Hand-Wing Index (HWI)

Definition of Hand-Wing Index (HWI):

• The ratio of the Kipp’s distance (the distance between the tip of the first secondary feather and the tip of the longest primary feather) to the total wing chord in birds. HWI can therefore be viewed as Kipp’s distance corrected for size. High HWI indicates pointed (high aspect ratio) wings suitable for efficient long-distance flight, whereas low HWI indicates rounded (low aspect ratio) wings associated with weaker or short-distance flight