So What Do Turtles Get Up To During The Winter Months?
Well, not much but what they do get up to is rather interesting.
There are eight species of turtles native to Ontario. All are freshwater turtles that inhabit a variety of aquatic habitats, including most wetlands, lakes, streams, rivers and even bogs. They are active from April to October, the other months of the year are spent in dormancy, being the subject of this article.
The emphasis of this article is on the Ontario turtles but we have included a bit of information about other animals as well. We personally find the subject of dormancy, the survival strategies and adaptions animals engage in a fascinating subject. There is a lot of information to cover. We have tried to keep this as brief as possible which is code for; this isn’t a short read. I’m hoping the interest factor with make that less noticeable.
THE DORMANCY PERIOD
Dormancy is a general term used to describe a period in an organism’s life cycle when metabolic activity is minimized and active development is temporarily suspended. Quite simply, it is a state of ‘self-preservation.’
Hibernation is a term often used to describe the dormancy period that the Ontario turtles transition into during the winter months. In fact, ‘hibernation’ is the dormancy period animals such as mammals transition into during the winter months, turtles instead utilize a reptile equivalent known as ‘brumation.’ Hibernation and brumation are both forms of dormancy that animals in this region use as a survival strategy to escape the cold temperatures, harsh winter conditions, other species that compete for the same food and space, limited food supplies and possible predators.
Why the different strategies to overcome and survive the same seasonal circumstances comes down to the metabolic processes involved and temperature regulation. At the core of both hibernation and brumation are some similarities that include the animal experiencing a reduction in body temperature, heart rate and breathing rate resulting in a reduced metabolic rate. These combined physiological changes are experienced to a different degree species to species and are for the purposes of conserving energy during the dormancy period. A period of dormancy is essential to ensure the survival of animals, so they can propagate their species. Every animal has a role, often far greater than we realize, in the network of ecosystems we are all part of in some way.
Notable mention (1): Among the animals that hibernate there are those that are considered to be ‘true hibernators’ and those that are not. This distinction is attributed to the deep dormancy state some animals enter into as compared to animals that instead enter into a light dormancy state. Ironically the animal most commonly associated with hibernation, the bear is not a true hibernator and is easily aroused from hibernation. An example of a true hibernator is the woodchuck whose heartbeat when active is 80 beats per minute and drops to 4 or 5 beats per minutes when in hibernation. Interestingly, the common poor will is the only bird species that is believed to hibernate.
To better understand why mammals hibernate and turtles brumate it is important to know about temperature regulation. Turtles, other reptiles, amphibians, invertebrates (lack a backbone) and most fish are ‘ectothermic.’ Meaning they cannot maintain a constant body temperature and therefore rely on outside sources to regulate their body temperature. Their body temperature changes with the environment they are situated in. This is why you see turtles basking on logs in the sun or on the warm pavement of the roads. Some turtle species brumate in groups to pool their combined body heat to help keep the entire group warm. As a point of interest, basking is also beneficial to their skin and shells, and speeds up their metabolism. Also a fun fact, a group of turtles is called a ‘bale’ and a group of tortoises is called a ‘creep.’
Birds, mammals and some fish (e.g. tuna, billfish, swordfish and some sharks species) are ‘endothermic’ meaning they maintain a constant body temperature independent of their environment as do humans. As a result of these differences, turtles could not survive the conditions associated with hibernation and mammals could not survive brumation. You may be more familiar with the terms cold-blooded (ecothermic) and warm-blooded (endothermic) but the scientific community has moved away from this terminology, as it suggests there are only two categories of body temperature. This is not the case, animal temperatures vary by species and even within species.
Notable mention (2): Spotted Turtles are the most cold-tolerant Ontario turtle species and are often the first to emerge from brumation to bask in the spring, sometimes sunning themselves next to mounds of melting snow.
This is where things start to get really interesting! Triggered by seasonal changes, the turtles as well as various mammals known as ‘hibernators’ recognize shortening days and falling temperatures as being the onset of winter and the dormancy period that comes with this. Instinctively some hibernators make dens specifically for hibernating called, ‘hibernaculum’ that are insulated, enclosed and often contain just in case food stores. Other hibernators seek out abandoned dens, caves or burrows. These site choices are suited to their need to be in an environment that has a constant supply of oxygen to see them through their brumation period.
