Recreating the Desert

A Guide to Enclosure Design and Environmental Research for Horned Lizards

By Benjamin Dragantha-Fabian

When contemplating the care of horned lizards, my vision consistently revolves around creating a naturalistic enclosure. I've dedicated considerable time to studying horned lizards in captivity, delving into a myriad of topics to ensure optimal care and enrichment for my animals. In a previous article for this magazine, I briefly discussed the enclosure design, lighting, and its desired appearance. Now, I aim to detail my process of recreating a segment of the natural habitat for horned lizards. From soil functionality to lights and plants, I intend to delve into every aspect and elucidate how it translates to my husbandry practices, impacting the well-being of my reptiles. Understanding the evolutionary context and environmental factors and figuring out how to adapt them to a smaller scale is crucial to mitigating numerous husbandry challenges.

 Behaviour and Husbandry

Examining various facets of horned lizard anatomy, behaviour, diet, temporal activity patterns, thermoregulation, and reproductive strategies can be intricately connected and analysed to gain a comprehensive understanding of the ecology of these captivating reptiles. The possession of a substantial gut necessitates a tank-like body structure, reducing speed and limiting the lizard's ability for evasive flight from predators. Consequently, natural selection has favoured a spiky body form and secretive behaviour over a streamlined physique and rapid movement, as observed in most other lizard species. The risks of predation are likely heightened during extended foraging periods in exposed areas. A tendency to minimize movement, even in the face of potential threats, could prove advantageous, as excessive movement might attract predators' attention and compromise the benefits of concealment through colouration and contour. This reduced movement likely contributes to the observed high variability in body temperature in Phrynosoma spp., surpassing that of all other coexisting lizard species.

Habitat Description 

As we already know, horned lizards occur in deserts and tend to occupy areas of loose soil and sand, dry riverbeds, grasslands and shrublands, as well as dunes and volcanic areas. In the wild, these animals are exposed to extreme temperature fluctuations between day and night and across seasons. Temperatures can reach up to 50°C during the day and drop to as low as -5°C at night. 

The following enclosure design will be based on a desert horned lizard (P. platyrhinos) habitat in the Oregon Desert…

Understanding the Desert

The Oregon Desert, often referred to as the “Oregon High Desert”, is part of the larger Great Basin Desert that extends into several western U.S. states. Oregon's high desert is characterized by arid conditions, low precipitation, and a variety of landforms. The soil and substrate in this region can vary, but there are some general aspects we can relate to while setting up the enclosure.

It's important to note that the Oregon Desert is not a uniform landscape, and there can be variations in soil and substrate composition across different areas within the region. Local geological features, climate patterns, and human activities all contribute to the diversity of soil types found in the Oregon Desert.

Plants & Soil

The vegetation in the Oregon High Desert is adapted to the region's arid climate, low precipitation, and harsh environmental conditions. While the vegetation can vary across different parts of the desert, several characteristic plant species are well-adapted to the challenging conditions of the high desert environment.

Many plants are xerophytic, meaning they are adapted to survive in environments with limited water availability. These plants have evolved various adaptations to survive in the arid conditions of the Oregon Desert, such as deep root systems to access water, drought-resistant foliage, and strategies to minimize water loss. The desert ecosystem is delicate, and these plants contribute to its unique biodiversity and ecological balance.

For example, Sagebrush (Artemisia sp.) is a common shrub in arid regions like the Oregon Desert. While it can tolerate various soil types, sagebrush tends to prefer well-drained, sandy to loamy soils. Various species of bunchgrasses, such as bluebunch wheatgrass (Pseudoroegneria spicata) and Idaho fescue (Festuca idahoensis), are also common. In nature these grasses play a crucial role in stabilizing soil, preventing erosion, and providing forage for wildlife.

Rabbitbrush is a shrub that is well-adapted to the dry conditions of the high desert. It produces yellow flowers and is an important component of the desert ecosystem, providing food and habitat for various insects and small animals.

In addition to many more plants, the desert soil is home to cryptobiotic soil organisms, including lichens, mosses, and cyanobacteria. These organisms play a crucial role in stabilizing the soil and preventing erosion.

The soil pH in the Oregon Desert exhibits variability, with many areas tending to be alkaline. Alkaline soil typically registers a pH level above 7.0, ranging from moderately to strongly alkaline, influenced by factors such as local geology, parent material, and the presence of alkaline minerals.

The alkaline nature of the soil can be attributed to the region's geological history, including volcanic activity. Common volcanic rocks like basalt, prevalent in the area, contribute to soil alkalinity through weathering processes.

Certain areas may contain sediment and soil deposits transported by water, especially in proximity to rivers or former watercourses. Horned lizards utilize loose soil for camouflage and thermoregulation.

