Intraspecific variation in avian pectoral muscle mass: constraints on maintaining manoeuvrability with increasing body mass
Hedenström, Anders, | Piersma, Theunis, | Dietz, Maurine W., | Brugge, Maarten,
1.Within a single year, long-distance migrants undergo a minimum of four cycles of fuel storage and depletion because their migrations have at least one stopover. Each cycle includes an almost twofold change in body mass (mb). Pervasive predation threats beg the question whether escape flight abilities keep up with such large changes in mb.2.We derive aerodynamic predictions how pectoral muscle mass (mpm) should change with mb to maintain constant relative flight power. 3.We tested these predictions with data on red knot Calidris canutus, a long-distance migrating wader that breeds in arctic tundra and winters in temperate and tropical coastal areas. We focused on the subspecies C. c. islandica. 4.mpm varied with mb in a piecewise manner. In islandica knots with mb = 148 g, the slope (1·06) was indistinguishable from the prediction (1·25). In heavy knots (mb > 148 g) the slope was significantly lower (0·63), yielding a mpm 0·81 times lower than predicted at pre-departure weights (210 g). 5.Manoeuvrability tests showed that above 160 g, knots were increasingly unable tomake a 90° angle turn. This is consistent with mpm being increasingly smaller than predicted. 6.Relatively low mpm enables savings on mass and hence flight costs, and savings on overall energy expenditure. We predict that reduced escape flight ability at high mb will be compensated by behavioural strategies to minimize predation risk.
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