When it's time to migrate, sparrows slash the amount of time they spend sleeping. But unlike long-haul truckers or college students cramming for exams, this avian insomnia may not take a serious toll on their cognitive skills. Understanding how the sparrows pull off this trick could provide a fresh insight into the nature of sleep.
Each spring, the white-crowned sparrow, Zonotrichia leucophrys gambelii, sets off from its wintering site in Southern California on a 4300-kilometer migration to its breeding site in Alaska. During their wintering and breeding seasons, songbirds like this sparrow are active during the day and sleep at night. During migration however, they undergo a profound behavioral shift and fly both day and night. How the birds manage such a feat of endurance has remained a puzzle. Nobody knows, for example, whether migrating birds are able to take 40 winks on the wing. Research published 13 July in PLoS Biology suggests that they may not have to.
To investigate the link between sleep and migration, Ruth Benca, a psychiatrist at the University of Wisconsin, Madison, turned to white-crowned sparrows. Instead of chasing migrating birds and watching them for signs of sleep, Benca kept an eye on captive birds when migration time rolled around. The birds become restless, Benca says, and her measurements of electrical activity in the birds' brains reveals that they sleep on average 63% less when it's time to migrate. A performance test, in which these hyperactive sparrows learn to peck on a sequence of buttons to earn seeds, suggests that they stay alert in spite of losing sleep. Understanding how they sleep less without impairment may provide insights into sleep disorders and seasonal mood disorders, she and her colleagues claim.
That may be pushing things a bit far, says Ullrich Wagner, a neuroendocrinologist at the University of Lübeck in Germany, but the research does raise some intriguing questions. The birds' ability to get by without sleep is an "amazing phenomenon," he says, and future work should focus on the underlying mechanism. In the longer term, experiments like these could even shed light on the function of sleep itself, says Pierre Maquet, a neurobiologist at the University of Liège in Belgium, although he cautions that what's true for sparrows won't necessarily apply to humans.