Thursday, March 30, 2017

March of the Moa Part 2: Anatomy and Action

In addition to being known from multiple complete skeletons, soft tissue remains including skin, feathers, muscle tissue, and organs have been found for moa. Because of this, the life appearances and anatomy of most species is relatively well-known with abundant genetic material. Moa were comparable in in some aspects to modern flightless ratites: all share, for example, a small head mounted on a long neck which is in turn connected to a rigid torso, long legs, with a covering of long strands of fur-like feathers on their bodies. In many aspects, however, moa were quite unique with a number of characteristics not seen in their modern relatives. This blog post will highlight these characteristics.

Side-by-side skeletal mounts of Ostrich (Struthio camelus) and the
North Island Giant Moa (Dinornis novaezealandiae).
Photo taken in 1870. Wiki.

Moa beaks and skulls are larger and broader than those of modern ratites, able to deal with a wider variety of plant matter (this will be addressed in greater detail in part 3 of this series). The orbits were large and the nostrils were located at the base of the beak. moa had exceptionally well-developed sense of smell as indicated by enlarged olfactory lobes, a feature which they share with kiwis. An enhanced ability to process odors suggest that chemical communication and other was an important aspect of moa behavior: note the prominent olfactory nerve (labeled CN1) in CT image of the moa brain in the video below which was generated by WitmerLab.


For as long as moa have been known to science, most skeletal mounts and early artistic portrayals have depicted them with an Ostrich-like posture: the neck being held vertically so that the head was held high above the rest of the body. However, recent examinations of moa vertebral and cranial anatomy indicate that these birds would have carried their heads in a lowered position when at rest: the neck was normally held in a curved position so that the head was level to the back. Modern kiwis and cassowaries adopt a similar position, which is more efficient for traveling through dense forest vegetation. Moa would have only adopted an erect-neck posture when browsing, during threat displays, or when surveying to their surroundings.


Two reconstructions of the Upland Moa (Megalapteryx didinus). The left image,
illustrated by George Edward Lodge in 1907 (source) shows the bird in the outdated,
ostrich-like posture with an erect neck. The left image shows the animal in a more
realistic head-lowered posture.

Moa legs were generally longer and more robust than those of modern ratites with particularly elongated tibiotarsi (in birds, the fusion of the tibia and some of the tarsal bones) and shortened tarsometatarsi (in birds, the fusion of the three main metatarsals and some of the tarsal elements). The feet were also larger and broader with most species having four toes. Small feet and elongated lower limb segments, physical characteristics shared among modern ostriches, rheas, and emus, are associated with cursoriality and maintaining high speeds over long distances. Moa limb proportions, with their shortened distal segments, suggest that they were not built for active running although they could still move reasonably fast when they needed to. However, moa may have been better suited for maneuverability than their more fleet-footed relatives. Modern cursorial ratites, despite their great running speeds, have wide turning circles and their slender limbs make sharp turns relatively difficult: the relatively open environments which these birds tend to inhabit lessens this apparent disadvantage. The sturdier legs and shorter foot bones of moa were potentially more adept at weaving through trees and other obstacles when evading aerial predators like the Haast’s Eagle (Harpagornis moorei). Kiwis have similar limb proportions.

Hindlimb skeletons of eight ratite species scaled  to the same femur length.
From left to right: Ostrich, Heavy-footed Moa, North Island Giant Moa,
Bush Moa, Mantell's Moa, Great Spotted Kiwi, Southern Cassowary, and
Upland Moa. Note that in moa and kiwi the lower limb segments are
proportionately much shorter compared those of other ratites, in which the
tibiotarsus and  tarsometatarsus are about the same length.

