White-crowned sparrow
Images courtesy of Christian Ziegler / PNAS
All sumer long, sparrows flit through the spruce and birch, alder and brush, bringing song and nervous motion to jungled forests of the Far North. Come freeze up, these sparrows and other tiny songbirds take wing and migrate south from Alaska.
These miniscule creatures often fly alone, at night, fighting high winds, navigating by an unknown alchemy that draws partly on the Earth’s magnetic fields and the position of the Sun. This mysterious ability carries the avian travelers across mountain ranges, ocean gulfs and steppes to the precise valley or woods where they spent the previous season.
How do the birds do it?
To help answer the question, a team of scientists from Princeton University intercepted a covey of white-crowned sparrows in northern Washington and released them more than 3,000 miles away in the woodlands of New Jersey.
The birds scattered. What happened next stunned the scientists, and suggested that wee adult sparrows may carry a reliable map of the continent in their pea-sized brains.