived in Africa and the Middle East.^[20] The oldest records of the genus Hippopotamus date to the Pliocene (5.3–2.6 million years ago).^[21] The oldest unambiguous records of the modern H. amphibius date to the Middle Pleistocene, though there are possible Early Pleistocene records.^[22]

Extinct species

Three species of Malagasy hippopotamus became extinct during the Holocene on Madagascar, the last of them within the past 1,000 years. The Malagasy hippos were smaller than the modern hippo, a likely result of the process of insular dwarfism.^[23] Fossil evidence indicates many Malagasy hippos were hunted by humans, a factor in their eventual extinction.^[23] Isolated individual Malagasy hippos may have survived in remote pockets; in 1976, villagers described a living animal called the kilopilopitsofy, which may have been a Malagasy hippo.^[24]

Hippopotamus gorgops from the Early Pleistocene to the early Middle Pleistocene of Africa and West Asia grew considerably larger than the living hippopotamus, with an estimated body mass of over 4,000 kg (8,800 lb).^[21][25][26] Hippopotamus antiquus ranged throughout Europe, extending as far north as Britain during the Early and Middle Pleistocene epochs, before being replaced by the modern H. amphibius in Europe during the latter part of the Middle Pleistocene.^[27] The Pleistocene also saw a number of dwarf species evolve on several Mediterranean islands, including Crete (Hippopotamus creutzburgi), Cyprus (the Cyprus dwarf hippopotamus, Hippopotamus minor), Malta (Hippopotamus melitensis), and Sicily (Hippopotamus pentlandi). Of these, the Cyprus dwarf hippo survived until the end of the Pleistocene or early Holocene. Evidence from the archaeological site Aetokremnos continues to cause debate on whether or not the species was driven to extinction or even encountered by humans.^[28][29]

Characteristics

The hippopotamus is a megaherbivore and is exceeded in size among land animals only by elephants and some rhinoceros species. The mean adult weight is around 1,480 kg (3,260 lb) for bulls and 1,365 kg (3,009 lb) for cows. Exceptionally large males have been recorded reaching 2,660 kg (5,860 lb).^[30] Male hippos appear to continue growing throughout their lives, while females reach maximum weight at around age 25.^[31] It is 2.90 to 5.05 m (9 ft 6 in to 16 ft 7 in) long,^[32] including a tail of about 35 to 56 cm (14 to 22 in) in length and 1.30 to 1.65 m (4 ft 3 in to 5 ft 5 in) tall at the shoulder,^[33][34] with males and females ranging 1.40 to 1.65 m (4 ft 7 in to 5 ft 5 in) and 1.30 to 1.45 m (4 ft 3 in to 4 ft 9 in) tall at the shoulder respectively.^[34] The species has a typical head–body length of 3.3–3.45 m (10.8–11.3 ft) and an average standing height of 1.4 m (4 ft 7 in) at the shoulder.^[35]

Hippos have barrel-shaped bodies with short tails and legs, and an hourglass-shaped skull with a long snout.^{[36][7]: 3, 19} Their skeletal structures are graviportal, adapted to carrying their enormous weight,^[7]: 8 and their dense bones and low centre of gravity allows them to sink and move along the bottom of the water.^[37] Hippopotamuses have small legs (relative to other megafauna) because the water in which they live reduces the weight burden.^[38] The toes are webbed and the pelvis rests at an angle of 45 degrees.^{[7]: 3, 9} Though chubby-looking, hippos have little fat.^[7]: 3 The eyes, ears, and nostrils of hippos are placed high on the roof of their skulls. This allows these organs to remain above the surface while the rest of the body is submerged.^[39]: 259 The nostrils and ears can close when underwater while nictitating membranes cover the eyes.^{[7]: 4, 116} The vocal folds of the hippo are more horizontally positioned, much like baleen whales. Underneath are throat tissues, where vibrations are transmitted to produce underwater calls.^[40]

The hippo’s jaw is powered by huge masseter and digastric muscles which give them large, droopy cheeks.^[39]: 259 The jaw hinge allows the animal to open its mouth at almost 180°.^[7]: 17 A folded orbicularis oris muscle allows the hippo to attain an extreme gape without tearing any tissue.^[41] On the lower jaw, the incisors and canines grow continuously, the former reaching 40 cm (16 in), while the latter can grow to up to 50 cm (20 in). The lower canines are sharpened through contact with the smaller upper canines.^[36] The canines and incisors are used mainly for combat instead of feeding. Hippos rely on their flattened, horny lips to grasp and pull grasses which are then ground by the molars.^{[39]: 259, 263} The hippo is considered to be a pseudoruminant; it has a complex three-chambered stomach, but does not “chew cud“.^[7]: 22

Hippo skin is 6 cm (2.4 in) thick across much of its body with little hair.^{[36][39]: 260} The animal is mostly purplish-grey or blue-black, but brownish-pink on the underside and around the eyes and ears.^[39]: 260 Their skin secretes a natural, red-coloured sunscreen substance that is sometimes referred to as “blood sweat” but is neither blood nor sweat. This secretion is initially colourless and turns red-orange within minutes, eventually becoming brown. Two highly acidic pigments have been identified in the secretions; one red hipposudoric acid and one orange norhipposudoric acid, which inhibit the growth of disease-causing bacteria and their light-absorption profile peaks in the ultraviolet range, creating a sunscreen effect.^[42][43] Regardless of diet, all hippos secrete these pigments so food does not appear to be their source; rather, they may be synthesised from precursors such as the amino acid tyrosine.^[43] This natural sunscreen cannot prevent the animal’s skin from cracking if it stays out of water too long.^[44]

The testes of the males do not fully descend and a scrotum is not present. In addition, the penis retracts into the body when not erect. The genitals of the female hippos are unusual in that the vagina is ridged and the vulval vestibule has two large, protruding diverticula. Both of these have an unknown function.^{[7]: 28–29}

A hippo’s lifespan is typically 40 to 50 years.^[39]: 277 Donna the Hippo was one of the oldest living hippos in captivity. She lived at the Mesker Park Zoo in Evansville, Indiana, in the US^[45][46] until her death in 2012 at the age of 61.^[47] The oldest hippo ever recorded was called Bertha; she had lived in the Manila Zoo in the Philippines since it first opened in 1959. When she died in 2017, her age was estimated to be 65.^[48] The oldest living hippopotamus in captivity is Lu the Hippo, from the Ellie Schiller Homosassa Springs Wildlife State Park. As of 2024, he is 64 years old.^[49]

