The Spiny-Tailed Lizard at home - Uromastyx acanthinurus in southern Morocco
A C Highfield & Tahar Slimani
Uromastyx acanthinurus, the Spiny-tailed lizard, inhabits the Sahara Desert from the Saharan Atlas to the Sudan, and from Mauritania to Egypt. In Morocco, this species is one of the most characteristic reptiles of the south-east of the country (from Ouarzazate to Er Rachidia) but it has also been found the whole length of the Moulouya valley to within 20 km of the Mediterranean Sea. The fact that this is essentially a Saharan species should not mislead one into believing that it therefore typically inhabits a sandy environment; Uromastyx acanthinurus occurs most frequently in rocky hamada and reg environments.
Uromastyx acanthinurus is a large and impressive lizard attaining up to 140 mm body length, plus a tail of 145 mm, with a heavily-built, stocky body supported by short, powerful limbs. The body mass is of an adult is typically around 450 grams, but this figure is subject to considerable seasonal variation. The tail is large, flat and covered with rings of spines, from which it takes its colloquial name. The dorsal scales are imbricate, and their size is noticeably smaller than the ventral scales.
The colouration of this lizard is highly variable. The basal colour is grey, but red, orange, green and yellow specimens are also encountered. The sides of the body are blackish with bluish 'reflections' or scintillating flashes of red or orange. Juveniles are typically plain grey with brown or darker spots. Adults increase visible pigmentation rapidly in the presence of bright light and heat; this is most noticeable as the animals warm up during their first basking session of the day. Unfortunately, there are no reliable external indicators from which the sex of a specimen may be determined.
Our mission to the Ouarzazate region of Morocco was inspired by concern at frequent sightings of crudely stuffed examples of these most remarkable lizards in souvenir shops and as decorations on traditional herbal medicine stalls. Despite some detailed studies of the thermal ecology and biochemistry of Uromastyx in Algeria published by a group of French researchers conducted in Algeria a few years ago (Grenot, et. al.), very little data on their habitats and behaviour in Southern Morocco has emerged. From the observed level of exploitation, it was obvious that, like the tortoise Testudo graeca graeca, and the chameleon Chameleo chameleon, this is a species which is potentially threatened by trade. We specifically wished to gather information on local collectors and trade levels, and, insofar as limited time allowed, on the habitats and diet of this species in Morocco.
Our route took us via the ancient walled city of Taroudannt, situated in the fertile Souss valley, through the stark and arid mountains of the Anti-Atlas. After several hours of driving on somewhat hazardous roads, a movement was noted by the track ahead as we left the town of Tazenakht - a young Uromastyx? These early hopes were dashed as it turned out that we had chanced upon a chameleon crossing the road. This particular chameleon appeared to be returning to its dry riverbank home from a feeding session on some rocky habitat on the opposite side of the road. We returned it safely to its trees and, after a rewarding photographic session, pressed on with our journey.
Our first Uromastyx was sighted approximately 40 minutes later, posing nicely on a large rock. Unfortunately, at the very moment it appeared on a steep rocky slope immediately adjacent to the road, we were driving at high speed with another car right behind us threatening to overtake at any moment. Driving in Morocco is perilous at best, and we had no intention of the first Uromastyx of this trip also being our last! By the time a safe stop could be arranged, it had long since disappeared and no amount of searching could reveal a trace of its burrow. We carefully noted details of the habitat and vegetation in the vicinity of the sighting, however.
The majority of plants which grow in Uromastyx habitats in southern Morocco are low-growing, thorny drought-resistant shrubs, including Genista, Thymus, and Artemisia spp., with Ziziphus lotus and Stipa tenacissima (Esparto grass, or Alfa - a plant valued for paper making). In the spring, these perennials are supplemented with a variety of ephemerals including Heliotropum, Chenopodium and Leontodon spp.
When we next encountered some similar looking habitat, we decided to stop and undertake a proper search. It was not long before we triggered a sudden rush to cover by a well-camouflaged Uromastyx. This animal disappeared into a large Ziziphus lotus (Wild Jujube) bush overhanging a large cluster of boulders. The burrow itself was clearly visible and plentiful Uromastyx droppings were also in evidence in the immediate vicinity. Samples were collected for later faecal-pellet analysis and details of all potential food plants in the locality were also recorded.
