Profiles of Mean Wind Speeds and Turbulence Intensities of Vertical Velocity Measured at Seashore and Two Inshore Sites Using Doppler Sodars

Black-tailed gulls alter their flight height and airspeed according to wind conditions during their coastal commuting trips

“…With the objective to relate wind speed and direction to the height and air speed of flapping flights in the realm of aerodynamics, we examined 2 hypotheses. First, since wind speed increases with height (Arya 2001, Iwatani et al 2005, we hypothesized that the gulls would fly higher with tailwinds to utilize greater wind force in their travel direction and minimize their cost of travel (Liechti 2006). Hence, we predicted a positive correlation between wind speed (in the direction of the aimed goal) and flight height.…”

“…Field observations show that birds fly at higher altitudes with tailwinds during both short-and long-range movements (Krüger & Garthe 2001, Kahlert et al 2012, Tarroux et al 2016. Since wind speed increases with altitude (Arya 2001, Iwatani et al 2005), flying higher in tailwind conditions may thus allow the birds to utilize greater wind support working in the direction of travel, which minimizes their energy expenditure (Liechti 2006). On the other hand, seabirds fly closer to the ocean surface in headwind conditions; they may then take advantage of wind shear (decreased wind speed with proximity to ocean surface/ground due to friction) to reduce movement costs.…”