The Uta Project's Journal

Today is at or around the solstice, so I figured it's time to do another observation of the week. In the month since the last observation summary (May 22), there have been nearly 1000 observations of Uta added to this site (914 according to iNat).

I just recently go caught up on identifications and have noticed that observations include many many many many hatchlings (by @nathanfrench, @kingmchris, @fran170, @lonnyholmes). In hand, or with a identifiable scale object in the picture, hatchlings can be recognized by size this time of year. Uta hatch at about 22-24 mm body length (from tip of nose to cloaca is called the snout-to-vent length...or just SVL). Beyond that there is a slight color difference between the head and body of Uta that is most pronounced at hatching, such as this observation (by @lonnyholmes). That is, hatchling Uta have this light milk chocolate color that differs from the gray of the body that is most vivid right after hatching. A third way to tell hatchlings without scale is their body:head proportions are just...off (such as here by @nathanfrench). Developmentally, most animals develop the head, eyes, brain early in development and may leave the rest of the body for later. In Uta hatchlings are born with a yolk plug of leftover yolk from the egg that sustains them the first three days or so before the gastro-intestinal tract is ready for them to feed. Hence, the head of hatchlings is much larger than should be for a body that size....just...off. It's a gestalt thing for sure.

In addition to early-season hatchlings entering the observation pool in the south, there continue to be numerous observations of copulations by @ishteva @chrisdellith) and even the occasional sighting of what is probably nesting (by @juan18346).

Where I've done work in the northern portions of their geographic distribution, females stop laying eggs around July 15 and I suspect it's the cessation on lengthening days that is the cue. It just takes them a while to get the message and finish up whatever part of the reproductive cycle they're in. Females with enlarged or yolked follicles right now (such as by @johnmartin @bobc) will finish that clutch, but it will take they 2-3 weeks to do so meaning the breeding season doesn't really end until mid-July. Afterwards females will all have this kind of spent look (by @fran170).

Despite all of the above really nice examples of various aspects of the breeding season, this week's observation of the week is this observation by @ishteva. The observation is of a female eating what looks to be a very large grasshopper with the abdomen still protruding out of her mouth. However, what makes the observation especially interesting is the male copulating with the female at the same time. Efficient.

As always, thank you to everyone who has observed a Side-blotched Lizards in the past few weeks. Your contributions are greatly appreciated.
—Pete Zani

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Since the last observation of the week on May 5, there have been 683 observations added to The Uta Project. There were many notable observations including:

—this pretty female Uta stanburiana stejnegeri by @georgezimmer.

—this nice male-female pair by @zachary488. I've seen males do laps between attending and courting females. I've also see a single male just hang out with a single female for a while.

—this very gravid female by @scubabruin.

—this male whose colors show even more sitting in the shade like this by @daniel0910.

—even the northern side-blotched lizards have started laying eggs, like this female by @alexsowers6.

—there are continued mating attempts being observed, such as this one or this one by @raphaela_fb and @dustdevil.

—this example or this example by @robtea and @cellomaniac of interspecific basking between a Fence Lizard and Side-blotched Lizard. These two species are surprisingly tolerant of one another.

Despite all of these observations, I am choosing as observation of the week this observation of a hatchling Uta by @lagardilla. This is amongst the very first hatchlings of the year and will not be the last. These can be hard to ID, so it's nice to note the even dark-light-dark stripes behind the eye. These stripes can be one of the only ways to tell these since their blotch often doesn't show until they sexually mature at age 10 months. Right now, the southern latitude/low elevation females are probably working on their third clutches, mid-latitudes/elevations on their 2nd clutches, and the northern latitude/higher elevation populations working on their 1st clutches still. The breeding season will usually continue into July, rain permitting. However, the monsoons can induce late-season clutches in some locations.

As always, thank you to everyone who has observed a Side-blotched Lizards in the past few weeks. Your contributions are greatly appreciated.
—Pete Zani

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20 June, 2024: efficient female

22 May, 2024: first hatchling

5 May, 2024: copulations

14 April, 2024: nesting female

23 March, 2024: early-season copulations

10 March, 2024: colorful male

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It's been three weeks since the last review of the observed Uta, so I thought it a good time to consider the status of spring. During the past three weeks there were over 1300 observations of Uta, all of which were Uta stansburiana. These observations spanned the range of this species, but with a definite focus in the range of U.s.elegans in Southern California.

