Thermals over the sea and gull flight behavior

Abstract

The flight performance of Herring Gulls relative to specific atmosphere and ocean conditions over the western North Atlantic indicates that large groups of gulls are able, through cooperative flight maneuvers, to induce ascending convective flow (thermals) in which they make extended soaring flights. These group flights in gull-induced thermals are limited to winds of 0 to ~ 1 m s⁻¹ and to sea-minus-air temperature differences (δT) of ~3 to 6‡C.

As wind speed increases from ~ 2 to 5 m s⁻¹, thermals are naturally induced, and the minimum δT required for soaring is inversely related to wind speed. At higher winds (~5 to 13 ms⁻¹), the minimum positive δT and minimum wind speed required for thermal soaring are directly related, thus indicating an apparent maximum efficiency for the natural production of thermals at wind speeds of about 5 m s⁻¹ and δT of 1 to 2 ‡C.