All flightless ratites evolved from volant (flying) ancestors which possessed hypertrophied forelimbs (wings) and a keeled sternum which supported enlarged pectoralis muscles to facilitate powered flight. When transitioning to a more terrestrial, flightless lifestyle, the sternum lost its keel with an accompanying reduction of the pectoral musculature and of the forelimb skeleton to varying degrees.
  • Ostriches and rheas demonstrate the least forelimb reduction among flightless ratites: the reason for this is because these birds utilize their forelimbs during visual displays and to stabilize themselves when running.
  • Kiwis, emus, and cassowaries demonstrate a more extreme form of reduction in which the forelimbs have become so small that they serve no obvious function and are almost never visible from within the plumage.
  • Moa have become the only known birds to completely lack any external forelimb structure due to the absence of the tbx5 gene: the gene responsible for forming the pectoral girdle. As a result, the sole remnant of the forelimb skeleton is a tiny vestige of bone known as the scapulocoracoid (the fusion of the scapula and coracoid bones) which lies against the ribcage and is no larger than a human finger.

Three grades of forelimb reduction observed in ratites. (A) long and slender
humerus with shortened forearm elements as seen in ostriches and rheas;
(B) short, stubby forearm as seen in most flightless ratites such as emus
and cassowaries; (C) complete absence of external limb elements with the
scapula and coracoid fused to form the scapulocorocoid, a feature which is
unique to moa.

The internal anatomy of moa is still mostly unknown. However, a few unique specimens of the Eastern Moa (Emeus crassus) and Stout-legged Moa (Euryapteryx curtus) have been found with ossified tracheal rings within their body cavities revealing the form and structure of the windpipe. These two species, and potentially other members of Emeidae, possessed a convoluted windpipe. From the neck, the windpipe passed downwards on the left side of the body before doubling back on itself and then backward into the lungs, almost doubling this organ’s length. Modern birds which have this adaptation (swans, cranes, etc) are known for producing deep, resonant vocalizations: the convoluted nature of the windpipe forming a structure analogous to the tubing of certain types of wind instruments. The Tetrapod Zoology blog discusses this adaptation in greater detail hereWe can imply that moa were highly vocal animals that could produce a broad range of situation-specific calls which could be heard over great distances including contact calls, alarm calls, and mating calls. These Sandhill Cranes (video) provide a reasonable analogue for potential moa vocalizations. 

A diagram approximating the shape of the windpipe in the 
Eastern Moa (Emeus crassus).

Moa plumage is particularly well-known thanks to the discovery of numerous desiccated specimens recovered from caves throughout New Zealand. Like modern ratites, moa plumage consisted of long, shaggy, and somewhat hair-like strands for insulation and repelling water. These birds possessed cryptic coloration which was adapted to camouflage them within their respective environments, much like modern kiwis or the Kakapo (Strigops habroptilus), a flightless New Zealand parrot. Base colors ranged from light yellowish-brown to reddish-brown and many feathers were tipped in white, which would have produced a mottled or speckled effect. Such coloration was ideal for concealment and likely evolved as a defensive measure against the keen-eyed flying predators with which these birds coevolved.

Characteristic morphology and color of moa feathers which are identified to
species via ancient DNA sequences. Feathers belong to (from left to right)
Upland Moa, South Island Giant Moa, Stout-legged Moa, and Heavy-footed
Moa. Figure 3 from Rawlence et al., 2009.

The nine known species of moa ranged in size from the diminutive Bush Moa (Anomalopteryx didiformis) to the large yet lanky South Island Giant Moa (Dinornis robustus); a range of 15 to 250kg. In addition, most species display female-biased sexual dimorphism (also known as "reverse dimorphism"), that is, the females grew noticeably larger than the males. For most moa, females typically ranged from 15 to 20% larger, which is typical of modern dimorphic ratites. Members of the genus Dinornis, however, display the most extreme dimorphism seen among any terrestrial vertebrate with females growing up to three times the mass of males. The size difference is so vast, in fact, that the male morph of both Dinornis species was once thought to be a species in its own right: called the Slender Moa (D. struthoides). DNA sequencing in 2003 has since corrected this mistake and several other formerly recognized moa 'species' which had been established based on size differences were also debunked.  

Comparison of coefficients of variation for femora lengths with male:female
body mass in moa. The relative size of male (blue) to females (pink) are given
for the genera Dinornis, Pachyornis, Euryapteryx, and Emeus.
Figure 3 in Huyen et al., 2003.

