Which aerodynamic effect increases for soaring birds when the thoracic air sacs expand?

💡 Explanation

When thoracic air sacs expand, the center of gravity shifts forward because mass redistribution alters inertial properties, which reduces induced drag at the wingtips due to modified wake interactions. Therefore, reduced induced drag results, rather than boundary layer separation, stall delay, or flow transition changes which require different flow conditions.

• Which outcome reduces soaring efficiency when damage disrupts feather alignment?
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