MYSTERY BIRD QUIZ & BEYOND: Part 1 - Ultimate mystery bird quiz question

They have stretched your mind, made you scratch your head and even forced you to cheat on google, but what do the Jerdon’s courser, Northern bald ibis, Slender-billed vulture, Amsterdam albatross, St Helena plover, Ivory-billed woodpecker, Montserrat oriole, Long-billed tailorbird, Kakapo, Fiji petrel, Balaeric shearwater and Dusky starfrontlet all have in common (other than being birds!!!)? I am after one specific common denominator.

Answer along with part 2 tomorrow!

Claire