Part 1: Evolution & History
Part 3: Paleoecology

References & Further Reading
Huynen L, Suzuki T, Ogura T, Watanabe Y, Millar CD, Hofreiter M, Smith C, Mirmoeini S, Lambert DM (2014). "Reconstruction and in vivo analysis of the extinct tbx5 gene from ancient wingless moa (Aves: Dinornithiformes)". BioMed Central Evolutionary Biology 14:75 <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>


Rawlence NJ, Wood JR, Armstrong KN, Cooper A (2009). "DNA content and distribution in ancient feathers and potential to reconstruct the plumage of extinct avian taxa". Proceedings of the Royal Society B 276: 3395-3402 <Full Article>

Huynen L, Millar CD, Scofield RP, Lambert DM (2003). "Nuclear DNA sequences detect species limits in ancient moa". Nature 425: 175-178 <Abstract>

Thursday, March 23, 2017

Heavy-footed Moa (Pachyornis elephantopus)

The Heavy-footed Moa (Pachyornis elephantopus) was the largest member of the genus Pachyornis and the third largest species of moa overall. This exceptionally heavily-built species lived in South Island during the Pleistocene and Holocene where it fed on relatively low-quality plant matter.

Heavy-footed Moa skeleton on display at the Exhibit Museum of
Natural History, University of Michigan. Wiki.

Etymology
The genus name Pachyornis is derived from the Greek words pachys (meaning “thick”) and ornis (meaning “bird”), a reference to members of this genus being particularly heavily-built compared to other moa genera. The species name elephantopus is a combination of the Greek words elephas (meaning “elephant”) and pous (meaning “foot”). Its full scientific name therefore translates as “Elephant-legged Bird” in reference to this species’ robust skeleton with particularly thick limb elements, a trait which is further emphasized by common name “Heavy-footed Moa”.

Habitat & Distribution
Heavy-footed Moa had an extensive late Quaternary fossil record. Their preferred habitat appears to have been lowland to montane grassland, shrubland, herbfields, and forest margin environments in the eastern and southern parts of South Island. The altitudinal limit for this species appears to have been 700m above sea level as no fossils for it have been found above this point. Heavy-footed Moa underwent significant changes in relative abundance and distribution in response to environmental changes during the late Pleistocene and Holocene. Climatic and environmental fluctuations during glacial cycles caused its preferred habitat to expand and contract repeatedly, resulting in two genetically distinct populations in the northern and southern halves of South Island. Like all other moa, it held a relatively constant population size until the arrival of the Maori in the late 13th century.


Physical Attributes
The Heavy-footed Moa is the third largest species of moa behind both species of Dinornis and is the heaviest moa relative to its size. It stood up to 120cm tall at the hips and 180cm tall when fully erect and weighed up to 145kg, with females being larger than the males. The skeleton was robust with relatively thick leg bones and shortened tarsometatarsi (in birds, the foot bone formed by the fusion of the metatersals). This species is known from desiccated soft tissue remains recovered from cave sites which have preserved skin, tendons, and feathers. From these subfossil remains, we know that this species had shaggy, white-tipped feathers which would give the living animal a mottled or speckled appearance and that the skin of its lower legs were covered in non-overlapping scales like those of most birds. The beak was long, sturdy, and downturned and its overall head was shaped somewhat differently from other moa and was adapted to handle particularly tough vegetation.

Ecology & Behavior
Plant remains from within coprolites and among gizzard stones reveal that Heavy-footed Moa were generalized mixed-feeders with a diet consisting of at least 21 species of particularly fibrous grassland, shrubland, and forest margin vegetation. It grazed on various types of herbs and grasses and browsed on the branchlets of trees and shrubs. As with most of the larger moa species, the only predator of adult Heavy-footed Moa was the Haast’s Eagle (Harpagornis moorei) with the smaller Eyle’s Harrier (Circus eylesi) possibly feeding on the smaller juveniles. Evidence from coprolites further shows that this species hosted several types of taxa-specific parasites.