 Light

Sunlight consists of particles known as photons, which serve as the fundamental units of electromagnetic radiation. Photons, discrete packets of energy, demonstrate both wave-like and particle-like characteristics. In the context of sunlight, these photons emanate from the Sun due to nuclear fusion reactions transpiring in its core.

Comprehending the role of distinct wavelengths in sunlight is pivotal for establishing appropriate captive environments for reptiles. In captivity, artificial lighting systems are frequently employed to furnish the requisite spectrum, encompassing UVB, UVA, visible light, and infrared. Customizing lighting configurations based on the specific needs of the reptile species, considering their natural habitat and behaviour, is imperative. 

Light holds paramount significance as an environmental factor for reptiles and plants, influencing diverse aspects of their behaviour, physiology, and overall well-being. Several key properties of light are vital for reptiles. While UVB is often perceived as the primary aspect of light in the hobby, and infrared is commonly regarded merely as a means of providing heat, offering the right combination of light sources can profoundly benefit the reptile's comprehensive care.

Reptiles frequently manifest specific behaviours and physiological responses aligned with the natural day-night cycle. Establishing a consistent photoperiod that mimics their native environment is crucial for upholding normal biological rhythms, encompassing activities such as feeding, breeding, and thermoregulation.

UVB (280-315 nm): Reptiles require UVB radiation to synthesize vitamin D3 in their skin, a crucial element for calcium metabolism, necessary for proper bone development and maintenance. In captivity, artificial UVB lighting is commonly used to ensure this need is met, mimicking the natural process where reptiles bask in sunlight to absorb UVB radiation.

UVA (315-400 nm): UVA radiation is also significant for reptiles, contributing to their overall well-being, and influencing feeding, mating, and behavioural patterns. Although not directly involved in vitamin D synthesis, exposure to UVA is considered beneficial for the psychological health of reptiles.

Visible Light (400-700 nm): Present in sunlight, visible light can impact reptile behaviour, affecting activity levels, feeding, and other physiological processes. Blue light is often incorporated into artificial lighting for reptiles to replicate natural conditions. While specific effects of visible light on reptiles are less studied compared to other wavelengths, it is generally recognized as part of their natural lighting environment.

Infrared (IR) Radiation (>700 nm): Infrared radiation provides the heat component in sunlight. Given their ectothermic nature, reptiles rely on external heat sources to regulate body temperature. Basking in sunlight or under heat lamps allows reptiles to absorb infrared radiation, aiding in maintaining optimal body temperatures for metabolic activities.

Enclosure preparation 

The foundations to my enclosures are wooden vivariums measuring 120cm x 60cm x 60cm (4x2x2). They are sealed with a water-based varnish and silicone to preserve moisture and provide protection against it. These enclosures are equipped with pre-drilled ventilation holes. Considering the need for a deep substrate layer for horned lizards, I added extra lower ventilation intakes at approximately 18cm from the bottom. Additionally, a 14mm hole was drilled to allow the passage of a hose, which will serve as an intake for watering the deeper levels of the substrate.

Horned lizards have high light requirements that need to be met. Some lamps may have a more balanced spectrum, closely resembling natural sunlight, while others may need to be supplemented with specific wavelengths. In general, it’s a good practice to combine lamps that are good at replicating one aspect of the sun's spectrum. While in Europe, UVB-producing Metal Halides are often used mistakenly as an “All in one” light source, they lack in some aspects and the UVB emitting parts can burn quicker than other elements.

For my enclosures, I use non-UVB-producing Metal Halides as a source of UVA and Visible Light. As a UVB Source, T5 tubes from reputable brands are very reliable in providing a stable output of UVB over a long time. For horned lizards, 12% or 14% (depending on enclosure height) are suitable. The fixture is attached to a wooden wedge to enable a light angle and better coverage at the basking zone.

Incandescent lamps emit infrared radiation, which is important for providing warmth to reptiles. Infrared heat is essential for maintaining the proper ambient temperature in the terrarium, especially during the night when visible light may not be needed. I set up those lamps in a “sun patch” orientation, maintaining the basking area the brightest. On this side I let the beams from all lamps overlap in one area while the other side will be more “shaded”.

The LED bar spans most of the enclosure's length, illuminating the plants, while UVB, heat, and Metal Halide are concentrated on the opposite side. It's crucial to stagger the lighting to mimic the day and night cycle. In the morning, the incandescent heat lamp activates first, followed shortly by the gradual increase of the dimmable LED bar over an hour. In the middle of this process, the UVB ramps up over 15-30 minutes, and finally, the Metal Halide simulates the midday sun.

