Seabird morphology determines operational wind speeds, tolerable maxima, and responses to extremes

Abstract

Storms can cause widespread seabird stranding and wrecking,^1,2,3,4,5 yet little is known about the maximum wind speeds that birds are able to tolerate or the conditions they avoid. We analyzed >300,000 h of tracking data from 18 seabird species, including flapping and soaring fliers, to assess how flight morphology affects wind selectivity, both at fine scales (hourly movement steps) and across the breeding season. We found no general preference or avoidance of particular wind speeds within foraging tracks. This suggests seabird flight morphology is adapted to a "wind niche," with higher wing loading being selected in windier environments. In support of this, wing loading was positively related to the median wind speeds on the breeding grounds, as well as the maximum wind speeds in which birds flew. Yet globally, the highest wind speeds occur in the tropics (in association with tropical cyclones) where birds are morphologically adapted to low median wind speeds. Tropical species must therefore show behavioral responses to extreme winds, including long-range avoidance of wind speeds that can be twice their operable maxima. By contrast, Procellariiformes flew in almost all wind speeds they encountered at a seasonal scale. Despite this, we describe a small number of cases where albatrosses avoided strong winds at close range, including by flying into the eye of the storm. Extreme winds appear to pose context-dependent risks to seabirds, and more information is needed on the factors that determine the hierarchy of risk, given the impact of global change on storm intensity.^6,7.

Keywords: bio-logging; extreme weather events; flight; storms; wing loading.

Graphical abstract

Figure 1

Distribution of wind speeds Wind speeds experienced during foraging trips (in color; colors correspond to wind speed, as in Figure 2) is compared with wind conditions across the entire breeding distribution and season over a 5-year period (in gray). Species are ordered by their wing loading, with the lowest wing loading at the top. Tropical species are indicated by a sun icon. See Table S1 for colony locations and wing loadings. See Figure S2 for coefficient of variation of wind speeds encountered by each species.

Figure 2

Wind fields at four selected instances where birds avoided the strongest winds The location of the bird at the time of avoidance of strongest available wind is shown. The full foraging trajectories are shown in the plot insets. In the top two panels, birds appear to avoid the strongest winds associated with cyclonic systems by tracking the low wind region in the eye of the storm (see also Video S1). In the bottom two panels, birds operated along the edge of strong frontal systems, again selecting the region of lower wind speeds. See Figure S3 for available and favored wind speed values.

Figure 3

The relationship between wing loading and wind speed The maximum wind speed encountered by seabirds at the hourly scale was correlated with wing loading (adjR² = 0.31, p < 0.05). Wing loading was predicted by the median (adjR² = 0.35, p < 0.05) but not the maximum (adjR² = −0.04, p = 0.64) wind speeds within the breeding range, indicating that morphological adaptations are a response to the median wind conditions. Shaded areas show the 95% confidence intervals of the regression lines. See Table S2 for complete model summaries.