How Migrating Birds Navigate at Night

Experiments with migrating birds in planetariums have shown that birds are not only aware of star patterns but also respond appropriately to changes in these patterns.

Roosting storks, Kromme River, South Africa

Credit for above photograph: Andrew Bartels, son of the author

These experiments prove that when birds migrate during cloudless nights, one of the ways they navigate is by constantly referring to constellations in the night sky above them.

Bird migration is not only a fascinating subject, it is also high drama.

Navigating by the Stars

It is four minutes after midnight on September 10th 2009. The plains of Serengeti in Tanzania are bathed in moonlight. The stillness of the African night is punctuated by the grunt of a hunting lioness. A herd of gazelle hear the grunt and freeze — ears twitching.

High above these moonlit plains an astonishing scenario is being played out. A swallow from Europe is flying south back to her summer home at the tip of Africa. She crossed into Africa at the Straits of Gibraltar and then overflew the vast and dangerous Sahara desert. Forced by hunger to migrate at night, she is now over the Serengeti.

She senses she is not quite on course so she glances up at the canopy of stars above her. Polaris, the North Star, is far behind her on the northern horizon. She notes the position and angle of the Constellations of Orion the Hunter and Taurus the Bull.

A slight course adjustment is called for so she makes it. She is back on course, streaking south ward through the night. It is now six minutes past midnight. Her journey continues.

What could be more dramatic? And remember. it is an adventure played out by thousands and thousands of migrating birds every night, all over the world.

Research Proves Birds Navigate by the Stars

Could such amazing feats of navigation be true? Yes, according to research carried out by E.G. Franz Sauer at the University of Freiburg and the Olbers Planetarium in Bremen, West Germany (Theatres of time and space: American Planetaria, 1930–1970 by Jordan D Marche (reproduced on Google Books).

Franz Sauer’s Work on Stellar Navigation by Birds

Sauer raised birds in captivity and made sure that they never saw the natural night sky. He then exposed them to the actual night sky outside. The birds immediately indicated that they wanted to migrate in a direction consistent with their species (they were old-world warblers). Clearly, seeing the night sky immediately helped the birds migrate in the correct direction. It seemed probable that the birds had “innate stellar recognition abilities” (Marche).

Next, Sauer used these birds for an experiment at the Oblers Planetarium. He exposed the birds to an artificial night sky synchronized with real night sky outside. The birds continued to display the correct direction to migrate.

Finally, Sauer adjusted the night sky above the birds to make it look as they would see it from lower latitudes. According to Sauer, the birds changed their flight paths appropriately.

Similar experiments have been conducted in the United States with similar results See for example the extract from Bird Migration, p. 363, by Thomas Alderstam, David A. Christie (Google Books).

There is no doubt now that birds navigate by the stars.

Back to the Serengeti — The Wonder of Bird Migration Continues

The swallow has been flying for several more hours. The southern border of the Serengeti is ahead. In the east to her left the faint glimmer of dawn appears and then the huge red, African sun.

The Constellations are now invisible. The swallow checks her direction by the angle of the sun, the time and the pull of the earth’s magnetic field. She makes a slight flight path correction and continues due south. She is on time and on course for the southern tip of Africa.

Another feat of amazing navigation has begun, this time during the day.

John Bartels