Distribution and status

Hippopotamus amphibius arrived in Europe around 560–460,000 years ago, during the Middle Pleistocene.^[50] The distribution of Hippopotamus amphibius in Europe during the Pleistocene was largely confined to Southern Europe, including the Iberian Peninsula,^[51] Italy,^[52][53] and Greece,^[54] but extended into northwestern Europe, including Great Britain (as far north as North Yorkshire), the Netherlands, and western Germany during interglacial periods, such as the Last Interglacial (130–115,000 years ago).^[55][56][57] The youngest records of the species in Europe are from the Late Pleistocene of Greece, dating to around 40–30,000 years ago.^[54][51]

Archaeological evidence exists of its presence in the Levant, dating to less than 3,000 years ago.^[58][59] The species was common in Egypt‘s Nile region during antiquity, but it has since been driven out. According to Pliny the Elder, in his time, the best location in Egypt for capturing this animal was in the Saite nome;^[60] the animal could still be found along the Damietta branch of the Nile after the Arab Conquest in 639. Reports of the slaughter of the last hippo in Natal Province were made at the end of the 19th century.^[61] Hippos are still found in the rivers and lakes of the northern Democratic Republic of the Congo, Uganda, Tanzania, and Kenya, north through to Ethiopia, Somalia, and Sudan, west to The Gambia, and south to South Africa.^[1]

Genetic evidence suggests common hippos in Africa experienced a marked population expansion during or after the Pleistocene, attributed to an increase in water bodies at the end of the era. These findings have important conservation implications, as hippo populations across the continent are currently threatened by loss of access to fresh water.^[9] Hippos are also subject to unregulated hunting and poaching. The species is included in Appendix II of the Convention on International Trade in Endangered Species (CITES) meaning international export/import (including in parts and derivatives) requires CITES documentation to be obtained and presented to border authorities.^[1][62]

As of 2017, the IUCN Red List drawn up by the International Union for Conservation of Nature (IUCN) lists the species as vulnerable, with a stable population estimated between 115,000 and 130,000 animals.^[1] The hippo population has declined most dramatically in the Democratic Republic of the Congo.^[63] By 2005, the population in Virunga National Park had dropped to 800 or 900 from around 29,000 in the mid-1970s.^[64] This decline is attributed to the disruptions caused by the Second Congo War.^[64] The poachers are believed to be Mai-Mai rebels, underpaid Congolese soldiers, and local militia groups.^[64][65] Reasons for poaching include the belief hippos are harmful to society, as well as financial gain.^[66] As of 2016, the Virunga hippo population appears to have increased again, possibly due to better protection from park rangers, who have worked with local fishermen.^[67] The sale of hippo meat is illegal, but black-market sales are difficult for Virunga National Park officers to track.^[65][66] Hippo meat is highly valued in some areas of central Africa and the teeth may be used as a replacement for elephant ivory.^[68]

A population of hippos exists in Colombia, descended from captive individuals that escaped from Pablo Escobar‘s estate after his death in 1993. Their numbers grew to 100 by the 2020s and ecologists believe the population should be eradicated, as they are breeding rapidly and are an increasing menace to humans and the environment. Attempts to control them include sterilisation and culling.^[69]

Behaviour and ecology

Video of hippos in the wild

Hippos are semiaquatic and require enough water to immerse in, while being close to grass.^[36] They mostly live in freshwater habitat, but can be found in estuaries.^[1] They prefer relatively still waters with gently sloping shores, though male hippos may also be found in very small numbers in more rapid waters with rocky slopes.^[39]: 264 Like most herbivores, hippos will consume a variety of plants if presented with them in captivity, but their diet in nature consists almost entirely of grass, with only minimal consumption of aquatic plants.^[70] Hippos spend most of the day in water to stay cool and hydrated. Just before night begins, they leave the water to forage on land. A hippo will travel 3–5 km (1.9–3.1 mi) per night, eating around 40 kg (88 lb) of grass. By dawn, they are back in the water.^[36]

Despite being semiaquatic, an adult hippo is not a particularly good swimmer, nor can it float. It rarely enters deep water; when it does, the animal moves by bouncing off the bottom. An adult hippo surfaces every four to six minutes, while young need to breathe every two to three minutes.^[7]: 3–4 Hippos move on land by trotting, and limb movements do not change between speeds. They can reach an airborne stage (a stage when all limb are off the ground) when they move fast enough. Hippos are reported to reach 30 km/h (19 mph) but this has not been confirmed.^[71] They are incapable of jumping but can walk up steep banks.^[36] The hippopotamus sleeps with both hemispheres of the brain resting, as in all land mammals, and usually sleeps on land or in water with the nostrils exposed. Despite this, it may be capable of sleeping while submerged, intermittently surfacing to breathe without waking. They appear to transition between different phases of sleep more quickly than other mammals.^[72]

Because of their size and their habit of taking the same paths to feed, hippos can have a significant impact on the land across which they walk, keeping the land clear of vegetation and depressing the ground. Over prolonged periods, hippos can divert the paths of swamps and channels.^[73] By defecating in the water, the animals also appear to pass on microbes from their gut, affecting the biogeochemical cycle.^[74] On occasion, hippos have been filmed eating carrion, usually near the water. There are other reports of meat-eating and even cannibalism and predation.^[75] Hippos’ stomach anatomy lacks adaptions to carnivory and meat-eating is likely caused by lack of nutrients or just an abnormal behaviour.^{[7]: 82–84}

Social life

It is challenging to study the interaction of bulls and cows because hippos are not sexually dimorphic, so cows and young bulls are almost indistinguishable in the field.^[76] Hippo pods fluctuate but can contain over 100 hippos. Although they lie close together, adults develop almost no social bonds. Males establish territories in water but not land, and these may range 250–500 m (820–1,640 ft) in lakes and 50–100 m (160–330 ft) in rivers. Territories are abandoned when the water dries up. The bull has breeding access to all the cows in his territory. Younger bachelors are allowed to stay as long as they defer to him. A younger male may challenge the old bull for control of the territory. Within the pods, the hippos tend to segregate by sex and status. Bachelor males lounge near other bachelors, females with other females, and the territorial male is on his own. When hippos emerge from the water to graze, they do so individually.^{[7]: 4–5, 49–50}

