Dry Dry Again on Desert Tortoise
Desert Tortoise (Gopherus agassizii)
Main sources: Stebbins, Robert, 1985, A Field Guide to Western Reptiles and Amphibians, Houghton Mifflin; Behler, John & Wayne King, 1979, The Audubon Society Field Guide to North American Reptiles and Amphibians, NY: Alfred Knopf. Additional reference: Van Devender, Thomas, ed., 2002, The Sonoran Desert Tortoise. Tucson: University of Arizona Press; Nagy, Kenneth, "Dry, Dry out Again", Natural History 12/2002-1/2003, pp. 50-55.
[Numerous images of our tortoises follow the text beneath, which discusses Desert Tortoise adaptations at some length -- and then if y'all desire to skip the text, just roll down past information technology.]
Note: The Mohave population of Desert Tortoises has been listed as an Endangered Species by the U.S. Fish and Wild animals Service (USFWS). Nagy, cited above, states that more desert tortoises are now living as captives in backyards of Los Angeles County than in the entire Mojave Desert -- p. 55 -- and the non-human predators which multiply near man concentrations -- feral dogs, coyotes, ravens, etc. -- are taking increasing tolls. The Sonoran Desert Tortoise is non listed equally Endangered, but the USFWS informally consider it a species of concern. (J.Grand. Howland and JC Rorabaugh, p. 348 in Van Devender, ed., listed above.) See also these links to The Desert Tortoise Preserve Committee and The Desert Tortoise Council for valuable additional information, including bibliographic sources.
Land-dwelling "Chelonians" (the Order of double-shell-encased reptiles) possessing domed shells and elephantlike limbs are found on all continents except Australia and Antarctica. They range into some of the most arid parts of the world, and most are herbivorous. Our Desert Tortoise -- remains of which take been plant in archaeological sites from southeastern California and southern Utah into Northern United mexican states since the late Pleistocene -- has a strongly domed crush and shows prominent growth lines on all of its shields. Its forelegs are defensively scaled, long, flattened, and muscular -- adapted for burrowing; hind legs are circular, stumpy, and elephantine.
The Desert Tortoise may be unique in its power to allow its internal trunk chemistry to vary with irresolute environment. They begin each year in a state of dormancy, in slanting underground burrows three to six anxiety deep, which they have constructed (often in the vicinity of Creosotebush, at any rate where soil has been softened somewhat). These burrows provide relatively humid, cool simply not freezing quarters during winter, when the tortoise burns very little energy and burrow humidity keeps down dehydration. (Recent studies bear witness they lose hardly any weight during the winter hibernation.) A tortoise may use the same burrow for several years.
Tortoises emerge from hibernation in the jump, to find highly variable green nutrient (herbs, grasses, etc.) in our Sonoran Desert climate. If the desert is green, they devour these plants, but if information technology is dry out they eat whatever dry out grasses are available. Rather than voiding excess water the plants take provided, the tortoises store their backlog water, and information technology so can exist reabsorbed through the bladder wall during dry out periods. By the time of full summertime drought, they retreat to their burrows, to endure "internal concentrations of chemicals well beyond those that would kill any mammal or bird and nigh all other reptiles" (Nagy, cited above, p.53). According to Nagy, where desert camels tin tolerate an increment of 40% in their "osmotic blood concentrations" (containing toxic wastes), desert tortoises can tolerate as much as 200% (ibid.). Should summer and fall remain dry, they may stay in their burrows and go directly into hibernation in October, though they may emerge when they sense approaching summer thunderstorms and even scrape out earth depressions to take hold of whatever rainfall comes and drink it immediately. If they do become a drink earlier winter hibernation, they will and then discharge their old, highly toxic urine (held maybe since the preceding wintertime) and drink some more. Multi-twelvemonth droughts even so may overwhelm this accommodation, killing them. And a well-known adage tells people not to pick up and overturn desert tortoises, since by reflex they will void their stored water -- which may deter a predator only also endanger their after survival.
Every bit you would look, in our area Desert Tortoises are nearly active during the Monsoons and just after, though males court females during the jump besides as the summer. The females exercise not skip reproduction during dry years (as practise some desert birds and reptiles), simply lay their eggs in their burrows from May-July, which hatch out in August-October. During this time, drivers of vehicles on our uplands must be almost warning for the presence along the wheel tracks of some very pocket-sized moving "pebbles" besides every bit their more football-sized parents, all of whom tend to utilize these dirt tracks as pathways: see for example this image below:
The white strip at the base of this epitome, taken in Baronial 1998 on the Pool Wash Ridge Route, is the front portion of the hood of the vehicle (which did end in fourth dimension). This tortoise was not as small as it looks -- it was probably 8-10 years old, and in width well-nigh the bridge of a man's hand. Younger ones would exist much more than difficult to come across particularly in the context of many like-sized pebbles.
Beneath is a youngster who was moving ambitiously beyond gravel-and-sand terrain in September of 2003. The carapace is no more than two 1/2 inches long by our casual method of measurement, which is merely sheer distance front to back as viewed from above. Length forth the curvature would exist a good bit longer.
Click on the correct-hand image for a closeup.
