 The fulvous whistling duck is 45 – 53 cm ( 18 – 21 in ) long ; the male weighs 748 – 1 @,@ 050 g ( 26 @.@ 4 – 37 @.@ 0 oz ) , and the female averages marginally lighter at 712 – 1 @,@ 000 g ( 25 @.@ 1 – 35 @.@ 3 oz ) . It is a long @-@ legged duck , mainly golden @-@ brown with a darker back and an obvious blackish line down the back of its neck . It has whitish stripes on its flanks , a long grey bill and grey legs . In flight , the wings are brown above and black below , with no white markings , and a white crescent on the rump contrasts with the black tail . All plumages are fairly similar , but the female is slightly smaller and duller @-@ plumaged than the male . The juvenile has paler underparts , and appears generally duller , especially on the flanks . There is a complete wing moult after breeding , and birds then seek the cover of dense wetland vegetation while they are flightless . Body feathers may be moulted throughout the year , although each feather is replaced only once annually . 
