Hippopotamuses are overwhelmingly plant-eaters, with grasses making up the bulk of their diet, but calling them strictly vegetarian oversimplifies their biology. Field observations across eastern and southern Africa have documented hippos eating meat, scavenging carcasses, and even feeding communally on animal remains. The reality is more interesting than either the “gentle herbivore” or the “secretly carnivorous” narrative suggests, and it touches on everything from disease outbreaks to the chemistry of entire river systems.
What Hippos Eat on a Typical Night
Hippos are grazers. They leave the water at dusk, walk to nearby grasslands, and spend hours cropping vegetation close to the ground with their wide, muscular lips. A feeding study in southwestern Ethiopia’s Dhidhessa Wildlife Sanctuary identified 34 plant species from 12 families in the hippo diet, with the grass family alone making up about 60% of total intake.1PLoS One. Feeding ecology and activity patterns of Hippopotamus amphibious in the Dhidhessa Wildlife Sanctuary, Southwestern Ethiopia Cattails and a handful of other grass species topped the list, but hippos are selective foragers, not indiscriminate lawn mowers. They show clear preferences for certain species and largely ignore others growing in the same area.
One persistent misconception is that hippos spend their days munching on aquatic plants. They do live in water for most of daylight hours, but their feeding happens primarily on land. A large-scale review of herbivore ecology classified hippos as “resident semi-aquatic species that live in water and forage mainly on land,” placing them in a distinct category from fully aquatic grazers. While hippos may nibble aquatic vegetation occasionally, the grasses they walk out to eat at night are their real diet.
Stable isotope analysis of hippo hair and tooth enamel confirms that the diet is variable across both seasons and years.2Journal of Zoology. Stable isotope ecology of the common hippopotamus Isotopic studies have also shown that hippos consume a meaningful amount of non-grass plants, particularly in forested or partially closed environments, rather than feeding exclusively on open savanna grasses. Fossil evidence from late Miocene hippopotamids suggests this dietary flexibility is ancient: hippo ancestors likely ate an even larger proportion of non-grass plants than modern hippos do.
Hippos Eat Meat, and It Is Not Rare
This is the part that surprises most people. Hippos have been observed eating meat on numerous occasions, and the behavior is not limited to starving individuals or freak events. A review published in Mammal Review described hippos as “facultative carnivores” that consume flesh and intestinal tissues from carcasses. The authors were clear that this is not an oddity confined to one region or a handful of unusual animals: carnivory occurs within hippo populations distributed across most of the species’ current range in eastern and southern Africa.3Mammal Review. Carnivory in the common hippopotamus Hippopotamus amphibius: implications for the ecology and epidemiology of anthrax in African landscapes
What makes this especially striking is that hippos often scavenge as a group. Rather than a lone hippo sneaking a bite, entire social groups have been documented feeding communally on a carcass. Reports include hippos eating the remains of impala, buffalo, elephants, and even other hippos. The behavior seems opportunistic: when a dead animal is available, hippos will take advantage of it. No one has observed hippos actively hunting prey in the way a predator would, so “carnivore” is a stretch, but “strict herbivore” no longer holds up either.
Why would an animal so clearly built for eating grass bother with meat? The honest answer is that researchers are still working this out. One possibility involves nutrient deficiencies, since many large herbivores occasionally chew bones or eat small animals to supplement minerals their plant diet lacks.4Journal of Archaeological Science. Osteophagia and bone modifications by giraffe and other large ungulates But the communal, repeated nature of hippo carnivory suggests something beyond a quick mineral fix. The full explanation may involve a combination of opportunity, social behavior, and nutritional need that varies by season and location.
The Disease Risk That Comes with Scavenging
Hippo meat-eating would be a quirky footnote in wildlife biology if it did not have real consequences for hippo populations. Anthrax, caused by the bacterium Bacillus anthracis, is one of the biggest infectious disease threats hippos face, and scavenging appears to be a major route of exposure. In Uganda’s Queen Elizabeth Protected Area, researchers studying anthrax outbreaks among hippos found that carnivory was directly linked to high mortality.5PLoS ONE. Spatio-temporal epidemiology of anthrax in Hippopotamus amphibius in Queen Elizabeth Protected Area, Uganda
The epidemiology is grim. When an infected animal dies in or near the water, anthrax spores can persist in the environment for years. Hippos’ social behavior makes things worse: they live in dense groups called schools, often packed together in the same stretch of river. Infectious carcasses can drift downstream with the current, exposing new groups along the way. So the same gregariousness that defines hippo life also amplifies the spread of anthrax once it enters a population. The combination of communal scavenging and tightly packed social groups turns what might be an isolated death into a mass mortality event.