Turtles instead seek refuge at the bottom of ice covered habitats such as ponds, lakes or other bodies of water that do not freeze solid. They burrow into the sand, gravel or muddy water bed or in between rock crevices, in rotted out logs on the water bed or under leafy debris at the bottom of the body of water they have chosen as their winter habitat. Each of the eight turtle species has particular preferences as to the type of seasonal habitats they prefer. Snapping turtles and other turtle species sometimes if the opportunity presents itself brumate in abandoned muskrat burrows or lodges. As a point of interest, researchers believe that when it comes to brumation much like nesting turtles will often go back to the same brumation site.
Hibernation and brumation differ in that hibernation is more characteristic of a state of sleep, and brumating turtles instead transition into a significantly reduced metabolic state by as much as 90% to 95%, thus a state of sluggishness and slowed down activity. With this drastic change a turtles heart rate drops and will beat as little as once every 5 to 10 minutes, depending on the species. Freshwater turtle’s brumate in water where their body temperatures remain relatively stable, and will not go below freezing.
In response to the cold water temperature a turtle situated at the bottom of an ice covered body of water is often just a few degrees above freezing. This low body temperature causes a significant decrease in their metabolic rate, thus in the turtle’s activity level and energy needs which are at a bare minimum, approximately one tenth of the normal requirements. Like fish turtles stop eating as their metabolism naturally slows. Further to this they do not eat during the winter months, growth ceases and for the most part they remain still, all the while remaining alert and responsive to changes in light and water temperature that signal spring. During brumation turtles are known to move around but far less than their typical activity levels. Bouts of movement are thought to possibly increase in relation to periodic elevations in water temperature during the winter months.
Although each turtles species has preferences regarding the winter habitat they will choose to brumate, a common factor is that it will be underwater. These brumation sites being underwater are in an environment that is, ‘hypoxic’ and characterized as having a low oxygen supply. Turtles are able to survive in a hypoxic environment and for an extended period of time because of their ability to reve down into such a depressed metabolic state, synthesize and store a sugar called, ‘glycogen’ in their liver and skeletal muscles and buffer lactic acid.
During brumation the turtles do have basic needs to meet, such as taking in oxygen at varied regular intervals and drinking water to keep hydrated. To ensure these needs are met and address the matter of breathing while situated at the bottom of an ice covered body of water, the turtles situate themselves in a body of water that has a moderate to constant flow of water to bring in a fresh supply of dissolved oxygen. A turtle would die if the body of water froze solid from surface to below the usual frost line or there was a lack of oxygen, due to a stagnant body of water. Surviving in hypoxic conditions is not without challenges and involves achieving a harmonious balance.
We will expand on how turtles breath underwater further along in the article.
Contrary to common belief animals do not start eating heavily just prior to their hibernation or brumation period, typically late fall, dependent on the temperatures. Hibernators need to pack on pounds in the summer and early fall. An animal that waited until the temperature dropped to start seeking extra calories would run the risk of leaving it too late. Turtles much like mammals accumulate fat reserves from the plentiful summer months. Unlike mammals that rely solely on their fat reserves as energy to see them through hibernation, turtles do not. To rely solely on fat reserves as do mammals would be far too taxing on a turtle in terms of energy expended and could prove to be fatal due to the amount of ‘lactic acid’ that would be produced. The problem with metabolizing fat in the absence of oxygen, as would be the in a hypoxic or anoxic
environment, is that the process creates lactic acid which in excess can cause ‘acidosis’ and be fatal. To enable turtles survive throughout the brumation period in a hypoxic environment dropping temperatures trigger a response that causes turtles to synthesize and store a type of sugar called, ‘glycogen’ in their liver and skeletal muscles. This is the predominant storage form of glucose and carbohydrates.
Turtles break down stored glycogen reserves in their liver and other skeletal muscles. This process releases enough energy to accommodate their bare minimum requirements and keep them functioning to the degree needed to see them through brumation. There is a drawback, that being the unavoidable moderate build-up of lactic acid. To counteract this a turtles shell and skeleton literally comes to the rescue by releasing calcium and magnesium carbonates that helps to neutralize the built-up lactic acid to avoid fatal acidosis. The buffered lactic acid is moved into the shell where it is stored to keep the turtles body chemistry in an acceptable range. So, not only do turtles shells serve as protection against predators, their shells are an essential part of their survival during the brumation period as well. It is possible that nearing the conclusion of the brumation period when glycogen reserves may be getting low is when fat reserves are relied upon in a minimal sense as energy reserves. Climate change could play a role in this if the brumation period is extended due to a delay in temperature increases associated with spring as was the case in 2018.