Heavy-footed Moa are thought to have been less abundant than other moa due to its less frequent representation in the fossil record. Females appear to outnumber males at natural fossil assemblages, suggesting that males were even less common in a given population. This relatively low number of males may be due to increased predation by Haast’s Eagles who likely targeted them more regularly due to their smaller size. Heavy-footed Moa eggs were among the largest of any moa and the only known moa embryos are also attributed to this species. The growth rate of this species is not known. It became extinct abruptly due to human overexploitation and habitat alteration.

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>

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>

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>

Oskam CL, Allentoft ME, Walter R, Scofield RP, Haile J, Holdaway RN, Bunce M, Jacomb C (2012). "Ancient DNA analyses of early archaeological sites in New Zealand reveal extreme exploitation of moa (Aves: Dinornithiformes) at all life stages". Quaternary Science Reviews 52: 41-48 <Full Article>

Rawlence NJ, Metcalf JL, Wood JR, Worthy TH, Austin JJ, Cooper A (2012). "The effect of climate and environmental change on the megafaunal moa of New Zealand in the absence of humans". Quaternary Science Reviews 50: 141-153 <Full Article>

Allentoft ME, Bunce M, Scofield RP, Hale ML, Holdaway RN (2010). "Highly skewed sex ratios and biased fossil deposition of moa: ancient DNA provides new insight on New Zealand’s extinct megafauna". Quaternary Science Reviews 29: 753–762 <Abstract>

Huynen L, Gill BJ, Millar CD, Lambert DM (2010). "Ancient DNA reveals extreme egg morphology and nesting behavior in New Zealand’s extinct moa". Proceedings of the National Academy of Science 107(37): 16201-16206 <Full Article>

Wood JR, Rawlence NJ, Rogers GM, Austin JJ, Worthy TH, Cooper A (2008). "Coprolite deposits reveal the diet and ecology of the extinct New Zealand megaherbivore moa (Aves, Dinornithiformes)". Quaternary Science Reviews 27: 2593–2602 <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>

Friday, March 17, 2017

Upland Moa (Megalapteryx didinus)

The Upland Moa (Megalapteryx didinus) was a small, abundant species of moa which lived in the mountainous areas of South Island. It is particularly well-represented by soft tissue remains including entire desiccated body parts with intact skin and feathers.

Upland Moa skeleton collected Mar 1987, Honeycomb Hill, Enduro, Map Grid 1385N 720E,
New Zealand. Field Collection 1982-1988. CC BY-NC-ND licence. Te Papa (S.023700)

Etymology
The Upland Moa is the only known member of the family Megalapterygidae and of the genus Megalapteryx, which is derived from the Greek words mega (meaning “big”) and apteryx (meaning “without wings”). The species name didinus means “resembling a Dodo”: didus being a Latinized generic name given to the Dodo (Raphus cucullatus) by Carolus Linnaeus. The common name for this species references its preferred habitat.

Habitat & Distribution
This species was specialized to live at the higher elevations of South Island’s alpine zone where it was common, while being rare in eastern and lowland areas. It was widespread in upland herbfields and forests up to 2,000m above sea level.

Physical Attributes
Upland Moa were a relatively small and agile moa, not as bulky as most members of Emeidae yet stockier and shorter-legged than members of Dinornithidae. It was about the size of a Greater Rhea (Rhea americana) but was more heavily-built: standing up to 95cm (3.2ft) at the hips and 160cm (5.3ft) to the top of the head, with a weight range of 17 to 40kg (37 to 90lbs). Unlike other known moa species, in which the females are noticeably larger than the males, Upland Moa do not display any obvious sexual dimorphism in regard to body size. The beak was particularly elongate and pointed. The feet were proportionally the largest of any moa with particularly long, strong toes and thick claws adapted for climbing up steep, rocky slopes and for walking across snowy terrain.


Articulated skeletal remains with dried soft tissue have been recovered from cave deposits. Among these, a complete head which included the tongue, eyeballs, part of the neck, and trachea. Feather pits in the skin show that the whole head up to the nostrils was covered in small feathers. A complete foot is also known for this species. Unlike other known moa which had scaly skin covering their lower legs, Upland Moa had feather pits extending down to the bases of the toes indicating that the whole leg and much of the foot was feathered. This is an adaptation seen among modern cold-adapted birds, such as ptarmigans (Lagopus), which provides insulation in deep snow. For the Upland Moa, this would have been ideal for the colder, windier conditions encountered at higher elevations. Upland Moa feathers were gray at the bases and deepened to a reddish-brown color toward the tips. Some of these feathers had pale-colored tips which would have given the living bird a speckled appearance similar to modern kiwis.

