Madison Area Herpetological Society

Reptile and Amphibian Overwintering: Where Do They Go in Winter?

Reptile and Amphibian Overwintering: Where Do They Go in Winter?

Reptiles and amphibians, which are collectively known as “herptiles”, or “herps” for short, are an amazingly diverse and highly adaptable group of animals, with thousands of different species exhibiting nearly every type of behavior, lifestyle, natural history, and reproductive method imaginable. But out of all of these unique traits these animals have evolved with over the course of thousands, and even millions of years, their ability to withstand and survive what many would consider to be the harshest temperatures, climates, and landscapes for at least certain times and portions of the year is especially amazing. Unlike many migratory birds and insects, and even some mammals, reptiles and amphibians are relatively slow moving and less mobile group of animals; they typically cannot fly or otherwise travel for hundreds or even thousands of miles to another area of the globe to escape seasonally cold temperatures, or to find more hospitable food and other resources at these certain times of the year. So how are these surprisingly successful animals able to cope with these times of year where they are, and where do they end up going?

As it turns out, reptiles and amphibians are, at least largely and in most cases, ectothermic animals, which are also more technically known as being “poikilothermic”. These means that these animals are unable to generate or regulate their own bodily temperatures internally, and instead rely upon their external environments and ambient surroundings to do so. These animals have evolved many different unique and successful strategies and behaviors for thermoregulation, although generally, and in most cases, they must do so by basking in areas where the natural sunlight reaches and/or is retained in order to raise their body temperatures, or seek shelter under or within cooler micro-environments in order to lower their body temperatures when necessary.

While it might seem then that animals which cannot regulate their own bodily temperatures internally would be at a grave disadvantage over other indigenous animals which can, such as birds and mammals, the opposite is actually quite true! Unlike many other animals, reptiles and amphibians have adapted and evolved to have become much more highly effective and efficient animals in many aspects of their lifestyles, and oftentimes require less food, water, and oxygen in order to survive and overwinter. So how do they do this? Unlike mammals, which oftentimes must build up internal food and fat reserves beforehand to be able to overwinter, and enter true states of full to partial “hibernation” depending on the species and their habits while burning higher amounts of calories, reptiles and amphibians are able to burn energy at much lower rates, and are able to physiologically slow their metabolisms and activity levels considerably, while oftentimes even using or requiring less oxygen to do so. For example, many aquatic to semi-aquatic turtles are able to absorb and use sufficient amounts of oxygen while overwintering by gaining it through use of their pharynx, or throat, and/or even their cloacas, or vents while remaining submerged, while many species of frogs and even some hatchling turtles possess highly specialized structures and properties in their blood cells which prevent them from freezing and rupturing, as would occur in most other animals. This enables some of these amazing animals to even freeze solid and then safely be able to survive re-thawing with no ill effects! In general, many species of indigenous, or native reptiles and amphibians are much more cold-tolerant than many may believe.

One commonly used term used to describe the overwintering state of many reptiles and amphibians, and how their overwintering methods may differ from true “sleep” or “hibernation” as seen in mammals is that of brumation. During “brumation”, the animals remain awake and conscious, and may even still move about within their overwintering area or even outside of it depending upon the temperatures and whether they are sufficient or conducive for doing so. However, in most cases, these animals still do not eat or feed during this time, and instead very slowly are able to expend glycogen stored in their fat and muscles. However, it must at least be acknowledged that the term “brumation” has come under some debate in recent times, and some scientists, biologists, and others may argue that “hibernation” would be a sufficient, broader term used to describe overwintering. Regardless of which terminology one chooses to use, or what one may wish to call it, many animals nonetheless become much less active during the wintertime while using fewer calories, and reptiles and amphibians are a group of animals which simply are able to take it to levels beyond many others.

