Just how do birds return to the same nest year after year after doing their long distance seasonal migration? Do they have a built-in map in their head? Perhaps they have magnetic compasses in their brains. Or maybe they can accurately detect sun angels by being able to see polarized light. For those that fly during the night, do they have a star map in their brains? Or maybe they can hear or smell navigational cues.
With so many different types of birds and wintering grounds, it is likely that they employ various methods. But just for fun, consider this data:
- When moved a significant distance from their nest site first-year fledgling birds couldn’t find their way to their wintering grounds. It suggest that birds either inherit a compass heading or direction to go or maybe accompany their parents or relatives on that first trip.
- Researchers who temporarily disrupted a group of catbirds’ sense of smell discovered that they lost their ability to navigate. Other catbirds that kept their smell but wore magnets on their heads navigated fine, implying that smell was more important than magnetic cues.
- On cloudy days starling have difficulty deciding which way to fly. But when the sun is visible, they orient perfectly. Perhaps they depend on a sun compass for navigation.
- Since most birds migrate at night, researchers put birds in a planetarium in cages designed with sloped sides to constantly force the birds to the middle. The birds oriented properly depending on the positions of the projected constellations, rather than any single star. When the sky was black, they became disoriented, strongly suggesting they use a star compass.
- German scientists placed caged birds in a room with no star or sun cues.
They still hopped in appropriate directions. When wire coils changed the direction of the earth’s weak magnetic field, it produced a statistically significant and appropriate adjustment in hopping direction, leading researchers to conclude that some birds may orient using a magnetic compass.
After decades of research, science has no definitive answers as to how birds acquire their map and their compass so that they can find their way so precisely. That is a delightful problem to keep working on thorough eternity .
