BioEd Online

Imagine trekking thousands of kilometres on just three hours' sleep a night. The lack of rest would tax the hardiest of travellers, but the white-crowned sparrow just keeps on going.

Researchers who have studied the bird find that it can stay alert during prolonged periods of sleep deprivation. It is hoped the discovery will shed light on brain disorders, such as depression, where sleep patterns can go haywire.

Every spring and autumn, tens of thousands of white-crowned sparrows (Zonotrichia leucophrys gambelii) migrate the 4,000 kilometres between Alaska and southern California. They fly by night and feed by day, prompting researchers to ponder how they cope with so little shut-eye.

Ruth Benca of the University of Wisconsin-Madison and colleagues studied the behaviour of 13 captive white-crowned sparrows over a year. Their findings are reported in PLoS Biology¹.

The lab birds became restless during periods when they would ordinarily be migrating. They slept two-thirds less than normal yet were no worse than other sparrows on tasks of learning and memory. Whether in migratory sleep-mode or not, birds were equally adept at pecking different buttons in a particular order to receive a food reward.

"These data argue that sleep requirements are driven by a hierarchy of biological needs and are not a fixed, immutable force," says sleep researcher Robert McCarley from VA Boston Healthcare System in Brockton, Massachusetts. When goals, such as migration, become significant, sleep becomes less important.

Highs and lows

Benca's team also attached electrodes to the birds' skulls and recorded their patterns of brain activity as they slipped into slumber. During the migratory period, sparrows entered more quickly into rapid eye movement (REM) sleep, which is typically associated with dreaming in humans.

Human patients with manic depression (also called bipolar disorder), who swing between periods of hyperactivity and depression, show a similar sleep pattern. "Understanding what is going on in the bird brain should help us to understand what is going on in the human brain during various mood disorders," says Benca.

At present, the neural mechanisms behind the birds' behaviour are unclear. But researchers hope to pin them down and use the information to help people who need to stay awake for long periods, such as pilots.