Hippos engage in “muck-spreading” which involves defecating while spinning their tails to distribute the faeces over a greater area. Muck-spreading occurs both on land and in water and its function is not well understood. It is unlikely to serve a territorial function, as the animals only establish territories in the water. They may be used as trails between the water and grazing areas.^{[7]: 5, 51–52} “Yawning” serves as a threat display.^[36] When fighting, bulls use their incisors to block each other’s attacks and their large canines as offensive weapons.^{[39]: 259–260} When hippos become over-populated or a habitat shrinks, bulls sometimes attempt infanticide, but this behaviour is not common under normal conditions.^[77]

The most common hippo vocalisation is the “wheeze honk”, which can travel over long distances in air.^[78] This call starts as a high-pitched squeal followed by a deeper, resonant call.^[7]: 5 The animals can recognise the calls of other individuals. Hippos are more likely to react to the wheeze honks of strangers than to those they are more familiar with.^[78] When threatened or alarmed, they produce exhalations,^[36] and fighting bulls will bellow loudly.^[7]: 5 Hippos are recorded to produce clicks underwater which may have echolocative properties.^[79] They have the unique ability to hold their heads partially above the water and send out a cry that travels through both water and air; individuals respond both above and below water.^[80]

Reproduction

Cows reach sexual maturity at five to six years of age and have a gestation period of eight months.^[81] A study of endocrine systems revealed cows may begin puberty at as early as three or four years.^[82] Bulls reach maturity at around 7.5 years. Both conceptions and births are highest during the wet season. Male hippos always have mobile spermatozoa and can breed year-round.^{[7]: 59–61, 66} After becoming pregnant, a female hippo will typically not begin ovulation again for 17 months.^[82] Hippos mate in the water, with the cow remaining under the surface,^[7]: 63 her head emerging periodically to draw breath. Cows give birth in seclusion and return within 10 to 14 days. Calves are born on land or shallow water^[36] weighing on average 50 kg (110 lb) and at an average length of around 127 cm (50 in). The female lies on her side when nursing, which can occur underwater or on land. The young are carried on their mothers’ backs in deep water.^{[7]: 4, 64}

Mother hippos are very protective of their young, not allowing others to get too close.^[36] One cow was recorded protecting a calf’s carcass after it had died.^[83] Calves may be temporarily kept in nurseries, guarded by one or more adults, and will play amongst themselves.^[36] Like many other large mammals, hippos are described as K-strategists, in this case typically producing just one large, well-developed infant every couple of years (rather than many small, poorly developed young several times per year, as is common among small mammals such as rodents).^[82][77] Calves no longer need to suckle when they are a year old.^[7]: 64

Interspecies interactions

Hippos coexist alongside a variety of large predators in their habitats. Nile crocodiles, lions, and spotted hyenas are known to prey on young hippos.^[36] Beyond these, adult hippos are not usually preyed upon by other animals due to their aggression and size. Cases where large lion prides have successfully preyed on adult hippos have been reported, but it is generally rare.^[84] Lions occasionally prey on adults at Gorongosa National Park and calves are sometimes taken at Virunga.^[85] Crocodiles are frequent targets of hippo aggression, probably because they often inhabit the same riparian habitats; crocodiles may be either aggressively displaced or killed by hippos.^[86] In turn, very large Nile crocodiles have been observed preying occasionally on calves, “half-grown” hippos, and possibly also adult female hippos. Groups of crocodiles have also been observed finishing off still-living male hippos that were previously injured in mating battles with other males.^[87][88]

Hippos occasionally visit cleaning stations in order to be cleaned of parasites by certain species of fishes. They signal their readiness for this service by opening their mouths wide. This is an example of mutualism, in which the hippo benefits from the cleaning while the fish receive food.^[89] Hippo defecation creates allochthonous deposits of organic matter along the river beds. These deposits have an unclear ecological function.^[70] A 2015 study concluded hippo dung provides nutrients from terrestrial material for fish and aquatic invertebrates,^[90] while a 2018 study found that their dung can be toxic to aquatic life in large quantities, due to absorption of dissolved oxygen in water bodies.^[91][92]

The parasitic monogenean flatworm Oculotrema hippopotami infests hippopotamus eyes, mainly the nictitating membrane. It is the only monogenean species (which normally live on fish) documented to live on a mammal.^[93]

Hippos and humans

Cut marks on bones of H. amphibius found at Bolomor Cave, a site in Spain preserving fossils dating from 230,000 to 120,000 years ago, provides evidence for Neanderthal butchery of hippopotamuses.^[94][95] The earliest evidence of modern human interaction with hippos comes from butchery cut marks on hippo bones found at the Bouri Formation and dated to around 160,000 years ago.^[96] 4,000–5,000 year art showing hippos being hunted have been found in the Tassili n’Ajjer Mountains of the central Sahara near Djanet.^[7]: 1 The ancient Egyptians recognised the hippo as ferocious, and representations on the tombs of nobles show humans hunting them.^[97]

The hippo was also known to the Greeks and Romans. The Greek historian Herodotus described the hippo in The Histories (written circa 440 BC) and the Roman naturalist Pliny the Elder wrote about the hippo in his encyclopedia Naturalis Historia (written circa 77 AD).^[60][98] The Yoruba people called the hippo erinmi, which means “elephant of the water”.^[99] Some individual hippos have achieved international fame. Huberta became a celebrity during the Great Depression for trekking a great distance across South Africa.^{[100][101]: 111–112}

Attacks on humans

The hippo is considered to be extremely aggressive and has frequently been reported charging and attacking boats.^[102] Small boats can easily be capsized by hippos and passengers can be injured or killed by the animals, or drown in the water. In one 2014 case in Niger, a boat was capsized by a hippo and 13 people were killed.^[103] Hippos will often raid farm crops if the opportunity arises, and humans may come into conflict with them on these occasions. These encounters can be fatal to either humans or hippos.^[104]

