tortoise hibernation


Tortoise: ‘Tis the Season for Hibernation

Research associate Daniel checks tortoise hatchling pens.

As we begin the new year at the San Diego Zoo Desert Tortoise Conservation Center (DTCC), almost all the tortoises have gone down into their burrows for their winter brumation (reptilian hibernation). During the winter months, we shift our responsibilities from feeding and processing tortoises (giving health assessments to those brought in to the DTCC) to doing surveillance in our assigned areas. We walk each section of pens looking for sick or injured tortoises and for damage that needs to be repaired in the pens.

Daniel checks tortoise pens to make sure the animals are in their burrows.

At this time of year, with consistently cool weather, all the tortoises should be pretty well entrenched in their burrows. After we are comfortable that the tortoises are down for the winter, we create a wall of earth in the opening of each burrow to provide an extra layer of protection against the elements. At this point, any tortoise found outside of their burrow is cause for concern. When we find tortoises out in cool weather, we bring them in for a complete health assessment.

All sick or injured tortoises are kept in the medical center for treatment, and the tortoises that appear healthy are put back in their pen and checked more frequently to monitor any change in their condition. Typically, tortoises that are awake and out of a burrow during the cold winter months usually have a health issue causing them to come out of brumation. Doing pen surveillance is the only way we can monitor the condition of the tortoises during the winter. Since it is not healthy to disturb the tortoises in their burrows, we have to closely monitor the behavior and condition of the tortoises that are active outside their burrows.

Rachel Foster is a research associate at the San Diego Zoo Desert Tortoise Conservation Center. Read her previous post, Saving Tortoises, One Urolith at a Time.


Saving Tortoises, One Urolith at a Time

An x ray shows an adult desert tortoise with a large urolith on the left.

The tortoises have begun their fall slow-down and are preparing for their winter brumation (reptilian hibernation) here at the San Diego Zoo Desert Tortoise Conservation Center in Las Vegas. This means that the priorities in the medical center will shift a bit. We will have a few tortoises staying awake for the winter because they are either too sick or injured to brumate. However, we will also have a number of residents staying in the medical center waiting to have surgery at the state-of-the-art Harter Veterinary Medical Center, located at the San Diego Zoo Safari Park. All of these tortoises have dangerous uroliths that have developed in their bladder (uroliths are analogous to kidney and bladder stones in people).

A large stone removed from an adult tortoise carcass

Uroliths develop for various reasons, the most common being improper nutrition or prolonged dehydration. One of the adaptations that tortoises have that allows them to thrive in the arid desert environment is the ability to store large amounts of water in their bladder and to reabsorb it as the body needs it. As they reabsorb the water in their bladder, the solid particles in the bladder become more concentrated and can stick together. As time goes on more solids are deposited in the bladder and combine with those already present, forming a stone. Therefore, stones are more likely to form if a tortoise goes long periods of time without consuming fresh water to flush and replace the stored water.

Small stones that form can pass out of the bladder when the animal eliminates. However, once the stone becomes a certain size, it can be too big to pass and remains in the bladder where it can continue to get larger. If the stone is there long enough, it can adhere to the walls of the bladder, making it very difficult to surgically remove it without damaging the bladder. Eventually the stone can get large enough to take up most of the bladder space, thereby taking up very important water storage space. This compounds the problem by increasing dehydration in the tortoise. Eventually the stone can block the urethra, preventing the tortoise from eliminating at all and causing a build up of toxins in the tortoise. The long-term presence of uroliths can result in a prolonged, painful death.

A desert tortoise recovers from surgery to remove a stone.

We palpate every tortoise during its health assessment to see if we can feel a coelomic mass. Sand or gravel in the bowels or eggs can feel similar to uroliths during palpation, so we x-ray every tortoise in which we feel a mass to determine what the mass is. Once we have x-ray confirmation that it’s a urolith, we send the tortoise to the hospital, where veterinarian Nadine Lamberski has developed a less invasive technique to remove the stone. Traditionally, the most common stone removal technique used by veterinarians was to remove part of the plastron (the bottom part of the shell) to get to the stone. This procedure is very invasive and can take a very long time to heal since the bone of the plastron has to be removed. The veterinarians at the Safari Park use a technique in which they make an incision in the skin of the prefemoral area (just in front of the hindlimb) so they can access the stone and break it down and remove it without having to remove part of the shell. This surgery can take up to 6 hours to perform, but the recovery time for the tortoise is much quicker for this procedure. I am very excited to say that the veterinarians have performed a number of these surgeries successfully, and our tortoises have been able to return to us with a much better future in store for them.

