Limits to load-lifting performance in a passerine bird: the effects of intraspecific variation in morphological and kinematic parameters

Abstract

Although more massive flight muscles along with larger wings, higher wingbeat frequencies and greater stroke amplitudes enhance force and power production in flapping flight, the extent to which these parameters may be correlated with other morphological features relevant to flight physiology and biomechanics remains unclear. Intraspecifically, we hypothesized that greater vertical load-lifting capacity would correlate with higher wingbeat frequencies and relatively more massive flight muscles, along with relatively bigger hearts, lungs, and stomachs to enhance metabolic capacity and energy supply, but also with smaller body size given the overall negative allometric dependence of maximum flight performance in volant taxa. To explore intraspecific correlates of flight performance, we assembled a large dataset that included 13 morphological and kinematic variables for a non-migratory passerine, the Eurasian tree sparrow (Passer montanus). We found that heavier flight muscles and larger wings, heavier stomachs and shorter bills were the most important correlates of maximum load-lifting capacity. Surprisingly, wingbeat frequency, wing stroke amplitude and masses of the heart, lungs and digestive organs (except for the stomach) were non-significant predictor variables relative to lifting capacity. The best-fit structural equation model (SEM) indicated that load-lifting capacity was positively correlated with flight muscle mass, wing area and stomach mass, but was negatively correlated with bill length. Characterization of individual variability in flight performance in a free-ranging passerine indicates the subtlety of interaction effects among morphological features, some of which differ from those that have been identified interspecifically for maximum flight performance in birds.

A comparison of flight energetics and kinematics of migratory Brambling and residential Eurasian Tree Sparrow

“…Each bird was evaluated for asymptotic load-lifting capacity in a rectangular flight chamber using a maximum load-lifting approach described in detail by Sun et al (2016) and Wang et al (2019). In brief, one highspeed video camera (GCP100BAC, JVC Kenwood Corporation, Yokohama, Japan; operated at 250 frames −1 ) placed on the top of the chamber was used to obtain wingbeat frequency and stroke amplitude (Additional file 1: Movie S1).…”

The role of wingbeat frequency and amplitude in flight power

“…Indeed, examples from the literature suggest that the relationship may not be straightforward. Some studies show that birds vary their power output with little to no change in wingbeat frequency [30][31][32], whereas others report that wingbeat frequency varies with the power output while the amplitude is unaltered [20]. It is, therefore, unclear whether birds vary frequency or amplitude to modulate power according to their flight mode (e.g.…”

The role of wingbeat frequency and amplitude in flight power

“…Indeed, examples from the literature suggest that the relationship is not straightforward: Some studies show that birds vary their power output with little to no change in wingbeat frequency (Tobalske & Biewener, 2008;Torre-Bueno & Larochelle, 1978;Wang et al, 2019), whereas others report that wingbeat frequency varies with the power output while the amplitude is unaltered (Ellerby & Askew, 2007). It is therefore unclear whether birds vary frequency or amplitude to modulate power according to their flight mode (e.g., hovering, climbing, manoeuvring, or level flight) or morphology.…”

“…The power can be shown to be proportional to the cube of both amplitude and frequency, if the product of wingbeat amplitude and frequency is substituted for velocity (as they both scale the same with velocity (Floryan et al, 2018)): Despite the importance of both wingbeat frequency and amplitude for overall power output, an overview of the scenarios under which birds modulate one or the other parameter is lacking. Indeed, examples from the literature suggest that the relationship is not straightforward: Some studies show that birds vary their power output with little to no change in wingbeat frequency (Tobalske & Biewener, 2008; Torre-Bueno & Larochelle, 1978; Wang et al, 2019), whereas others report that wingbeat frequency varies with the power output while the amplitude is unaltered (Ellerby & Askew, 2007). It is therefore unclear whether birds vary frequency or amplitude to modulate power according to their flight mode (e.g., hovering, climbing, manoeuvring, or level flight) or morphology.…”