Intraspecific variation in avian pectoral muscle mass: constraints on maintaining manoeuvrability with increasing body mass

• Published in: Functional Ecology
• Main Authors: DIETZ, MAURINE W., PIERSMA, THEUNIS, HEDENSTRÖM, ANDERS, BRUGGE, MAARTEN
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2007
• Subjects: Calidris canutus; Red Knot; Tundra
• Online Access: http://dx.doi.org/10.1111/j.1365-2435.2006.01234.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1365-2435.2006.01234.x; https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2435.2006.01234.x

Summary 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 ( m b ). Pervasive predation threats beg the question whether escape flight abilities keep up with such large changes in m b . We derive aerodynamic predictions how pectoral muscle mass ( m pm ) should change with m b to maintain constant relative flight power. 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 . m pm varied with m b in a piecewise manner. In islandica knots with m b ≤ 148 g, the slope (1·06) was indistinguishable from the prediction (1·25). In heavy knots ( m b > 148 g) the slope was significantly lower (0·63), yielding a m pm 0·81 times lower than predicted at pre‐departure weights (210 g). Manoeuvrability tests showed that above 160 g, knots were increasingly unable to make a 90° angle turn. This is consistent with m pm being increasingly smaller than predicted. Relatively low m pm enables savings on mass and hence flight costs, and savings on overall energy expenditure. We predict that reduced escape flight ability at high m b will be compensated by behavioural strategies to minimize predation risk.