Brumation

Its fall in Albuquerque. The smell of chili roasting, balloon fiesta prep is in motion, and everyone’s backyard chelonians (i.e. turtles, tortoises) are gearing up for a long winters rest. That’s right, it’s time for our reptilian friends to begin their preparations for brumation.

Brumation is a form of hibernation that reptiles within a natural temperate zone undergo to survive through the hardships of winter months. Although very similar to hibernation there are some small differences. Brumation is more associated with ectotherms (i.e. cold-blooded critters) and is a period of reduced activity to survive extreme temperature rather than reduced resources. Hibernation lasts for a long duration, allowing hibernating mammals to wait out the lack of food sources during this period of the year. Brumation, on the other hand, only lasts for as long as temperature ranges are outside the species “preferred optimum temperature zone." However, both hibernation and brumation are hallmarked by a drastic reduction in metabolism to survive, which is why the terms are often interchanged by the general public.

So how does it all happen? First, outdoor temperatures begin falling and the thyroid tissue slows its hormonal release. This triggers the general metabolism to slow in the body leading to a progressively lowered appetite. You will know that this first step is beginning when night temperatures are consistently dropping between 40- and 60-degrees Fahrenheit. In Albuquerque, September is a typical starting month for these triggers. This is not necessarily a hard rule and start dates can vary with species.

As appetite drops, excess nutrients begin to mobilize and set up storage in the liver for utilization during brumation. Gut mobility starts to slow as well, further driving appetite to a halt. Because of this, about 4-5 weeks prior to the next step of brumation (1-2 weeks for smaller species), any supplemental foods should be discontinued and the chelonian should only have access to backyard grasses, weeds, and leaves. This allows time for the gut to empty. This is important as the low temperatures experienced during brumation cause putreficatio, not digestion. Imagine that last meal you ate rotting in your stomach rather than providing you nourishment. It is also helpful to ensure there is plenty of water available during this period and, if able, soaking them daily. This helps to increase the water storage in their bladders to provide them hydration during brumation.

Once daytime temperatures begin to drop as well (usually October or November in Albuquerque), step two begins.  In this step, instinct drives chelonians to their hibernacula. A hibernaculum is an area below the frost line where brumation will occur. It is slightly warmer than the surrounding environment and provides constant moisture. This will allow the chelonian to avoid freezing and drying out like a mummy. Often, hibernacula will be deep under loosened soil. If chosen correctly, the chelonian will be provided a temperature of 52-61 degrees Fahrenheit and have ample moisture to support their sensitive membranes. Terrestrial chelonians should never be allowed to brumate in an area prone to flooding or pooling water as this will lead to freezing or drowning before emergence. Additionally, chelonians in general should not be allowed to brumate in compost or composting piles. There is a significant difference in bacteria, pH, and moisture content that leads to sickness and death when brumation occurs in these substrates.

Step three begins in the chelonians cozy winter bed. Metabolism slows to a dead crawl and only minimal essential energy needs are met. Fat stored in the belly and tail are utilized first before drawing on reserves in the liver. If the hibernaculum was well chosen and the chelonian healthy prior to brumation then, weather permitting, the winter months will fly by. If the chelonian was sick prior to brumating, there may be severe issues during or after the event. The immune system is not functioning well during brumation and earlier infections may take advantage of the situation. Likewise, appropriate caloric intake may not have occurred prior and when fat stores run out the body will begin “eating itself” through a process called catabolism. This typically leads to death prior to emergence. In general, a chelonian should not lose more than 6-7% of their body weight over brumation.  This is why it is so important for chelonians to have a full physical examination and bloodwork prior to this process.

In step four, rising temperatures trigger the thyroid to start functioning at full capacity again. In Albuquerque, this is typically between March and April (but again, this can vary with species). Metabolism starts to rise and fat reserves in the liver are drawn upon in full to start meeting the higher energy demands. This will cause emergence of chelonians from their hibernacula and feeding will begin. This is also often a trigger for mating and it is not uncommon for males to emerge before females. Some sexually-driven chelonians, those "jersey shore wannabes," will even remain anorexic until after mating has occurred. Even though this behavior may be normal, if a chelonian hasn’t eaten for more than 72hrs after emergence then it should be evaluated for illness. Even if eating well, it is best to keep a close eye during this period as it is normal for chelonians to emerge dehydrated and immunocompromised making them vulnerable to disease.

Step five is the remaining months occurring after mating season and lasts until the next brumation period. This is the “normal” metabolic and behavior period for chelonians. Depending on where the species is from, this may also include a very short period of aestivation. Aestivation is like brumation for the summer, a little reptile siesta if you will. Fewer reptiles undergo this process and it is triggered by extremely warm temperatures.

Given the number of species kept as pets, it is important to note that not all reptiles brumate. Only those that would live in a temperate zone are likely to undergo this process and tropical species are not built for the task. Common pet chelonians that are not built for brumation, and need to be kept close to their environmental conditions during the winter, include African Sulcatas, African Pancake Tortoises, Greek Tortoises, and Red-Footed Tortoises. This is by no means a comprehensive list so please check to see if your specific species brumates. Also, just in case you have a few of these roaming your yard too, most of the common native New Mexican chelonians will brumate except the Yellow Mud Turtle. Red-Eared Sliders and Rio Grande River Cooters will undergo a brumation-like period but it does differ slightly from other chelonians.

Along with chelonians, other temperate zone reptiles such as the bearded dragon are known to brumate in the wild. The difficulty is that the trigger for brumation is temperature, not lighting or day length. This means that well cared for reptiles that are housed indoors may not be receiving the triggers for this event and thus we don’t think about it. Some will still lose appetite during these months but full brumation will never occur. The importance of allowing brumation in some of these species is yet unknown. However, we do know that species not naturally brumating in tropical zones still undergo a period of anorexia during cooler months coinciding with “ramp up” for the breeding season. Additionally, there is an internal cue for mating behaviors following brumation that may indicate a function of reproductive health in brumation. Could this be part of the reason we see so many issues with reproductive health in captive reptiles? Regardless, it is generally considered ideal by herpetologists and herp-veterinarians to have all temperate zone chelonians brumate if in good health, even those that are indoor pets. There are even methods to provide a shortened simulated brumation for indoor chelonians (which is a topic for another day). With that said, I pose to you this question:  Is this something that we should be considering with other captive temperate zone reptiles as well?

Hopefully, you’ve come to realize that there is much more to brumation than the disappearance and reappearance of your backyard inhabitants. As global climate changes shift seasonal temperatures, we may begin to see different durations and survival outcomes to brumation in general. This makes it even more important to understand the triggers and pitfalls that occur with the process. Overall, the best preventions start with basic health. If you have a brumating chelonian at your home, please have them seen by your herp-friendly veterinarian prior to brumation to ensure a safe winters rest.