In the first chapter of Skeptics and True Believers I told the story of the red knot, a bird that may hold the record for long-distance migration, from the Canadian Arctic to Tierra del Fuego -- and back. Juvenile birds make the trek without adults to guide them and without ever having made the journey before.
A recent issue of Science tells of the migratory habits of the northern wheatear, a little ground bird that lives in northern Eurasia, Iceland Greenland and eastern Canada and migrates to the open savannas south of the Sahara. I got to know the wheatear in Ireland. It's name, by the way, derives from "white-arse," which is perfectly descriptive.
A German research team collected wheatear hatchlings from nests in Norway and Iceland and raised them in the lab. As migration time approached, the birds bulked up with food for the journey, and -- here is the kicker -- they ate in proportion to the distance they would have had to fly had they been left in their native environment.
The urge to migrate, the preparatory feeding, the destination and the navigational tools to get there are all in the genes, written in a four-letter code on the birds' DNA. Each bird's life begins as a single, microscopic fertilized cell, and each cell contains the equivalent of a set of charts, a compass, a sextant and maybe even something akin to a satellite navigation system. The wheatear is able to learn from experience, to rewire its brain as necessary (to evade a storm, for example), but the bird's brain comes ready wired for its ancient migration.
And if that doesn't make your head spin, then nothing will. As the British cartographer and author Tim Robinson said: Miracles are explainable, it's the explanations that are miraculous.