I have seen something similar on the upperwing of Wedge-tailed before (all the greater coverts gone, leaving a white panel), but not on the underwing.

• 我以前看过一只长尾水剃鸟的翼上出现类似的情况（所有的大覆羽都不见了，造成一个白色的翼窗），但是还没看过在翼下出现这种情况。