Horned lizard characteristics, habitat, reproduction, nutrition

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Basil Manning
Horned lizard characteristics, habitat, reproduction, nutrition

The horned lizard (Phrynosoma cornutum) is a reptile of the order Squamata and the family Phrynosomatidae. Despite its wide distribution and geographic variability, the horned lizard does not have recognized subspecies.

They are lizards of daytime activity. During the nights they take refuge in shallow burrows or burrow into the ground to avoid nocturnal predators. Being ectothermic animals, during the mornings they are usually observed sunbathing. When the heat rises at noon, they usually shelter under bushes until mid-afternoon..

Horned lizard (Phrynosoma cornutum) By Ben Goodwyn [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/)]

They are cryptic lizards with their natural ecosystems, so their coloration varies according to the predominant type of substrate. These lizards are capable of collecting rainwater on their bodies and drinking it by interception and transport through the integument..

On the other hand, it is a species that can move daily distances of between 50 and 100 meters in search of food. During the reproductive season these animals undertake the search for mates so they mobilize a little more.

These animals hibernate during the cold months of winter and late fall. They also have several defensive strategies to avoid or face predators.

In summer the mobilization decreases to avoid excessive loss of water. Due to their high mobility, it has not been concluded whether these lizards are territorial. The overlap of their home-range with other lizards indicates that they may be avoided to decrease competition for resources..

Article index

  • 1 General characteristics
    • 1.1 Head
    • 1.2 Body
    • 1.3 Coloring
  • 2 Habitat and distribution
    • 2.1 Habitat
    • 2.2 Distribution
    • 2.3 Conservation
  • 3 Playback
  • 4 Nutrition
  • 5 Behavior
    • 5.1 Rainwater harvesting
    • 5.2 Defensive strategies
  • 6 References

General characteristics

They are medium-sized, sexually dimorphic reptiles. The length of the males, not including the tail, is between 6 and 10 centimeters, while the females are slightly larger, measuring between 7 and 12 cm. The males present more ornamentation than the females and the cephalic scales are more developed.

Head

The head of these lizards is as long as it is wide. They have a pair of well-developed and widely spaced occipital spines..

They also have three pairs of spines in the region of the temporal bone of the head, above eye level, which are shorter than the occipital spines. They have a small interoccipital spine. Above the eyes, they have ridges that end in a short and thick superciliary spine. The eardrum is distinctive and is not covered with scales.

They have three groups of lateral spines on each side of the neck. They also have a row of spines that are enlarged anteroposteriorly along each margin of the lower jaw, separated from the infralabial scales by two rows of small scales..

Body

They have two complete rows of enlarged fringe-shaped lateral abdominal scales on each side of the body, and one of those rows on each side of the tail. The tail is relatively long, at least twice the length of the head region. The scales on the belly are more flattened and have weak ornamentation.

The scales of the extremities are strongly keel and they are large and pointed, so these scales are prominent. The dorsal scales of the body are heterogeneous in size and shape. Most of these are modified with short, vertical spines and have four distinctive keels, one of them located at the posterior base of the scale..

At the microscopic level of the dorsal integument, these small lizards present a series of channels of constant diameter, approximately 10 micrometers, that channel rainwater into the mouth..

Coloration

Phrynosoma cornutum By Hillebrand Steve, U.S. Fish and Wildlife Service [Public domain]

Its background coloration can vary from brown, to reddish brown, yellow or greyish. They have a clear dorsal midline. On each side of the body they present a series of dark brown rounded spots delimited by a color that varies from yellowish cream to orange.

On each side of the neck, behind the occipital and temporal spines, they present a large dark brown spot. On the head they have two to three dark bands that come off the eyes, one of these bands is directed backwards to the temporal spines and the rest forward vertically, towards the lines of the mouth.

Habitat and distribution

Habitat

The common habitat of this species throughout its entire distribution is arid and semi-arid zones. They occupy desert areas, meadows and grasslands and coastal edges with sparse vegetation and scattered shrubs. They also occupy areas with dunes devoid of vegetation, thorny bushes with the presence of cacti and areas with rocky soils..

