How Birds Navigate the Night Sky

In autumn, millions of songbirds migrate at night to their winter homes in Central and South America from breeding grounds in the northern United States and Canada.

Warblers, thrushes, and buntings are just some of the species that are night migrants, and occasionally these birds can be observed (with the aid of binoculars) crossing the full Moon. Birds leave as soon as the Sun sets; peak migration is between 11:00 PM and 1:00 AM at altitudes of 2,000 to 5,000 feet—with some flying as high as 21,000 feet.

Navigating the Night Sky

In the 1960s, German ornithologists Franz and Eleanore Saver discovered that birds navigate the night sky by using the stars. A decade later, a Cornell scientist was able to identify the specific star patterns used by the indigo bunting. For indigo buntings, orientation to the night sky develops as the young birds observe the stars. When star patterns are reversed in a planetarium, buntings will change their orientation 180 degrees, showing that they use the stars to guide themselves.

While they are programmed to orient to the North Star (Polaris), they require a rotating sky to first obtain a fix on Polaris. Stars have fixed positions, but since Earth rotates on its axis, the sky appears to be rotating. Polaris is stationary, however, and Cornell scientists determined that buntings can orient from Polaris or other constellations within 35 degrees of Polaris, especially the constellation Orion.

Earth’s Magnetic Field and the Sun

Birds migrating by day use the Sun to navigate, adjusting their angle to the Sun as the Sun’s position moves from east to west.

Some birds, like robins, use Earth’s magnetic field to assist in migration. It is believed that they have magnetic crystals near their nostrils to help them sense the field and orient themselves. Birds also use landmarks such as islands, trees, and buildings, as well as sounds and smells, when they search for nesting grounds in spring.

Credit: Cephas CC BY-SA 3.0

Spotlight on the Blackpoll Warbler

The blackpoll warbler, which nests in northern New England and Canada, makes the longest migration of any North American songbird. Headed to South America, this warbler makes an 88-hour flight from Maritime Canada and Maine directly over the Atlantic Ocean to the Amazon, a nonstop flight of some 2,200 miles. In the weeks before making this flight, they more than double their weight by gorging themselves on insects and berries.

Near Bermuda, flocks can reach sizes of up to 1,000 birds as they take advantage of northeast trade winds. They increase their altitude to 15,000 feet—and sometimes to as high as 21,000 feet—where the air is calmer. They finally drop to land near Aruba.

This flight over Bermuda was discovered not by using radar, but by an ornithologist sitting by the pool in Bermuda on a September evening and recognizing the distinctive call notes of hundreds of blackpoll warblers in the sky.

So, keep your eyes and ears pointed toward the sky this season—you never know what fascinating birds you may discover overhead!