Soaring styles of extinct giant birds and pterosaurs

The largest extinct volant birds (Pelagornis sandersi and Argentavis magnificens) and pterosaurs (Pteranodon and Quetzalcoatlus) 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 over the land or the sea; and dynamic soaring, used by albatrosses, which involves the use of wind speed differences with height above the sea surface. Previous studies have suggested that Pelagornis sandersi used dynamic soaring, while Argenthavis magnificens, Pteranodon, and Quetzalcoatlus used thermal soaring. However, the performance and wind speed requirements of dynamic and thermal soaring for these species have not yet been quantified comprehensively. We quantified these values using aerodynamic models and compared them with that of extant birds. For dynamic soaring, we quantified maximum flight speeds and maximum upwind flight speeds. For thermal soaring, we quantified the animal′s sinking speed circling at a given radius and how far it could glide losing a given height. Our results confirmed those from previous studies that Pteranodon and Argentavis magnificens used thermal soaring. Conversely, the results for Pelagornis sandersi and Quetzalcoatlus were contrary to those from previous studies. Pelagornis sandersi used thermal soaring, and Quetzalcoatlus had a poor ability both in dynamic and thermal soaring. Our results demonstrate the need for comprehensive assessments of performance and required wind conditions when estimating soaring styles of extinct flying species.