...Vance A. Tucker ABSTRACT The anterior-most primary feathers of many birds that soar over land bend upwards and separate vertically to form slotted wing tips during flight. The slots are thought to reduce aerodynamic drag, although drag reduction has never been demonstrated in living birds. Wing...

.... The tail can generate an estimated 10% of the hawk’s total lift at maximum wing span and 5 % or less at shorter wing spans. I moved the centre of area of the hawk’s wings forward experimentally by clipping 76 mm from primary feathers 6–10 and 38 mm from primary feather 5. The effect of this operation...