, ▁it ▁was ▁behaviour ally ▁flight less , ▁similar ▁to ▁other ▁island ▁birds , ▁such ▁as ▁some ▁par ro ts . ▁Though ▁the ▁Lord ▁How e ▁sw am phen ▁was ▁similar ▁in ▁size ▁to ▁the ▁Austral as ian ▁sw am phen , ▁it ▁had ▁proportion ally ▁shorter ▁wings ▁and ▁therefore ▁a ▁higher ▁wing ▁load ▁– ▁perhaps ▁the ▁highest ▁of ▁all ▁sw am ph ens . ▁ ▁Van ▁Gr ouw ▁and ▁H ume ▁pointed ▁out ▁that ▁a ▁white ▁colour ▁aber r ation ▁in ▁birds ▁is ▁rarely ▁caused ▁by ▁al bin ism ▁( which ▁is ▁less ▁common ▁than ▁formerly ▁believed ), ▁but ▁by ▁le uc ism ▁or ▁progress ive ▁gre ying ▁– ▁a ▁phenomen on ▁van ▁Gr ouw ▁described ▁in ▁ 2 0 1 2 ▁and ▁ 2 0 1 3 . ▁These ▁conditions ▁produce ▁white ▁fe athers ▁due ▁to ▁the ▁absence ▁of ▁cells ▁which ▁produce ▁the ▁p ig ment ▁mel an in . ▁Le uc ism ▁is ▁inherited , ▁and ▁the ▁white ▁fe ather ing ▁is ▁present ▁in ▁ju ven iles ▁and ▁does ▁not ▁change ▁with ▁age ; ▁progress ive ▁gre ying ▁causes ▁normally - col oured ▁ju ven iles ▁to ▁lose ▁p ig ment - produ cing ▁cells ▁with ▁age , ▁and ▁they ▁become ▁white ▁as ▁they ▁mou lt . ▁Since ▁contemporary ▁accounts ▁indicate ▁that ▁the ▁Lord ▁How e ▁sw am phen ▁turned ▁from ▁black ▁to ▁bl u ish - gre y ▁and ▁then ▁white , ▁Van ▁Gr ouw ▁and ▁H ume ▁concluded ▁that ▁it ▁under w ent ▁inher itable ▁progress ive ▁gre