The closeup shows the states a series of v or 6 rings -- indicating possibly four years of growth? (Rings form only in years of practiced forage.) The animals below are all a slap-up deal larger than this youngster.
Below Left: about the Windmill, September 2000 (this carapace was about vii inches long -- again, by our overhead method of measurement); right: Puddle Wash ridge route, August 2000; far below, right: July 2001
Sexual differences in tortoises include the length and angle of the gular horn (the forward portion of the lower shell), which is longer and upturned in males; the shape of the rear lower beat, which is concave in males, apartment in females; and the length of the tail, which is longer in males. Since we try to keep our distance from our tortoises, we oasis't regularly sexed them, but the Windmill tortoise shown in a higher place is probably female (small gular horn, below left), while both the Survivor Tortoise (long gular horn, below center -- this tortoise is further discussed below); and the logo tortoise shown at the page top are probably male (concave rear lower shell, long tail -- here, below right):
Also the vagaries of food supply, Desert Tortoises face many other hazards and difficulties while working to survive in the Saguaro-Juniper zone. Evidence of some of these appeared recently when we encountered one elder (below) on a archaic road above Hot Springs Canyon Wash on August 28, 2002, the day before the first substantial Monsoon rain of the flavour hit our lands. Interestingly, Desert Tortoises have been observed to anticipate coming rains in various parts of our Northward American Deserts, emerging out of their burrows a day or so before rain begins to fall on their terrain. Notice its dirty carapace (in contrast to others photographed here), which suggests the animal may have emerged from its den only a short time before. Anyway, the photos below at middle and correct testify an interesting characteristic: an open fissure on the correct edge of the carapace just in front of the right rear leg.
Below left: a closeup of the head contour of this animate being shows some distinctive features which should assist time to come identification. Beneath right: Simply who will need them? Viewing the same individual from the left-mitt side, we see a much larger scissure and a second scissure as well in front of the rear leg. This tortoise has suffered a partial squashing of the unabridged rear portion of its carapace, but has survived nevertheless.
While one might propose a number of possible scenarios for this traumatic outcome (several people suggested a vehicle running over information technology, but this seems unlikely), our shared experience in Saguaro Juniper lands suggests that the injury very likely occurred from a fall -- downwardly one of the numerous cliffsides, or deep, fissure-like ravines that are constitute in our area, and over the edges of which modest creatures may well be borne in a wink-flood. Some of these precipices are close to a hundred feet of sheer driblet. While exploring Saguaro Juniper lands around the edge of Hot Springs Coulee Wash, we accept occasionally plant skeletal remains of Desert Tortoises at or near the base of such ravines. One, which we call the Cleft, contained such a skeleton right at the base of its sheer waterfall. In the photos below, on the left a smaller crack can be seen clearly, appearing as merely a narrow crack in the San Manuel Germination. But this crack runs well back into the Germination, and one can walk into information technology at the base of operations for a considerable distance. In the center photograph, visitors to the Cleft sit protected from the bright springtime sun; the half-cylinder rock wall at the dorsum is palely illuminated past much more indirect light billowy down the h2o-eroded vertical chimney all the way from the wash top, maybe fourscore feet in a higher place. On the right, another visitor is dwarfed within a similar waterfall chimney carved into San Manuel Formation nearly Rabbit Ears Saguaro Colina. (Nosotros call this one a "Meditation Surface area" though no one should meditate at that place during 1 of our rainstorms!) (Click on the left and eye images to enlarge them.)
Some Desert Tortoise corpses have been found in washes merely beneath clefts such as these, for instance:
Another likely cause of such injuries is from rock-falls off cliffs or very steep slopes, especially later on rains. Roadways along our washes often contain scatterings of large, freshly-eroded boulders following fifty-fifty fairly modest rain events. In that location is definitely some run a risk for anyone walking at the base of such slopes during or presently subsequently rains. And of course any creatures walking our washes during flash floods are likely to be tumbled by rushing masses of rock. For example: On September 10, 2004, walking a brusk way above the Lower Hot Springs Coulee Windmill -- less than a week after the stream had run in overflowing all the way down to the San Pedro River -- we found this corpse of an elderly Desert Tortoise, beneath: (Click on each image to enlarge it.)
This Tortoise must have been swept upwards by this terminal alluvion at a signal well upstream, battered thoroughly by rocks and drowned, and eventually deposited at this spot against a Hymenoclea establish. You can tell it is quite old from the shell rings on the enlarged image at far right.
And so Desert Tortoises may take hold of trouble from many directions -- from all sides, and higher up as well every bit beneath.
Two days after encounter with the survivor tortoise higher up, some other was sighted walking forth a different roadway in a higher place Hot Springs Canyon. This i was smaller than Survivor Tortoise, but appears to be fairly old:
Our imprint-photograph Desert Tortoise (displayed at the pinnacle of our page, above) was about on August 25, rapidly moving from grass clump to grass dodder, enjoying the newly emerged greenery. Our photographic camera was a vintage camcorder, and so we didn't get very clear photos, but we remember it was a male (too shown here below). They appear to waste little time once fresh grasses are out.
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