Migrating Birds Measure Longitude
Migrating birds are able to get back on course, even when released 1000 km east of their normal migration path. This shows that long-distance migrating birds are capable of true bicoordinate navigation: the ability to make course corrections both in latitude and longitude. The results of experiments, published in Current Biology,1 left the researchers baffled: how do they do it?
Measuring latitude is easy: just judge the height of the sun in the sky. Longitude (east-west orientation), however, is much more challenging because it requires accurate timekeeping. The difficulties sailors throughout history had in determining longitude has been described in Dava Sobel’s historical novel Longitude. Somehow, a team of Russian and German scientists found, birds know the trick. A flock of migrating Eurasian reed warblers was flown 1000 km to the east of their usual take-off point. They found their way to their normal nesting ground by shifting their bearing northwest instead of the usual northeast. “This finding is surprising and presents a new intellectual challenge to bird migration researchers, namely, which cues enable birds to determine their east-west position,” they said.
However it is accomplished, the skill must be learned, because a previous study by Princeton scientists showed that juvenile birds did not correct for longitude when flown off course (see 11/05/2007). Still, it is unclear how the birds in this new study pulled it off. Do they read the stars? Do they gauge the earth’s magnetic field? Did they measure their jet lag? “To show what cues the birds use to determine their east-west location,” they said, “will be a big challenge for researchers in this field in the years to come.”
1. Chernetsov, Kishkinev and Mouritzen, “A Long-Distance Avian Migrant Compensates for Longitudinal Displacement during Spring Migration,” Current Biology, Volume 18, Issue 3, 12 February 2008, Pages 188-190.
Many wonderful and intriguing science projects remain to be performed. These scientists did not mention evolution and had no need of it. They saw an amazing phenomenon in present-day, observable nature and sought to understand the design behind it.