We have a number of tortoises ready for surgery this winter. Once they recover, they will be able to be released to the wild Mojave Desert in the healthiest condition possible next year to live out their long lives in a natural environment.

Rachel Foster is a research associate at the San Diego Zoo Desert Tortoise Conservation Center. Read her previous post, Desert Tortoise Hibernation: Not for All.


A Long Winter’s Sleep

A desert tortoise hatchling heads for a burrow.

It’s that time of year again: the time for desert tortoises to sleep for the winter. As some animals head south for the winter in search of warmer weather, desert tortoises stay in their favorite burrows right here in the Mojave Desert to escape the winter chill. Every year around October, desert tortoises begin to slow down and find a perfect burrow to hibernate in for at least the next few months of winter. At the San Diego Zoo Desert Tortoise Conservation Center (DTCC), we dig artificial burrows for many of the tortoises to make sure they are well protected over winter, and we berm them in by building up a mound of dirt in front of the burrow to prevent cold air and winter monsoon rains from getting in.

Desert tortoise hatchlings have their choice of burrows at the DTCC.

It is not uncommon for the Mojave Desert to receive some rainfall during winter months, and occasionally desert tortoises come out to have a drink. That was certainly the case a few weeks ago when it rained for seven days straight, and we were completely flooded! In most cases, tortoises come out of their winter sleep because of the smell of the rain and creosote in the air, and they either find low-level ground where water has collected, or, in some instances, they actually dig a small impression in the ground so water can pool up for drinking. After their drink, they return to their burrows to sleep for the rest of their hibernation period.

Things are a bit different around here for little desert tortoises, though. As winter approaches, young tortoises are also starting to go to sleep for the winter, but before they can hibernate, we must do a health assessment on them to make sure they are healthy. Neonates (hatchlings from this year) and very young desert tortoises that weigh less than 3.5 ounces (100 grams) and are less than 3.1 inches (80 millimeters) long are kept in special predator-proof enclosures until they are large enough to be moved to an unprotected pen. Every one of the tortoises that is held in these pens must undergo a pre-hibernation health assessment, and this keeps us really busy!

A juvenile desert tortoise enjoys time in the sun.

This winter there are over 400 young tortoises in the predator-proof pens, so it took us two full weeks to assess them all. Luckily, almost all of them were in great condition and were ready for hibernation, but the few that weren’t feeling so well were taken to the medical center for special care over the winter (see post Desert Tortoise Hibernation: Not for All). The best thing for a young desert tortoise to do over the winter is to hibernate; we have seen that young tortoises that are allowed to hibernate outdoors, especially in their first year of life, grow up healthier than those that don’t! But if a little one is not healthy enough to hibernate, then it’s best to allow it to stay inside and awake over winter so he or she can get the care needed before spring.

Daniel Essary is a research associate at the San Diego Zoo Desert Tortoise Conservation Center. Read his previous post, Desert Invasions.


Desert Tortoise Hibernation: Not for All

An ill desert tortoise enjoys the heat lamp this winter.

As our second season ends here at the San Diego Zoo’s Desert Tortoise Conservation Center in Las Vegas, the tortoises have gone deep into their burrows for brumation (winter hibernation). For the most part, this means we get to take a bit of a breather as well. However, there are a few tortoises that are not brumating this year due to health issues that we hope can be resolved over the winter months. These special tortoises are staying with me in the medical center until the spring. Although in most cases it is better (and necessary) for any species that would normally hibernate to do so, there are some instances in which it may be better for individuals with certain types of medical conditions to stay awake through the winter.

We have a few tortoises undergoing treatment for severe upper respiratory symptoms (cloudy nasal and ocular discharge and labored breathing). Although the treatment takes about two weeks, by the time their treatment ends, it is too cold for them to safely go out into a pen. Instead, they are staying in the medical center where their immune systems will have time to recover from their illnesses so that by spring, they will be strong and healthy again.

