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Most readers are likely aware of the fact that all reptiles and amphibians are ectothermic (cold-blooded) animals, relying on their environment for thermoregulation. That said, these animals have evolved and adapted incredible survival strategies to ensure survival when environmental conditions become unsatisfactory. One such adaptation is brumation. Brumation is a term used for the hibernation-like state that cold-blooded animals utilize during very cold weather.
On the other end of the spectrum is a state known as aestivation, which like brumation, provides a way for reptiles to handle temperature extremes. However, aestivation occurs when environmental temperatures become too high for healthy physiological function to occur, and thus is beyond the scope of this article.
What is Brumation?
As previously mentioned, brumation can be loosely equated to hibernation among mammals. When a reptile brumates, it becomes lethargic, sometimes not moving at all for the duration of the cold season. In nature, these animals typically find hibernaculums within their environment in which they can be somewhat insulated. A hibernaculum is simply the place where the reptile spends these periods of inclement weather. Burrows, rock crevices, caves and leaf litter are a few examples of hibernaculums documented in nature. Some temperate species can even brumate under water!
The amount of time that a reptile brumates is dependent on a number of factors. Perhaps the biggest variable is in regards to whether the animal is in the wild or being maintained in captivity. In the case of the latter, environmental conditions can be easily manipulated by the keeper at any given time. Other considerations include the age of the animal, its gender, geographical origin, and varying natural conditions. Due to the wide range of species and habits, it is futile to make quantitative generalizations regarding how long a reptile will brumate. In the broadest of terms, reptiles will enter brumation in the late fall (when temperatures drop and the days get shorter) and come out of brumation in spring, triggered by increased temperatures, longer days, and changes in barometric pressure.
Why do Reptiles Brumate?
As ectothermic organisms, reptiles cannot raise their body temperature independently of environmental conditions, and as such must contend with the conditions that nature presents them with. The vast majority of our planet experiences seasonal temperature extremes, from the deserts to the plains to even the tropics. The amount of temperature variation does change from region to region. For example, sub-tropical animals, as well as those found near the equator, often do not undergo what herpetoculturists call a "true brumation." However, these animals are just as receptive to natures cues as those from more northern or southern climates. They may slow down, i.e. reduce food intake, eat less, etc, but not enter a true state of brumation.
Conversely, many reptile species inhabit regions that do in fact get very cold in the winter, and accordingly must have behavioral adaptations in order to survive. In the most basic sense, brumation is a survival tactic - a tactic that has been hard wired into the brains of these animals for well over a million years.
Take for example, the Russian tortoise (Testudo horsfieldi). Over much of their range they experience summer highs well over 100 degrees Fahrenheit, and in the winter temperatures fall far below freezing. Without the option of brumation, these animals would perish. Instead, they construct burrows, sometimes as deep as six feet, and remain in them until conditions become favorable. During this time, the tortoises physiological functions grind to nearly a halt. Feeding obviously ceases, as does digestion and defecation. Heart and respiratory rates also drop.
Suspended animation is a phrase often used to describe this state among reptiles. In fact, there are theories suggesting that these long periods of inactivity may actually lengthen the lives of wild herps much the way your car would last you longer if you kept it garaged and purged of all fluids for 5 months of the year.
Aside form serving as a survival tactic during seasonal weather fluctuations, brumation (and winter slowing in general) does have an effect on reptile reproduction. Please keep in mind that there are exceptions, but in general, cooler temperatures trigger the production of sperm in males, and prepares females fro ovulation in spring.
Despite this widely accepted theory, many breeders have found that only slight drops in temperature are needed to trigger this reproductive behavior, while others have found to be completely unnecessary. Renowned monitor breeder Frank Retes is well known for his successful captive breeding attempts with a number of Australian, Indonesian, and African monitor species. He is equally well known within the monitor keeping circle for his unique methodology. His monitors are kept warm year round. His motto, "Heat them, feed them, breed them" has proven quite successful. In fact, in an interview in The Vivarium Magazine in the mid 90s he shared that his monitors also have light 24 hours a day.
This radical approach to breeding may seem outlandish, but experimental techniques such as those of Mr. Retes have allowed us to better understand reptiles in captivity. It remains clear that a short period of slight reduction in temperature and/or photoperiod can be vital in triggering reptiles to reproduce, but not always completely necessary.
In my experience, and in the experience of many of my colleagues and friends, true brumation does not seem to be a requirement in maintaining healthy, reproductively active reptiles. Generally a brief, slight change in conditions (as mentioned above) is all that is needed. Furthermore, in most American homes, this requires little work on the part of the keeper, as seasonal fluctuations and physiological cues will occur regardless of husbandry.
This is not to say that allowing temperate herps to brumate at cooler temperatures for longer periods of time is harmful if done properly. In some species, males that have been cooled are much more fertile than those which were not, and therefore more likely to produce viable clutches with a similarly cycled female.
Brumation in Nature
In the wild, reptiles are presented with both internal and external cues that it is time to brumate. Herpetologists have classified these cues into two main categories. The first are endogenous cues, which originate within the animal. Theories regarding endogenous cues suggest that some reptiles (but certainly not all) undergo hormonal changes as well as shifts in neurotransmitter levels and amino acid concentrations. These factors are directly affected by circadian rhythms and the environment, making these biological cues little more than a secondary function of natural climatic changes. The question remains as to whether these internal changes occur spontaneously and trigger brumation, or if the animal begins to brumate and then these physiological changes occur.
