In the turtles’ community, stacking is when multiple turtles gather instinctively in particular spots then get on top of each other to create a tower-like formation.
There isn’t too much fighting over positions among turtles participating in the stacking activity because each position in the “tower” offers a different advantage.
If you have pet turtles or you’re simply curious about the ins and outs of this fascinating behavior, then you’ve come to the right place! Today’s article dives deep to thoroughly answer the question: why do turtles stack?
So, who is stacking a thing? What drives turtles to get on top of each other like that? Well, there are a few possible reasons as follows:
The main reason why turtles stack on one another is to obtain more UV rays as well as additional warmth. The turtles at the top levels of the tower are exposed to more sunlight, whereas the turtles at the bottom levels are in a better position to benefit from the stack’s collective warmth.
You see, turtles are ectothermic animals. Unlike warm-blooded animals, turtles can’t regulate their own body temperature through internal processes.
As such, they have to resort to using the elements of their environment to control their body temperature effectively. This is why turtles are always on the move from cooler to warmer areas and the other way around.
For example, standard pond turtles (such as red-eared sliders, yellow-bellied sliders, and painted turtles) enjoy being around water and swimming in it. Since water cools down their bodies, they’ll engage in basking from time to time to bring their temperature back up.
These turtles bask by climbing on top of each other, enabling them to warm up quickly even if the available basking area is limited. Thanks to being in very close proximity to one another, the heat from their bodies travels via convection, which warms them up faster.
Animals often see the world in a different way than humans. Being so close to the ground, turtles end up viewing other animals a lot bigger than reality, even more so depending on how tall the animal is.
Just like we’re advised to try to look larger by raising our arms and opening/spreading our jackets if faced with a mountain lion to intimidate the beast into not attacking, many animals also apply such tricks when they come across a more imposing creature.
Turtles resort to a similar technique when they encounter larger predators, which is stacking to appear in a bigger form. For example, turtles do this for protection against alligators — one of their greatest threats.
In this case, when turtles sit on top of each other, there’s a higher chance that the alligator will see them as a much more challenging snack. While one turtle on its own will seem like an easy target, a stack of turtles would be a lot harder to deal with.
In our example, the alligator would have to bite through multiple shells in one go if it wants to reach any meat. The shell of one turtle is already incredibly tough, so the force required to overcome several shells can be so much that the alligator thinks this meal just isn’t worth the trouble.
Other than appearing larger and being tougher to bite through, turtles may also seek protection from stacking by keeping a better lookout from a higher point. After all, multiple pairs of eyes can see better than one!
Consequently, if one turtle spots a potential danger and dives off the tower, this action would alert other turtles of the stack that a threat is nearby.
Another explanation for why turtles stack is that it gives them a way to make up for limited basking spots. While ponds can have plenty of water for turtles to swim around, they may not have enough desirable places for the turtles to dry off and bask in the sun.
Ponds may offer only a few good rocks or logs where a turtle can hang out and receive its fix of sun rays. As sun “worshipers”, turtles want that perfect spot and will settle for nothing less.
Typically, this leads to many turtles needing to bask and only a few good spots to accommodate them. Luckily, turtles don’t fight each other and avoid harming themselves or one another over basking locations.
Instead, they have a more peaceful approach to resolve the issue — enter stacking. Turtles will simply chill out on top of each other, sharing the sun and warming all members of the tower.
There’s no such thing as the best position when it comes to a turtle stack. Each position in the tower offers its own advantage to the turtle parked there, which is why you’ll never see turtles seriously fighting over positions as they climb onto one another.
The turtle at the top of the tower will receive the most UV rays from being more exposed to the sun. However, it’ll only get a little heat from the turtle underneath.
On the other hand, the turtle at the bottom of the tower will receive a lot of heat but still not the most heat as there’s no turtle below it.
So, from a UV or heat perspective, neither being on top nor at the bottom is the best position, yet it beats basking alone by miles. This is because all turtles forming a stack will benefit; they’ll definitely get much more warmth than they ever would alone.
Granted, the top position is seemingly better. But does that mean turtles will compete to secure it? The chances of this happening are minimal.
Similarly, turtles will probably never actively try to avoid being at the bottom despite it not being the most beneficial. Why is that though? Well, aside from the fact that it’s still better than solo basking, every turtle will get a chance to reside in a better position at some point.
You see, a turtle’s position in a stack isn’t permanent. Even if most of the pictures of stacks you see online show the smallest turtle at the top and the biggest turtle is at the bottom, this isn’t a constant rule. Larger turtles chilling on top of smaller ones isn’t an uncommon thing to witness, so any turtle will have up days and down days — literally.
With all the different benefits turtles can achieve by stacking, you may be wondering about the state of the turtles at the bottom. Does stacking hurt or cause any sort of pain to the turtle stuck down there?
You’ll be relieved to know that the answer is no. Thanks to the immense strength of a turtle’s shell, carrying multiple turtles on top of it has no harmful effects whatsoever to the bottom turtle.
The shell of a turtle is just too tough to allow for any feeling of pain as a result of stacking. The fracture toughness (the amount of force that can break through a surface) of an average turtle shell is 36.4MPa m1/2.
To help you imagine its strength, the fracture toughness of aluminum is 22MPa m1/2. This means that a turtle’s shell is stronger than aluminum!
