Moa

Moa
Fossil range: Miocene - 1500 CE (Holocene)
Moa attacked by a Haast's Eagle
Moa attacked by a Haast's Eagle
Conservation status
Status iucn3.1 EX.svg
Extinct (IUCN 3.1)
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Superorder: Paleognathae
Order: Struthioniformes
Family: †Dinornithidae
Bonaparte, 1853
Genera

†Anomalopteryx (bush moa)
†Euryapteryx (stout-legged/coastal moa)
†Megalapteryx (upland moa)
†Dinornis (giant moa)
†Emeus(eastern moa)
†Pachyornis(Mappin’s/Heavy-footed/crested moa)

The moa[1][2] were ten species (in six genera) of flightless birds endemic to New Zealand. The two largest species, Dinornis robustus and Dinornis novaezelandiae, reached about 3.6 m (12 ft) in height with neck outstretched, and weighed about 250 kg (550 lb).

Moa are members of the order Struthioniformes (or ratites). The ten species of moa are the only wingless birds, lacking even the vestigial wings which all other ratites have. They were the dominant herbivores in New Zealand forest, shrubland and subalpine ecosystems for thousands of years, and until the arrival of the Māori were hunted only by the Haast's Eagle. All species are generally believed to have become extinct by 1500 CE, mainly due to hunting by Māori.

Contents

Taxonomy

Comparison of a kiwi, ostrich, and Dinornis robustus, each with its egg

The kiwi were formerly regarded as the closest relatives of the moa, but comparisons of their DNA suggest they are more closely related to the Australian emu and cassowary.[3]

Although dozens of species were described in the late 1800s and early 1900s, many were based on partial skeletons and turned out to be synonyms. Currently, ten species are formally recognised, although recent studies using ancient DNA recovered from bones in museum collections suggest that distinct lineages exist within some of these. One factor that has caused much confusion in moa taxonomy is the intraspecific variation of bone sizes, between glacial and inter-glacial periods (see Bergmann’s rule and Allen’s rule) as well as sexual dimorphism being evident in several species. The giant moa seem to have had the most pronounced degree of sexual dimorphism, with females being up to 150% taller and 280% heavier than males—so much bigger that they were formerly classified as separate species until 2003) (Huynen et al., 2003; Bunce et al., 2003) (see also below).

Although moa were traditionally reconstructed in an upright position to create impressive height, analysis of their vertebral articulation indicates that they probably carried their heads forward[4], in the manner of a kiwi. This would have allowed then to graze on low-level vegetation, while being able to lift their heads and browse trees when necessary.

Ancient DNA analyses have determined that there were a number of cryptic evolutionary lineages in several moa genera. These may eventually be classified as species or subspecies; Megalapteryx benhami (Archey) which is synonymised with M. didinus (Owen) because the bones of both share all essential characters. Size differences can be explained by a north-south cline combined with temporal variation such that specimens were larger during the Otiran glacial period (the last ice age in New Zealand). Similar temporal size variation is known for the North Island Pachyornis mappini.[5] Some of the other 'Large' ranges in variation for moa species can probably be explained by similar geographic and temporal factors.[6]

Sometimes, the Dinornithidae are considered to be a full order (Dinornithiformes), in which case the subfamilies listed below would be advanced to full family status (replacing "-inae" with "-idae").

Reconstruction of two moa species, Otago Museum, Dunedin. Otago Museum holds the world's largest collection of moa remains.

