Flight Speeds among Bird Species: Allometric and Phylogenetic Effects

Abstract

Flight speed is expected to increase with mass and wing loading among flying animals and aircraft for fundamental aerodynamic reasons. Assuming geometrical and dynamical similarity, cruising flight speed is predicted to vary as (body mass)1/6 and (wing loading)1/2 among bird species. To test these scaling rules and the general importance of mass and wing loading for bird flight speeds, we used tracking radar to measure flapping flight speeds of individuals or flocks of migrating birds visually identified to species as well as their altitude and winds at the altitudes where the birds were flying. Equivalent airspeeds (airspeeds corrected to sea level air density, U e) of 138 species, ranging 0.01–10 kg in mass, were analysed in relation to biometry and phylogeny. Scaling exponents in relation to mass and wing loading were significantly smaller than predicted (about 0.12 and 0.32, respectively, with similar results for analyses based on species and independent phylogenetic contrasts). These low scaling exponents may be the result of evolutionary restrictions on bird flight-speed range, counteracting too slow flight speeds among species with low wing loading and too fast speeds among species with high wing loading. This compression of speed range is partly attained through geometric differences, with aspect ratio showing a positive relationship with body mass and wing loading, but additional factors are required to fully explain the small scaling exponent of U e in relation to wing loading. Furthermore, mass and wing loading accounted for only a limited proportion of the variation in U e. Phylogeny was a powerful factor, in combination with wing loading, to account for the variation in U e. These results demonstrate that functional flight adaptations and constraints associated with different evolutionary lineages have an important influence on cruising flapping flight speed that goes beyond the general aerodynamic scaling effects of mass and wing loading.

Genome size and wing parameters in passerine birds

“…Wing span and wing area were strongly related to each other (rZ0.97, p!0.0001, nZ74), but WAR and WLI were not correlated with each other ( pO0.71; cf. Alerstam et al 2007 for a broader taxonomic sample of birds).…”

“…Bennett & Harvey 1987;Anderson & Jetz 2005;Bishop 2005;Alerstam et al 2007); but these datasets will need to be expanded and matched with reliable genome size estimates for the same species before analyses can be conducted. Data bearing on migration capabilities also would be of interest, but it would be important to distinguish between long-distance direct flights and more gradual seasonal range shifts.…”

“…Birds with higher WLI must fly faster per unit mass to generate sufficient lift (e.g. Norberg 1995), and it has been shown that WLI scales with flight speed with an exponent of 0.32 (Alerstam et al 2007).…”

Post-breeding migration of Night Herons Nycticorax nycticorax tracked by GPS/GSM transmitters

“…The differences in migration strategy between Purple Herons and Night Herons could be due to differences in wing loading, which is significantly lower in the former than in the latter (Alerstam et al 2007; Fig. 2 in Van der Winden et al 2010).…”

“…This implies a flight distance from Poland to the Sahel of at least 4,000 km (Betleja, 2001;Zwarts et al 2009). As flapping flight incurs relatively high energy costs, we expected that, because of the higher wing loading (4.8 kg/m 2 ) in comparison with Purple Heron (3.6 kg/m 2 ), Night Heron should make at least one long stopover to refuel during migration, as do other species with a high wing loading (Alerstam et al 2007;Fig. 2 in Van der Winden et al 2010;e.g., Beekman et al 2002).…”