It should be made clear that the role of endogenous cues in reptilian brumation is still poorly understood. Exogenous cues on the other hand are those with which we are already familiar and include factors such as photoperiod (day length), barometric pressure, humidity, and temperature. Exogenous cues seem to be of most importance to herps inhabiting temperate zones. Sub-tropical herps, because of the relatively constant conditions they experience, appear to rely more on internal (endogenous) cues.
Brumation is an extremely trying time for all reptile species. As we have discussed, it is a survival tactic at which many species are quite proficient. Nonetheless, many wild reptiles that enter brumation never emerge in the spring. Sometimes the choice of hibernaculum is a poor one, and when conditions become extremely harsh these areas simply do not provide adequate protection. Other times, reptiles may enter brumation with an injury or illness which would normally require supplemental warmth and nutrition to heal properly. In the brumative state these animals tend to succumb to their ailments.
As mentioned above, the length of time that a reptile brumates is extremely variable. A few generalizations can be made, although they are merely guidelines, and should not be considered definitive. Temperate and desert species tend to brumate much longer than sub-tropical and tropical species. In fact, some species originating from truly equatorial ranges do not brumate at all, but simply undergo a mild shift in activity and feeding patterns. Male reptiles typically emerge prior to females, allowing them ample time to establish breeding territories to further their chances of reproductive success.
Brumation in Captivity
Just as brumation can be risky to wild herps, the same holds for captive reptiles. Although they have the added advantage of being carefully monitored by attentive keepers, this does not rule out all associated risks. In general, brumating reptiles in captivity is the subject of much debate. On one end of the spectrum there are those saying that brumation is natural and will ultimately make your reptile live longer. On the other hand, does this unproven potential for longevity outweigh the risks previously discussed? This debate has been a longstanding one, and will continue to be further explored in the future.
I have adopted the following philosophy regarding brumating my reptiles, and have found it to be entirely successful thus far. Keep in mind that because your animals are in captivity, does not mean that they do not receive subtle cues from the outside world. With the exceptions of snakes being kept and bred in rack units (where all light and heat is regulated by the keeper) reptiles will begin showing signs of a winter slow-down and/or brumation regardless of what environmental conditions you provide.
Many temperate, desert, and sub-tropical herps will become less active and feed less in the winter, even when normal ambient and basking temps are provided. I do not adjust the husbandry of my bearded dragons from season to season. They are provided with the same photo-period and heating protocol year round. Yet year after year they begin losing interest in food in late fall, and remain in this psuedo-brumation until spring. During this time, all of my animals will migrate away from all heat sources, and make themselves comfortable in the cooler regions of their enclosure.
The above anecdote should provide some credibility to the idea that reptiles are going to brumate or not regardless of what you do. With the vast majority of pet species, this type of maintenance is not a problem. When you begin dealing with species that undergo a true brumation in winter (and subsequently animals originating in climates with harsh winters) different actions must be taken.
Box turtles (Terepene sp.) are a prime example, and one that has been more closely looked at than most other species. If a box turtle begins showing signs that true brumation is eminent (less activity, burrowing, lack of appetite) you are going to have to prepare a suitable hibernaculum. A hibernaculum is basically a well insulated box that will hold moisture and maintain a relatively constant temperature during brumation. Air holes should be provided to ensure air exchange. For turtles and tortoises (which coincidentally are most commonly brumated using this method), they are typically placed in a plastic bin with 10 to 12 inches of soft, fluffy, and barely moist earth. This can be sterile (no fertilizers, etc) potting soil, sandy soil, Eco Earth, or your own favorite blend. Finely shredded paper is another popular choice, although extended exposure to moisture may lead to disintegration.
This box will become the inner chamber, and will have to be closely monitored for temperature. I highly recommend the use of a quality digital thermometer with a probe that can be placed deep into the hibernaculum substrate. Many breeders actually tape the thermometers probe to the carapace of the turtle. This ensures that you know exactly what temperatures your animals are being subjected to. Remember, not cold enough and your pet will not be truly brumating. Too cold, and they may not wake up at all.
The inner chamber is then placed into another slightly larger box, leaving a 1 to 2 inch space between the walls of the inner and outer chambers. This space can be filled with packing peanuts, shredded paper, or any number of other insulating materials. The idea here is to ensure a constant temperature within the inner chamber, as significant environmental fluctuations during brumation can be problematic.
Although reptiles do not typically feed during brumation, the hydration of the animal must be considered. In the wild most reptiles dig deep into the ground to brumate, providing them with an adequate amount of environmental humidity to keep them from dehydrating. In captivity, it is recommended that your animals be offered water once or twice during brumation. While digging out you slumbering reptiles in the middle of winter may seem counterintuitive, it is very important, and the small amount of time that your animal spends awake will not affect the overall outcome of the brumative process.
Before closing, I would like to re-emphasize that both in the wild and in captivity, brumation is risky business for reptiles. It puts a great strain on their bodies, but one that is nonetheless necessary to the survival of their species.
The guidelines above are just that; guidelines, and should not be construed or interpreted as a definitive source of information on this dynamic subject. If you are considering brumating your reptiles, I would expect you to consult with an experienced herpetoculturist or other expert prior to undergoing this task.
Similarly, if you have any doubt regarding your ability to properly brumate your animals, please get advice from a knowledgeable source. Although once mastered, brumation can be simple and streamlined, it remains one of the most complex and frustrating aspect of reptile husbandry. For this reason alone it should not be taken lightly.
As always, research the needs of your pet in depth prior to obtaining them. This way you can be best prepared to provide them with the best possible of care.
By Jonathan Rheins