How Birds Calibrate Their Navigating Maps
Three researchers tracked birds in the wild and concluded that “night-flying thrushes set their course using a magnetic compass, which they calibrate to the setting sun before takeoff each evening.” The team of three captured thrushes in Illinois and attached small radio transmitters to them, then followed their flight for up to 1100 kilometers. By tricking them with false magnetic fields, they were able to steer them off course. But after next sunset, the birds were back on track, apparently having recalibrated their maps by the position of the sun. Erik Stokstad, reporting on the research, adds more interesting details:
This work may explain why birds don’t get lost when they cross the equator. That had been an enigma because birds can’t tell magnetic north from south. Instead, they check the inclination of the field lines relative to the ground; the angle becomes steeper near the poles. A bird using only its magnetic compass would risk getting turned around near the equator, but calibrating it to the sunset would keep it on track. Of course, the position of the sunset changes with latitude and season, but Wikelski thinks that birds may be able to correct for that through a biological clock that tells them the time of year.”
This is the first time birds have been monitored for navigation in the wild. The team must have looked odd chasing birds with “meter-tall antenna mounted on top of a battered 1982 Oldsmobile.” According to Stokstad, “Many nights, the team was delayed when suspicious police officers pulled over the electronics-laden car.”
See also: National Geographic News.
1Erik Stokstad, “Songbirds Check Compass Against Sunset to Stay on Course,” Science Vol 304, Issue 5669, 373, 16 April 2004, [DOI: 10.1126/science.304.5669.373a].
Thus multiple levels of correction and calibration are involved in this mind-boggling ability of little birdbrains to use natural cues to migrate vast distances unerringly, day and night, north and south, east and west. Congratulations to creative and diligent scientists who risk jail to find out these amazing feats in the animal kingdom for us to enjoy and ponder.