A Digestive System That Defies Easy Categories
Hippos are sometimes loosely called “ruminants” because they are large, hoofed, and eat grass. They are not ruminants. Hippos do have a multi-chambered forestomach where microbial fermentation breaks down plant fiber, which is broadly similar to what happens in a cow’s rumen, but the mechanics are different. Studies tracking the passage of food through hippo guts found that the excretion patterns do not match those of ruminants at all. Instead, they resemble the digestive patterns seen in kangaroos, suggesting a plug-flow style of digestion where food moves through the forestomach in a more orderly front-to-back sequence rather than the constant mixing and regurgitation that defines rumination.6PubMed. Intake, ingesta retention, particle size distribution and digestibility in the hippopotamidae
Hippos also do not chew cud. A cow spends hours each day regurgitating food and re-chewing it to extract more nutrition. Hippos skip this step entirely. Their digestive system extracts what it can in a single pass, aided by the microbial community in the forestomach. This turns out to be enough, because hippos have an unusually low metabolic rate for their size. They simply do not need as much energy per kilogram of body weight as you would expect from an animal that can weigh over a thousand kilograms. Digestion studies on captive hippos confirmed this extremely low metabolic rate, noting that it explains a well-known problem in zoos: hippos fed energy-dense pelleted feeds become obese quickly.7PubMed. Digestion studies in captive Hippopotamidae: a group of large ungulates with an unusually low metabolic rate
Jaws Built for Combat, Not for Grinding
If you look at a hippo skull, the teeth seem almost comically oversized for eating grass. The enormous canines and tusk-like incisors are weapons, not feeding tools. Research on chewing mechanics and tooth wear in both common hippos and pygmy hippos found that hippo jaws have evolved to favor up-and-down chewing rather than the side-to-side grinding motion that most grazing mammals use.8PubMed Central. Chewing, dentition and tooth wear in Hippopotamidae (Hippopotamus amphibius and Choeropsis liberiensis) In common hippos, the interlocking upper and lower incisors actually prevent the jaw from moving laterally. This is the opposite of what you see in horses or cattle, whose flat molars and mobile jaws are optimized for grinding tough grasses into paste.
The researchers argue that this rigid jaw evolved under pressure from intraspecific combat, meaning fights between hippos. Being able to open the mouth extremely wide and deliver powerful bites with dagger-like canines is more important to a hippo’s survival and reproductive success than efficient grinding of food. The trade-off is that hippos chew their food less thoroughly than most grazers, which is a disadvantage their slow metabolic rate and long gut passage time partly compensate for. Wear patterns on the teeth suggest that hippo ancestors may have once had a lateral chewing motion that was gradually lost as the jaws became more specialized for fighting. The wide gape, the huge canines, the rigid bite: these are all features of an animal shaped as much by territorial aggression as by dietary needs.
When Hippos Raid Farms
The plant-based diet that dominates hippo feeding brings them into direct conflict with farmers across sub-Saharan Africa. Hippos do not limit themselves to wild grasses when cultivated crops are available along riverbanks. Around Lake Tana in Ethiopia, every single respondent in one survey reported crop damage as the main cause of human-hippo conflict, with over 90% calling the severity of damage high. Maize, teff, finger millet, and rice were all targeted.9PubMed Central. Human-hippo conflicts around Lake Tana Biosphere Reserve, Ethiopia: Vulnerability of hippopotamus in human-dominated landscape
In the Dhidhessa Wildlife Sanctuary region, a similar pattern emerged. About 63% of respondents identified crop damage as the primary source of conflict, while the rest pointed to physical threats to people or livestock losses. Maize was the most frequently raided crop, followed by sugarcane and sorghum. Most of the damage happened at night, during the rainy season, when hippos were already active and crops were at their most vulnerable seedling or early growth stages.10PLoS ONE. Human- common hippo (Hippopotamus amphibius)-conflict in the Dhidhessa Wildlife Sanctuary and its surrounding, Southwestern Ethiopia Farms closest to the river suffered the worst, which makes sense: hippos follow established paths from the water to feeding areas, and the nearest fields are the easiest targets.
This conflict is one of the biggest conservation challenges facing hippos. Farmers whose livelihoods depend on a maize harvest are understandably hostile toward a two-ton animal that can destroy an entire field in a single night. Retaliatory killing is common, and it puts pressure on hippo populations already declining from habitat loss. The irony is that hippos are only raiding crops because they are doing exactly what they have always done: walking inland from water at dusk and eating the most accessible grasses. The grasses just happen to have been planted by people now.