It is the turtle’s significantly reduced metabolic state that helps to diminish the rate at which both the stored glycogen is used up and lactic acid is produced. This is important because maintaining adequate energy reserves is not only vital to see a turtle through brumation but also post brumation. Once the turtles emerge from brumation they pretty near hit the ground running, at turtle speed, as reproductive activity in the spring begins soon after. It is during this period when turtles have emerged from brumation and their metabolic state has returned to a normal range that stored fat reserves from the plentiful summer serve to help the turtles boost their energy level for the active season ahead. Mating occurs in the spring soon after brumation and can extend through to mid-July. Females turtles that nest early in the season may lay a second clutch in July.
Notable mention (3): Props go to painted turtles and rightfully so because they are so well adapted for brumation that they can not only survive in hypoxic conditions but impressively an ‘anoxic’ environment, being one that has no oxygen supply. They are able to do this because they possess a large liver, 4% of body their mass with a high glycogen content (8–10%), plus additional stores of glycogen in skeletal muscles. Painted turtles during brumation and their active period have the ability to stay under water for up to five months because they are able to hold their breath longer than any other air-breathing vertebrate in the world.
Notable mention (4): The spiny soft-shell turtle having a rubbery shell as opposed to the ‘keratin’ shell make-up of other species does not have the same capabilities as other species that use their shell to neutralize lactic acid. As a result of this, they favor underwater sites for brumation that have a more constant supply of oxygen and are unlikely to become hypoxic or anoxic, such as large lakes and rivers with deep pools.
All turtles have lungs and during their active period spring, summer and early fall most species meet their oxygen requirements by breathing in the usual way. However, the usual way for turtles when on land or poking their head out of the water due to their unique anatomy isn’t so usual and differs to other animals.
Having evolved over 260 million years present day turtles do not have a rib cage. They have a modified version of ribs that are broadened, flattened and fused along with the spinal column to the bones that make up the underside of the upper shell, known as the ‘carapace.’ All turtles breathe air and have a set of lungs they breathe with. Since a turtle’s shell cannot expand and contract the way other animal’s ribs do, turtles have muscles inside their shells that expand and contract to move air in and out of the lungs. The muscles used work in unison to pull their body outwards, towards the openings of the shell to allow the turtle to inhale followed by using more muscles to press their body against the lungs causing a turtle to exhale. As a point of interest, turtles have the ability to empty their lungs more completely than most other vertebrates.
Breathing by using their lungs is a labor intensive process and when turtles are not brumating it serves them well. During brumation, when a turtle most needs to conserve as much energy as possible and minimize the risk of lactic acid build-up, as can be the case every time a muscle is used, this process would cause a turtle to expend far too much energy resulting in dire consequences. To avert this likelihood, turtles resort to an ingenious adaption known as ‘Cloacal Respiration’ or simply stated breathing through their posterior orifice, okay … butt! Yup, we’re serious, their BUTT! On a turtle the butt is known as, the ‘cloaca.’ This is an opening located at the back end of the turtle under the tail. Interestingly, it is the same opening a turtle urinates, excretes waste, mates and lay eggs.
This reference to breathing is of course not in the typical exhaling and inhaling sense, it is a process that involves the muscles located just inside/outside the cloaca opening to expand and contract causing water to be forced in and out of the cloaca. In this manner, when water enters the cloaca it then travels a short distance to the ‘cloaca bursae’ which are a pair of internal pouch-like structures located either side of the cloaca. The cloaca bursae are lined with very fine filament like projections called, ‘papillae’ that are highly vascularized thus flush with ‘capillaries’ (blood vessels) that absorb (uptake/extract) oxygen from the water. The capillaries are made of thin, permeable skin able to absorb the oxygen from the water. This process uses little energy which is essential during brumation. This allows a turtle to remain underwater in a hypoxic environment for the duration of the brumation period and meet their oxygen needs. The process is comparable to how the gills of a fish work, circulating water across internal body surfaces that are flush with capillaries that absorb oxygen.
Turtles using cloacal respiration to meet their oxygen needs is not exclusive to the brumation period. Some turtles, such as snapping turtles use it during extended periods of time when they are on the bottom of lakes scavenging for carrion (dead animal and plant matter). In addition to cloacal respiration, there are other breathing adaptions utilized by the various Ontario turtle species that include breathing underwater through their skin, throat lining and other mucus membranes that are well vascularized and flush with capillaries (blood vessels) and/or papillae enabling them to absorb oxygen from the water. The previously mentioned breathing adaptions play a part in prolonged deep water dives.
Notable mention (5): Spiny Soft-Shell Turtles are highly aquatic and can stay underwater for up to five hours, getting nearly half the oxygen they need by breathing through their skin.
