Monday, June 4, 2012

Why do Western skinks have bright blue tails?

Youthful blue tail fades then turns dirty orange.

In my last post I mentioned seeing Western skinks (Plestiodon sketonianus) hanging out with Western fence lizards. I always thought skinks were shiny because they're moist, like salamanders, but, really, it's that their scales are so smooth and rounded that they reflect light like a piece of glass. When they're young their tails are a bright, screaming blue. As they age the blue fades and eventually their tails are a dull orange brown. When I first began to watch them I thought that blue tail, though really pretty, seemed like a terrible idea. It's awfully easy to find the youngsters as they hunt just by watching for that flash of blue. It's like a bright neon sign pointing the way to an otherwise secretive creature.

A breeding male with paler tail and orange on chin and face

When I asked Google why skinks have blue tails I found many websites promoting slightly different versions of the same story, which is that Western skinks have blue tails so that predators are attracted to the tail rather than the skink's body. Then, when the predator grabs the tail, the skink separates itself from the tail and runs off to be free, if quite a bit shorter. Each time I read the story I became more skeptical about it. For instance, why would only the young skink need that kind of protection? For that matter, why would any creature want to attract a predator to any part of it's body? Why not be like so many drably colored creatures that blend beautifully into their surroundings? I decided that this explanation of the blue skink tail was a very poor one and kept following links, hoping to find something more plausible.

Western skink lying in wait for breakfast

Several pages into my Google search I came across an article written in 1970 for a publication called Herpetologica. The authors shared my skepticism about what they called the decoy theory. Although their article was about a different species of skink, they proposed that the blue tail was a way of letting mature males know not to get territorial and aggressive toward the youngsters they crossed paths with during breeding time. The authors conducted a not entirely conclusive study to support their theory. Their explanation and theory seem a bit more convincing but I think that, for now, blue tail might just be one of those lovely mysteries that must remain unsolved. For now, anyway.

Another day, another young skink hunting.
References:

•Kaweah Oaks
•Function of the Blue Tail-Coloration of the Five-Lined Skink (Eumeces fasciatus)Author(s): Donald R. Clark, Jr. and Russell J. HallReviewed work(s):Source: Herpetologica, Vol. 26, No. 2 (Jun., 1970), pp. 271-274. Published by: Herpetologists' LeagueStable

4 comments:

  1. Your posts are so much fun to read! I like the skinks (love that name) slinking around the drawings. I especially like the last one! Very good work!

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  2. Thank you Katherine. Skinks Slinking sounds like a good name for a rock band.

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  3. "Dirty orange?" And you're an artist, no less. Why not burnt umber, copper, tawny brown or salmon? Can you tell I grew up with sisters who I was told had "sandy" hair, not "dirty blonde?" ;)

    Very nice drawings. It's not just your western skinks that have blue tails, lots of American skinks have blue tails, especially while young. One of our local species even has a bright pink tail that turns more coppery-orange as an adulthood.

    You may notice the blue tails appears black in low light situations, where skinks spend most of their lives skulking about in search of insects. So, the blue color is not a liability in the shadows, only when they must move out of cover and across an exposed gap. I have seen a few skinks that appeared to be basking a bit, but it was very brief, a minute or so and not nearly as much as far as I have seen other lizards bask.

    I have to go with the consensus, after autotomy of the tail (breaking away at its brittle connection point), the bright blue tail trashing on the ground creates a distraction that may allow the skink a moment, all it usually needs to escape back into the leaf litter, under tree bark, or beneath a nearby stone.

    I have watched, more than once, as a fascinated cat played with a skink's still twitching tail for a minute or more - with no visible sign of the rest of the lizard.

    But, I will throw out yet another option to consider. I have heard the following story many times, about dogs or cats known by their owners to routinely catch and eat lizards (our current Labrador catches and "plays" with geckos). In each instance, a pet barfed up a blue-tail, or a lizard with a blue tail, or a lizard AND a blue tail. Could it be that skinks are noxious? I have never heard of that with a reptile. But, why don't the pet-owners find barfed up anoles and geckos, too? Hmmm.

    There is a well-known rule of thumb: don't attempt to capture or handle brightly colored wildlife unless you know what it is and how to handle it. Many, probably most, wild animals are camouflaged - their colors match their habitat. Some have cryptic patterns, to break up their outline, like tigers and zebras.

    Those that don't need to hide are often capable fairly effective self-defense. Some good examples include:

    red, yellow and black of coral snakes,
    bold black and white stripes (or spots) on skunks,
    black and yellow on hornets,
    red and black "velvet ant" (really a wingless wasp).

    Insects in particular often display bright colors to advertise that they are noxious, if eaten: monarch butterflies and their caterpillars are a famous example. Naive animals may try one, but they'll remember the experience and avoid testing similar insects in the future.

    I still suspect, with skinks, that the color is all about distraction after the initial attack. But, keep an open mind, and continue to observe, learn, and draw....

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  4. I almost missed these beautiful skinks, Debbie. Gorgeous blue. I spend quite a lot of time just sitting watching the little bright green lizards here.

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