Flight altitude of Whooper Swans and Northern Pintails at a wintering site in Northern Japan

Abstract

To examine avian flight characteristics of species at risk for bird strikes on tall structure such as power-generating wind turbines, we used GPS transmitters to track the flight behavior of five Whooper Swans Cygnus cygnus and two Northern Pintails Anas acuta at Lake Izunuma, Miyagi Prefecture, a wintering site in Northern Japan. During 2017, the five swans were tracked during a total of seven daily flights between roosting and foraging sites, and pintails were tracked twice. On average, the swans increased their flight altitude by 20.4 ± 6.7 (SD) m per km after takeoff (n=7), and Northern Pintails increased altitude more quickly (47.3 & 99.5 m / km) (n=2). Swans gradually and steadily increased flight altitude until finally taking a landing posture to descend. The swans’ rate of altitudinal increase was clearly lower than the sustainable increase estimated from the dynamic model (Pennycuick 2008, Pennycuick et al. 2013). These results suggest a need to clarify why swans do not increase their altitude as fast as predicted by the dynamic model, with the goal of developing strategies to reduce the risk of bird strike.