Abstract
It proved possible to sex Eastern Spot-billed Duck Anas poecilorhyncha zonorhyncha on the basis of plumage color; 43 males and 37 females were collected in Tochigi Prefecture in May, 1987, and their sex determined by dissection. Sexual differences were found in the upper and under tail-coverts, and belly. Males have lustrous black upper and under tail-coverts, and a deep rufous-black belly. Females have rufous-black upper and under tail-coverts with pale buff-brown fringes or spots, and a belly similar to the breast.