When inactive, these animals dig burrows in the ground or hide in shelters from some rodents or under rocks. When rainfall is high, they avoid flooding by climbing tree trunks.

The higher densities of these lizards do not depend on the availability or presence of a large number of ant hills. These animals are more abundant in areas where vegetation cover is scarce..

Habitats are frequently characterized by grasses interspersed with cacti, woody shrubs of the genera Yucca Y Prosopis and other small trees in open and bare areas.

Distribution

This species has a wide distribution in the North of the American continent. In the United States it extends in hundreds of locations from southwestern Missouri and central Kansas to southeastern Colorado. Also present in southern and western Oklahoma and Texas.

In New Mexico there are populations in the east and south, it also occurs in southwestern Arizona, following the Madre Occidental mountain range to Mexican territory..

In Mexico there are also hundreds of records. It extends to the regions of Sonora, Chihuahua, Durango, Sinaloa, Nuevo León and Aguas Calientes.

At present, the records for Missouri and Arkansas remain uncertain. In addition, the species is likely not native to Louisiana. In several areas of the southwestern United States, the species has been introduced, including North Carolina, Alabama, and Florida..

Conservation

This species has a wide distribution in North America. The size of their populations is large, they remain stable despite some decreases to the northeast, in their marginal areas of distribution..

Populations have declined in Texas, Oklahoma, and Kansas. Currently the species is in the category of least concern according to the IUCN.

The decline of this species in some areas of the United States appears to be related to control measures to prevent the spread of fire ants (Solenopsis).

The use of insecticides, the management of land for agricultural activities and the expansion of urban and suburban areas are the most serious threats. Another problem facing the species is the overextraction of individuals from the wild to use them as pets..

These lizards are especially sensitive to the disappearance of harvester ants as a result of the use of pesticides.

In some places of their distribution they are frequently run over, the males being especially vulnerable in Arizona and New Mexico between the months of May and June. In Mexico, the species seems to be better conserved.

Reproduction

The reproduction of these animals occurs shortly after the arrival of spring, from April to mid-July. Females appear to mature until the second season after birth, when they reach a snout-cloaca length of 7 centimeters.

The coloration of these lizards intensifies during the reproductive season in both sexes.

Each female can lay a single clutch that is made up of an average of 29 eggs. Young females can lay around 13 eggs while developed females can lay large clutches of up to 50 eggs..

The eggs are placed in underground chambers that are 12-20 cm deep. These chambers are generally excavated by females. On the other hand, if rocks are abundant in the areas where these lizards live, the eggs can be placed under them. In the following video you can see two specimens mating:

Nutrition

These small lizards are almost strict myrmecophagi, this means that they feed mainly on ants. In addition to this, they can consume a wide variety of insects. In general, these animals do not have a fixed home range, indicating that they are actively moving in search of resources..

These lizards actively search for ants and feed near or on mounds of collector ants of various species of the genus. Pogonomyrmex preferably. These ants have a powerful venom that works very well against various predators, however lizards of the genus Phrynosoma are resistant to these toxins.

Each time they detect a nest they feed until the individuals of the colony take refuge. Once this happens, the lizards move to other areas and it is very rare that they return to the same colony again..

The time a lizard spends feeding on a particular colony appears to depend on the number of ants that make up the colony. Spiny lizards feed strategically on each anthill to ensure their availability in the future.

In areas with high density of nests with few ants they spend more time foraging, in contrast to those places that have few nests with numerous colonies..

Behaviour

Rainwater harvesting

Horned lizards have a very striking system for collecting water. Most of the habitats that this species occupies are characterized by being dry areas with little rainfall. Knowing this, these lizards channel rainwater through the entire surface of their body.

The behavior to collect the water begins by raising the abdomen in an arc, with the legs wide and fully extended. Both the dorsal area and the ventral region of the body widen laterally. On the other hand, the tail and the head remain inclined towards the substrate.

