Geese use dive-and-glide flight to save energy

NPR : Every year, the bar-headed goose migrates from the Indian subcontinent to central Asia and back, flying over the Himalayan mountains along the way. Charles Bishop of Bangor University in the UK and his colleagues began tagging and tracking the geese on their migrations and discovered an unusual behavior. Instead of reaching and maintaining a high altitude, the geese stayed relatively close to the surface, climbing and diving along the contours of the mountains. The trackers the researchers put on the geese recorded not just altitude but also wing-beat frequency and heart rate. Bishop’s team was able to determine that the climb-and-dive pattern reduced the energy that the geese had to exert in comparison to level flight. The thinner air at higher altitudes required an increase in wing-beat frequency, which translated to a significant increase in heart rate. By diving and gliding, the geese could travel farther with less flapping.