The short answer is no, dolphins (like all other mammals) aren’t cold-blooded.
Dolphins are marine mammals and just like humans and other land dwelling mammals maintaining body heat is a major component in a dolphin’s ability to survive.
In comparison to marine mammals fish and many amphibian species are cold-blooded and will adjust to match the temperature of their environment.
Cold-blooded animals do not require much if any body fat/blubber since their body adapts to varying climates and thus requires much fewer (heat generating) calories to function.
Characteristics that are found among land dwelling mammals and marine mammals including:
- Mammals are warm-blooded and have body fat or blubber to keep them warm
- Mammals have hair in order to better deal with cold wind and freezing environments
- Mammals giving birth to babies (a very few species produce eggs) Note: Most mammals give birth to a single offspring.
- Mammals breathe air (they are unable to extract oxygen from the water like fish and amphibians)
- Mammals produce milk to feed their babies (nurture is often an important factor in a young developing mammals life)
Characteristics that are found among fish and amphibians include:
- Fish and amphibians are often cold-blooded and are able to adjust to the temperature in their environment without needing body fat or blubber to stay warm.
- Fish and amphibians are not known to possess hair. Instead they may have moist skin, scales or an exoskeleton
- Fish and amphibians typically lay eggs and some species may produce thousands of eggs in a single year
- Being able to extract oxygen directly from the water through the use of gills or specialized organs
- Fish and amphibians aren’t known to provide much nurture to their children and many species are left to hunt and fend for them selves as soon as they are born.
In order for dolphins to maintain their body heat in cold climates dolphins have developed a thick layer of insulated blubber which helps protect their vital organs from the cold oceanic waters.
The thickness of the dolphins blubber however is only one important factor in keeping a dolphin warm.
The blubber’s lipid concentration plays an equally important role in maintaining body heat.
Dolphins that have a high concentration of lipid but a thin layer of blubber may actually be better equipped at staying warm than a dolphin with a thicker layer of blubber but a lower lipid concentration.
Simply put having a higher lipid concentration equals better insulation from the cold.
Another interesting feature that helps prevent dolphins from freezing is their body’s ability to increase its metabolic rate which increases the amount of calories the dolphin burns allowing it to produce and transfer heat throughout their blood, vital organs and muscles when they are in extremely cold environments.
In fact most warm-blooded mammals require significant amounts of calories to maintain their body heat and keep themselves healthy as their metabolism requires large amounts of energy to function properly.
Also just like a human when a dolphin is in a cold environment its muscles may cause involuntary shivering which helps keep the dolphin warm by burning calories, creating friction and producing heat.