Watching a flock of birds flying high over a plain, you may wonder what their experience and view of the areas they fly over is like. Scientists often wondered as much, until they discovered that the birds sleep while flying.
This by all means explains how it is possible for birds to fly constantly for weeks on end, as many migratory birds do.
Dr Niels Rattenborg of the Max Planck Institute for Ornithology leads a group that studies sleep among birds. They equipped fourteen large frigate-birds (or frigate-petrels, birds similar to pelicans that snatch fish from the see) with small measuring devices that monitored their brain activity and then studied the records.
Rattenborg confirmed that these migratory birds sleep during long flights but that they are never in deep or very long sleep. When on land, frigate-birds sleep for as long as twelve hours a day. However, during flights that last several weeks they only sleep for about a total of 41 minutes a day, but never longer than twelve seconds at a time.
When a frigate-bird sleeps, one half of its brain is switched off, and sometimes even both halves are. This happens when it is floating on air currents and does not have to flap its wings. As one brain hemisphere is usually active, the bird keeps its eyes open and is able to use visual navigation.
(M.Đ.)