Flying high: Limits to flight performance by sparrows on the Qinghai-Tibet Plateau

Abstract

Limits to flight performance at high altitude potentially reflect variable constraints deriving from the simultaneous challenges of hypobaric, hypodense and cold air. Differences in flight-related morphology and maximum lifting capacity have been well characterized for different hummingbird species across elevational gradients, but relevant within-species variation has not yet been identified in any bird species. Here we evaluate load-lifting capacity for Eurasian tree sparrow (Passer montanus) populations at three different elevations in China, and correlate maximum lifted loads with relevant anatomical features including wing shape, wing size, and heart and lung masses. Sparrows were heavier and possessed more rounded and longer wings at higher elevations; relative heart and lung masses were also greater with altitude, although relative flight muscle mass remained constant. By contrast, maximum lifting capacity relative to body weight declined over the same elevational range, while the effective wing loading in flight (i.e. the ratio of body weight and maximum lifted weight to total wing area) remained constant, suggesting aerodynamic constraints on performance in parallel with enhanced heart and lung masses to offset hypoxic challenge. Mechanical limits to take-off performance may thus be exacerbated at higher elevations, which may in turn result in behavioral differences in escape responses among populations.

The role of climate factors in geographic variation in body mass and wing length in a passerine bird

“…However, although we found no significant difference in body mass between the sexes, males had longer wings than females. These results are consistent with those obtained for other populations or other subspecies of the Eurasian Tree Sparrow (St. Louis and Barlow 1991;Mónus et al 2011;Sun et al 2016). Although sexual displays in birds require much energy (Gil and Gahr 2002;Ward and Slater 2005), male Eurasian Tree Sparrows can behave in the same intensity during autumnal sexual recrudescence as they commonly do at prebreeding (García-Navas et al 2008;Pinowski et al 2009).…”

“…In birds, wing length is commonly considered an index of lean body mass (Nolan and Ketterson 1983), so the increased body mass at higher altitudes could be mainly the result of an increase in wing size and flight muscle (Sun et al 2016), or an increase in the size of metabolic and respiratory organs, i.e. the heart and lungs (Hartman 1955;Carey and Morton 1976;Sun et al 2016).…”

“…Birds living at higher altitudes typically have a larger heart and lungs in order to provide adequate oxygen to meet metabolic requirements, especially the requirements of flight (Hartman 1955;Carey and Morton 1976;Monge and Leon-Velarde 1991;Scott 2011). The hearts and lungs of Eurasian Tree Sparrows collected at higher altitudes were heavier than those of conspecifics collected at lower altitudes (Sun et al 2016). This suggests that the positive correlations between body mass or wing length and altitude may not only reflect adaptations to reduce energy consumption, but also to ensure an adequate oxygen supply.…”

Life-history dependent relationships between plasma alkaline phosphatase activity and body condition in male Eurasian Tree Sparrows

“…Previous studies have demonstrated that the body mass or body condition of Eurasian Tree Sparrows vary with life-history stage (Li et al 2008(Li et al , 2011(Li et al , 2012Zheng et al 2014) and living environment (Zhang et al 2011;Sun et al 2016Sun et al , 2017. Furthermore, male sparrows during the early breeding stage had significantly greater Hct values compared to those from the early wintering stage, whereas there were no significant differences in SCM between the two life-history stages (Zhao et al 2017).…”

Comparative transcriptomic and metabolomic analysis reveals pectoralis highland adaptation across altitudinal songbirds

“…Either size modi cation of muscle ber or myo bril in highland birds plays an important role on heat production through shivering thermogenesis for maintenance of a constant core body temperature [17]. Various modi cations of muscle phenotype across altitudinal birds are probably associated with the ight performance in hypoxic environment for an increased size of myo bril which would produce more contractile force to prevent ightless, probably accounting for why highland tree sparrows perform a weak ight capacity [18].…”