Washington (AFP) - In humans, nodding off for a few seconds is a clear sign of insufficient sleep -- and can be dangerous in some situations, such as when driving a car. But a new study published on Thursday finds chinstrap penguins snooze thousands of times per day, accumulating their daily sleep requirement of more than 11 hours in short bursts averaging just four seconds. The flightless birds might have evolved this trait because of their need to remain constantly vigilant, according to the authors of the paper in Science. The researchers argued that the findings show, contrary to prior a...