Migratory birds use magnetic GPS
Bird migration is fascinating. How do they find their way back and forth across the globe? For many years, the earth’s magnetic field has been suspected as one of several navigation clues.1
Now an international team of researchers in Austria has advanced our knowledge with ingenious experiments with reed warblers.2
The earth’s magnetic field is best known for providing a compass direction. But a direction alone is not always enough. How far along in the required direction does the bird need to go? In reality, the magnetic field has more information (see diagram, below).
Intensity: the strength of magnetic attraction. In general, this is strongest near the poles and weakest near the equator.
Declination: the Magnetic North Pole is not at the Geographic North Pole. So the field will be deflected relative to true north, and the angle is called declination.
Inclination: the field is not horizontal (parallel to the earth’s surface), except at the magnetic equator. Rather, it inclines (dips) downward in the northern hemisphere and straight down at the North Magnetic Pole. Towards the south, inclination rotates upward until it’s straight up at the South Magnetic Pole.
Different locations have different combinations of these three parameters. If birds could detect them, they would usually know where they are on the earth’s surface. So the researchers tested this on migratory warblers near their summer nesting grounds in Austria. In autumn, they would be starting their migration to their winter grounds in sub-Saharan Africa. But the researchers exposed them to a magnetic field that matched the coordinates of Neftekamsk, Russia—2,500 km (1,600 mi) northeast from their real location. This city was chosen for two reasons: First, it is far from anywhere the birds would go, and second, it would make them fly in a very different direction from their typical migrating path.
Sure enough, despite other visual cues to the contrary, they reacted as if they had started from Neftekamsk.3 One of the researchers, Richard Holland of Bangor University in Wales, explained:
It shows what an important cue this magnetic field must be to them. Despite everything else still telling them they’re on their normal route, they react as though they’ve been displaced two and a half thousand kilometers to the northeast.
In the natural environment, this ‘magnetic GPS’ is an excellent navigation tool. Dr Holland further explains: “So, you’ve got this really neat Cartesian coordinate map, which is kind of the theoretical construct behind what we think the birds are doing.”
Of course, the birds are unaware of the ingenious concepts involved in what they do. This programmed ingenuity speaks of a Master Programmer.
References and notes
- Catchpoole, D., Wings on the wind: How do migrating birds know exactly when, and where, to go? Creation 23(4):16–23, 2001; creation.com/migration. Return to text.
- Kishkinev, D. and 6 others, Navigation by extrapolation of geomagnetic cues in a migratory songbird, Current Biology 31(7):1563–1569, 21 Apr 2021. Return to text.
- Fritts, R., Lost birds rely on earth’s magnetic field to get back on track, audobon.org, 4 Mar 2021. Return to text.