ck ed ▁sw an ▁( C yg n us ▁mel anc ory ph us ) ▁is ▁a ▁sw an ▁that ▁is ▁the ▁largest ▁water f ow l ▁native ▁to ▁South ▁America . ▁ ▁Description ▁Ad ult s ▁average ▁ ▁and ▁we igh ▁. ▁The ▁wings pan ▁ranges ▁from ▁. ▁The ▁body ▁pl um age ▁is ▁white ▁with ▁a ▁black ▁neck ▁and ▁head ▁and ▁grey ish ▁bill . ▁It ▁has ▁a ▁red ▁kn ob ▁near ▁the ▁base ▁of ▁the ▁bill ▁and ▁white ▁stri pe ▁behind ▁eye . ▁The ▁sex es ▁are ▁similar , ▁with ▁the ▁female ▁slightly ▁smaller . ▁The ▁c yg net ▁has ▁a ▁light ▁grey ▁pl um age ▁with ▁black ▁bill ▁and ▁feet . ▁The ▁black - ne ck ed ▁sw an ▁was ▁formerly ▁placed ▁in ▁monot yp ic ▁genus , ▁S then el ides . ▁ ▁The ▁black - ne ck ed ▁sw an , ▁like ▁its ▁nearest ▁relatives ▁the ▁black ▁and ▁m ute ▁sw an ▁is ▁relatively ▁silent . ▁Also , ▁unlike ▁most ▁wild f ow l , ▁both ▁parents ▁regularly ▁carry ▁the ▁c yg net s ▁on ▁their ▁back s . ▁The ▁female ▁l ays ▁four ▁to ▁six ▁eggs ▁in ▁a ▁nest ▁of ▁veget ation ▁m ound . ▁The ▁di et ▁consists ▁mainly ▁of ▁veget ation , ▁insect s ▁and ▁fish ▁spawn . ▁ ▁Distribution ▁and ▁habitat ▁The ▁smallest ▁member ▁in ▁its ▁genus , ▁it ▁is ▁found ▁in ▁fresh water ▁mar sh es , ▁l ago on ▁and ▁lake ▁sh ores ▁in ▁southern ▁South ▁America . ▁The ▁black -