Notable mention (6): The Eastern Musk Turtle, also known as a ‘Stinkpot’ was a mystery for years because it does not have cloaca bursae, does not come up for air, its skin is too thick to breathe through and is poorly supplied with blood. Amazingly the musk turtle has a unique organ for aquatic respiration, it’s tongue, as such it is lined with papillae that absorb oxygen from the water.
Painted turtle hatchlings are robust wee marvels that incredibly often spend their first winter in their nest or below the nest cavity, only a few inches below the frost line. This is a survival strategy known as, ‘overwintering.’ Ice crystals form around them and marginally in them but a self-generated type of antifreeze prevents them from an assured death. They remain in a super cooled state until the spring when the ground thaws, and they emerge from their nest. Please be on the lookout for little painted turtles in the coming weeks as the spring temperatures set in. There are many potential predators between the nest and their intended body of water, as well as the possibility their travels may include crossing a road. It is hoped as many as possible little painted turtles from last years hatchings can be intercepted and safely released to go on to live a long and fruitful life.
Notable Mention (7):Turtles have been reported as being observed mating under the ice. This is not typical behavior but may be attributed to climate change and seasonal shifts. The ways that climate change is effecting turtles and other animals these past years is considerable. Erratic weather patterns and temperature fluctuations have become the norm and every year is now strange but in a different way. Last year, very much effected turtle behavior. In Ontario, we actually had spring in winter and then winter in spring. By the time the turtles emerged from brumation last spring they were close to a month behind. Turtles resorting to strategies such as mating under the ice likely to adhere to ‘their schedule’ isn’t surprising, they are masters of adapting.
FORMS OF DORMANCY
Before finishing with this subject, we just have to include a bit of information about other survival strategies and adaptions that include; (a) Aestivation, (b) Torpor, (c) Diapause and (d) Overwintering. The reasons for using these various strategies varies based on seasonal environmental conditions, environmental stresses, food shortages and/or to evade predators.
(a) Aestivation is similar to hibernation but entered into by some endotherms and ecotherms as a way of escaping the adverse effects of hot temperatures, dry season, droughts and the associated water and food shortage. e.g. Desert Tortoises and Western Swamp Turtle. The Ontario spotted turtle dissimilar to the other seven turtle species aestivate during the summer to avoid a hot dry weather.
(b) Torpor is similar to hibernation and aestivation but is sustained for a varying period of time. It is sometimes referred to as, ‘temporary hibernation.’ Some endotherms and ecotherms will enter into torpor for a day, days or weeks in response to brief bouts of poor conditions such as cold nights, hot days or intermittent food shortages at various times of the year. e.g. Echidnas in Australia will enter into a state of torpor after fires during which food is scarce and it will take time for resources to rebound. Lungfish switch to a torpor state if their pool of water dries out.
(c) Diapause is a ‘sleep time’ found mostly in insects and can occur at any stage of the life cycle. It is characterized by suspension of growth and development in the immature insects between autumn and spring and by stopping of sexual activity in the adult insect. It is a way for insects to live through extreme temperature, droughts, or lack of food. In mammals, diapause is a delay in the attachment of the embryo to the uterus, also known as ’embryonic diapause.’ This ensures that the young are born in spring, during more favorable conditions. Some mammals that undergo embryonic diapause include rodents, bears, armadillos, weasels, badgers and kangaroos.
(d) Overwintering: Hibernation and migration are two ways in which overwintering is accomplished in addition to the painted turtle hatchlings approach. Overwintering is how an insect passes the winter season. Other insects, such as the monarch butterfly, migrate and overwinter in warmer areas.
We hope you found this article interesting and informative. If you are able to, we would encourage you to read more on the subject of dormancy and/or the survival strategies as they pertain to the animal and plant kingdom. Whether it is hibernation, brumation, aestivation or a combination of these processes, animals have an amazing ability to adapt and survive in their different environments. As always nature has the skill set to look after itself. We are merely spectators to a world that is mysterious, harsh and beautiful, that without human encumbrances and interference would continue to function with an unparalleled competence we have no part in. We can research, study and speculate all we want but never truly know all there is to know as such nature and all it encompasses is entitled to the respect it so adamantly deserves.
If you have any questions regarding this subject or other turtle related matters please do not hesitate to contact Think Turtle Conservation Initiative at 647-606-9537 (phone/text) or e-mail firstname.lastname@example.org. Thank you for looking out for wildlife!
Snapping turtle observed under the ice.