The water collected on the dorsal surface is channeled through channels present between the scales, in the integument. This occurs apparently by capillary action, up to the jaws of the lizard. When it rains gently, these animals are observed in the position indicated above, opening and closing their jaws to ingest the water..

Defensive Strategy of the Horned Lizard By Burton Robert, U.S. Fish and Wildlife Service [Public domain]

Defensive strategies

These lizards have an anti-predatory strategy against canids such as Vulpes macrotis. These lizards are capable of expelling a stream of blood through the sinus tissue in their eye socket, once they are disturbed by the presence of one of these foxes..

This strategy has been proposed as an anti-predatory response only against canids, since this behavior has not been observed against other possible predators such as roadrunners. Geococcyx californianus.

This behavior provokes adverse responses from the foxes, which react by shaking their heads at the deterrent chemicals present in the blood and completely avoiding new interactions with this lizard. Foxes learn to avoid this species of lizard once they have an encounter.

No difference has been determined between the blood expelled by these lizards and the blood present in the rest of the circulatory system. Chemical constituents that deter predators appear to be in all blood.

Other defensive behavior of Phrynosoma cornutum before predators like Onychomys torridus involve displays that increase the apparent size of the lizard, intimidating attacks, and standing still to avoid detection.

References

  1. Ballinger, R. E. (1974). Reproduction of the Texas horned lizard, Phrynosomacornutum. Herpetology, 321-327.
  2. Endriss, D. A., Hellgren, E. C., Fox, S. F., & Moody, R. W. (2007). Demography of an urban population of the Texas horned lizard (Phrynosomacornutum) in central Oklahoma. Herpetological, 63(3), 320-331.
  3. Fair, W. S., & Henke, S. E. (1999). Movements, home ranges, and survival of Texas horned lizards (Phrynosomacornutum). Journal of Herpetology, 517-525.
  4. Hammerson, G.A. 2007. Phrynosomacornutum. The IUCN Red List of Threatened Species 2007: e.T64072A12741535. http://dx.doi.org/10.2305/IUCN.UK.2007.RLTS.T64072A12741535.en. Downloaded on 17 December 2019
  5. Howard, C. W. (1974). Comparative reproductive ecology of horned lizards (Genus Phrynosoma) in southwestern United States and northern Mexico. Journal of the Arizona Academy of Science, 9(3), 108-116.
  6. Middendorf III, G. A., & Sherbrooke, W. C. (1992). Canid elicitation of blood-squirting in a horned lizard (Phrynosomacornutum). Copeia, 519-527.
  7. Middendorf, G. A., Sherbrooke, W. C., & Braun, E. J. (2001). Comparison of blood squirted from the circumorbital sinus and systemic blood in a horned lizard, Phrynosomacornutum. The Southwestern Naturalist, 46(3), 384-387.
  8. Price, A. H. (1990). Phrynosomacornutum. Catalog of American Amphibians and Reptiles (CAAR).
  9. Sherbrooke, W. C. (1990). Rain-harvesting in the lizard, Phrynosomacornutum: behavior and integumental morphology. Journal of Herpetology, 302-308.
  10. Sherbrooke, W. C., & Middendorf III, G. A. (2004). Responses of kit foxes (Vulpesmacrotis) to antipredator blood-squirting and blood of Texas horned lizards (Phrynosomacornutum). Copeia, 2004(3), 652-658.
  11. Sherbrooke, W. C., Scardino, A. J., de Nys, R., & Schwarzkopf, L. (2007). Functional morphology of scale hinges used to transport water: convergent drinking adaptations in desert lizards (Moloch horridus and Phrynosomacornutum). Zoomorphology, 126(2), 89-102.
  12. Schmidt, P. J., Sherbrooke, W. C., & Schmidt, J. O. (1989). The detoxification of ant (Pogonomyrmex) venom by a blood factor in horned lizards (Phrynosoma). Copeia, 603-607.
  13. Whiting, M. J., Dixon, J. R., & Murray, R. C. (1993). Spatial distribution of a population of Texas horned lizards (Phrynosomacornutum: Phrynosomatidae) relative to habitat and prey. The Southwestern Naturalist, 150-154.

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