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 fact dolphins, whales and porpoises are all marine mammals and make up what is commonly referred to as the cetacean species.
In comparison to marine mammals fish and many amphibian species are cold-blooded and will match the temperature of their environment.
Cold-blooded animals do not require much if any body fat since their body adapts to varying climates and thus requires much fewer (heat generating) calories to function.
Other characteristics that are found among land dwelling mammals and marine mammals including:
- Mammals are warm-blooded and have body fat to keep them warm
- Mammals have hair in order to better deal with cold wind and freezing environments
- Mammals giving birth to babies (very few produce eggs)
- Mammals breathe air
- Mammals produce milk to feed their babies
In order to maintain their body heat in cold climates dolphins develop a thick layer of insulated blubber which helps protect their vital organs from the cold oceanic waters.
The thickness of the dolphins blubber however may be less important in keeping a dolphin warm than its blubber’s lipid concentration.
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.
Also just like a human when the dolphins muscles may cause involuntary shivering which helps keep the dolphin warm in colder climates by burning calories, creating friction and producing heat.