Hippos communicate through a combination of loud vocalizations, visual displays, and scent marking, but their most remarkable trick is broadcasting sound through air and water at the same time. Their calls can travel over a kilometer, and they can distinguish between the voices of familiar pod members and strangers.
The Wheeze-Honk and Other Calls
The signature hippo vocalization is the wheeze-honk, a tonal call that often builds into a chorus of overlapping voices across a pod. If you’ve ever heard hippos at a zoo or in wildlife footage, this is the thunderous, almost laughing sound that carries across rivers and lakes. These choruses can spread from one territory to the next for many kilometers, making them one of the loudest calls of any African mammal. Even a single hippo’s call is clearly audible from more than half a mile away.
Beyond the wheeze-honk, hippos produce a range of other sounds including screams, grunts, and bellows. Each serves a different social function, from asserting dominance to signaling distress. The calls are rich enough in individual detail that hippos can actually tell each other apart by voice alone.
Broadcasting in Air and Water Simultaneously
Hippos spend most of their time in a characteristic posture: eyes and nostrils poking above the waterline while the mouth and throat remain submerged. This amphibious position turns out to be crucial for communication. When a hippo vocalizes in this posture, the sound transmits into both air and water at the same time. Other hippos nearby hear the airborne component through their ears while also detecting the underwater component, likely through vibrations conducted through the skull and jaw.
Researchers confirmed this dual-channel ability by playing recorded hippo screams underwater at volumes that were completely inaudible in the air above. Hippos with their heads in the typical amphibious position still responded to these submerged sounds, proving they can hear in both media simultaneously. This is a rare adaptation in mammals. It means a single call from one hippo can reach neighbors on the riverbank and others submerged dozens of meters away, all at once.
Whether this dual broadcast evolved deliberately or is simply a physical consequence of vocalizing with a partially submerged body remains an open question. It may be that the airborne call is the “intended” signal and the underwater portion is a byproduct, or vice versa. Either way, hippos clearly use both channels.
Recognizing Friends and Strangers by Voice
A 2022 study at the Maputo Special Reserve in Mozambique revealed that hippos don’t just hear calls. They process who is calling. Researchers played back recorded vocalizations from three categories: hippos living in the same pod, hippos from a neighboring territory, and hippos from a distant, unfamiliar group. The responses were strikingly different depending on the source.
When hippos heard calls from their own group, they responded calmly. Calls from neighboring groups prompted moderate alertness. But when the recorded call came from a completely unfamiliar hippo, the listeners reacted with visible agitation and, in many cases, a dramatic spray of dung. This dung-spraying response had been observed before as a territorial marking behavior, but the study was the first to show that an unfamiliar voice alone could trigger it. In other words, hippos maintain a mental map of who belongs in their social landscape and treat unknown voices as potential threats.
Dung Spraying as a Signal
The dung spray itself is a form of chemical communication. Hippos defecate while rapidly flicking their flat, paddle-like tails, creating a wide fan of feces that coats surrounding vegetation, rocks, and water. This marks territory with scent and serves as a visual display of presence. Males use it most aggressively along territorial boundaries, but females and younger hippos do it too.
The combination of vocal recognition and dung response creates a layered communication system. A hippo hears an unfamiliar call, identifies it as a stranger, and responds with a scent mark that says “this area is occupied.” The chemical signal persists long after the sound fades, giving it a different temporal function than vocalizations. Calls are immediate and conversational. Dung marks are lasting signposts.
Visual and Physical Displays
Hippos also communicate through body language, particularly during conflicts over dominance and territory. The most recognizable visual signal is the gape, where a hippo opens its jaws as wide as possible to display its massive canine teeth. This is a direct threat. Field observations in Tanzania’s Retima Hippo Pool found that gaping and jaw-to-jaw confrontations were the most common aggressive behaviors, especially during morning hours when hippos are packed closely together in the water.
Aggression escalates through a predictable sequence: gaping leads to jaw clashing, which can progress to lunging and biting. Submissive hippos signal surrender through a distinct set of behaviors, including opening the mouth passively (without the tension of a threat gape), turning away, lying flat in the water, or simply leaving the area. These signals help resolve conflicts without every encounter turning into a potentially fatal fight, which matters for an animal whose lower canines can grow over a foot long.
How It All Works Together
What makes hippo communication unusual among large mammals is how many channels operate at once. A dominant male patrolling his stretch of river is simultaneously broadcasting wheeze-honks that travel through air and water, reading the vocal signatures of hippos calling from adjacent territories, scanning for visual threat displays from rivals, and layering the riverbank with chemical markers. Each channel carries different information at different ranges and timescales.
Vocalizations handle long-range identification and group coordination. Visual displays manage close-range social negotiations. Chemical signals provide persistent territorial boundaries. And the amphibious sound transmission ensures that no hippo in the area, whether lounging on a sandbar or fully submerged, misses the message. For an animal that can seem sluggish on the surface, the communication system running underneath is surprisingly sophisticated.