Which of the following organisms maintain their own body temperature?

The answer is: the birds .

Many organisms, such as fish and birds, have the ability to maintain their body temperature in the face of changing environmental conditions. This is known as thermoregulation, and is an important adaptation that allows animals to survive extreme temperatures. Fish are particularly well suited to this, as they have physiological adaptations that allow them to regulate their body temperature. Fish also have special organs that can detect temperature changes in their environment and respond accordingly. Birds, on the other hand, rely on their feathers and other features to keep their bodies warm. Both methods of thermoregulation ensure that organisms can survive at variable temperatures.