How Hippo Feeding Reshapes Rivers
The sheer volume of plant material a hippo population processes has consequences that extend far beyond the grasslands they graze. Hippos eat on land but spend most of each day in the water, where they defecate in large quantities. This creates a biological conveyor belt, moving carbon, nitrogen, and phosphorus from terrestrial grasslands into aquatic systems. In Kenya’s Mara River, researchers estimated that the local hippo population deposits roughly 36,200 kilograms of feces into the river each day (wet mass). That translates to daily inputs equivalent to about 670% of the coarse organic matter, 27% of the total nitrogen, and 29% of the total phosphorus entering the river from the upstream catchment.11Freshwater Biology. The hippopotamus conveyor belt: vectors of carbon and nutrients from terrestrial grasslands to aquatic systems in sub‐Saharan Africa
The nutrient transport goes beyond carbon and nitrogen. Hippos also move large amounts of silicon from the grasses they eat into the water, and silicon is a critical nutrient for diatoms, the microscopic algae that form the base of many freshwater food webs. One study estimated that hippos transport about 0.4 metric tons of silicon per day into the Mara River by eating silica-rich grass on land and excreting it in water, affecting up to 76% of the river’s total silicon flux.12PubMed Central. Hippos (Hippopotamus amphibius): The animal silicon pump Without hippos, the downstream lakes that depend on diatom productivity would receive far less of a nutrient that directly controls how much algae can grow.
But this nutrient loading is not always beneficial. In river pools where hippo density is high, the concentrated waste drives oxygen levels to zero between periods of water flow. These anoxic pools become chemical stews, exporting ammonia, hydrogen sulfide, and methane downstream.13Ecosystems. Alternative Biogeochemical States of River Pools Mediated by Hippo Use and Flow Variability When rain or a dam release flushes one of these pools, the sudden pulse of deoxygenated, toxic water can cause fish kills downstream. So hippos fertilize rivers and sometimes poison them, depending on density and flow conditions. Losing hippos from a river system does not simply remove a large animal; it fundamentally changes the chemistry and ecology of the water.
Feeding Hippos in Zoos
Captive hippos present a dietary puzzle that mirrors the wild picture in some ways and departs from it in others. In the wild, hippos eat relatively low-energy grass and walk considerable distances each night to get it. In a zoo, the walking is eliminated and the food is often more energy-dense than anything a wild hippo would encounter. The standard captive diet typically consists of hay and concentrated pellets, and the results are predictable: zoo hippos are prone to obesity. Digestion studies testing captive hippos on a hay-and-concentrate diet versus a hay-only diet confirmed that the species’ low metabolic rate makes them especially sensitive to calorie-rich foods.7PubMed. Digestion studies in captive Hippopotamidae: a group of large ungulates with an unusually low metabolic rate
Zoo nutritionists have increasingly moved toward high-fiber, low-energy diets that better approximate what hippos evolved to eat. Hay forms the bulk of the ration, with limited fresh produce and minimal grain-based concentrates. Some facilities add leafy greens or small amounts of fruit as enrichment, but the central goal is to avoid the metabolic mismatch that comes from feeding a slow-burning animal like a hippo as though it were a horse. Even in captivity, no reputable zoo feeds hippos meat, because their digestive system is fundamentally designed for plant fermentation. The occasional carnivory observed in the wild appears to be tolerated by the gut rather than optimized for it.
Why the “Vegetarian” Label Falls Short
The question of whether hippos are vegetarian turns on what you mean by the word. If vegetarian means “eats plants as the overwhelming majority of its diet,” then yes, hippos qualify. Grasses dominate their intake in every population that has been studied, across seasons and across their geographic range. But if vegetarian means “never eats animal tissue,” the answer is clearly no. Hippos scavenge meat regularly enough, and across enough of their range, that the behavior cannot be written off as abnormal.3Mammal Review. Carnivory in the common hippopotamus Hippopotamus amphibius: implications for the ecology and epidemiology of anthrax in African landscapes
Hippos are not unique in this. Many animals we casually label “herbivores” will eat animal matter when the opportunity arises. Deer have been photographed eating birds. Cattle will eat bones and even small animals. Large ungulates commonly gnaw on bones and antlers to supplement minerals.4Journal of Archaeological Science. Osteophagia and bone modifications by giraffe and other large ungulates The clean line between “herbivore” and “carnivore” is a teaching tool, not a law of nature. Most large animals fall somewhere on a spectrum, and hippos sit far toward the plant-eating end but not at the absolute edge of it.
What makes the hippo case especially interesting is the scale and social nature of the meat-eating. A deer chewing on a dead bird is a solitary, furtive act. Hippos feeding together on a carcass is a group event. That communal element, combined with the disease consequences and the sheer physical impressiveness of a hippo eating an impala, is why the phenomenon has drawn so much scientific attention over the past two decades. The herbivore label is not wrong for hippos. It is just incomplete.