Tuesday, March 14, 2017

Bush Moa (Anomalopteryx didiformis)

The Bush Moa (Anomalopteryx didiformis) was one of the smallest and most widespread moa species which lived during the Quaternary, inhabiting the forests of both of New Zealand’s main islands. This relatively slender species became extinct shortly after the arrival of the Maori.

The Bush Moa is the only member of the genus Anomalopteryx, which is derived from the Greek words anomalus (meaning “abnormal” or “odd”) and pteryx (meaning “wing”). The species name didiformis means “of the form of the Dodo”, suggesting that Sir Richard Owen who first described this moa in 1844 likened it to the Dodo (Raphus cucullatus): another flightless bird which had gone extinct about 150 years prior to Owen’s lifetime. Taken together, the full scientific name for this species may mean “Dodo-like Bird with Abnormal Wings”. Other common names for this species include “Little Bush Moa”, “Lesser Moa”, and “Slender Bush Moa”.

Habitat & Distribution
The Bush Moa was the most widespread of all the moa species, inhabiting the closed-canopy lowland forests of both North Island and South Island, although they appear to have been more abundant on the former. It is known from complete skeletons, eggshell fragments, and soft tissue specimens including feathers and skin.

Physical Attributes
Bush Moa rivalled the Mantell’s Moa (Pachyornis geranoides) for the title of smallest moa species. Both are similar in terms of linear measurements, however the Mantell's was heavier and more robust. The Bush Moa was a slender animal with relatively long legs adapted for speed and agility, therefore making it the smallest moa in terms of mass. This species stood about 75cm (2.5ft) tall at the hips and up to 120cm (4ft) tall when fully erect, with a body mass ranging from 13 to 30kg (28 to 66lbs). The head was proportionally the largest of any moa with a relatively short, sharp-edged beak. Desiccated carcasses of this species have shown that this species was covered in yellowish-brown to pale colored feathers which measured up to 23.8mm in length.

Ecology & Behavior
The Bush Moa diet is well-known because of analyses of coprolites and gizzard contents, hall of which indicate that this species browsed on a variety of woody and fibrous plants within its forested environment. Furthermore, its sharp-edged beak was better adapted to cutting than those of other moa, and a 2016 biomechanical study has confirmed that Bush Moa fed using a unilateral clipping action. Predators of Bush Moa included the Haast’s Eagle (Harpagornis moorei), which actively hunted all species of moa, as well as the smaller Eyles’ Harrier (Circus eylesi).

Eggshell fragments attributed to this species have also been found in caves which, when reconstructed, would measure about 165 x 119mm. Nests were made in secluded locations where the males would take sole incubation duties. A 2005 study of moa cortical bone marks has shown that Bush Moa chicks took about 8 years to reach their adult size, one of the slowest growth rates known for any moa species second only to the Mantell’s Moa. Due to its small stature, Bush Moa may have been relatively gregarious compared to other moa, an advantageous behavior which limits the chances of predation on any one individual.

Like other moa, this species was the victim of overexploitation by the Maori settlers which arrived 700 to 600 years ago. Bush Moa bones have commonly been unearthed in archaeological sites, showing that the Maori actively hunted them.

An assortment of moa bones in Ngarua Caves. Note the complete Bush Moa
skeleton  in the center of this image. Wiki.

References & Further Reading
Attard MRG, Wilson LAB, Worthy TH, Scofield P, Johnston P, Parr WCH, Wroe S (2016). "Moa diet fits the bill: virtual reconstruction incorporating mummified remains and prediction of biomechanical performance in avian giants". Proceedings of the Royal Society of London B 283: 20152043 <Full Article>

Rawlence NJ, Wood JR, Scofield RP, Fraser C, Tennyson AJD (2013). "Soft-tissue specimens from pre-European extinct birds of New Zealand". Journal of the Royal Society of New Zealand DOI:10.1080/03036758.2012.704878 <Full Article>

Wood JR, Wilmshurst JM, Richardson SJ, Rawlence NJ, Wagstaff SJ, Worthy TH, Cooper A (2013). "Resolving lost herbivore community structure using coprolites of four sympatric moa species (Aves: Dinornithiformes)". PNAS 110(42): 16910-16915 <Full Article>

Wood JR, Wilmshurst JM, Worthy TH, Cooper A (2012). "First coprolite evidence for the diet of Anomalopteryx didiformis, an extinct forest ratite from New Zealand". New Zealand Journal of Ecology 36(2): 164-170 <Full Article>

Turvey ST, Green OR, Holdaway RH (2005). "Cortical growth marks reveal extended juvenile development in New Zealand moa". Nature Letter 435 doi:10.1038/nature03635 : 940-944 <Abstract>

TH Worthy (1990). "An analysis of the distribution and relative abundance of moa species (Aves: Dinornithiformes)". New Zealand Journal of Zoology 17(2): 213-241 <Full Article>

Forrest RM (1987). "A partially mummified skeleton of Anomalopteryx didiformis from Southland". Journal of the Royal Society of New Zealand 17(4): 399-408 <Full Article>

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