So there are 285 species of turtles and, obviously, their behaviors very depending on where they live and their size and their social habits.
The most noticeable thing about turtles, of course, is their shell. They, actually, are the only animal that exists like this. The upper shell or the top shell is called the carapace and the lower shell is called the plastron. When turtles are scared or feel threatened, they will often withdraw into the shell, so it is protective for them. Some species are very shy. You're gonna find them kind of hiding under logs and burying themselves more in the dirt. They're just generally quieter.
The aquatic turtles, like this red-eared and this map turtle, some of the behaviors you'll see with them are basking behaviors. So, again, they spend a lot of their life in the water but they will come out onto the banks of rivers and lakes and onto rocks and logs and bask in the sun. That tends to be when we see them. Again, when you approach them, they may not withdraw into their shell but they'll actually retreat into the water.
So, one misconception about turtles is that they're very slow. This is not true, and I think anyone who has one as a pet and ever lets it run around in their home or outside will agree with me. They can be quite fast. The other thing that they are quite good at is climbing and digging. So, if you house a turtle outdoors, be sure that you have a protective fence around its enclosure and just know that some of them can dig, actually, quite deeply into the ground.
When you have a pet turtle, you will obviously get to know what behavior is normal for them. I always encourage people to read about what their behaviors would be like in their natural environment, but you can also tell, over time, your turtle will become accustomed to your presence and will know that you're also the one that feeds it. Most turtles, once you've had them in your home for some time, should be bright. They should be alert, they should be responsive, they should seem comfortable and active. If you ever notice that your turtle is not eating, if it becomes very lethargic or tired, if it seems like it's having trouble breathing, if it's hiding all the time, those could be signs that there's something wrong with your turtle. So, again, there are many different types of behaviors in turtles, and I encourage everyone to read about them, and if you notice something wrong with your pet turtle and its behavior, definitely call a reptile veterinarian.