Fastest bird in level flight

In a report published by French and British researchers working in the sub-Antarctic, the mean estimated groundspeed recorded for a satellite-tagged grey-headed albatross (Thalassarche chrysostoma) is of 127 km/h (78.9 mph) sustained for over 8 hours while returning to its nest at Bird Island, South Georgia, in the middle of an Antarctic storm.

The report was published by the Paulo Catry, Richard A. Phillips and John P. Croxall of the British Antarctic Survey, Natural Environmental Research Council (The Auk 121(4):1208-1213, 2004).

It's worth noting that, owing to the weather conditions, it's generally accepted that much of the albatross's speed was attributable to tailwinds rather than being self-powered. In calmer conditions, the fastest bird in level flight that has been scientifically measured is the common swift (Apus apus), which in one study conducted by Lund University (Sweden) attained speeds of 31 ms−1 (69 mph; 111.6 km/h); Henningsson et al, 2010.