But the question remains, how do reptiles and amphibians “know” when it is the right time of year to begin overwintering, and how do they know where to go? As it turns out, many reptile and amphibian species exhibit a moderate to high level of site fidelity, or philopatry. In more layman’s terms, these terms simply mean that many of these animals tend to remain in or near, or habitually return to a specific, or particular area at certain times each year. In many cases, they may make annual or seasonal migrations of up to several miles between areas where they overwinter, and those areas where they forage and feed during the summer or their other active times of the year. Oftentimes, these areas are also birthplaces, where gravid females of the species tend to remain at for longer durations throughout the year in order to mate, breed, and reproduce, or to more adequately gestate their eggs or young internally.

While there remains much to be learned and understood about these animal’s lives in the wild, many recent studies and findings have also at least begun to shed some light on the subject, and have now demonstrated that these animals essentially “know” when to begin overwintering, or making their journeys to or from their overwintering sites through being able to sense barometric changes in their environments associated with the changing temperatures and seasons of autumn and winter. All animals and their seasonal and even daily activity patterns are influenced in some degree or another by the sun, and are also widely known as their circadian patterns, or rhythms. These patterns can influence their many different habits and behaviors, and in simpler terms, can often be seen and thought of as the animal’s internal biological clock which is able to let them know when to eat, sleep, thermoregulate, forage, overwinter or hibernate, and even mate and reproduce. The sun is a vital and essential component for all life.

In many cases, these overwintering sites can also oftentimes be characterized as extending well beneath the frostline, and can retain ambient temperatures of at least 40 to 50 degrees F during even the coldest times of the year above the surface. Self-excavated or existing burrows constructed by other animals, rock outcroppings, crevices, fissures, and stone or concrete walls or foundations, and even individual or other piles of rock, logs, leaf litter, and other sufficient vegetative debris, or beneath mud and other substrates, can all serve as examples of these overwintering sites, in which different reptiles and/or amphibians may utilize depending on the species.

But what about the opposite end of the spectrum where local conditions may become too warm or inhospitable in other ways for these animals? Many may believe that because reptiles and amphibians are ecothermic animals, they must therefore “enjoy” or “tolerate” hot conditions much more readily than other animals. While this may be true to an extent, and some species may readily bask and forage in relatively hot temperatures, they also still do not have the more effective or efficient means of dissipating heat from their bodies as humans and other mammals do, and can still fatally overheat if they are unable to effectively thermoregulate as ectotherms. A reptile’s comparatively thicker skin and scales act as sealants for retaining their water and moisture in even seemingly inhospitable climates, but they too can still desiccate, while many amphibians possess smooth, slimy skin without scales, and therefore, must be able to keep their bodies moist and lubricated in order to remain hydrated and for their respiration porpoises. In order to effectively cope with these relatively harsh conditions in areas of the world characterized by these environments, or during extended periods of higher temperatures in more temperate areas, many reptiles and amphibians will also therefore enter a state of dormancy similarly characterized by inactivity and lessened metabolic states known as “aestivation” until conditions improve again.

To summarize, reptiles and amphibians are an amazing and incredibly diverse and successful group of animals with a wide range of behaviors and adaptations for surviving and thriving in the areas that they do, and because of this, are able to occupy and fill many different environments and niches. While much of what has been covered above addresses how the vast majority of our native, or temperate species of reptiles and amphibians in Canada and the United States tend to overwinter, in other areas of the world, these animals have evolved even more, sometimes extreme and bizarre ways of being able to do so and cope with the environments they live in that certainly would take another entire educational article to discuss and highlight.

There continues to be much that we can learn from, and be inspired by these animals, and many more advances we as humans and civilization can look to these animals for in our developments in many different industries, from advances in pharmaceutical and bio-technology, to  engineering, human health and medicine, and many others. In fact, these developments are even known as bio-mimicry, and these animals in particular, are among the leading and most well-known examples of such as our populations and communities continue to grow, develop, and evolve, all hopefully towards being able to co-exist for the better. Ultimately, if one considers the many adverse effects humankind has made, we only, after all, have only one planet Earth and one chance to share it with these amazing species while hopefully making it better for all of our planet’s diversity.