IngentaConnect Intraspecific variation in avian pectoral muscle mass: constraint...

Abstract:

Summary

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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.

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We derive aerodynamic predictions how pectoral muscle mass (m_pm) should change with m_b to maintain constant relative flight power.

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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.

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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).

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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.

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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.

Functional Ecology (2007) 21, 317-326

doi: 10.1111/j.1365-2435.2006.01234.x

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