They report also that some of the data was difficult to read, because the songbirds sometimes hide in dark places during daylight hours. In their study, the researchers report that they were able to retrieve 27 of the loggers, of which 15 contained useful data for both spring and fall migrations. They were also able to calculate longitude by establishing the midpoint of the days and nights. While it might seem like not much could be learned from such simple measurements, the team explains that putting the data together allowed for creating light curves, which allowed for calculating day length and from that approximate latitude. The birds were recaptured when they returned to the breeding grounds, a year later allowing for the data to be retrieved from the loggers. The loggers recorded light and temperature readings every five to ten minutes over the entire course of a migratory trip. In this latest effort, the researchers took a new approach, attaching tiny loggers to 80 pied flycatchers captured and released from a breeding ground in the Netherlands. As the researchers note, over two billion songbirds cross the Sahara each year as part of their migration path, but because of their small size and huge numbers it has been nearly impossible to tell if the birds stop along the way or fly straight through-to date there has been conflicting information, due to an inability to connect hard data with actual bird sightings.
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