According to the Ptolemaic historian Manetho, the pharaoh Menes was carried off and then killed by a hippopotamus.^[105]

In zoos

Hippos have long been popular zoo animals. The first record of hippos taken into captivity for display is dated to 3500 BC in Hierakonpolis, Egypt.^[106] The first zoo hippo in modern history was Obaysch, who arrived at the London Zoo on 25 May 1850, where he attracted up to 10,000 visitors a day and inspired a popular song, the “Hippopotamus Polka”.^[107]

Hippos generally breed well in captivity; birth rates are lower than in the wild, but this can be attributed to zoos’ desire to limit births, since hippos are relatively expensive to maintain.^[107][108] Starting in 2015, the Cincinnati Zoo built a US$73 million exhibit to house three adult hippos, featuring a 250,000 L (55,000 imp gal; 66,000 US gal) tank. Modern hippo enclosures also have a complex filtration system for the animal’s waste, an underwater viewing area for the visitors, and glass that may be up to 9 cm (3.5 in) thick and capable of holding water under pressures of 31 kPa (4.5 psi).^{[101]: 158–159}

Cultural significance

In Egyptian mythology, the god Set takes the form of a red hippopotamus and fights Horus for control of the land, but is defeated. The goddess Tawaret is depicted as a pregnant woman with a hippo head, representing fierce maternal love.^[109] The Ijaw people of the Niger Delta wore masks of aquatic animals like the hippo when practising their water spirit cults,^[110] and hippo ivory was used in the divination rituals of the Yoruba.^[111] Hippo masks were also used in Nyau funerary rituals of the Chewa of Southern Africa.^[101]: 120 According to Robert Baden-Powell, Zulu warriors referred to hippos in war chants.^[112] The Behemoth from the Book of Job, 40:15–24 is thought to be based on the hippo.^[113]

Hippos have been the subjects of various African folktales. According to a San story, when the Creator assigned each animal its place in nature, the hippos wanted to live in the water, but were refused out of fear they might eat all the fish. After begging and pleading, the hippos were finally allowed to live in the water on the condition they would eat grass instead of fish, and fling their dung so it can be inspected for fish bones. In a Ndebele tale, the hippo originally had long, beautiful hair, but it was set on fire by a jealous hare and the hippo had to jump into a nearby pool. The hippo lost most of his hair and was too embarrassed to leave the water.^[114]

Hippopotamuses were rarely depicted in European art during the Renaissance and Baroque periods, due to less access to specimens by Europeans. One notable exception is Peter Paul Rubens‘ The Hippopotamus and Crocodile Hunt (1615–1616).^{[101]: 122–123} Ever since Obaysch inspired the “Hippopotamus Polka”, hippos have been popular animals in Western culture for their rotund appearance, which many consider comical.^[107] The Disney film Fantasia featured a ballerina hippo dancing to the opera La Gioconda. The film Hugo the Hippo is set in Tanzania and involves the title character trying to escape being slaughtered with the help of local children. The Madagascar films feature a hippo named Gloria.^{[101]: 128–129} Hippos even inspired a popular board game, Hungry Hungry Hippos.^[115]

Among the most famous poems about the hippo is “The Hippopotamus” by T. S. Eliot, where he uses the animal to represent the Catholic Church. Hippos are mentioned in the novelty Christmas song “I Want a Hippopotamus for Christmas” that became a hit for child star Gayla Peevey in 1953. They also featured in the popular “The Hippopotamous Song” by Flanders and Swann.^{[101]: 128, 136}

Kangaroos are marsupials from the family Macropodidae (macropods, meaning “large foot”). In common use the term is used to describe the largest species from this family, the red kangaroo, as well as the antilopine kangaroo, eastern grey kangaroo, and western grey kangaroo.^[1] Kangaroos are indigenous to Australia and New Guinea. The Australian government estimates that 42.8 million kangaroos lived within the commercial harvest areas of Australia in 2019, down from 53.2 million in 2013.^[2]

As with the terms “wallaroo” and “wallaby“, “kangaroo” refers to a paraphyletic grouping of species. All three terms refer to members of the same taxonomic family, Macropodidae, and are distinguished according to size. The largest species in the family are called “kangaroos” and the smallest are generally called “wallabies”. The term “wallaroos” refers to species of an intermediate size.^[3] There are also the tree-kangaroos, another type of macropod, which inhabit the tropical rainforests of New Guinea, far northeastern Queensland and some of the islands in the region. This kind of kangaroo lives in the upper branches of trees.^[4] A general idea of the relative size of these informal terms could be:

• wallabies: head and body length of 45–105 cm and tail length of 33–75 cm; the dwarf wallaby (the smallest of all known macropod species) is 46 cm long and weighs 1.6 kg;
• tree-kangaroos: ranging from Lumholtz’s tree-kangaroo: body and head length of 48–65 cm, tail of 60–74 cm, weight of 7.2 kg (16 lb) for males and 5.9 kg (13 lb) for females; to the grizzled tree-kangaroo: length of 75–90 cm (30 to 35 in) and weight of 8–15 kg (18–33 lb);
• wallaroos: the black wallaroo (the smaller of the two species) with a tail length of 60–70 cm and weight of 19–22 kg (41.8–48.5 lb) for males and 13 kg (28.6 lb) for females;
• kangaroos: a large male can be 2 m (6 ft 7 in) tall and weigh 90 kg (200 lb).

Kangaroos have large, powerful hind legs, large feet adapted for leaping, a long muscular tail for balance, and a small head. Like most marsupials, female kangaroos have a pouch called a marsupium in which joeys complete postnatal development.

Because of its grazing habits, the kangaroo has developed specialized teeth that are rare among mammals. Its incisors are able to crop grass close to the ground and its molars chop and grind the grass. Since the two sides of the lower jaw are not joined or fused together, the lower incisors are farther apart, giving the kangaroo a wider bite. The silica in grass is abrasive, so kangaroo molars are ground down and they actually move forward in the mouth before they eventually fall out, and are replaced by new teeth that grow in the back.^[5] This process is known as polyphyodonty and, amongst other mammals, only occurs in elephants and manatees.

