Hibernation Guidelines for Turtles and Tortoises
©1994, 2002 Paula Morris. Originally published in The Bridge, September 1994
Hibernation is nature's mechanism to protect its cold-blooded creatures (and some warm-blooded animals as well) in cold weather or when food and water are scarce.
Dormancy also seems to affect the reproductive cycles of chelonian species, whether non-tropical or tropical, and zoos often provide a "cooling period" to stimulate breeding activity when temperatures normalize. To keep the information general, I'm dividing turtles and tortoises into only two categories: non-tropical (those species that do hibernate), and tropical (those species that do not).
Turtles and tortoises can hibernate up to a full eight months of the year, depending upon latitudinal location. The rule-of-thumb to guide you on your research should be: The farther from the equator the species occurs naturally, the more likely it is to hibernate; the closer to the equator, the less likely.
Species Need Hibernation Or A Period Of Dormancy?
Whether as a response to extreme cold or extreme heat, a turtle or tortoise is going to try to create for itself a "microclimate" when it digs into the soil. 80% soil humidity seems to be the norm. Soil humidity-NOT to be confused with the rain-soaked soil of our California winters--is a critical factor in their ability to survive in the wild. But in captivity you're taking a chance allowing your animals to hibernate in the back yard. A combination of wet and cold will kill a digging or burrowing chelonian, even though our California winters are temperate by the nation's standards.
Some commonly kept species that will try to hibernate are the Desert tortoises (Gopherus); the Russian tortoise (T. horsfieldii); the Box turtles; the Wood turtles (Clemmys insculpta); the Spotted turtles (Clemmys guttata); the Snapping turtles (illegal/protected in several states, by the way); and Red-eared sliders (Trachemys scripta elegans).
You must be able to determine which of your animals needs to hibernate. Your local club or any number of sources on the internet can help you. Joining a forum dedicated to the species you keep is also a great way to learn what's working for others.
Tropical species like Red-foots (Geochelone carbonaria), Yellow-foots (Geochelone denticulata), Elongatas (Indotestudo elongata), South American Wood turtles (Rhinoclemmys), and the African species don't hibernate, but can slow down for a period of time when the weather cools and the daylight shortens. In non-tropical climes they need to be kept artificially warm and/or humid indoors. A humidity gauge in the terrarium will help you keep track of their comfort.
Arid-dwelling, non-hibernating species like Egyptian tortoises (Testudo kleinmanni), Radiated tortoises (Geochelone radiata), Pancake tortoises (Malacochersus tornieri), Sulcata (Geochelone sulcata), and Leopards (Geochelone pardalis), to name a few, must also be sheltered from wet and cold and are particularly vulnerable to respiratory trouble and infection when damp. They must never be left outside. But even these species have a humidity requirement, albeit not as high as the tropical species. You will have to set up "microclimates" for them that will offset the dryness caused by indoor heating. This can be accomplished by having ready access to water for drinking, soaking and voiding, plus a dry area where there is heat and shelter. A good humidity gauge and a thermometer are valuable tools, no matter what species you're keeping.
As a keeper you are responsible for determining the geographic range of the species you have, and whether your animal should hibernate. You must make provisions based on locale and climate for its safe sleep or period of dormancy. But if you have recently acquired an animal, have one that is ill or recovering, or a hatchling that is under three years old, do not hibernate them; this group is highly vulnerable to dying if allowed to hibernate.
Any species that is being kept in a climate not endemic to its evolution (which applies to the majority of captive animals) is going to require research on your part. You have some careful decisions to make based on the species, its health and weight, its age, and its known history.
If the animal is light for its size or hasn't been eating well and hasn't adequate fat reserves to see it through the months of hibernation, it must be kept awake or fed up to sufficient weight. You can then allow it a shorter sleep period, usually several weeks, in a place where you can monitor its well-being. The immune system isn't effective in hibernation and a sleeping animal has no resistance to infection, either internal or external.