Desiccated type specimen of Upland Moa NHM A16
collected from Crown Range, Central Otago:
A-B, Head and neck from left( A) and right( B) side.
C-D, Right lower leg in medial (C) and lateral view (D).
Figure 5 from Rawlence et al. 2013.

Ecology & Behavior
Evidence from coprolites and gizzard contents shows that Upland Moa fed on a wide variety of alpine herbs and browsed from shrubs and trees. The presence of parasites in the coprolites such as Trematotodes, Catatropis, and Notocotylus (which typically afflict aquatic or wading birds) suggest that Upland Moa also fed around the margins of alpine lakes where they would eat aquatic vegetation. Like modern herbivores which inhabit high-altitude environments, Upland Moa would have engaged in altitudinal migrations in response to snowfall and food availability: during the autumn and winter months they would move to lowland areas where food was more accessible, returning to their upland feeding grounds during spring and summer. Predators of this species included the Haast’s Eagle (Harpagornis moorei) and the Eyles’ Harrier (Circus eylesi).


Upland Moa eggs are estimated to be about 162x111mm in size and were greenish-blue in color, unlike other moa which seem to have had white-shelled eggs. Newly-hatched chicks were able to move from the nest soon after hatching and studies of cortical bone growth show that Upland Moa took about 5 years to reach their full adult size. The fact that this species exhibited minimal dimorphism suggests that ecological segregation among sexes was limited, implying that Upland Moa were potentially more gregarious than other moa species: modern herbivores which occur in mixed-sex herds display minimal dimorphism in body size and overall appearance. The best modern analogue for reconstructing Upland Moa social behavior may be the South Island Takahe (Porphyrio hochstetteri), a flightless bird which forms family groups consisting of a monogamous breeding pair and their offspring.

Upland Moa are rarely found in archaeological sites, suggesting that they may not have been hunted as heavily as their lowland relatives. This could, in part, be due to the colder and less habitable alpine environments in which they lived: most Maori settlements were established at lower elevations. Upland Moa were therefore most likely to have been hunted by humans when they occupied lowland areas during certain times of the year. Habitat alteration may have been the primary cause of this species’ decline. It has been suggested that Upland Moa may have outlived other moa by as much as 100 years before they finally became extinct.

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, Rawlence NJ, Bonner KI, Worthy TH, Kinswlla JM, Cooper A (2013). “A megafauna’s microfauna: gastrointestinal parasites of New Zealand’s extinct moa (Aves: Dinornithiformes)”. PLoS ONE 8(2): e57315 <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>

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>

Rawlence NJ, Wood JR, Armstrong KN, Cooper A. (2009). "DNA content and distribution in ancient feathers and potential to reconstruct the plumage of extinct avian taxa". Proceedings of the Royal Society B 7(1672): 3395-3402 <Full Article>

Gill BJ (2007). "Eggshell characteristics of moa eggs (Aves: Dinornithiformes)". Journal of the Royal Society of New Zealand 37: 139-150 <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>

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.


Etymology
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>

Wednesday, March 8, 2017

South Island Giant Moa (Dinornis robustus)

The South Island Giant Moa (Dinornis robustus) was the largest of all known moa species and the tallest bird yet discovered. It inhabited South Island, New Zealand during the Quaternary.

Skull of the South Island Giant Moa, Dinornis robustus, collected 15 Mar 1992,
Maximus Cave, New Zealand. Field Collection 1986. CC BY-NC-ND licence.
Te Papa (S.028225)

Etymology
In reference to its great size, the name Dinornis is derived from the Geek words deinos, meaning “prodigious” or “terrible”, and ornis, meaning bird. Its common name denotes South Island, New Zealand to which this bird was endemic. Another species, D. struthoides, which was described based on its similar morphology but much smaller size, is now known to have been the male morph of D. robustus as of 2003.

