Tiger snakes, Notechis scutatus, are highly venomous and equipped with a powerful neurotoxin. They are amongst the most venomous snakes on Earth. They can have a variety of markings depending where they are found in Australia and representing different sub species. The tiger snakes of Western Australia and those on Carnac Island, are black with yellow banding. Measuring up to 2.1 m in length, they are formidable and well equipped hunters. Tiger snakes normally feed on fast moving prey such as lizards, mice, and frogs, and use eyesight as well as movement and heat to detect their prey.
Tiger Snakes Can Hunt Without Sight
Carnac Island, a Class A National Nature Reserve off the coast of Western Australia, is home to Australian sea lions and abundant bird life and is unusual in that it is also host to a large population of blind tiger snakes. Researchers found that these tiger snakes were not blind at birth and so did not represent a sub species or genetically separate population. Observations showed that the tiger snakes were actually being blinded by the adult silver gulls, Larus novaehollandiae, on the island whilst defending their nests and chicks from attack by the snakes.
What baffled researchers was how the tiger snakes continued to thrive given vision is likely an important sense used in hunting their prey. There appeared no reduction in survival rate, rates of growth and even the acquisition and mating with females in blind tiger snakes, compared to sighted ones. Hunting prey presented a mystery until scientists found that the diet of blinded snakes was almost exclusively made up of sessile and easy to capture prey species such as the silver gull chicks.
It further seems that the loss of a major sensory system to the snakes has not impeded their success. Indeed blind tiger snakes appear to thrive. This led scientist to suggest that some species such as tiger snakes are “over designed” in that evolution has equipped them with more sensory systems than are actually required.
It is also likely that behavioural adaptations such as shifting prey species, and increasing use of other senses (scent and movement detection for example) are being utilized. The actual origin of the tiger snake population on Carnac Island remains unknown but it has provided a valuable natural experiment illustrating adaptation to harsh island environments by a species.
References
Aubret, Fabien ; Bonnet, Xavier ; Pearson, David ; Shine, Richard (2005) "How can blind tiger snakes (Notechis scutatus) forage successfully?" Australian Journal of Zoology.
Sarah Curran-Ragan - Science journalist and marine biologist, Sarah Curran Ragan, keeps you informed about our Oceans.
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