Flight efficiency explains differences in natal dispersal distances in birds

Abstract

The factors responsible for variation in dispersal distances across species remain poorly understood. Previous comparative studies found differing results and equivocal support for theoretical predictions. Here I re-examine factors that influence natal dispersal distances in British birds while taking into account the cost of transport as estimated from proxies of long-distance flight efficiency.First, I show that flight efficiency, as estimated by the hand-wing index, the aspect ratio or the lift-todrag ratio, is a strong predictor of dispersal distances among resident species. Most migratory species showed a similar pattern but a group of species with relatively low aerodynamic efficiency showed longer than expected dispersal distances making the overall trend independent of flight efficiency.Ecological, behavioral, and life history factors had a small or nil influence on dispersal distances with most of their influence likely mediated by adaptations for the use of space reflected in flight efficiency. This suggests that dispersal distances in birds are not determined by adaptive strategies for dispersal per se but are predominantly influenced by the energetic cost of movement.

AVONET: morphological, ecological and geographical data for all birds

“…In addition to direct measurements, we also calculated the hand‐wing index (HWI), a metric of flight efficiency and dispersal ability in birds (Claramunt, 2021). Although a global HWI dataset following BirdTree taxonomy has been published previously (Sheard et al, 2020), we update HWI scores to reflect additional sampling under the BirdTree taxomomy, and provide species averages aligned with BirdLife and eBird species lists.…”

Morphological adaptations linked to flight efficiency and aerial lifestyle determine natal dispersal distance in birds

“…Specifically, higher aspect ratio bird wings may be an adaptation not only to long‐distance migration, but also to a more aerial lifestyle (Claramunt, 2021; Sheard et al., 2020). Regardless of migratory distance, HWI is predicted to correlate with the degree to which a species relies on flight during daily routines (Claramunt, 2021; Evans, 2021; Sheard et al., 2020). Thus, species with lifestyles dependent on frequent flight, for example because of an aerial foraging behaviour or daily movements between foraging and roosting areas (Table 1), may evolve elongated wings with increased flight efficiency.…”

Flight hampers the evolution of weapons in birds

“…Although HWI has typically been linked to long‐distance migration or dispersal (e.g. Claramunt, 2021; Claramunt et al, 2012; Kennedy et al, 2016), species that fly more often tend to have high HWI even if they are sedentary (Stoddard et al, 2017). It is thus likely that HWI expresses not only how efficiently, but also how frequently individuals of a species fly.…”