Frigate birds: Airborne for months at a time

A telemetric study of the trajectory and flight strategy of frigate birds(Fregata minor), led by Henri Weimerskirch of the Centre d'études biologiques de Chizé (CNRS/Université de La Rochelle) in partnership with colleagues based in La Réunion, the United Kingdom, Canada, and Germany has revealed that they can remain airborne for over two months. This happens during their transoceanic migrations. Frigate birds make their transoceanic flights between Africa and Indonesia. The birds have extraordinary ability to glide and climb in updrafts without beating its wings. They track the edge of the doldrums to take advantage of favorable winds and strong convection.Locally, they use a roller-coaster flight, relying on thermals and wind to soar within a 50- to 600-meter altitude band under cumulus clouds and then glide over kilometers at low energy costs. To deal with the local scarcity of clouds and gain longer gliding distances, birds regularly soar inside cumulus clouds to use their strong updraft, and they can reach altitudes of 4000 meters, where freezing conditions occur.

Details appear in the latest issue of journal Science.