The large kangaroos have adapted much better than the smaller macropods to land clearing for pastoral agriculture and habitat changes brought to the Australian landscape by humans. Many of the smaller species are rare and endangered, while kangaroos are relatively plentiful, despite a common misconception to the contrary.^[6][7]

The kangaroo along with the koala are symbols of Australia. A kangaroo appears on the Australian coat of arms^[8] and on some of its currency,^[9] and is used as a logo for some of Australia’s most well-known organisations, such as Qantas,^[10] and as the roundel of the Royal Australian Air Force.^[11] The kangaroo is important to both Australian culture and the national image, and consequently there are numerous popular culture references.

Wild kangaroos are shot for meat, leather hides, and to protect grazing land.^[12] Kangaroo meat has perceived health benefits for human consumption compared with traditional meats due to the low level of fat on kangaroos.^[13]

Terminology

The word kangaroo derives from the Guugu Yimithirr word gangurru, referring to eastern grey kangaroos.^[14][15] The name was first recorded as “kanguru” on 12 July 1770 in an entry in the diary of Sir Joseph Banks; this occurred at the site of modern Cooktown, on the banks of the Endeavour River, where HMS Endeavour under the command of Lieutenant James Cook was beached for almost seven weeks to repair damage sustained on the Great Barrier Reef.^[16] Cook first referred to kangaroos in his diary entry of 4 August. Guugu Yimithirr is the language of the people of the area.

A common myth about the kangaroo’s English name is that it was a Guugu Yimithirr phrase for “I don’t know” or “I don’t understand”.^[17] According to this legend, Cook and Banks were exploring the area when they happened upon the animal. They asked a nearby local what the creatures were called. The local responded “kangaroo”, said to mean “I don’t know/understand”, which Cook then took to be the name of the creature.^[18] Anthropologist Walter Roth was trying to correct this legend as far back as in 1898, but few took note until 1972 when linguist John B. Haviland in his research with the Guugu Yimithirr people was able to confirm that gangurru referred to a rare large dark-coloured species of kangaroo.^[18][19] However, when Phillip Parker King visited the Endeavour River region in 1819 and 1820, he maintained that the local word was not kangaroo but menuah perhaps referring to a different species of macropod.^[20] There are similar, more credible stories of naming confusion, such as with the Yucatán Peninsula.^[18]

Kangaroos are often colloquially referred to as “roos”.^[21] Male kangaroos are called bucks, boomers, jacks, or old men; females are does, flyers, or jills; and the young ones are joeys.^[22] The collective noun for a group of kangaroos is a mob, court, or troupe.^[23]

Taxonomy and description

There are four extant species that are commonly referred to as kangaroos:

• The red kangaroo (Osphranter rufus)^[24] is the largest surviving marsupial anywhere in the world. It occupies the arid and semi-arid centre of the country. The highest population densities of the red kangaroo occur in the rangelands of western New South Wales. Red kangaroos are commonly mistaken as the most abundant species of kangaroo, but eastern greys actually have a larger population.^[25] A large male can be 2 metres (6 ft 7 in) tall and weigh 90 kg (200 lb).^[26]
• The eastern grey kangaroo (Macropus giganteus)^[24] is less well-known than the red (outside Australia), but the most often seen, as its range covers the fertile eastern part of the country. The range of the eastern grey kangaroo extends from the top of the Cape York Peninsula in northern Queensland down to Victoria, as well as areas of southeastern Australia and Tasmania. Population densities of eastern grey kangaroos usually peak near 100 per km² in suitable habitats of open woodlands. Populations are more limited in areas of land clearance, such as farmland, where forest and woodland habitats are limited in size or abundance.^[25]
• The western grey kangaroo (Macropus fuliginosus)^[24] is slightly smaller again at about 54 kg (119 lb) for a large male. It is found in the southern part of Western Australia, South Australia near the coast, and the Murray–Darling basin. The highest population densities occur in the western Riverina district of New South Wales and in the western areas of the Nullarbor Plain in Western Australia. Populations may have declined, particularly in agricultural areas. The species has a high tolerance to the plant toxin sodium fluoroacetate, which indicates a possible origin from the southwest region of Australia.^[25]
• The antilopine kangaroo (Osphranter antilopinus)^[24] is, essentially, the far northern equivalent of the eastern grey and western grey kangaroos. It is sometimes referred to as the antilopine wallaroo, but in behaviour and habitat it is more similar to the red, eastern grey and western grey kangaroos. Like them, it is a creature of the grassy plains and woodlands, and gregarious. Its name comes from its fur, which is similar in colour and texture to that of antelopes. Characteristically, the noses of males swell behind the nostrils. This enlarges nasal passages and allows them to release more heat in hot and humid climates.^[25]

In addition, there are about 50 smaller macropods closely related to the kangaroos in the family Macropodidae. Kangaroos and other macropods share a common ancestor with the Phalangeridae from the Middle Miocene.^[27] This ancestor was likely arboreal and lived in the canopies of the extensive forests that covered most of Australia at that time, when the climate was much wetter, and fed on leaves and stems.^[28] From the Late Miocene through the Pliocene and into the Pleistocene the climate got drier, which led to a decline of forests and expansion of grasslands. At this time, there was a radiation of macropodids characterised by enlarged body size and adaptation to the low quality grass diet with the development of foregut fermentation.^[28] The most numerous early macropods, the Balbaridae and the Bulungamayinae, became extinct in the Late Miocene around 5–10 mya.^[29] There is dispute over the relationships of the two groups to modern kangaroos and rat-kangaroos. Some argue that the balbarines were the ancestors of rat-kangaroos and the bulungamayines were the ancestors of kangaroos.^[30] while others hold the contrary view.^[31]

The middle to late bulungamayines, Ganguroo and Wanburoo lacked digit 1 of the hind foot and digits 2 and 3 were reduced and partly under the large digit 4, much like the modern kangaroo foot. This would indicate that they were bipedal. In addition, their ankle bones had an articulation that would have prohibited much lateral movements, an adaptation for bipedal hopping.^[29] Species related to the modern grey kangaroos and wallaroos begin to appear in the Pliocene. The red kangaroo appears to be the most recently evolved kangaroo, with its fossil record not going back beyond the Pleistocene era, 1–2 mya.^[32]