Thus, the currently recognised genera and species are:

Regional faunas

Analyses of fossil moa bone assemblages (for example: Worthy 1998a; 1998b; Worthy & Holdaway 1993; 1994; 1995; 1996: compiled by Worthy & Holdaway 2002) have provided detailed data on the habitat preferences of individual moa species, and revealed distinctive regional moa faunas:

South Island

Pachyornis elephantopus skeleton

The two main faunas identified in South Island include: 1. The fauna of the high rainfall west coast beech (Nothofagus) forests that included Anomalopteryx didiformis and Dinornis robustus; and 2. The fauna of the dry rainshadow forest and shrublands east of the Southern Alps that included Pachyornis elephantopus, Euryapteryx gravis, Emeus crassus and Dinornis robustus. The two other moa species that existed in South Island; Pachyornis australis and Megalapteryx didinus might be included in a ‘subalpine fauna’, along with the widespread Dinornis robustus. P. australis is the rarest of the moa species, and the only one yet to have been found in Maori middens. It’s bones have been found in caves in the northwest Nelson and Karamea districts (such as Honeycomb Hill Cave), and some sites around the Wanaka district. M. didinus is more widespread. Its name ‘upland moa’ reflects the fact its bones are commonly found in the subalpine zone. However, it also occurred down to sea level where there was suitable steep and rocky terrain (such as Punakaiki on the west coast and Central Otago).

North Island

Significantly less is known about North Island paleofaunas, due to a paucity of fossil sites compared to South Island, however the basic pattern of moa-habitat relationships were the same (Worthy & Holdaway 2002). Although South Island and North Island shared some moa species (Euryapteryx gravis, Anomalopteryx didiformis), most were exclusive to one island, reflecting divergence over several thousand years since lower sea level had resulted in a land bridge across Cook Strait. In the North Island, Dinornis novaezealandiae and Anomalopteryx didiformis dominated in high rainfall forest habitat; a similar pattern to South Island. The other moa species present in North Island (Euryapteryx gravis, E. curtus, and Pachyornis geranoides) tended to inhabit drier forest and shrubland habitats. P. geranoides occurred throughout the North Island, while the distributions of E. gravis and E. curtus were almost mutually exclusive, the former having only been found in coastal sites around the southern half of North Island (Worthy & Holdaway 2002).

Biology

It has been long suspected that the pairs of species of moa described as Euryapteryx curtus/E. exilis, Emeus huttonii/E. crassus, and Pachyornis septentrionalis/P. mappini constituted males and females, respectively. This has been confirmed by analysis for sex-specific genetic markers of DNA extracted from bone material (Huynen et al., 2003). For example, prior to 2003 there were three species of Dinornis recognised: South Island giant moa (D. giganteus), North Island giant moa (D. novaezealandiae) and slender moa (D. struthioides). However, DNA showed that all D. struthioides were in fact males, and all D. giganteus were females. Therefore the three species of Dinornis were reclassified as two species, one each formerly occurring on New Zealand's North Island (D. novaezealandiae) and South Island (D. robustus) (Huynen et al., 2003; Bunce et al., 2003); robustus however, comprises three distinct genetic lineages and may eventually be classified as many species as discussed above.

Diet

Although feeding moa were never observed by scientists their diet has been deduced from fossilised contents of their gizzards[7][8], coprolites[9], as well as indirectly through morphological analysis of skull and beak, and stable isotope analysis of their bones[10]. Moa fed on a range of plant species and plant parts, including fibrous twigs and leaves taken from low trees and shrubs. The beak of Pachyornis elephantopus was analagous to a pair of secateurs, and was able to clip the fibrous leaves of New Zealand flax (Phormium tenax) and twigs up to at least 8mm in diameter[8]. Like many other birds, moa swallowed gizzard stones (gastroliths), which were retained in their muscular gizzards, providing a grinding action that allowed them to eat coarse plant material. These stones were commonly smooth, rounded quartz pebbles, but stones over 110mm in length have been found amongst preserved moa gizzard contents[8]. Dinornis gizzards could often contain several kilograms of stone[10].

Locomotion

Footprints of a large moa found in 1911

Approximately eight moa trackways, with fossilised moa footprint impressions in fluvial silts have been found throughout the North Island, including Waikanae Creek (1872), Napier (1887), Manawatu River (1895), Marton (1896), Palmerston North (1911) (see photograph to right), Ragitikei River (1939), and underwater in Lake Taupo (1973). Analysis of the spacing of these tracks indicate walking speeds of between 3 and 5 km/h (Worthy & Holdaway 2002).