Not to mention, being at the bottom actually grants that turtle an edge that it needs more than UV rays, which is a whole lot of warmth compared to turtles residing higher up the tower. Also, the bottom turtle is the most protected one in the face of alligator attacks or those by other predators.
That said, we’re not denying that turtle bullying is something that takes place. However, it doesn’t typically manifest in the form of stacking.
Instead of piling over each other to “bully”, turtles usually prefer to bite. These animals just don’t have the concept of wrestling or body-slamming hardwired into their nature.
If you notice your pet turtles often engaging in stacking and you’re curious to understand why this happens, the following are a few possible reasons and how you can prevent them:
If the basking area in your tank is too small, your pet turtles will have no choice but to pile up on top of one other. At some point, this will force your turtles to get competitive over the top spot because of the lack of exposure to UV rays.
In the end, one of your turtles will dominate the rest and the bottom turtle won’t receive nearly enough UV rays because it can’t get any other position. Even if the turtles are equally dominant, there’s still a high chance they’ll hurt one another and this is obviously an issue as well.
To avoid such problems, you should have your turtles living in a tank with plenty of basking space to ensure a peaceful environment where no fights occur to obtain a good spot.
Another issue that could force your pet turtles to stack is your basking area being poorly heated. If the tank is lacking warmth, the turtles will have to resort to stacking so that they can receive the necessary heat for regulating their body temperature.
If you check and find that the heat level across the basking platform and within the enclosure is too low, then you must crack it up to the required temperature. This could be because the output of the lamp isn’t high enough, in which case you need to install a greater wattage lamp.
Make sure you use a thermometer and a thermostat to monitor and control the heat output of the lamp.
A lot of turtle keepers may not realize this, but the issue could be with the light or heating coverage across the basking platform or within the enclosure. Now, if this is the case, you can’t resolve it by increasing the wattage/output of the installed lamp.
If you do this unnecessarily, you can risk overheating or even burning the turtles.
The right solution here is to use two lower wattage lamps instead of the single heat lamp you currently have. This way, you’re ensuring that the temperature within the enclosure stays unchanged, while the area exposed to the light gets larger creating a wider basking platform.
If you’re a turtle keeper, you may have noticed that the more dominant turtles are typically the ones positioned higher up the stack. In this case, it’s a possibility that turtles display their dominance by attempting to obtain more light and heat than the other individuals in the enclosure.
This makes sense because light and warmth are vital for turtles to thrive. A setup that allows plenty of these elements is crucial for the health and growth of your pet turtles.
The lack of such resources can cause problems that make turtles weak and ill. For example, insufficient UV rays can lead to metabolic bone disorders and deformations.
As we’ve established by now, stacking is generally harmless and doesn’t usually affect the health of the turtles engaging in the activity. However, this doesn’t dismiss the fact that the turtles at the bottom of the pile would be getting less light and heat in comparison with the ones at the top of the tower.
Now, suppose there’s a particular turtle that always finds its way to the bottom of the stack. This can cause it to suffer from vitamin D deficiency, even more so if the lights you’re using within the enclosure have a sub-optimal output of UV light.
But is this scenario likely to happen? Not really. In captivity, the major hazard associated with basking is developing burns.
In the wild, burns aren’t a concern because being a couple of inches closer to the sun doesn’t make a difference. But in an enclosure where a heat lamp is the primary main source of warmth, being a few inches closer to the light makes a huge difference.
Not to mention, if you have enough turtles, they can pile up so high that they touch the heat lamp and sustain burns. We recommend holding the light fixture using a lampstand to avoid such incidents, as well as installing a screen at the top of the enclosure with a lock for extra security.
This is highly unlikely to occur because it requires a bunch of variables to line up at the same time including:
- The turtle at the bottom should almost always end up down there.
- The turtle(s) at the top should prevent all UV rays from reaching the turtle(s) below.
- The turtle(s) at the top should prevent all warmth from reaching the turtle(s).
As you can expect, for all three of these factors to happen simultaneously is pretty much impossible.
When it comes to possible hazards of turtle stacking that you should be worried about, nothing is probably worth your sweat except maybe bullying or fighting.
That being said, there’s no reason for us to believe that turtle stacking is in any way a result or a cause for bullying or fighting in the vast majority of cases.
This makes sense because as we already explained when turtles pile up on top of one another, they’re actually helping each other to get more UV rays and heat, as well as to intimidate potential predators by appearing larger in size.
Moreover, we also know that no one turtle always ends up in the same position — whether it’s at the top or the bottom. It can happen often, but not every time.
Not to mention, if turtle stacking was an act of aggression, then how come smaller turtles sometimes reside higher up the pile? That just doesn’t add up.
In short, the answer is no. Although several species of turtles live in big communities, we aren’t talking about social animals. Such turtles just happen to share the same habitat while generally ignoring their companions.
In their natural homes (places such as rivers, lakes, or ponds), turtles will choose the same spots to bask including bid rocks, logs surfacing from the water, or nearby branches. If these spots are packed, turtles will simply stack on top of each other to “make” room.
The only reason turtles do this is that they need light and warmth, not that they want to interact or fulfill a social urge.
As far as science knows today, turtles’ communities don’t follow like, say, a wolf pack. Instead, they just do what’s beneficial, which happens to require the help of one another.
There you have it, a complete guide to answer the question: why do turtles stack? The reasons are several, but the main one is to seek UV rays and warmth so they can effectively regulate their body temperature.