Newborn dolphins and orcas don't catch any zzz's during the first few months of their lives, a finding that scientists say raises questions about the necessity of sleep.

To aid growth and development, most animals maximize rest and sleep after birth, but the two sea mammal species seem to be an exception.

Researchers in California studied two adult orcas (Orcinus orca) and their calves for five months at SeaWorld San Diego.

The sleep study focused on captive dolphins, like this one at the West Edmonton Mall.

Young orcas stayed active 24 hours a day for at least the first month of their development, the scientists report in Thursday's issue of the journal Nature.

Mothers also got little sleep during this period, the researchers found. They based part of their sleep observations on whether the animals kept at least one eye open.

"Somehow these seafaring mammals have found a way to cope with sleep deprivation, facilitating rather than hindering a crucial phase of development for their offspring," Jerome Siegel, a neuroscientist at the University of California - Los Angeles, said in a statement.

Coping without sleep

As the calves grew, their sleep levels gradually reached adult levels of resting five to eight hours per day floating at the surface or lying on the bottom of the pool, rising occasionally for air.

Bottlenose dolphins (Tursiops truncates) at a research station in the Black Sea region of Russia showed similar sleeping patterns.

The researchers don't know how the cetaceans cope with so little sleep, but they say it may offer some advantages to the calves:

• By moving continuously, the risk from predators is reduced.
• The young maintain their body temperature while they develop insulating blubber.
• The animals can swim to the surface more often, aiding respiration.
• Lack of sleep may help the animals' brains and bodies to grow rapidly.

The findings suggest sleep isn't required for development, raising the question of "whether humans and other mammals have untapped physiological potential for coping without sleep," Siegel said.

The results run contrary to previous research on rats and flies that suggests forced sleep deprivation for two to three weeks can be lethal. Based on those results, scientists suspected sleep is crucial early in life for land-dwelling mammals.