Hearing ability is a highly variable trait across the animal kingdom, tuned by the specific demands of an organism’s environment and survival strategies. The capacity to detect sound is a specialized adaptation reflecting how an animal hunts, communicates, or avoids danger. For many species, limited hearing is a biological trade-off, where energy is invested in a more valuable sense, such as superior sight, smell, or vibration detection. This results in animals having extremely narrow frequency ranges or requiring sounds to be remarkably loud before they can be perceived.
How Auditory Range is Measured
The scientific definition of poor hearing relies on two primary physical parameters: the frequency range and the auditory threshold. Frequency, measured in Hertz (Hz) or kilohertz (kHz), determines the pitch of a sound, representing the full spectrum of sounds an animal can detect. Poor hearing is often characterized by an extremely narrow frequency range, meaning the animal can only perceive a small slice of the available sound environment.
The auditory threshold defines the minimum loudness required for an animal to detect a sound, measured in decibels (dB). An animal with a high auditory threshold has poor sensitivity, requiring significantly louder sounds to register them than an animal with a low threshold. For example, some aquatic species may require a sound pressure level of over 100 dB just to hear at their most sensitive frequency. Researchers plot an animal’s sensitivity across its frequency range on an audiogram, which illustrates the limitations in both pitch and volume.
Evolutionary Reasons for Limited Hearing
The evolution of limited hearing often results from a sensory trade-off, where an animal’s existence does not require a complex auditory system. Animals that rely heavily on other senses, such as chemoreception (smell/taste) or mechanoreception (vibration), gain little survival advantage from sophisticated hearing. For instance, many burrowing animals prioritize detecting ground vibrations over airborne sound, making complex middle-ear structures energetically wasteful.
The ancestral inner ear structure, known as the basilar papilla in reptiles and amphibians, is often short and simple in species with limited hearing. This structure processes higher frequencies; thus, a small or rudimentary papilla physically limits the upper frequency an animal can perceive. Furthermore, many reptiles and amphibians possess only a single auditory ossicle (stapes) in their middle ear, compared to the three found in mammals. This simpler apparatus is less efficient at transferring airborne sound energy, resulting in a higher auditory threshold.
Specific Animals with the Worst Auditory Sensitivity
Species that depend on low-frequency vibration detection, rather than sound pressure, exhibit some of the most limited auditory sensitivity.
Fish
Many fish species are considered “hearing generalists” because they lack a specialized connection between the inner ear and the gas-filled swim bladder. These fish, which include flatfish and some sharks (elasmobranchs), are primarily sensitive to the particle motion (vibration) component of sound, not the pressure component. Their hearing is often limited to frequencies below 1,000 Hz, with minimum thresholds sometimes exceeding 120 dB re 1 µPa at their best frequency.
Reptiles
Among reptiles, the Tuatara and many species of turtles possess notably poor hearing due to their highly simplified auditory anatomy. The Tuatara, a lizard-like reptile, has an ancestral-type inner ear that is only capable of perceiving sound frequencies below 1,000 Hz. Turtles possess auditory thresholds that are at least 20 dB less sensitive than those of other reptiles. This means they require a sound to be substantially louder than what would be heard by a lizard or crocodile to register it.
Invertebrates
Invertebrates like cephalopods (octopus and squid) lack the specialized structures necessary for detecting sound pressure waves in the water. Instead, they rely on a gravity and acceleration-sensing organ called the statocyst to perceive low-frequency particle motion. This apparatus limits their “hearing” to the detection of vibrations in the extremely low-frequency range, often in the order of 10 Hz. This sensitivity allows them to detect close-range water displacement but not the higher-frequency sound pressure waves that travel over long distances.