Males are in full breeding colors in all corners of Uta's distribution. Examples of colorful males include:

—this male by @erayner

—this male by @jmaughn

—this male by @tmessick

—this male by @sunbelt

There continue to be good observations of gravid females as the spring breeding season progresses. Many of which come from Southern California and some look about to pop which is good indicator of how close they are to laying their eggs. Examples of gravid females include:

—this female by @plascenciaivett

—this female by @jonrobson

—this female by @joseph92

—this female by @cjustus320

For observation of the week I have chose a pair of observations of Uta in the act of mating by @knight17 and @roadddog. Mating in Uta can be quick, lasting no more than a minute or so. Courtship involves circling behavior and lots of headbob displays by both male and female. The female will also use body postures like a raise as part of the courtship. Mating only occurs once females have ovulated and so will often reject courtship displays before or after that time in her cycle, which takes about 28 days early in the spring or as few as 16 days in the heat of summer. Once mating occurs, it can still take several weeks for the female to yolk and then shell the egg before laying, so mating is an important time point in the breeding season. Mating will continue from now until mid-to-late June with last clutches usually laid by mid-July most places.

As always, thank you to everyone who has observed a Side-blotched Lizards in the past few weeks. Your contributions are greatly appreciated.
—Pete Zani

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I have updated the range map for Uta stansburiana and the five continental subspecies based on some recent work in the field the past couple years. The map can be found as this observation. Some areas of these distributions are still poorly understood, such as much of the non-Baja distribution in Mexico (especially at the subspecific level) and where U.s.elegans, U.s.nevadensis, and U.s.stansburiana come together in the Great Basin Desert. Let me know if you have any questions.
—Pete Zani

On the iNaturalist forum, I recently came across an older 'feature request' to allow the iNat Computer Vision to suggest annotations, such as for males or females. As part of that discussion it was pointed out that the model would need observations already annotated for training purposes. Hence, in the past few months I have been making a concerted effort to add to the 'sex' annotation for Uta to make that possible when/if that happens (feel free to vote on this feature request if you like). However, it occurs to me that you, dear reader, might be interested in learning how to identify the sexes of Uta, some of which is knowledge applicable to other lizards as well.

Tail Bulge

The most reliable way to distinguish males from females is via morphology. Squamate reptiles (lizards and snakes) have what are called 'hemipenes,' which are paired penile organs that are stored in the base of the tail for use during copulation. Males fill one of these with blood during copulation, which causes the hemipene (left or right) be everted and inserted into the female for sperm transfer (see here for example). The presence of hemipenes in males, but not females, means the shape of the base of the tail is different between the sexes.

In males, the base of the tail is slightly wider where the hemipenes sit before quickly tapering to a more modest width that then gradually tapers the rest of the length of the tail. It's this rapid change in width just behind the hind legs that is diagnostic. Here's a nice close up of this feature as well example observations where this bulge should be readily apparent for each of the primary subspecies of Uta stansburiana (listed alphabetically): U.s.elegans, U.s.nevadensis, U.s.stansburiana, U.s.stejnegeri, U.s.uniformis .

In females, the base of the tail is slightly narrower, but more importantly, it has an even taper along the length of the tail. Here are example observations where this bulge should be readily apparent for each of the primary subspecies of Uta stansburiana (listed alphabetically): U.s.elegans, U.s.nevadensis, U.s.stansburiana, U.s.stejnegeri, U.s.uniformis .

While the bulge in the base of the tail works on many lizards species, not just Uta, the bulge can be very subtle in some taxa like skinks or gecko. There is a second morphological feature, enlarged post-anal scales, which allows the sexes to be distinguished. However, this trait is limited to Family Phrynosomatidae.

Enlarged Post-Anal Scales

On the under side of the tail just behind the cloaca (the term for the single opening for metabolic and nitrogenous waste) are two scales that are noticeably larger than the surrounding scales in males. In females, all the scales behind the cloaca are the same size. Interestingly, this feature is diagnosable at hatching meaning phrynosomatids of any age can be sexed. However, in hatchlings this feature is so tiny that usually a magnifying hand lens is necessary to see it. Here are examples of the enlarged post-anal scales in males (see picture #7) and females (see pictures #4 & 5).

