Strapping a geolocator to a bunch of animals is usually a pretty good way to see what kind of migrations they pull off. But it doesn't work if the animals in question can hardly move under the weight of those geolocators: Until the last several years, our tracking devices were too heavy for songbirds. That all changed in 2007, when, for the first time, researchers developed trackers that were light enough for wood thrushes and purple martins; they hooked up 34 birds, and even though only seven of the tagged birds were found the next year, these seven gave the scientists major insight--and newfound respect--into the migratory lives of these silver-voiced flyers.

"We learned that in the fall, purple martins leave the northern U.S. and they fly to the Yucatan in less than a week," says Bridget Stutchbury, a biologist at York University in Canada. "They can fly over 1,000 miles in a mere seven days." They also discovered interesting patterns, such as how the birds fly up to six times as fast during their northward flight than they do in their southward migration. But by and large, the speed of the birds are what really impressed the researchers. "These birds are smaller than a Coke can--the idea that they can travel so far so fast is just astounding to me," Stutchbury adds.