30 August, 2024

Did you know Common Side-blotched Lizards have an alternate common name in the literature? There are a few papers from the 1960's and 70's that refer to Uta stansburiana as "Brown-shouldered Lizards". I've always liked that name because it often applies. The featured observation this "week" are all of the great observations of adults and juveniles on which the brown shoulder is apparent in Uta. Here are some things I've noticed about the brown shoulder of Uta.

—the brown shoulder is usually more apparent in juveniles than adults. The brown shoulder seems to fade with age and many adults lose the brown shoulder altogether it seems.

—the brown shoulder can be really subtle, as in here, here, or here.

—the presence/absence and characteristics of the brown shoulder can be individually variable in a single population with either a single enlarged dark spot above the forelimbs or as several brown spots. I should point out that to make the point of hyper-variablity in this trait I used observations by the same observer (@bonnienickel) on the same day and same general area.

—finally, the brown-shoulder does not appear everywhere in the range of Uta. Rather, it is much more common in the northewestern portion of the range of U. s. elegans. So, it can be readily observed in triangle created by Joshua Tree, San Diego, and Los Angeles, but is less common in Phoenix, Tucson, and Baja California.

—it seems that the brown shoulder is less common but does occur in U. s. stansburiana in Utah. In fact, I still haven't come up with a visual way to distinguish U. s. stansburiana from elegans.

—in U. s. stejnegeri the brown shoulder is a tiny dot at best. If it does show in New Mexico or Texas, the brown shoulder is very small and subtle. Interestingly, the brown shoulder seems to hold into adulthood better in this Eastern subspecies than in Western Side-blotched Lizards.

—the pattern in U. s. uniformis is so faded out that the brown shoulder is usually not readily apparent except as slightly darker spot over the shoulder.

—finally, the brown shoulder doesn't really show as readily in adults of U. s. nevadensis, but can be apparent in hatchlings or juveniles in particular. It is typically limited to a single dark shoulder spot.

—because there are so few observations on iNaturalist available, it is hard to say if this trait appears in other Uta. For instance, Uta squamata only has 15 observations, but no clear sign of a dark shoulder.

—despite the lack of clear evidence of the brown shoulder in other Uta, other Sceloporinae do show the trait. For example, I also see the brown shoulder in Sceloporus graciosus hatchlings such as here, but usually as double spots oriented vertically.

Overall, the individual and population variation in the characteristics and presence of the brown shoulder mean that it is probably not a useful trait for identification purposes. So, while the brown shoulder of Uta is not a good identification trait, they are an interesting aspect of the color and pattern of these animals that I wanted to share for your consideration. Something to look for next time you see a Side-blotched Lizard.

.

If you would like to see more posts like this on your dashboard, feel free to join The Uta Project. To see previous project posts like this, see here.
—Pete Zani

.

I gratefully acknowledge all of the authors of observations used in this post:
@kyle_eaton_photography
@ark234
@editwench
@naturephotosuze
@decoyhedgehog
@rreams
@erikatwell
@drcolbert2
@khitz
@dalemeister
@bonnienickel
@alexegreen
@spiderviking
@bkyardnature
@deanwalton
@wild-about-texas
@melissa_duron
@dan2465
@cjustus320
@rogerlatham
@jmaughn
@petermudde
@luxquine
@jdflores
@bhollingsworth
@bajapelagica

Posted on August 30, 2024 05:02 PM by petezani