The first kangaroo to be exhibited in the Western world was an example shot by John Gore, an officer on Captain Cook’s ship, HMS Endeavour, in 1770.^[33][34] The animal was shot and its skin and skull transported back to England whereupon it was stuffed (by taxidermists who had never seen the animal before) and displayed to the general public as a curiosity. The first glimpse of a kangaroo for many 18th-century Britons was a painting by George Stubbs.^[35]

Comparison with wallabies

Kangaroos and wallabies belong to the same taxonomic family (Macropodidae) and often the same genera, but kangaroos are specifically categorised into the four largest species of the family. The term wallaby is an informal designation generally used for any macropod that is smaller than a kangaroo or a wallaroo that has not been designated otherwise.^[3]

Biology and behaviour

See also: Red kangaroo § Behaviour, and Eastern grey kangaroo § Behaviour

Locomotion

Kangaroos are the only large mammals to use hopping on two legs as their primary means of locomotion.^[36] The comfortable hopping speed for a red kangaroo is about 20–25 km/h (12–16 mph), but speeds of up to 70 km/h (43 mph) can be attained over short distances, while it can sustain a speed of 40 km/h (25 mph) for nearly 2 km (1.2 mi).^[37] During a hop, the powerful gastrocnemius muscles lift the body off the ground while the smaller plantaris muscle, which attaches near the large fourth toe, is used for push-off. Seventy percent of potential energy is stored in the elastic tendons.^[38] At slow speeds, it employs pentapedal locomotion, using its tail to form a tripod with its two forelimbs while bringing its hind feet forward. Both pentapedal walking and fast hopping are energetically costly. Hopping at moderate speeds is the most energy efficient, and a kangaroo moving above 15 km/h (9.3 mph) maintains energy consistency more than similarly sized animals running at the same speed.^[32]

Diet

Kangaroos have single-chambered stomachs quite unlike those of cattle and sheep, which have four compartments.^[39][40] They sometimes regurgitate the vegetation they have eaten, chew it as cud, and then swallow it again for final digestion. However, this is a different, more strenuous, activity than it is in ruminants, and does not take place as frequently.^[41]

Different species of kangaroos have different diets, although all are strict herbivores. The eastern grey kangaroo is predominantly a grazer, and eats a wide variety of grasses, whereas some other species such as the red kangaroo include significant amounts of shrubs in their diets. Smaller species of kangaroos also consume hypogeal fungi. Many species are nocturnal,^[42] and crepuscular,^[43][44] usually spending the hot days resting in shade, and the cool evenings, nights and mornings moving about and feeding.

Absence of digestive methane release

Despite having herbivorous diets similar to ruminants such as cattle, which release large quantities of digestive methane through exhaling and eructation (burping), kangaroos release virtually none. The hydrogen byproduct of fermentation is instead converted into acetate, which is then used to provide further energy. Scientists are interested in the possibility of transferring the bacteria responsible for this process from kangaroos to cattle, since the greenhouse gas effect of methane is 23 times greater than carbon dioxide per molecule.^[45]

Social and sexual behavior

Groups of kangaroos are called mobs, courts or troupes, which usually have 10 or more kangaroos in them. Living in mobs can provide protection for some of the weaker members of the group.^[23] The size and stability of mobs vary between geographic regions,^[28][46][47] with eastern Australia having larger and more stable aggregations than in arid areas farther west.^[28] Larger aggregations display high amounts of interactions and complex social structures, comparable to that of ungulates.^[28]

One common behavior is nose touching and sniffing, which mostly occurs when an individual joins a group.^[32] The kangaroo performing the sniffing gains much information from smell cues. This behavior enforces social cohesion without consequent aggression. During mutual sniffing, if one kangaroo is smaller, it will hold its body closer to the ground and its head will quiver, which serves as a possible form of submission.^[32] Greetings between males and females are common, with larger males being the most involved in meeting females. Most other non-antagonistic behavior occurs between mothers and their young. Mother and young reinforce their bond through grooming. A mother will groom her young while it is suckling or after it is finished suckling.^[32] A joey will nuzzle its mother’s pouch if it wants access to it.

Sexual activity of kangaroos consists of consort pairs.^[48] Oestrous females roam widely and attract the attention of males with conspicuous signals.^[48] A male will monitor a female and follow her every movement. He sniffs her urine to see if she is in oestrus, a process exhibiting the flehmen response. The male will then proceed to approach her slowly to avoid alarming her.^[28] If the female does not run away, the male will continue by licking, pawing, and scratching her, and copulation will follow.^[28] After copulation is over, the male will move on to another female. Consort pairing may take several days and the copulation is also long. Thus, a consort pair is likely to attract the attention of a rival male.^[48] As larger males are tending bonds with females near oestrus, smaller males will tend to females that are farther from oestrus.^[28] Dominant males can avoid having to sort through females to determine their reproductive status by searching for tending bonds held by the largest male they can displace without a fight.^[28]

Fighting has been described in all species of kangaroos. Fights between kangaroos can be brief or long and ritualised.^[32] In highly competitive situations, such as males fighting for access to oestrous females or at limited drinking spots, the fights are brief.^[32] Both sexes will fight for drinking spots, but long, ritualised fighting or “boxing” is largely done by males. Smaller males fight more often near females in oestrus, while the large males in consorts do not seem to get involved. Ritualised fights can arise suddenly when males are grazing together. However, most fights are preceded by two males scratching and grooming each other.^[32] One or both of them will adopt a high standing posture, with one male issuing a challenge by grasping the other male’s neck with its forepaw. Sometimes, the challenge will be declined. Large males often reject challenges by smaller males. During fighting, the combatants adopt a high standing posture and paw at each other’s heads, shoulders and chests. They will also lock forearms and wrestle and push each other as well as balance on their tails to kick each other in the abdomen.^[32]

Brief fights are similar, except there is no forearm locking. The losing combatant seems to use kicking more often, perhaps to parry the thrusts of the eventual winner. A winner is decided when a kangaroo breaks off the fight and retreats. Winners are able to push their opponents backwards or down to the ground. They also seem to grasp their opponents when they break contact and push them away.^[32] The initiators of the fights are usually the winners. These fights may serve to establish dominance hierarchies among males, as winners of fights have been seen to displace their opponent from resting sites later in the day.^[32] Dominant males may also pull grass to intimidate subordinate ones.^[28]

Predators

Kangaroos have a few natural predators. The thylacine, considered by palaeontologists to have once been a major natural predator of the kangaroo, is now extinct. Other extinct predators included the marsupial lion, Megalania and Wonambi. However, with the arrival of humans in Australia at least 50,000 years ago and the introduction of the dingo about 5,000 years ago, kangaroos have had to adapt.