Three very different types of desert are encountered in Morocco:
U. acanthinurus has been recorded in all three environments, but is far more common in hamada and reg than it is in erg, where it is an atypical resident. In true Saharan erg, Uromastyx is typically replaced by Varanus griseus, the Desert monitor. In each of these substrates a favoured microhabitat comprises cliffs at the edges of dry rivers, or oueds, which are created after the infrequent but intense rainstorms which are typical of such regions. Burrows are usually excavated in earthy dry river banks in full sun, often at the base of a bush. The Ziziphus lotus bush is especially favoured for this purpose. Burrow openings are typically approximately 150 mm wide by 75 or 80 mm high, with a gently arched 'roof. Each bush may conceal several burrow openings; we observed one Uromastyx enter one burrow and emerge, a few minutes later, via a different exit. Natural cracks and crevices in rocks are also utilised where the substrate is too stony to permit easy excavation. Uromastyx acanthinurus tends to prefer steep rocky faces, steep inclines or cliffs in which to excavate its burrows in hamada type habitats, although in reg environments burrows are found in a variety of situations, from the banks of roads through stabilised sand-dunes.
- the 'solid rock' desert or hamada where a refuge is found in rock crevices or beneath fallen boulders. In Arabic, hamada means 'unfruitful', an apt description of its agricultural potential.
- the 'gravelly' desert or reg in which a mantle of loose fragments covered with a remarkable desert varnish overlies a sandy layer which is sufficiently coherent to support Uromastyx burrows. The Arabic word reg means 'becoming smaller'. In some localities, a sandy reg occurs, where small drifting sand dunes overlay the rocky layer.
- the sandy desert or erg
Uromastyx acanthinurus are found in regions where a considerable flux in maximum and minumum temperatures occur, from an absolute annual low of -7 °C to a maximum of 60 °C . Daily temperatures also vary by a considerable amount, and a diurnal variation of 35 °C is not uncommon. Despite this temperature range, the lizards usually manage to maintain their body at a minimum temperature of around 20 °C by making use of the extensive burrows that they excavate. These burrows, which can be as much 80 cm deep, provide a stable and secure microclimate able to sustain the animals through periods of excessive heat, cold or drought. Temperatures in the burrows are a fairly constant 20 - 25 °C and ambient humidity ranges between 50 to 90% depending upon the time of year, locality and history of precipitation. Rain in these regions is, however, a great rarity and is restricted to just a few months a year, typically from September to March. Even then, the total annual rainfall is typically less than 135 mm. Immediately following an episode of rain quiescent vegetation bursts into life and for a brief period, provides the desert fauna with a prolific source of nutrition and fluid-bearing greenery. At this time of year, the body weight of the Spiny-tailed lizard attains its annual peak, and its TBW (Total Bodyweight of Water) can represent 75% of its body mass. In drought years, however, food will be scarce, and several successive years of drought (as has occured relatively often in this region) will see an increase in mortality and a general decline in the condition of surviving individuals comprising the population.
In the Ouarzazate region which has an altitude of approximately 1,100 metres above sea level, the coldest month is January where the average daily minimum temperature is -1.5 °C. Peak daily temperatures during the same month are typically in the order of 26 °C (average 16.9 °C). This permits some Uromastyx activity to continue, albeit at a very much reduced level compared to that experienced in the summer months when average daily maximum temperature soars above 40 °C. Sunshine is not a scare commodity here, even during the winter months; December experiences an average of 220 hours, whilst in June, the monthly sunshine total rises to 348 hours. The overall number of sunshine hours experienced in Ouarzazate is typically at least 3,300 per year.
Uromastyx are strictly diurnal in habit and are enthusiastic baskers, usually leaving their burrows only when the outside temperature exceeds 20 °C. On rare cold or dull days, they often fail to appear at all. In April, I observed one colony actively basking by 9.30 a.m when temperatures were already elevated above 24 °C. Peak basking occured between the hours of 11 a.m. and 1.00 pm when temperatures rose to 28 °C. By 4.30 p.m.a few individuals were still out and about in the immediate vicinity of their burrows even though the day had turned unseasonably overcast and temperatures felt decidedly cool at approximately 18°C, with a light breeze.
If disturbed during basking, the lizard will retreat with great rapidity into its nearby burrow. It may not emerge again for several hours. Capturing Uromastyx for study is not easy, and extracting them from burrows is particularly difficult as they grasp their sides firmly with their strong claws, and also use their spiny tail to considerable effect. In the case of a deep burrow, they disappear entirely and are impossible to extract without casing an unacceptable level of damage to their habitat. Juveniles, however, are much easier to both locate and handle. Instead of utilising deep burrows, juveniles live under stones or in shallow scrapes. When surprised, they 'freeze' for several seconds, then search, with considerable hesitation, for a nearby hiding place.
