Fine-scale flight strategies of gulls in urban airflows indicate risk and reward in city living

Abstract

Birds modulate their flight paths in relation to regional and global airflows in order to reduce their travel costs. Birds should also respond to fine-scale airflows, although the incidence and value of this remains largely unknown. We resolved the three-dimensional trajectories of gulls flying along a built-up coastline, and used computational fluid dynamic models to examine how gulls reacted to airflows around buildings. Birds systematically altered their flight trajectories with wind conditions to exploit updraughts over features as small as a row of low-rise buildings. This provides the first evidence that human activities can change patterns of space-use in flying birds by altering the profitability of the airscape. At finer scales still, gulls varied their position to select a narrow range of updraught values, rather than exploiting the strongest updraughts available, and their precise positions were consistent with a strategy to increase their velocity control in gusty conditions. Ultimately, strategies such as these could help unmanned aerial vehicles negotiate complex airflows. Overall, airflows around fine-scale features have profound implications for flight control and energy use, and consideration of this could lead to a paradigm-shift in the way ecologists view the urban environment.This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’.

Intercolony variations in movement patterns and foraging behaviors among herring gulls (Larus argentatus) breeding in the eastern Wadden Sea

“…Previous studies demonstrated that flights over land consumed less energy than expected, and flight costs were reduced using fine‐scale structures (e.g., dykes) to increase orographic lift (Shamoun‐Baranes, Bouten, van Loon, Meijer, & Camphuysen, 2016; Shepard, Williamson, & Windsor, 2016). Furthermore, birds prefer foraging habitats with predictable prey distributions during the breeding season (Camphuysen, 2013; Weimerskirch, 2007), as expected in terrestrial habitats (Gorke & Brandl, 1986; Palm, van Schaik, & Schröder, 2013; Sibly & McCleery, 1983).…”

The energy landscape predicts flight height and wind turbine collision hazard in three species of large soaring raptor

“…When flying in orographic uplift, we could assume that (i) the effect of terrain decreased with height above ground, yielding a low upper bound for flight height above ground when riding orographic uplift (Shepard, Williamson & Windsor 2016); (ii) in orographic currents, the bird simply followed the terrain and therefore maintained a relatively constant flight height above ground (Katzner et al 2015). Whether this behaviour in orographic currents translates into a decrease or increase in collision hazard compared to when alternating between thermal soaring and gliding is likely to be situation-specific (Johnston, Bradley & Otter 2014;Miller et al 2014;our results).…”

Avian Sensor Packages for Meteorological Measurements

“…Understanding more about the flight strategies of these avian "platforms" for the sensors will allow their flight capabilities to be harnessed to probe maximally the meteorological feature(s) of interest. Shepard et al (2016) have begun this process by investigating airflow in urban areas by remotely observing gull interactions with airflow around buildings. Although, the present study used raptorial species at a remote (nonurban) location, it is reasonable to propose that raptors carrying our sensors be used for meteorological work in urban centers.…”