Species:

Plestiodon skiltonianus

Western Skink

Subspecies I've seen:
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Coronado Skink
P. s. interparietalis
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Skilton's Skink
P. s. skiltonianus
Subspecies:

Plestiodon skiltonianus interparietalis

Coronado Skink

Parque Nacional Constitución de 1857, Baja California, Mexico
Coronado Skink (Plestiodon skiltonianus interparietalis)
Of the various skink species with bright blue tails as youngsters, this is the first adult I've seen that still has a blue tail, but only on the very tip. Maybe I just need to get out more?
Parque Nacional Sierra de San Pedro Mártir, Baja California, Mexico
Coronado Skink (Plestiodon skiltonianus interparietalis)
Other than the plentiful Southern Sagebrush Lizards, this was the only herp I photographed on a cool, dry day in the Sierra de San Pedro Mártir.
Subspecies:

Plestiodon skiltonianus skiltonianus

Skilton's Skink

Andrew Molera State Park, Monterey County, California
Skilton
Like whiptails, these lizards are hard to photograph because they're very skittish and they rarely stop moving.
Sheep Dung Estates, Yorkville, Mendocino County, California
Skilton
Young western skinks and some related species have amazingly bright blue tails. The general consensus is that this attracts the attention of predators towards the disposable tail and away from the significantly less disposable head and body. But some herpetologists wonder whether making yourself so conspicuous can really be a good thing predation-wise, so perhaps there's another explanation for the color.
Del Monte Forest, Pebble Beach, Monterey County, California
Skilton
This skink has lost the last inch or so of its tail. It was slithering around in the leaf litter doing its skinky best to avoid having its picture taken. I caught it and calmed it down with gentle strokes before setting it on this log, where it remained for several minutes.

Just to the right of its back left foot you can see one coil of a slender salamander that's snuggled in a small hole in this log.

Garland Ranch Regional Park, Monterey County, California
Skilton
Here's another young tyke with a brilliant blue tail. This one was under a rock on a fairly chilly February day. If you look closely you can see that it has little beads of moisture on its body.
Robert Louis Stevenson State Park, Napa County, California
Skilton
Yet another youngster with a tail of blue.
Fort Ord Public Lands, Monterey County, California
Skilton
This one's a little older, and has developed some red under the chin while not yet completely losing the pretty blue tail.
Coy Flat, Tulare County, California
Skilton
This skink and one other (perhaps its mate) were hanging out on and near the trunk of a redwood tree near a clearing. For a usually skittish species, this was a remarkably calm individual, choosing to frequently pause in near-plain sight.
Fort Ord Public Lands, Monterey County, California
Skilton
The fading blue tail indicates that this skink is transitioning into adulthood.
Lake Sonoma Recreation Area, Sonoma County, California
Skilton
My first lizard of 2010 was basking on a board on a cool winter day.
Contra Costa County, California
Skilton
This skink was found in an area that could potentially have either Plestiodon skiltonianus or Plestiodon gilberti. Some populations are easy to identify; for instance, some but not all Plestiodon gilberti have pink tails as youngsters, whereas all Plestiodon skiltonianus have blue tails as youngsters. My friend Jackson Shedd has published a paper about the confusing similarities and differences of these two species. He helped me by identifying this adult male skink as probably P. skiltonianus, based on where it was found and some subtle appearance characteristics. Thanks Jackson!