Breeding

Examination of growth rings present in moa cortical bone has revealed that these birds were k-selection, as are many other large endemic New Zealand birds (Turvey et al. 2005). They are characterised by having low fecundity and a long maturation period, taking approximately ten years to reach adult size. The large Dinornis species took the same length of time to reach adult size as small moa species, and as a result had accelerated rate of skeletal growth during their juvenile years (Turvey et al. 2005).

Eggs

Fragments of moa eggshell are often encountered in archaeological sites and sand dunes around the New Zealand coast. A total of 36 whole moa eggs exist in museum collections and vary greatly in size (from 120-240mm in length and 91-178mm wide)[11]. The outer surface of moa eggshell is characterised by small slit-shaped pores. The eggs of most moa species were white, although the upland moa (Megalapteryx didinus) is known to have had blue-green coloured eggs.

Nests

There is no evidence to suggest that moa were colonial nesters. While evidence of moa nesting is often inferred from accumulations of eggshell fragments found in caves and rockshelters, little evidence exists of the nests themselves. Excavations of rockshelters in the eastern North Island during the 1940s uncovered moa nests, which were described as "small depressions obviously scratched out in the soft dry pumice"[12]. Moa nesting material has also been recovered from rockshelters in the Central Otago region of South Island, where the dry climate has resulted in the preservation of plant material used to construct the nesting platform (including twigs that have been clipped by moa bills)[13]. Seeds and pollen within moa coprolites found amongst the nesting material provide evidence that the nesting season was late spring to summer[13].

Vocalisation

Although there is no surviving record of what sounds moa made, some idea of their calls can be gained from fossil evidence. The trachea of moa were supported by many small rings of bone known as tracheal rings. Excavation of these rings from articulated skeletons has shown that at least two moa genera (Euryapteryx and Emeus) exhibited tracheal elongation, that is, their trachea were up to 1 metre (3 ft) long and formed a large loop within the body cavity (Worthy & Holdaway 2002). These are the only ratites known to exhibit this feature, which is also present in several other bird groups including swans, cranes and guinea fowl. The feature is associated with deep, resonant vocalisations that can travel long distances.

Feathers and soft tissues

Preserved Megalapteryx foot, Natural History Museum

Several remarkable examples of moa remains have been found that exhibit soft tissues (muscle, skin, feathers), preserved through desiccation when the bird died in a naturally dry site (for example, a cave with a constant dry breeze blowing through it). Most of these specimens have been found in the semi-arid Central Otago region, the driest part of New Zealand.

Megalapteryx didinus head

These include: dried muscle on bones of a female Dinornis robustus found at Tiger Hill in the Manuherikia River Valley by goldminers in 1864 (Owen 1879) (currently held by Yorkshire Museum); several bones of Emeus crassus with muscle attached, and a row of neck vertebrae with muscle, skin and feathers collected from Earnscleugh Cave near the town of Alexandra in 1870 (Hutton & Coughtrey 1875) (currently held by Otago Museum); an articulated foot of a male Dinornis rubustus with skin and foot pads preserved found in a crevice on the Knobby Range in 1874 (Buller 1888) (currently held by Otago Museum); the type specimen of Megalapteryx didinus found near Queenstown in 1878 (Owen 1879) (currently held by Natural History Museum, London; see photograph of foot on this page); the lower leg of Pachyornis elephantopus with skin and muscle from the Hector Range in 1884 (Buller 1888; Anderson 1989) (currently held by the Zoology Department, Cambridge University); the complete feathered leg of a Megalapteryx didinus from Old Man Range in 1894 (Hamilton 1894) (currently held by Otago Museum); and the head of a Megalapteryx didinus found near Cromwell sometime prior to 1949 (Vickers-Rich et al. 1995 (currently held by the Museum of New Zealand). Two specimens are known from outside the Central Otago region: a complete foot of Megalapteryx didinus found in a cave on Mount Owen near Nelson in 1980’s (Worthy 1989) (currently held by the Museum of New Zealand) and a skeleton of Anomalopteryx didiformis with muscle, skin and feather bases collected from a cave near Te Anau in 1980 (Forrest 1987). In addition to these specimens, loose moa feathers have been collected from caves and rockshelters in the southern South Island, and so some idea of the moa plumage can be gained. The preserved leg of Megalapteryx didinus from Old Man Range reveals that this species was feathered right down to the foot. This is likely to have been an adaptation to living in high altitude snowy environments, and is also seen in the Darwin’s Rhea which lives in a similar seasonally snowy habitat (Worthy & Holdaway 2002). Moa feathers are up to 23cm (9 inches) long and a range of colours have been reported, including reddish brown, white, yellowish and purplish (Worthy & Holdaway 2002). Dark feathers with white or creamy tips have also been found, and indicate that some moa species may have had plumage with a speckled appearance.

