Telling tails

Juvenile Gilbert’s skinks

Skinks are one of the largest group of lizards, with over 3000 species. They look similar to true lizards, but often they have a more snake like appearance. Many species have long snakelike bodies with no pronounced necks, and they often have pretty small limbs. Some species have barely any legs at all (like for example the Florida sand skink).

Like many other lizards, most skinks have the ability to amputate their tail at will as a way to avoid being eaten by predators. This ability is called autotomy. After a tail has been amputated, they can regrow the tail, but not perfectly. This self amputation is also very demanding on the skinks body, so if it can, it will return later to eat the tail.

Many species of skinks have very colourful tails (often bright blue) as adolescents, but as they grow older they change color to a more uniform green or brown. One example is the Gilbert’s skink, native to California. Skinks of this species have tails that can be not only blue, but also bright pink or purple. So why do these lizards sport these colours, and why do they change color as they grow older? According to this research study published in Behavioural Ecology in 2006, the color of the lizards is connected to how active they are. When the lizards are young, they are more active, so the colourful tails acts as a diversion for any predator that wants to attack them. If something tries to eat them, they aim for the tail instead of the vulnerable body, allowing the skink to amputate the tail and escape.

So what lies behind the choice of colour for these tail displays? According to this study published in the Journal of Zoology last year, the color of the tails is adapted to the colour vision of the main predator in the area. For example, snakes can detect UV light, but weasels can’t.

So, doesn’t it seem like a bit of a strange strategy to advertise yourself as a living target like this? That’s what many biologists thought too, so this “risky decoy” hypothesis was dismissed for a long time, but more and more studies seem to support it today. 

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