The problem with post-anal scales is one needs a ventral view of the lizard. However, there are situations where post-anal scalation can be all one needs for identifying a lizard's sex. For example, this observation of a dead lizard lying on its back where one of the two enlarged post-anal scales is barely distinguishable.

Color/Pattern

Another feature that is often a useful indicator of anatomical sex is a lizard's color or pattern. However, this is more limited because a) breeding colors can be quite muted out of the breeding season and b) some subspecies, namely U.s.uniformis, are very similar in color and pattern. In fact, this is why they were named uniformis...the sexes are uniform. For the remaining subspecies of Uta stansburiana, there are differences described below and organized by subspecies.

Three of these subspecies (U.s.elegans, U.s.stansburiana, U.s.stejnegeri) are all similar in that males have blue flecks on the back (dorsum) and atop the tail. These flecks are usually composed of small groupings of 3-5 blue scales. Even when the blue is faint, these flecks are light colored on a dark ground color as in this observation. In some populations, such as in Grand Canyon, the blue tail can be a vibrant or electric blue, especially when agitated during courtship or stressed by handling. Females never have the blue as in males. Thus, the blue in undisturbed males can be quite muted, but still present, as in this observation. Check out the difference between undisturbed (picture #4) and handled (picture #5) blue color in this male (yes, that's the same animal).

The only subspecies really different (other than U.s.uniformis) is U.s.nevadensis where the blue on the dorsum is still present, but the tail is instead vibrant orange. Again, the blue becomes more vibrant during interactions with other lizards and during handling. In U.s.nevadensis, males more consistently have orange coloration along their flanks. One thing to note, as one approaches the southern limits for this subspecies in Nevada and California the orange tail and flanks can be much more difficult to distinguish, such as this male from near Hawthorne, NV.

While the pattern can be variable within and between the subspecies as mention above, the blue flecks are fairly consistent. Females on the other hand lack these blue flecks even in their most colorful. So it's really the presence of color that suggests a male, but the absence of much color, other than dark and light flecks on a gray/brown ground color, is more consistent with females. This is true regardless of the chevroned, striped, or mixed morphs present in females.

So there you have it. Three ways to recognize males from females. Keep in mind that Uta are highly variable in color and pattern, which is why I list it third and tried to focus on those hard morphological traits like tail shape that help me in identification of the anatomical sexes. Hopefully these notes help you as well.
—Pete Zani

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It has been a couple weeks, so I thought I would summarize the observations of Uta over the past few weeks. Since the start of April, there have been 643 observations of Side-blotched Lizards. As expected as spring develops, there continue to be a number of observations of females that appear to be gravid. While exact stage of gravidity is nearly impossible to tell visually (I rely on physical palpation to score gravidity), the expansion of the lower abdomen as follicles develop give females a characteristic bulge just in front of the hind limbs. Once females oviposit their abdomens are not nearly as distended, such as this or this female (by @todd-black and @tsirtalis, respectively). However, size is an important determinant of when females lay eggs for the first time each spring, so while the presence of the bulge is indicative of gravidity, the absence of the bulge cannot be interpreted without information on the body size of the female.

Females with the telltale bulge ranged from southern California, Texas/Mexico, Nevada, Utah, and Arizona (submitted by @zeevng, @joseph1008, @cesarponce17, @skylermckinnon, @chrisjensen1, and @nolinad, respectively). As of right now, these observations are limited to the more southern populations/subspecies (U.s.elegans and U.s.stejnegeri), but will expand northward as the spring continues. While copulations began back in late March, as observed by @naturephotosuze, it is this observation (by @festuca59) of a female that appears to be nesting that I have selected for observation of the week.

