Soaring styles of extinct giant birds and pterosaurs

Abstract

Extinct large volant birds and pterosaurs are thought to have used wind dependent soaring flight, similar to modern large birds. There are two types of soaring: thermal soaring, used by condors and frigatebirds, which involves the use of updrafts to ascend and then glide horizontally; and dynamic soaring, used by albatrosses, which involves the use of differences in wind speed with height above the sea surface. However, it is controversial which soaring styles were used by extinct species. In this study, we used aerodynamic models to comprehensively quantify and compare the soaring performances and wind conditions required for soaring in two of the largest extinct bird species, Pelagornis sandersi and Argentavis magnificens (6–7 m wingspans), two pterosaur species, Pteranodon (6 m wingspan) and Quetzalcoatlus (10 m wingspans), and extant soaring birds. For dynamic soaring, we quantified how fast the animal could fly and how fast it could fly upwind. For thermal soaring, we quantified the animal's sinking speed circling in a thermal at a given radius and how far it could glide losing a given height. Consistently with previous studies, our results suggest that Pteranodon and Argentavis used thermal soaring. Conversely, the results suggest that Quetzalcoatlus, previously thought to have used thermal soaring, was less able to ascend in updrafts than extant birds, and Pelagornis sandersi, previously thought to have used dynamic soaring, actually used thermal soaring. Our results demonstrate the need for a comprehensive assessment of performance and required wind conditions when estimating soaring styles of extinct flying species.