Flight of Auks (Alcidae) and Other Northern Seabirds Compared with Southern Procellarhformes: Ornithodolite Observations

Abstract

Airspeeds in flapping and flap-gliding flight were measured at Foula, Shetland for three species of auks (Alcidae), three gulls (Landae), two skuas (Stercorariidae), the fulmar (Procellariidae), the gannet (Sulidae) and the shag (Phalacrocoracidae). The airspeed distributions were consistent with calculated speeds for minimum power and maximum range, except that observed speeds in the shag were unexpectedly low in relation to the calculated speeds. This is attributed to scale effects that cause the shag to have insufficient muscle power to fly much faster than its minimum power speed. The wing adaptations seen in different species are considered as deviations from a ‘procellariiform standard’, which produce separate effects on flapping and gliding speeds. Procellariiformes and the gannet flap-glide in cruising flight, but birds that swim with their wings do not, because their gliding speeds are too high in relation to their flapping speeds. Other species in the sample also do not flap-glide, but the reason is that their gliding speeds are too low in relation to their flapping speeds.