The South Island adzebill, and the closely related North Island adzebill, have been placed as the sister taxa to all other New Zealand rails. An early Miocene (19-16 million-years-old) adzebill, Aptornis proasciarostratus, has been described from the St Bathan’s Formation, central Otago.
The South Island adzebill was about 20% heavier than its North Island counterpart. This large flightless bird had a massive, thick-walled skull with a remarkable bill that was long, pointed, down-curved, and robust. The wing bones were very much reduced and the wing would not have been visible in the living bird. The sternum was reduced and the keel was almost absent. Reduced wings, lack of a keel, and large size meant the bird was flightless. The legs and toes were short and robust.
Distribution and habitat
The South Island adzebill was found at scattered sites throughout the South Island. It is thought that the species preferred dry podocarp forests, and was largely absent from the West Coast and Central Otago. They were widespread during the cold, dry climate of the Pleistocene, but became restricted to drier eastern areas in the succeeding Holocene. South Island adzebills were found at altitudes up to 1000 m, but were absent from subalpine habitats.
Threats and conservation
The South Island adzebill became extinct before European settlement. The presence of adzebill bones in middens indicates that early Polynesian settlers hunted the species, and this is the most likely cause of the bird’s extinction.
Richard Owen suggested that the adzebill used its formidable beak to grub in the soil for animal, rather than plant material. Owen suggested that giant worms may have been among the prey targets. The small sets of gizzard stones recovered from two complete skeletons indicate a predatory rather than herbivorous life style, and this was confirmed by an analysis of bone gelatine proteins which had the characteristic nitrogen-isotope composition typical of predators. They probably hunted a variety of vertebrates such as lizards, tuataras, and birds as well as larger invertebrates.
Gill, B.; Martinson, P. 1991. New Zealand’s extinct birds. Random Century, Auckland.
Lanfear, R.; Bromham, L. 2011. Estimating phylogenies for species assemblages: a complete phylogeny for the past and present native birds of New Zealand. Molecular Phylogenetics and Evolution 61: 958-963.
Tennyson, A.; Martinson, P. 2006. Extinct birds of New Zealand. Te Papa Press, Wellington.
Wood, J.R.; Scofield, R.P.; Hamel, J.; Lalas, C.; Wilmshurst, J.M. 2017. Bone stable isotopes indicate a high trophic position for New Zealand’s extinct South Island adzebill (Aptornis defossor) (Gruiformes: Aptornithidae). New Zealand Journal of Ecology 41: 240-244.
Worthy, T H.; Holdaway, R.N. 2002. The lost world of the moa. Indiana University Press, Bloomington and Indianapolis.
Worthy, T.H.; Tennyson, A.J.D.; Scofield, R.P. 2011. Fossils reveal an early Miocene presence of the aberrant gruiform Aves: Aptornithidae in New Zealand. Journal of Ornithology 152: 669-680.
Michaux, B. 2013 [updated 2017]. South Island adzebill. In Miskelly, C.M. (ed.) New Zealand Birds Online.
South Island adzebill
- Breeding season
- Egg laying dates