The Genius of Birds

by Jennifer Ackerman

WHAT IS THIS MAP made of? It may work like our Cartesian coordinate system, with different environmental cues that vary predictably along gradients providing information about latitude and longitude. To use these gradients, says Richard Holland of Queen’s University, Belfast, a bird “would have to learn that they vary predictably in intensity with space (and possibly time) within their home range and extrapolate this beyond the learned area.” But what are the sensory cues contributing to the map’s coordinates? Does it even have coordinates? Despite a welter of studies over the past four decades, we’re still trying to uncrumple the much crumpled matter of mapping cues. The gradient map may be partly geomagnetic. Holland and a colleague lately made a curious discovery. The pair picked up several European robins that had stopped over at a resting stage on their migratory path and exposed them to a strong magnetic pulse, temporarily disrupting their magnetic sense. Then they let the birds go. The young robins (which had no previous navigation experience) seemed unbothered by the pulse and continued on their expected path, guided by their innate program. But the adults flew off in the wrong direction. The researchers speculated that the adult birds had built up magnetic maps in their heads during their migrations, which they used to help them navigate on subsequent journeys. The pulses may have “reset” those maps, confusing the birds.