Pigeon researchers found that the birds had sleep stages like humans. 15 pigeons trained to sleep were observed using fMRI and infrared video cameras. Pigeons have REM and non-REM sleep, according to experts.

The researchers tracked the pigeons’ eye movements during REM sleep and found substantial brain activity in visual processing and flight analysis regions. The research suggests that pigeons dream about flying in REM sleep, like humans.

The amygdala, which processes emotions, was also recorded. During REM sleep, pigeons’ pupils constricted quickly, like when they court or fight. Sleep cycles clear brain trash. Birds have denser brains than mammals, thus their processes may be more important. Birds have shorter, more frequent REM periods.

Since birds and mammals shared a common ancestor 315 million years ago, the findings are startling. Nature Communications published the study. Pigeons may pay for vivid dreams.

“We think that the increased flood of blood into the brain during REM sleep, which supports the elevated brain activity, might block the cerebral spinal fluid from moving from the ventricles into the brain,” explains ornithologist Niels Rattenborg. This shows that REM sleep and its activities may cost brain waste removal.”