ly pis ▁was ▁C ath ar ope za ’ s ▁closest ▁relative . ▁This ▁was ▁argued ▁by ▁comparing ▁various ▁characteristics ▁of ▁Ph ae oth ly pis , ▁D end ro ica , ▁and ▁C ath ar ope za . ▁For ▁example , ▁C ath ar ope za ▁has ▁a ▁dark ▁pl um age , ▁while ▁D end ro ica ▁has ▁a ▁green ▁one , ▁and ▁C ath ar ope za ’ s ▁for aging , ▁morph ology , ▁and ▁song ▁were ▁more ▁similar ▁to ▁Ph ae oth ly pis ’ ▁than ▁D end ro ica ’ s . ▁Other ▁studies ▁believed ▁D end ro ica ▁was ▁C ath ar ope za ’ s ▁closest ▁relative . ▁The ▁clos eness ▁in ▁relationship ▁between ▁D end ro ica ▁and ▁C ath ar ope za ▁has ▁been ▁widely ▁recognized . ▁When ▁chart ed ▁according ▁to ▁tax on , ▁they ▁are ▁often ▁placed ▁adjacent ▁to ▁each ▁other ▁due ▁to ▁their ▁similar ities ▁in ▁morph ology ▁and ▁song . ▁A ▁study ▁that ▁sequ enced ▁the ▁DNA ▁of ▁D end ro ica ▁and ▁C ath ar ope za ▁found ▁that ▁C ath ar ope za ’ s ▁closest ▁relative ▁in ▁the ▁D end ro ica ▁genus ▁was ▁the ▁D end ro ica ▁pl um be a ▁species . ▁ ▁Description ▁ ▁The ▁wh ist ling ▁war b ler ▁is ▁often ▁compared ▁to ▁a ▁w ren ▁in ▁appearance . ▁It ▁has ▁a ▁dust y - black ▁pl um age , ▁with ▁a ▁dark ▁head ▁and ▁bill . ▁Some ▁interpret ations