ying . ▁Progress ive ▁gre ying ▁is ▁a ▁common ▁cause ▁of ▁white ▁fe athers ▁in ▁many ▁types ▁of ▁birds ▁( including ▁rails ), ▁although ▁such ▁spec im ens ▁have ▁sometimes ▁been ▁in ac cur ately ▁referred ▁to ▁as ▁al bin os . ▁The ▁condition ▁does ▁not ▁affect ▁car oten oid ▁p ig ments ▁( red ▁and ▁yellow ), ▁and ▁the ▁bill ▁and ▁legs ▁of ▁the ▁Lord ▁How e ▁sw am ph ens ▁retained ▁their ▁colour ation . ▁The ▁large ▁number ▁of ▁white ▁Lord ▁How e ▁sw am ph ens ▁may ▁be ▁due ▁to ▁its ▁small ▁found ing ▁population , ▁which ▁would ▁have ▁facil itated ▁the ▁spread ▁of ▁inher itable ▁progress ive ▁gre ying . ▁ ▁Ext inction ▁ ▁Although ▁the ▁Lord ▁How e ▁sw am phen ▁was ▁considered ▁common ▁during ▁the ▁late ▁ 1 8 th ▁century , ▁it ▁appears ▁to ▁have ▁disappeared ▁quickly ; ▁the ▁period ▁from ▁the ▁island ' s ▁discovery ▁to ▁the ▁last ▁mention ▁of ▁living ▁birds ▁is ▁only ▁two ▁years ▁( 1 7 8 8 – 9 0 ). ▁It ▁had ▁probably ▁van ished ▁by ▁ 1 8 3 4 , ▁when ▁Lord ▁How e ▁Island ▁was ▁first ▁settled , ▁or ▁during ▁the ▁following ▁de cade . ▁Wh al ers ▁and ▁se al ers ▁had ▁used ▁the ▁island ▁for ▁supplies , ▁and ▁may ▁have ▁h unted ▁the ▁bird ▁to ▁ext inction . ▁Hab itat ▁destruction ▁probably ▁did ▁not ▁play ▁a ▁role , ▁and ▁animal ▁pred ators ▁( such ▁as ▁r ats ▁and ▁c ats ) ▁arrived ▁later . ▁Several