Snakes Put in Soundproof Room To Find Out if They Can Hear Without Ears
Snakes may have no external ears but that doesn’t mean they are deaf. Research from Queensland, Australia, has shown that snakes are able to respond to both airborne and ground-based sound vibrations.
The researchers conducted 304 controlled experiments with 19 snakes from seven different species. The snakes were placed in a soundproof room and were subjected to controlled sounds at three different ranges of frequencies: 0 to 150 Hz; 150 to 300 Hz; and 150 to 300 Hz. For context, the human voice sits at a range of about 100 to 250 Hz.
The behavior of the snakes was observed in response to these three sounds, only the first of which produced ground vibrations. The other two were airborne only. This allowed the researchers to test for both tactile hearing—feeling vibrations through the ground—and airborne hearing through the inner ear. The results have been published in the journal PLOS One in February.
First author, Christina Zdenek of the University of Queensland, said in an article for The Conversation that, although there had been previous studies into the ability of snakes to respond to sounds within this frequency range, theirs was the first to investigate the responses of multiple species to sound in a space where they can move around freely. Previous experiments had involved partially anaesthetized animals and others that had been restricted to a steel mesh basket.
The study not only demonstrated that the snakes were able to respond to airborne sounds, but it also suggested a clear differentiation in responses between species. For example, the non-venomous woma python, endemic to Australia, significantly increased its movement in response to the sound, and raised its body towards it. By contrast, the death adders, taipans and brown snakes were more likely to move away from the sound, signaling an avoidant behavior.
Zdenek said that these differences were likely evolved responses to support the survival, reproduction and hunting strategies of the different species. Woma pythons are large, nocturnal snakes with few predators while taipan snakes are preyed on by raptors and actively pursue their prey.
In the experiment, the snakes were presented with sounds at a distance of 4 feet and an intensity of about 85 decibels, roughly the same as a loud human voice. Zdenek said that, while snakes probably hear a more muffled version of the world than us, it seems safe to say that they would be able to hear us when we shout over the garden wall, or when we scream.
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