Understanding Heat

      A key to successfully keeping reptiles is understanding the role of heat. Bearded dragons are ectotherms, which means that they depend on environmental temperatures to achieve and maintain optimal body temperatures. However, bearded dragons are not passive in their relationship with environmental temperatures. They adjust their body temperatures with various behaviors, including selection of thermal zones. For example, after a cool night in the desert, a lizard may crawl out into sunlight at midmorning, flatten its body, and adopt an overall darker coloration to increase heat absorption so that it can quickly warm up to an effective operating temperature, which allows it to be alert and act quickly.

      Once it reaches an optimal temperature, the lizard may hunt insects, perform displays for other lizards, and be watchful for potential predators. However, as the midday sun causes air and surface temperatures to rise even higher, the lizard may begin to overheat and will move out of the sun to rest in shade or under shelter until the temperature cools down. This is known as thermoregulation, and it is a critical aspect for those of us caring for our dragons in indoor enclosures. When we talk about thermoregulation, or assuring a proper temperature gradient in a bearded dragon’s enclosure, this is what we mean. As mentioned the bearded dragon needs to be able to move from the basking spot to a cooler zone that is 20 degrees cooler than the basking spot. In this way, it regulates its internal body temperature as necessary. Heating up under the basking light will stimulate hunger and allow for digestion of food and calcium supplements. Moving to the cool side of the enclosure allows him to cool down, lowering his internal body temperature.

      One of the interesting features of reptiles is that that they heat up quickly and cool down relatively slowly. In fact, one of the studies showing this was done with the Eastern bearded dragon (Bartholomew and Tucker, 1963). Individuals with a 68-degree F body temperature placed in a 103-degree F chamber heated up to 101 degrees F in about thirty-eight minutes but, under reverse conditions, required more than fifty minutes to cool from 103 to 68 degrees F. Thus, a heated reptile can store heat and maintain a relatively high body temperature for an extended period of time.

      Optimal temperatures allow efficient metabolism and immune-system activity in bearded dragons. If a dragon is kept too cool, its metabolic processes will occur at a slower rate, and the immune system will become depressed. Cool temperatures reduce digestion rate, too, which can lead to gastrointestinal problems, such as decomposition of food in the gut and bloating. The equilibria of bacteria and protozoa in the gut may also be thrown out of balance. Moreover, the rate of clearing uric acid and other compounds through the kidneys is reduced at suboptimal temperatures and the risks of kidney disease increased. Growth rate, which depends on appetite, rapid digestion, and effective metabolism, is directly affected by temperature. Therefore, keeping a bearded dragon at the correct basking and cool side temperatures results in a bright, healthy animal. Incorrect temperatures or an incorrect temperature gradient will result in sickness and ultimately death.

      A cool spot, around 20 degrees F cooler than the basking area, is essential in a dragon’s enclosure.

      Lighting

      Good lighting is critical to the health of bearded dragons. Without it, they are less spirited, less active, and dull in color. As you probably know, even the moods of humans are affected by low light exposure. How could one expect a sun-loving animal from Australia (which is an extremely bright continent) to thrive under low light conditions? You may have seen bearded dragons in pet stores kept under low light conditions, with only a ceramic infrared heater as the primary source of heat. In addition to incandescent-type lights as heat and light sources for basking, bearded dragons need full-spectrum or high-UVB reptile bulbs provided overhead in fluorescent fixtures that run the length of the enclosure. There are new compact fluorescent-type UVB bulbs on the market. However, in our experience, the long-tube fluorescent-type UVB bulbs produce far more visual light than compact screw-in types.

      We also recommend that you locate your dragon in a bright, well-lit room of the house. We have found that when bearded dragons are kept in a very bright environment, they eat better, are brighter in color, and are much more active than without bright light.

      Providing UVB is critical to aiding the dragon in generating vitamins and minerals. It is hypothesized that basking lizards, such as bearded dragons, manufacture vitamin D3 when exposed to UVB radiation from sunlight. Because lizards need vitamin D3 to effectively absorb calcium, a lack of this vitamin in the diet or a lack of exposure to a UVB source can lead to calcium deficiency in the dragon. This condition becomes very noticeable in baby lizards, which require large amounts of calcium to build their rapidly growing skeletons.

      A calcium deficiency in bearded dragons further results in metabolic bone disease (MBD), a crippling disease that deforms the bones, especially those in the back. To prevent MBD, provide appropriate amounts of calcium and vitamin D3 in your dragon’s diet along with exposure to UVB radiation in the form of sunlight or UVB-generating bulbs or fluorescent-type tubes.

      Our observations suggest that bearded dragons do, in fact, eat more, grow faster, and remain healthier and more active when provided with sunlight or full-spectrum/reptile UVB fluorescent tubes. In one experiment, specimens that were fed ad libitum grew from hatchling to 14 inches long in fourteen weeks by combining a spotlight heat source with full-spectrum bulbs placed 6 inches above the experimental group. This group’s growth rate was significantly greater compared to specimens raised under conditions where any of three factors—light-generated heat, UVB-generating light, and food availability—were limited.

      Light goes hand-in-hand with heat in providing an optimal bearded dragon environment.

      Mercury vapor bulbs sold in the reptile trade fit incandescent fixtures, produce good levels of UVB, and emit heat. They are effective as a UVB source; however, you must ensure that your dragon does not become dehydrated in an enclosure with a mercury vapor bulb. We would never recommend that you use them with juvenile bearded dragons because the results are usually disastrous. There are also bulbs, such as Mega-Ray bulbs, that produce very little to no heat but do provide UVB. If you use this product, make sure to give your dragon a basking lamp for heat and also some sort of visual lighting.

      One easy way to provide UVB is to expose lizards to sunlight. The safest way to expose them to sunlight is to use a screen-sided “basking cage,” which reduces the risks of overheating. A commonly used alternative is to place the bearded dragons in a large opaque or white plastic storage container with a screen top. Glass-sided, clear, or bare-floor plastic containers risk overheating and are often lethal to dragons when placed in the sun. Instead, use sand and cover part of the storage container with cardboard for shade. Even with screen-sided enclosures, you should always provide an area of shade so your bearded dragon can get out of the sun. Placement of basking cages is also important: grass and soil are safe, but beware of concrete patios or asphalt surfaces, which build up heat in the sun and can kill your dragon.

      Light, Heat, and Coloration

      Proper light and heat can help bring out your bearded dragon’s true colors. The bright orange-reds

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