Along with dingoes, introduced species such as foxes, feral cats, and both domestic and feral dogs, pose a threat to kangaroo populations. Kangaroos and wallabies are adept swimmers, and often flee into waterways if presented with the option. If pursued into the water, a large kangaroo may use its forepaws to hold the predator underwater so as to drown it.^[49] Another defensive tactic described by witnesses is catching the attacking dog with the forepaws and disembowelling it with the hind legs.

Adaptations

Kangaroos have developed a number of adaptations to a dry, infertile country and highly variable climate. As with all marsupials, the young are born at a very early stage of development—after a gestation of 31–36 days. At this stage, only the forelimbs are somewhat developed, to allow the newborn to climb to the pouch and attach to a teat. In comparison, a human embryo at a similar stage of development would be at about 7 weeks gestation (even in a modern intensive care unit, premature babies born at less than 23 weeks gestation are usually not mature enough to survive). When the joey is born, it is about the size of a lima bean. The joey will usually stay in the pouch for about 9 months (180–320 days for the Western Grey) before starting to leave the pouch for small periods of time. It is usually fed by its mother until reaching 18 months.

The female kangaroo is usually pregnant in permanence, except on the day she gives birth; however, she has the ability to freeze the development of an embryo until the previous joey is able to leave the pouch. This is known as embryonic diapause and will occur in times of drought and in areas with poor food sources. The composition of the milk produced by the mother varies according to the needs of the joey. In addition, the mother is able to produce two different kinds of milk simultaneously for the newborn and the older joey still in the pouch.

Unusually, during a dry period, males will not produce sperm and females will conceive only if enough rain has fallen to produce a large quantity of green vegetation.^[50]

Kangaroos and wallabies have large, elastic tendons in their hind legs. They store elastic strain energy in the tendons of their large hind legs, providing most of the energy required for each hop by the spring action of the tendons rather than by any muscular effort.^[51] This is true in all animal species which have muscles connected to their skeletons through elastic elements such as tendons, but the effect is more pronounced in kangaroos.

There is also a link between the hopping action and breathing: as the feet leave the ground, air is expelled from the lungs; bringing the feet forward ready for landing refills the lungs, providing further energy efficiency. Studies of kangaroos and wallabies have demonstrated, beyond the minimum energy expenditure required to hop at all, increased speed requires very little extra effort (much less than the same speed increase in, say, a horse, dog or human), and the extra energy is required to carry extra weight. For kangaroos, the key benefit of hopping is not speed to escape predators—the top speed of a kangaroo is no higher than that of a similarly sized quadruped, and the Australian native predators are in any case less fearsome than those of other countries—but economy: in an infertile country with highly variable weather patterns, the ability of a kangaroo to travel long distances at moderately high speed in search of food sources is crucial to survival.

New research has revealed that a kangaroo’s tail acts as a third leg rather than just a balancing strut. Kangaroos have a unique three-stage walk where they plant their front legs and tail first, then push off their tail, followed lastly by the back legs. The propulsive force of the tail is equal to that of both the front and hind legs combined and performs as much work as what a human leg walking can at the same speed.^[52]

A DNA sequencing project of the genome of a member of the kangaroo family, the tammar wallaby, was started in 2004. It was a collaboration between Australia (mainly funded by the State of Victoria) and the National Institutes of Health in the US.^[53] The tammar’s genome was fully sequenced in 2011.^[54] The genome of a marsupial such as the kangaroo is of great interest to scientists studying comparative genomics, because marsupials are at an ideal degree of evolutionary divergence from humans: mice are too close and have not developed many different functions, while birds are genetically too remote. The dairy industry could also benefit from this project.^[55]

Blindness

Eye disease is rare but not new among kangaroos. The first official report of kangaroo blindness took place in 1994, in central New South Wales. The following year, reports of blind kangaroos appeared in Victoria and South Australia. By 1996, the disease had spread “across the desert to Western Australia”.^[56] Australian authorities were concerned the disease could spread to other livestock and possibly humans. Researchers at the Australian Animal Health Laboratories in Geelong detected a virus called the Wallal virus in two species of midges, believed to have been the carriers.^[57][58] Veterinarians also discovered fewer than 3% of kangaroos exposed to the virus developed blindness.^[56]

Reproduction and life cycle

See also: Red kangaroo § Reproduction, and Eastern grey kangaroo § Reproduction

Kangaroo reproduction is similar to that of opossums. The egg (still contained in the shell membrane, a few micrometres thick, and with only a small quantity of yolk within it) descends from the ovary into the uterus. There it is fertilised and quickly develops into a neonate. Even in the largest kangaroo species (the red kangaroo), the neonate emerges after only 33 days. Usually, only one young is born at a time. It is blind, hairless, and only a few centimetres long; its hindlegs are mere stumps; it instead uses its more developed forelegs to climb its way through the thick fur on its mother’s abdomen into the pouch, which takes about three to five minutes. Once in the pouch, it fastens onto one of the four teats and starts to feed. Almost immediately, the mother’s sexual cycle starts again. Another egg descends into the uterus and she becomes sexually receptive. Then, if she mates and a second egg is fertilised, its development is temporarily halted. This is known as embryonic diapause, and will occur in times of drought and in areas with poor food sources. Meanwhile, the neonate in the pouch grows rapidly. After about 190 days, the baby (joey) is sufficiently large and developed to make its full emergence out of the pouch, after sticking its head out for a few weeks until it eventually feels safe enough to fully emerge. From then on, it spends increasing time in the outside world and eventually, after about 235 days, it leaves the pouch for the last time.^[59] The lifespan of kangaroos averages at six years in the wild^[60] to in excess of 20 years in captivity, varying by the species.^[61] Most individuals, however, do not reach maturity in the wild.^[62][63]