Assessing UVB, Brightness, Temperature, and Power Density

For horned lizards, a targeted UVI range of 4.5-9.5 is recommended for the basking spot. The basking area should be the most luminous and warmest segment, reaching temperatures between 42°C and 45°C. In contrast, the shaded side should experience a significant temperature drop, ranging from 25°C to 28°C.

The collective brightness, gauged through Lux as a proxy, should be a minimum of 50,000 lux at the brightest spot where all light sources converge.

Surface temperatures can vary a lot through the colour and properties of the rocks and sand. The variation between a bright and dark rock can make up to 10°C difference. The mixing of different light sources with different spectre will also affect radiation.

Since surface temperatures on basking spots don't accurately reflect their output, we must turn to a different metric known as "power density," measured in watts per square meter. Power density, like intensity, measures the energy flow from a lamp. Much like UVB provision, the provision of IR-A (mainly emitted by a basking lamp at full power) remains consistent and is unaffected by temperature.

To achieve an optimal level of approximately 300-350 W/m^2 of IR-A, suitable for a horned lizard resembling mid-morning IR-A levels, is the goal. Surface temperatures only become relevant once the correct IR-A power density is achieved. If temperatures are excessively high despite the correct power density, adjustments to the surface are necessary. The precise surface temperature is not critical; it can fluctuate within a comfortable range as long as IR-A provision remains stable and accurate.

 Constructing the Substrate Layers

Horned lizards instinctively seek shelter or bury themselves in deeper substrate layers for thermoregulation and concealment. Deep substrate proves essential during brumation, offering isolation and a consistent, suitable temperature. This is particularly beneficial when females create egg chambers. Ideally, the substrate depth should range from 10 to 20 cm.

In the drainage layer, the initial setup involves a silicone hose, capped off, anchored at the bottom, and cut at 5 cm intervals. This design facilitates external watering of the deeper layers, benefiting both plants and reptiles. The drainage components consist of hydroculture balls and lava rock, effectively collecting and retaining moisture, and distributing it across the layered structure.

Once the drainage is in place, the first layers of substrate (each approximately 2-3 cm thick) can be added. This mixture comprises play sand, organic topsoil, and clay. The first three layers incorporate minerals to elevate the pH, aiming for a more alkaline substrate.

The subsequent three layers emphasize play sand, reducing the amount of topsoil and clay. This adjustment aids water percolation to the drainage, maintaining a dry surface while allowing plant access to water.

To enhance the naturalistic environment and cater to reptile needs, crushed red and black lava rock, along with play sand and small gravel, are incorporated. This not only aids camouflage but also complements the overall habitat for the reptiles.

The final layer will comprise various materials, either purchased or naturally sourced, such as dried grasses, brushes, and leaves. This addition aims to introduce more diversity and create microclimates, providing additional hiding spaces for the inhabitants.

 Décor and Plants

When establishing the primary lava stones for the basking area, it's crucial to ensure they are at the right distance from the lights and securely positioned to prevent animals from burrowing underneath. To address this, I placed my two main basking stones on top of old bricks, effectively eliminating the issue and rendering the space beneath the rocks accessible. Additionally, the other selected pieces are both functional and aesthetically arranged, with proper securing measures in place. Precautions must be taken to avoid accidents resulting from inadequately secured decorations.

Obtaining plants from North America can pose a challenge, often involving the purchase of seeds and the cultivation of plants from scratch. During your plant research, consider exploring substitute species available in your local area. I have introduced Sagebrushes (Artemisia cana) that I cultivated into the enclosure. As a substitute for a native Achnatherum spp., I identified another subspecies with similar requirements.

All the plants are planted in pots with the same mixture available in the enclosure. While these plants are adapted to the conditions we aim to replicate, providing a means to directly address their needs is advisable. Planting them directly into the soil might impede maintenance and reduce usable space for the lizards.

Once the setup is finished, I proceed with the cycling process. During this period, the plants can establish and grow while I monitor the temperature and UVI. Additionally, I determine the appropriate wattage for both the heat source and metal halide lighting. 

 Bioactive Boom

A bioactive reptile enclosure is designed as a vivarium to emulate a self-sustaining ecosystem within the reptile's habitat. In contrast to conventional reptile setups relying on artificial substrates and decorations, bioactive enclosures integrate living organisms like beneficial bacteria, fungi, plants, and invertebrates to establish a dynamic and harmonious environment. While the trend has enhanced enrichment for inhabitants by pursuing a more naturalistic setup, the actual creation of a bioactive enclosure is often widely misunderstood.

For horned lizards, I do not recommend opting for a bioactive approach. The primary reasons include the need to closely monitor their food availability in preparation for brumation, and the desert conditions we aim to replicate are not particularly conducive to bioactivity on a smaller scale.