Crocodilians are ectotherms, that is, they rely on external sources of heat to raise their body temperatures. Unlike mammals, crocodilians are unable to maintain a constant body temperature by physiological means, for this reason they are referred to as being "cold-blooded”. Crocodiles lack insulation, such as hair or feathers and have no internal means, such as shivering, to raise their body temperature above that of the environment. Consequently, crocodilians are today restricted to those parts of the world where the average temperature of the coldest month of the year does not drop below 10 – 15 degrees Celsius.
Crocodilians have a "preferred" body temperature of around 30-33 degrees celsius, and to achieve such temperatures they move back and forth between warm and cool parts of their environment. In cold weather they bask in the sun to heat up, and in hot weather they seek shaded, cool areas to avoid overheating.
Basking crocodilians will usually orient themselves so that the maximum body surface is exposed to the sun. However, as they warm, they often face the sun, thereby reducing heat uptake by the relatively small head, whilst the body continues to heat up. When oriented in this way crocodilians will often open their mouths, allowing the brain to cool through evaporative cooling, while the rest of the body is heating. This "mouth-gaping" posture, however, is also a behavioral display, used even at night, or when it is raining.
Some crocodiles also dig burrows into the banks of lakes or rivers. Burrows may extend for several metres in length and end in a chamber where individuals seek refuge from drought or cold.