Like most lizards, female Side-blotched Lizards excavate their own burrows for egg laying and this particular female looks both gravid and like she's burrowing. I did a lab experiment years ago to see how deep females would dig given soil of unlimited depth and noted that they went about three body lengths down before laying eggs...so about 6" (15 cm). Burrow construction can take several days and oviposition often happens late in the heat of a nice sunny day. However, it can be really difficult to spot female burrowing because they often start the burrow next to a rock or other cover object, but they are usually out in the open and not under bushes. This behavior will continue as females oviposit at which time we should start seeing more females with the post-reproductive skinny look before they produce a second, third, and even fourth clutch of eggs. A study years ago near Las Vegas estimated that females there had enough time to lay perhaps seven (7!) clutches of eggs and in Oregon I have observed females producing at least four clutches. The breeding season is long and productive in good years and with all the recent rains, this appears to be a good year for many populations of Uta.

—Pete Zani

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In the past two weeks there were nearly 500 observations of Uta. Most of those (~300) were from southern California, which is continuing to give insight into the timing of reproduction in this the Western Side-blotched Lizard (Uta stansburiana elegans in particular). But other sub-species are starting to show up such as Nevada Side-blotched Lizards (U.s.nevadensis) and Eastern Side-blotched Lizards (U.s.stejnegeri) and Plateau Side-blotched Lizards (U.s.uniformis).

Good candidates for lizard of the week were these two or three colorful males (by @somebees, @vlmanning, @naturaltwenty, @bill-blauvelt, and @tmills), or this observation (by @zeevng) of what appears to be a colorful male and two females under the same cover object, but instead I went with this copulating pair (by @naturephotosuze)....the first observation of the year of mating Side-blotched Lizards. Hopefully the first of many. This observation, or somewhere around it, were the 50,000th Uta added to iNaturalist, which is another reason to celebrate it.

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As part of the The Uta project, each week I will summarize the observations from that past week and select an observation to highlight as observation of the week. This is the inaugural such post.

During the first full week of March, 2024, there were 211 observations of Uta added to iNaturalist that achieved research grade. Of these, 140 observations were made during this week. All 140 of these were of Uta stansburiana and came from three subspecies. Most observations were of Uta stansburiana elegans with a few from U. s. stejnegeri and U. s. uniformis. This abundance of the Western Side-bliotched Lizard subspecies is not a surprise as their range encompasses nearly all of California, western Arizona, and southern Nevada where urban centers of Los Angeles, San Diego, Phoenix, Tucson, and Las Vegas help inflate the number of observations for this species. One thing I'm noticing is that males are starting to get their more intense spring breeding coloration. For example, here, here and here are nicely colored males observed this week (shared by @acleverpearl, @laradrizd, and @bill-blauvelt, respectively). This involves more intense colors such as orange on the throat that males use for communicating with other lizards. Meanwhile, females are starting to show the characteristic morphology associated with being gravid. For example, here, here, and here are females (shared by @debaraj, @quandary, and @sphilbin, respectively) I would predict are with enlarged follicles of their first reproductive event of the year. The cycle in these lizards takes about 28 days this time of year and progresses from through follicle enlargement to yolking and eventual shelling prior to egg laying. The subtle curvature of the abdomen just in front of the hind legs as well as the height of the body (see this observation by @sphilbin), which expands as the follicles develop is what I use to gauge their stage in the cycle, but physical palpation is a much better way to assess this as each phase feels slightly different. Mating and fertilization usually takes place sometime during the late enlargement or yolking phase, but I have not yet see any observations of mating yet.

Rather, this week's observation of the week is of this colorful male shared by @little_swift. The male is in full breeding colors with the intense blue tail and dorsal color characteristic of this subspecies. What's more, it shows off one of the regional color variants of this species with the orange eyeshadow. The orange over the eye like this really only occurs in a region between about Joshua Tree National Park and San Diego. Not every lizard shows this look and I estimate it only occurs in maybe 5-10% of the population, but it sure is a pretty look for this species. Another reason I selected this observation for highlighting this week is the male is doing a nice display that includes gular extension in which the under side of the throat is extended and enlarged. Males will combine this with head bobs as part of their communication with other Side-blotched Lizards.

I would like to thank everyone who shared observations this past week; keep it up. If you would like to receive future notifications from this project, feel free to become a member of The Uta project.

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As part of the The Uta project, each week I will summarize the observations from that past week and select an observation to highlight as observation of the week.

2024

20 June, 2024: efficient female

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