Using weather radar to track songbird migrations
Lindsay N Deel
Scientists and birders have long struggled to observe the elusive nighttime migrations of songbirds, but an innovative approach (IEEE Geosci Remote S 2015; doi:10.1109/TGRS.2015.2443131) developed by doctoral students at the University of Oklahoma (Norman, OK) relies on weather radar to detect the behaviors of these birds in the Great Plains of the US. Most songbirds migrate at night and often fly at heights that are very difficult to detect visually from the ground. According to author Kyle Horton, “To begin to understand how a migrant bird moves from one destination to another, you generally need two different measurements: track and orientation”. Track is calculated from wind characteristics (speed and direction) and the bird's velocity, whereas orientation is the compass direction in which the bird aligns itself. “You can think of track in terms of swimming across a river. You want to go straight across, but the current of the river causes you to drift downstream; this resultant direction is the track”, explains Horton. “Track is easily measured for most aerial organisms using radar techniques; however, orientation is much harder [to gauge].”
Horton, a biologist, and lead author Phillip Stepanian, a meteorology and electrical engineering student, used the US weather surveillance system (Next-Generation Radar or NEXRAD) to examine –for the first time – track and orientation independently and at frequent intervals. The method allows researchers to determine how migrant birds cope with unfavorable wind patterns and how avian behavior changes over space and time. The approach has the added benefit of providing fine-scale measurements of bird migrations that occur over very broad scales.
Horton and Stepanian are already exploring different ways to apply NEXRAD to investigate other biological phenomena. This has been a big challenge, given that the system was originally designed to remotely monitor precipitation and wind patterns. “Our technique is just one method to extract orientation measures of migrants aloft, and I see no reason to think that this method won't be improved upon”, says Horton. “As we learn more about the data products, we'll begin to better understand what is working and what isn't.”