Although predominantly herbivorous, Uromastyx acanthinurus in Morocco also consumes a variety of insects, especially tenebrionides (beetles) and hymenopters (ants). The young are considerably more insectivorous than are adults. Among plants commonly eaten, the family Chenopodia (fat hen/spinach family) is prominent. The salt tolerant Atriplex genus is also regularly consumed. Uromastyx lizards possesss a special excretory gland in the nares to provide a means of eliminating salts with the absolute minimum wastage of water - a critical advantage in a desert environment. This gland is more efficient at eliminating potassium than it is at eliminating sodium. The vast majority of potential food plants which occur in Uromastyx habitats are thorny, drought-resistant and highly fibrous. For barely a couple of months each year, following rain, a wider variety of ephemeral plants appear and are consumed enthusiastically. Should the rains fail, as often happens, ephemeral vegetation is non-existent.
Populations and reproductive behaviour
Uromastyx lizards usually live as groups of several individuals, typically occupying very extensive territories. Typical populations range from 10 to as many as 100 animals per km2 , each with a home range of 1 to 5 hectares. Territorial behaviour is marked, by both males and females, the latter of which can become highly aggressive both to males and to other females during the breeding season. Sexual maturity is attained at approximately 4 years of age, at which point males begin marking their territory by means of excretions from their femoral and anal glands. Mating is preceded by a display in which the male shakes his head from side to side. He may also engage in a series of "press-ups" in view of the female (similar behaviour has been noted during basking, and when a lizard becomes aware of being observed). He then siezes the female by the neck or side and holds her firmly during copulation. In Morocco, eggs are usually laid in June or July. These have a parchment-like shell and a typical clutch comprises of 10-12 eggs, but as many as 15 may be laid by large females. The eggs themselves measure about 35 mm in length and 20 mm in diameter.
Threats and conservation
There is a fairly extensive commercial trade in Uromastyx as souvenir objects. Large numbers are also sold live at souks (traditional local markets) in the south, and they are commonly offered for sale at the roadside by children, especially along the roads between Ouarzazate and Zagora and the roads between Ouarzazate and Er Rachidia. Many are sold to tourists at prices ranging from 15 to 40 Dirhams (about $1.75 to $4.70) In some localites in the south-east, this lizard is also used extensively by healers and certain tribes use its skin as an infant feeding bottle. The Spiny-tailed lizard is also utilised in traditional medicine and is frequently seen decorating the market stalls of herbalists. In summer a large number are found dead on the roads connecting Amerzagane to Taznakht. Attracted to the paved road surface in search of a prime basking site, they are frequently struck down by passing cars.
The habitats of U. acanthinurus are, in most cases, not directly threatened in the forseeable future as they mainly comprise desert of no commercial value, away from human habitation, and which are of only limited use for grazing. Collecting remains the major threat to Uromastyx populations, and it is important that this activity is carefully monitored and that steps are taken to control unsustainable exploitation of what is undoubtedly one of Morocco's most fascinating reptiles.
- Bons, J. 1959. Les Lacertiliens du sud-ouest Marocain. Trav. Inst. Sci. Cherifien, Ser. Zool. (18):1-130.
- Vernet, R., Lemire, M., Grenot, C. J., and Francaz, J. 1988. Ecophysical comparisons between two large Saharan lizards, Uromastix acanthinurus (Agamidae) and Varanus griseus (Varanidae). Journal of Arid Environments (14):187-200.
- Grenot, C. 1976. Observations physio-ecologiques sur la regulation thermique chez le lezard saharien Uromastix acanthinurus Bell. Bull. Soc. Zool. France, 106(1):49-55
- Grenot, C. and Loirat, F. 1973. L'Activite et le comportment thermoregulateur du lezard saharien Uromastix acanthinurus Bell. Terre & Vie:435-455.
Andy C. Highfield is the director of British Tortoise Trust and is the author of the Practical Encyclopedia of Keeping & Breeding Tortoises and Freshwater Turtles (Carapace Press). He has 7 years field experience in Morocco.
Tahar Slimani is a lecturer in biology at Marrakech University and is the author of numerous papers on Moroccan herpetofauna.