Large Birds can Migrate Fast: The Post-Breeding Flight of the Purple Heron Ardea purpurea to the Sahel

Large and heavy birds usually use soaring flight during long-distance migration or make regular stopovers en route for substantial refuelling. Purple Herons are large, long-distance migrants. Because of their size, large herons migrating southwards from Europe to Africa were expected to make one or more stop-overs to refuel. However, data from seven Purple Herons, fitted with satellite transmitters, showed that the herons were able to cover the distance into the Sahel of about 4000 km within 5–7 days. One individual even flew 5600 km non-stop, mostly over sea. The herons migrated mostly at night and partly during the day with a high travel speed indicative of flapping flight. The herons made few diurnal stops in Europe and North Africa. Substantial ‘stopover’ time was limited entirely to a period of several weeks before departure, and after arrival south of the Sahara. We assume that this is energetically possible for birds with a maximum wing load of 4–5 kg body mass per m2 of wing surface. Larger wing l...