 The whistling ducks , Dendrocygna , are a distinctive group of eight bird species within the duck , goose and swan family Anatidae , which are characterised by a hump @-@ backed , long @-@ necked appearance and the whistled flight calls that give them their English name . They were an early split from the main duck lineage , and were predominant in the Late Miocene before the subsequent extensive radiation of more modern forms in the Pliocene and later . The fulvous whistling duck forms a superspecies with the wandering whistling duck . It has no recognised subspecies , although the birds in northern Mexico and the southern US have in the past been assigned to D. b. <unk> , described as having paler and brighter underparts and a lighter crown than D. b. bicolor . 