Interaction with humans

The kangaroo has always been a very important animal for Aboriginal Australians, for its meat, hide, bone, and tendon. Kangaroo hides were also sometimes used for recreation; in particular there are accounts of some tribes (Kurnai) using stuffed kangaroo scrotum as a ball for the traditional football game of marngrook.^[64] In addition, there were important Dreaming stories and ceremonies involving the kangaroo. Aherrenge is a current kangaroo dreaming site in the Northern Territory.^[65]

Unlike many of the smaller macropods, kangaroos have fared well since European settlement. European settlers cut down forests to create vast grasslands for sheep and cattle grazing, added stock watering points in arid areas, and have substantially reduced the number of dingoes. This overabundance has led to the view that the kangaroo is a pest animal as well as requiring regular culling and other forms of management. There is concern that the current management practices are leading to detrimental consequences for kangaroo welfare, landscape sustainability, biodiversity conservation, resilient agricultural production and Aboriginal health and culture.^[66]

Kangaroos are shy and retiring by nature, and in normal circumstances present no threat to humans. In 2003, Lulu, an eastern grey which had been hand-reared, saved a farmer’s life by alerting family members to his location when he was injured by a falling tree branch. She received the RSPCA Australia National Animal Valour Award on 19 May 2004.^[67][68][69]

There are very few records of kangaroos attacking humans without provocation; however, several such unprovoked attacks in 2004 spurred fears of a rabies-like disease possibly affecting the marsupials. Only two reliably documented cases of a fatality from a kangaroo attack have occurred in Australia. The first attack occurred in New South Wales in 1936 when a hunter was killed as he tried to rescue his two dogs from a heated fray.^[70] The second attack was inflicted on a 77-year-old man from a domesticated kangaroo in Redmond, Western Australia in September 2022.^[71] Other suggested causes for erratic and dangerous kangaroo behaviour include extreme thirst and hunger. In July 2011, a male red kangaroo attacked a 94-year-old woman in her own backyard as well as her son and two police officers responding to the situation. The kangaroo was capsicum sprayed (pepper sprayed) and later put down after the attack.^[72][73]

Kangaroos—even those that are not domesticated—^[74] can communicate with humans, according to a research study.^{[74][clarification needed]}

Collisions with vehicles

Nine out of ten animal collisions in Australia involve kangaroos. A collision with a vehicle is capable of killing a kangaroo.^[75] Kangaroos dazzled by headlights or startled by engine noise often leap in front of cars. Since kangaroos in mid-bound can reach speeds of around 50 km/h (31 mph) and are relatively heavy, the force of impact can be severe. Small vehicles may be destroyed, while larger vehicles may suffer engine damage. The risk of harm or death to vehicle occupants is greatly increased if the windscreen is the point of impact. As a result, “kangaroo crossing” signs are commonplace in Australia.

Vehicles that frequent isolated roads, where roadside assistance may be scarce, are often fitted with “roo bars” to minimise damage caused by collision. Bonnet-mounted devices, designed to scare wildlife off the road with ultrasound and other methods, have been devised and marketed, but are ineffective.

If a female is the victim of a collision, animal welfare groups ask that her pouch be checked for any surviving joey, in which case it may be removed to a wildlife sanctuary or veterinary surgeon for rehabilitation. Likewise, when an adult kangaroo is injured in a collision, a vet, the RSPCA Australia or the National Parks and Wildlife Service can be consulted for instructions on proper care. In New South Wales, rehabilitation of kangaroos is carried out by volunteers from WIRES. Council road signs often list phone numbers for callers to report injured animals.

Emblems and popular culture

Main article: Kangaroo emblems and popular culture

The kangaroo is a recognisable symbol of Australia. The kangaroo and emu feature on the Australian coat of arms. Kangaroos have also been featured on coins, most notably the five kangaroos on the Australian one dollar coin. The Australian Made logo consists of a golden kangaroo in a green triangle to show that a product is grown or made in Australia.

Registered trademarks of early Australian companies using the kangaroo included Yung, Schollenberger & Co. Walla Walla Brand leather and skins (1890); Arnold V. Henn (1892) whose emblem showed a family of kangaroos playing with a skipping rope; Robert Lascelles & Co. linked the speed of the animal with its velocipedes (1896); while some overseas manufacturers, like that of “The Kangaroo” safety matches (made in Japan) of the early 1900s, also adopted the symbol. Even today, Australia’s national airline, Qantas, uses a bounding kangaroo for its logo.^[76]

The kangaroo appears in Rudyard Kipling‘s Just So Stories, “The Sing-Song of Old Man Kangaroo“, while the kangaroo is chased by a dingo, he gives Nqong the Big God’s advice, that his legs and tail grew longest before five o’clock.^[77]

The kangaroo and wallaby feature predominantly in Australian sports teams names and mascots. Examples include the Australian national rugby league team (the Kangaroos) and the Australian national rugby union team (the Wallabies). In a nation-wide competition held in 1978 for the XII Commonwealth Games by the Games Australia Foundation Limited in 1982, Hugh Edwards’ design was chosen; a simplified form of six thick stripes arranged in pairs extending from along the edges of a triangular centre represent both the kangaroo in full flight, and a stylised “A” for Australia.^[76]

Kangaroos are well represented in films, television, books, toys and souvenirs around the world. Skippy the Bush Kangaroo was a popular 1960s Australian children’s television series about a fictional pet kangaroo. Kangaroos are featured in the Rolf Harris song “Tie Me Kangaroo Down, Sport” and several Christmas carols.

Meat

Main article: Kangaroo meat

The kangaroo has been a source of food for indigenous Australians for tens of thousands of years. Kangaroo meat is high in protein and low in fat (about 2%). Kangaroo meat has a high concentration of conjugated linoleic acid (CLA) compared with other foods, and is a rich source of vitamins and minerals.^[78] Low fat diets rich in CLA have been studied for their potential in reducing obesity and atherosclerosis.^[13][79]

Kangaroo meat is sourced from wild animals and is seen by many as the best source of population control programs^[80] as opposed to culling them as pests where carcasses are left in paddocks. Kangaroos are harvested by licensed shooters in accordance with a code of practice and are protected by state and federal legislation.^[81][82]

Kangaroo meat is exported to many countries around the world. However, it is not considered biblically kosher by Jews or Adventists.^[83] It is considered halal according to Muslim dietary standards, because kangaroos are herbivorous.^[84]