If the animal has eyes that appear sunken (enothalmic), it's a sign of major dehydration or a physical problem that has reduced blood volume or fluid in the cells. A healthy well-hydrated chelonian has bright, clear eyes, and plump and supple limbs and tail.
Turtles and tortoises usually instinctively stop eating on their own prior to hibernation, but it's best if you regulate food availability. Andy Highfield draws a correlation between the size of the animal and its metabolic rate (determined by temperature) and the amount of time it takes to start winding down to hibernation through fasting. A larger animal may require up to three weeks to clean out its system while a box turtle or a Horsfields tortoise may need only two weeks. Dr. James Jarchow believes that a bit of grass ingested prior to hibernation isn't harmful, but large of amounts of food are. Omnivorous species like turtles must be kept from feeding at least two weeks prior to being put into hibernation to avoid food decomposing in the upper part of the digestive system; tympanic gas will form and suffocate the sleeping turtle. Fruit whose sugars ferment are particularly dangerous.
And Tropical Species
Terrestrials And Semi-Aquatics Indoors And Out
Hibernating species can tolerate a temperature between 39°F and 50°F (3.8°C and 10°C) when artificially hibernated. A temperature above 50°F may precipitate torpor, not a true hibernation, and your turtle or tortoise may use up precious fat reserves with its raised metabolism. If that happens and too much fat has been expended, you'll have to take the turtle or tortoise out of its hibernation container and allow it to gradually come up to a warmer temperature. The animal must then be fed and maintained at non-hibernating temperatures. One way to tell your tortoise isn't truly hibernating is if it is active in its hibernation box or if you find it has urinated . Remove him and hydrate him and move the box to a cooler, protected spot. Provide fresh, dry substrate and monitor him to be sure he will sleep.
It's critical to weigh your turtle or tortoise prior to hibernation and chart its weight throughout the hibernation period. Invest in a digital scale for weighing the smaller species (under 6 lbs.) for best accuracy. Based upon the size-to-weight ratio, your vet or another keeper can tell you if hibernation is safe. During hibernation your frequent checks can be used as a time to gently weigh your tortoise. An excellent rule-of-thumb is that a tortoise or turtle should lose only 1% of its body weight per month of hibernation. For example, a 400 gram tortoise should not lose more than 4g per month. Multiply the animal's weight in grams by 0.01: 0.01 X 400 = 4.0 grams. Chart it on a piece of paper you keep taped close to the hibernaculum/container as a guide for next year's hibernation.
Wild tortoises and turtles will select a burrow that has slightly humid soil or leaf litter to decease evaporative water loss through the skin and lungs. Captives that are being hibernated in unnatural conditions indoors risk dehydration due to low humidity. However, because they're poikilotherms, they mustn't be allowed to become wet and chilled, either; they won't be able to dry off. Check the skin condition of animals spending the winter sleeping indoors. If the skin is drier than usual or the animal has lost too much body mass in that period, wake it and soak it in shallow (below the bridge), room-temperature water for two hours to regain lost fluid. Dry it thoroughly (but do not warm it!) and return it to its box. Younger tortoises and turtles (hatchlings and juveniles) should have this done for them every three weeks if necessary.
Body water partitioning in hibernating turtles and tortoises changes in the fall, allowing them to store more water in winter than in summer, so hydration is critical to a successful hibernation. If your hibernating turtle or tortoise voids its water stores (you find the substrate is wet), you absolutely must bring it out for rehydration in shallow water as previously explained.
If your animal is used to hibernating outdoors, make sure it has access to drinking water at all times, but don't let it hibernate where rain can drown it or wet it to the point it gets chilled. Check the hibernation spot frequently. If you see a turtle or tortoise out trying to bask on a rainy or cloudy day, it's indicative that something's wrong with the hibernation process. Bring the animal indoors for an examination to determine whether hibernation should be allowed to continue. Better to be safe than sorry!
Intimidated? You should be. Attention to detail makes the difference a successful hibernation and one that harms your animal. But you've got several good tools with which to work: a scale, a thermometer, a humidity gauge-and resources like your club and the internet.
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