A monograph of the Trochilid, or family of humming-birds /.London :Printed by Taylor and Francis ;1861 [i.e. 1849-1861].biodiversitylibrary.org/page/35246209
From Buller's Birds of New Zealand: North Island Ko-kako, Callaeas cinerea wilsoni (left) and South Island Ko-kako, Callaeas cinerea cinerea (right--likely extinct). Some sources give the species name as "cinera", others as "cinereus".