Hippos are remarkably vocal creatures with a complex array of sounds, though they do not produce a typical “roar” like a lion. Their diverse vocalizations serve various purposes. This article explores the sounds hippos make, the reasons for their vocalizations, and the unique biological mechanisms enabling their sound production and transmission.
The Diverse Sounds of Hippos
Hippos produce a wide variety of distinct sounds for communication. These vocalizations include grunts, growls, moans, honks, and bellows. Characteristic sounds also include “wheezy breathing sounds,” “snorts,” and “chuffing.” The “wheeze honk” is a particularly well-known vocalization, sometimes compared to a growling laugh.
Beyond airborne sounds, hippos also produce calls underwater, including clicks, tonal whines, and pulsed croaks. Some sounds can be very loud, reaching up to 115 decibels, comparable to a rock concert. These powerful calls can be heard from over a mile away, carrying significant distances through their aquatic environment.
Why Hippos Vocalize
Hippo vocalizations serve various purposes within their social structures. They use sounds for general communication among individuals in their groups, often called “bloats.” Vocalizations also establish and defend territory, warning potential rivals. Male hippos use specific calls to attract mates during courtship displays.
Sounds also maintain social cohesion and coordinate group movements. Hippos identify each other through their voices, distinguishing between members of their own group, neighboring groups, and strangers. Their responses vary with familiarity; familiar calls elicit subdued reactions, while unfamiliar calls provoke stronger, more aggressive responses. Specific sounds convey different intentions: deep grunts signal a warning, a rapid series of honks indicates aggression, tonal whines are associated with submissive behavior, and croaks are common during interactions between younger hippos.
Remarkable Sound Production and Transmission
Hippos possess unique biological adaptations for producing and transmitting diverse vocalizations in their semi-aquatic environment. They vocalize simultaneously both in the air and underwater. Above the surface, sounds emerge from their nostrils. For underwater communication, vibrations travel through fatty tissues in their necks and jawbones.
Their vocal cords generate sound. The hippo’s larynx is large and rotated 90 degrees to direct air into an expandable sac. This specialized anatomy, along with fat surrounding their vocal cords and neck having a density similar to water, facilitates efficient sound transmission into the aquatic medium. This enables them to produce infrasound, low-frequency sounds inaudible to humans, which travel long distances underwater.
To listen effectively underwater, hippos close their external ears to prevent water ingress. They perceive underwater sounds through their jaws, which are directly connected to their middle ears. This unique bone conduction allows sound vibrations to bypass the outer ear, enabling them to hear submerged communications. Approximately 80% of hippo communication is believed to occur underwater.