Extinction

Reconstruction of a moa hunt from the early 20th century

The moa's only predator was the massive Haast's Eagle—until the arrival of human settlers.

The Māori arrived sometime before A.D. 1300, and all moa genera were soon driven to extinction by hunting and, to a lesser extent, forest clearance. By about A.D. 1400 all moa are generally thought to have become extinct, along with the Haast's Eagle which had relied on them for food. Recent research using carbon-14 dating of middens strongly suggests that this took less than a hundred years[14]; rather than the period of exploitation lasting several hundred years which had been earlier believed.

Some authors have speculated that a few Megalapteryx didinus may have persisted in remote corners of New Zealand until the 18th and even 19th centuries, but the view is not widely accepted.[15]

Discovery by science

Sir Richard Owen with Dinornis robustus skeleton

Joel Polack, a trader who lived on the East Coast of the North Island from 1834 to 1837, records in 1838 that he had been shown 'several large fossil ossifications' found near Mt Hikurangi. He was certain that these were the bones of a species of emu or ostrich, noting that 'the Natives add that in times long past they received the traditions that very large birds had existed, but the scarcity of animal food, as well as the easy method of entrapping them, has caused their extermination'. Polack further noted that he had received reports from Māori that a 'species of Struthio' still existed in remote parts of the South Island (Polack 1838, cited in Hill 1913:330). Dieffenbach (1843 (II):195) also refers to a fossil from the area near Mt Hikurangi, and surmises that it belongs to 'a bird, now extinct, called Moa (or Movie) by the natives'. In 1839, John W. Harris, a Poverty Bay flax trader who was a natural history enthusiast, was given a piece of unusual bone by a Māori who had found it in a river bank. He showed the 15 cm fragment of bone to his uncle, John Rule, a Sydney surgeon, who sent it to Richard Owen who at that time was working at the Hunterian Museum at the Royal College of Surgeons in London. Owen became a noted biologist, anatomist and paleontologist at the British Museum.

Owen puzzled over the fragment for almost four years. He established it was part of the femur of a big animal, but it was uncharacteristically light and honeycombed. Owen announced to a skeptical scientific community and the world that it was from a giant extinct bird like an ostrich, and named it Dinornis. His deduction was ridiculed in some quarters but was proved correct with the subsequent discoveries of considerable quantities of moa bones throughout the country, sufficient to reconstruct skeletons of the birds.

In July 2004, the Natural History Museum in London placed on display the moa bone fragment Owen had first examined, to celebrate 200 years since his birth, and in memory of Owen as founder of the museum.

Moa bone deposits

Since the discovery of the first moa bones in the late 1830s, thousands more bones have been found. These bones occur in a range of late Quaternary and Holocene sedimentary deposits, but are most common in three main sites:

Caves
Moa bones scattered across the floor of 'Moa Cave', Honeycomb Hill Cave System. This cave is a closed scientific reserve.

