Researchers studied 19 snakes across five genera; find different snakes react differently to what they hear
Until now, snakes were believed to be able to hear sound vibrations only through the ground. New research has debunked this, showing the reptiles also hear airborne sound vibrations and react to this. The observations may help humans deter snakes and avoid snakebites.
A recent study published in journal PLOS One, Sound garden: How snakes respond to airborne and groundborne sounds, observed 19 snakes across five genera — Acanthophis (death adders), Aspidites (Woma Pythons), Hoplocephalus, Oxyuranus (taipans) and Pseudonaja (brown snakes).
The researchers conducted 304 controlled experiments in a soundproof room and at a consistent temperature for the study. They found that hearing still plays an important role in snakes’ sensory repertoire.
The researchers used three sets of sound frequencies: 1-150 hz, 150-300 hz and 300-450 hz. For comparison, the human voice range is about 100-250 hz. Silence was used as the control, one sound produced ground vibrations and two others airborne.
Though external ears are not visible among snakes, they are not deaf, the scientists found. The reptiles hear mainly from sound-induced head vibrations received by their quadrate and columella bones attached to the jawbone, the paper said.
Oxyuranus species demonstrated all behaviours apart from periscoping, while Acanthophis and Hoplocephalus showed “freeze and cautious exploration responses,” respectively. Many snakes raise their heads and remain in their position, which is called periscoping.
Acanthophis snakes are ambush predators and exhibited low activity levels and freeze response associated with potential danger to escape detection, the report said. The snakes moved away from the speaker but showed more sensitivity to ground vibrations.
This may be because their lower jaw profiles are naturally flattened towards the ground, enabling higher sensitivity to ground vibrations.
The researchers also included genus Pseudonaja as it is known for frequent conflicts with humans and the presence of overt defensive behaviours. The snakes showed a wide dichotomous response to sound where they either remained still or moved a large distance.
Meanwhile, Hognose Snakes (Heterodon platirhinos) showed a known response of inverted bodies, mouth open and motionless to predators such as humans and owls. On similar lines, 21 species of rattlesnakes reacted to scents of snake-consuming snakes by depicting the same behaviour.
On the contrary, 20 Peruvian snake species revealed behaviour responses to predator simulations against genetic-related behaviour.
The scientists observed Pseudonaja responding to sound by demonstrating jaw drops and hisses, while Aspidites showed behaviours like periscoping and head jerking.
The researchers found Acanthophis, an ambush predator genus, showing the least tongue flicks and overall movement about inheritable behaviour that is pre-programmed stimuli in a genus. It also oriented itself based on sound.
Aspidites tended to move towards the sound, contrary to other genera such as Acanthophis, Oxyuranus and Pseudanaja, who moved away from the sound source, indicating avoidance behaviour.
In response regarding frequencies, genus Oxyuranus behaved significantly cautious and defensively, indicating a fear response towards that particular sound between frequencies 10 hz and 100-kilo hz.
Compared with frequencies of 150-300 hz, Aspidites froze and periscoped less, while Oxyuranus increased higher freezing behaviour with head jerks and less hissing to explore cautiously. Pseudonaja also showed less hissing and more freezing, periscoping and head jerking.
Their data noted that Australian snakes respond to both airborne and groundborne sounds between the frequency range of 0-450 hz and their behaviour differs significantly depending on the genus.
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