We also have a few very emaciated tortoises that we felt were too skinny to survive hibernation this year. Our goal is to fatten them up over the winter! With daily feedings, we hope to get their weight stabilized enough so that they will be ready to go back out in the spring.

The last few tortoises we have in the medical center are waiting to go to the Paul Harter Veterinary Medical Center at the San Diego Zoo Safari Park to have urolith (bladder stone) surgery. We get a number of tortoises each year that have uroliths that are too large for them to pass. This can result in a very long and painful death if they are not removed surgically. Our amazing veterinarian, Nadine Lamberski, has developed surgical techniques to safely remove these stones.

Since Dr. Lamberski has to work these unexpected surgeries into her normally very busy schedule, these tortoises are hanging out with me in the medical center until they can be transferred to the Safari Park. Don’t worry, though, that we are not acting fast enough to remove these uroliths; although tortoises can eventually die from them, they can actually live for years with them, which is one of the reasons that most pet owners don’t realize their tortoise even has one!  As they wait for their surgeries, they are happily munching away on hay and tortoise chow and spend most of their time comfortably basking under their combination heat and UVB lamps. The first two of these urolith tortoises will be headed to the hospital next week!

Rachel Foster is a research associate at the San Diego Zoo Desert Tortoise Conservation Center. Read her previous post, Tortoises Need Heat and Light.


Winter at the Desert Tortoise Conservation Center

Snow dusts the Spring Mountains.

Spring Mountains, to the west of the DTCC, dusted in a layer of light winter snow in December 2009.

In the winter, the Mojave Desert can feel pretty deserted—the plants die back significantly, there are no insects buzzing in the sky, very few birds can be seen, the mammals and reptiles seem to disappear, and the air is quiet.

At the San Diego Zoo’s Desert Tortoise Conservation Center (DTCC) it is hard to imagine we have so many tortoises on site because all of them are underground sleeping in burrows.

This winter hibernation, called brumation for tortoises, is actually very important for the health of the desert tortoise, because it allows for substantially reduced metabolic activity and aids in normal growth patterns during the active season by providing a period of little or no growth in the winter. Temperatures can drop below freezing during the winter here, so to protect themselves, tortoises dig natural burrows that are often curved, providing wind and rain breaks.

Volunteer Kelly Garron constructing a berm in front of an artificial tortoise burrow.

Volunteer Kelly Garron constructing a berm in front of an artificial tortoise burrow.

Often tortoises will backfill the area around them at the deep end of their burrows, providing even more protection from the elements. But for tortoises that are currently living in our quarantine area at the DTCC because they are relatively new arrivals, we dig artificial burrows that are angled deep beneath the surface of the earth (12 to 36 inches or 30 to 91 centimeters, depending on the size of the tortoise). Since artificial burrows do not have curves like natural burrows do, we provide these tortoises with added protection from the elements by creating a berm (mound) of soil at the mouth of the burrows that the tortoises can easily knock down when they are ready to emerge in the spring.

Many people think of the desert as a hot, dry place, and for much of the year it is; however, during the winter the average highs are in the 50s while the lows are in the 30s. Chilling, seemingly relentless winds whip through the desert frequently and can exceed speeds of 40 mph. In December 2009, just last month, we saw snow at the DTCC! It didn’t stick, but the Spring Mountains to our west were dusted in a light blanket.

At this time of year we also receive roughly 2 inches (5 centimeters) of rainfall, which is pretty impressive considering that the Las Vegas area averages less than 5 inches (13 centimeters) per year! In 2010, we have had 0.29 inches (0.7 centimeters) of rain so far, but most of our rain usually falls in February (according to National Oceanic and Atmospheric Administration), so we are hopeful winter rains will be plentiful here. The winter rains are vital to the spring bloom, which can be very impressive, and they also support much needed food and water sources for tortoises when they come out of hibernation.

So while we finish berming tortoises in for the winter to keep them safe and protected, we will hope for more rain and a beautiful spring bloom to report!

Kirsten Dutcher is a research associate at the San Diego Zoo’s Desert Tortoise Conservation Center. Read her previous post, Reptile Diversity at Desert Tortoise Conservation Center.