Bones are commonly found in Caves or ‘tomos’ (Maori word for doline or sinkhole; often used to refer to pitfalls or vertical cave shafts). The two main ways that the moa bones were deposited in such sites were: 1. Birds that entered the cave to nest or escape bad weather, and subsequently died in the cave; and 2. Birds that fell into a vertical shaft and were unable to escape. Moa bones (and the bones of other extinct birds) have been found in caves throughout New Zealand, especially in the limestone/marble areas of northwest Nelson, Karamea, Waitomo and Te Anau.

Dunes

Moa bones and eggshell fragments sometimes occur in active coastal sand dunes, where they may erode from paleosols and concentrate in ‘blowouts’ between dune ridges. Many such moa bones predate human settlement, although some can originate from Maori midden sites which frequently occur in dunes near harbours and river mouths (for example the large moa hunter sites at Shag River, Otago and Wairau Bar, Marlborough).

Swamps/mirings

Densely intermingled moa bones have been encountered in swamps throughout New Zealand. The most well-known example is at Pyramid Valley in north Canterbury (Holdaway & Worthy 1997), where bones from at least 183 individual moa have been excavated. Many explanations were historically proposed to explain how these deposits had formed, ranging from poisonous spring waters to floods and wildfires. However the currently accepted explanation is that the bones accumulated at a slow rate over thousands of years, from birds that had entered the swamps to feed and became trapped in the soft sediment (Wood et al. 2008).

Claims of moa survival

Though scientists agree there is no doubt that moa are extinct, there has been occasional speculation—since at least the late 1800s,[16][17] and recently as 2008[18]—that some moa may still exist, particularly in deepest south Westland, a rugged wilderness in the South Island. Cryptozoologists and others reputedly continue to search for them,[19] but their claims and supporting evidence (such as of purported Moa footprints[20] or blurry photos[21]) have earned little attention from mainstream experts, and are widely considered pseudoscientific.[15]

Experts contend that moa survival is extremely unlikely, since this would involve the ground-dwelling birds living unnoticed in a region visited often by hunters and hikers.[20]

While the rediscovery of the Takahē in 1948 (after none had been seen since 1898), showed that rare birds may exist undiscovered for a long time, the Takahē was rediscovered after its tracks were identified—yet no reliable evidence of moa tracks has ever been found.

Footnotes

  1. ↑ In Māori words do not use s to indicate plural, and thus "moa" is both plural and singular. Some English speakers apply this rule to their use of the word within English, though others use the regularly formed English plural "moas".
  2. ↑ In some other polynesian languages (Tahitian, Cook Islands Maori, Samoan...), "moa" is the generic name for chicken, fowl (Dictionary of the tahitian academy {fr/ty}; Jasper Buse, Raututi Taringa, "Cook islands maori Dictionary" (1995); Samoan lexicon)
  3. ↑ Turvey et al 2005
  4. ↑ Worthy & Holdaway '2002
  5. ↑ Worthy 1987
  6. ↑ Worthy et al 1988
  7. ↑ Burrows et al. 1981
  8. ↑ 8.0 8.1 8.2 Wood 2007
  9. ↑ Horrocks et al. 2004
  10. ↑ 10.0 10.1 Worthy & Holdaway 2002
  11. ↑ Gill 2007
  12. ↑ Hartree 1999
  13. ↑ 13.0 13.1 Wood 2008
  14. ↑ Holdaway & Jacomb 2000
  15. ↑ 15.0 15.1 Anderson 1989
  16. ↑ Gould, Charles. 1886 Mythical Monsters. W.H. Allen & Co
  17. ↑ Heuvelmans, Bernard. 1959. On the Track of Unknown Animals. New York, Hill and Wang
  18. ↑ Laing, Doug. "Birdman says moa surviving in the Bay" 2008. from Hawks Bay Today.
  19. ↑ Hall, Jamie. 2006. "The Cryptid Zoo: Moas and Other Giant Flightless Birds".
  20. ↑ 20.0 20.1 Laing, 2008
  21. ↑ Coleman, Loren. 2007. "Mystery Moa Photo".

References

See also

External links