Habitat & Distribution
South Island Giant Moa had a relatively broad range of habitat preferences, occurring in nearly all vegetated habitats on South Island. Widespread and abundant, the population of this species has been estimated to have been around 479,000 individuals prior to the arrival of human settlers.

Physical Attributes
The South Island Giant Moa stands out as the largest of all the moa and the tallest bird known to have ever lived. Fully grown females stood up to 2m tall at the hips, up to 3.6m when the neck was held fully erect, and weighed a maximum of 250kg (550lbs). Among recently extinct birds, only the Elephant Bird (Aepyornis maximus) of Madagascar was more massive, albeit not as tall. Adult male South Island Giant Moa were considerably smaller, at up to two-thirds the height and one-third the weight of the females. This species had a stilt-legged, rangy skeleton which would have made it very agile despite its great size. It differs from the North Island Giant Moa (Dinornis novaezelandiae) in its larger size, having a relatively shorter, stronger neck, and its deeper, less downcurved beak. Preserved soft tissue remains are known from this species, including an intact foot complete with dried skin, ligaments, and muscles adhering to the bones. Known plumage shows that most of its body except for its lower legs was covered in long, reddish-brown hair-like feathers up to 18cm in length.


Ecology & Behavior
Evidence from coprolites and gizzard contents shows that the South Island Giant Moa was a mixed feeder which grazed and browsed on various trees, shrubs, herbs, and grasses within its environment. Their great height further enabled them to feed on vegetation which other moa could not reach, thus minimizing competition for available food taxa. Biomechanical studies have shown that South Island Giant Moa fed by performing a lateral shaking motion of its head when browsing. Aided by an exceptionally broad head and beak, this behavior enabled them to break twigs and branches of considerable width. Furthermore, evidence suggests that a strong sex-related niche stratification existed within this species. Females appear to have browsed within forested environments where they subsisted on lower-quality, fibrous plant matter while males were more likely to feed on herbfields and forest clearings.

The only natural predator to adult South Island Giant Moa was the Haast’s Eagle (Harpagornis moorei), which was large and powerful enough to fell even the larger females of this species, although the eagle may have been more likely to target the smaller juveniles and adult males due to their more manageable sizes. Preferential hunting of males by the eagles may partly explain why female South Island Giant Moa significantly outnumber their male counterparts at natural fossil-bearing deposits. The eggs and chicks of South Island Giant Moa were more likely to have been preyed upon by South Island Adzebills (Aptornis defossor) or Eyles’ Harrier (Circus eylesi) respectively.

Size comparison between Haast's Eagle (Harpagornis moorei) with male and
female South Island Giant Moa (Dinornis robustus). 

Large, white eggs measuring 240x178mm and weighing an estimated 4kg when fresh have been attributed to this South Island Giant Moa. Females laid 1 to 2 eggs in shallow nests constructed by males who would take on sole incubation duties for at least 2 months. Like modern birds which demonstrate high degrees of female-biased sexual dimorphism, females are likely to have mated with multiple males within their home range and would have competed aggressively with each other over nests. Chicks were likely precocial and able to forage on their own soon after hatching and attained their adult size within just 3 years after hatching.

South Island Giant Moa were heavily exploited by the Maori and became extinct in as little as 100 years after their arrival. Their bones are widespread in Maori middens and comprise a disproportionately large number of males and eggs: the opposite of what seems to have been the case in a natural setting where it seems that adult females were more numerous than males at a given locality. The reason for the large number of male birds and eggs found at archaeological sites may indicate that the Maori chose to collect male birds while they were tending to their nests and were relatively sedentary. This strategy may have been easier than hunting the larger and potentially more aggressive females, but in doing so the Maori would have further reduced the already limited number of breeding males and cut the number of moa which would have survived to maturity. This would have resulted in catastrophic population declines from which the slow-breeding birds could not recover.

Mounted skeleton of South Island Giant Moa in
Yorkshire Museum collections. 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>

Oskam CL, Allentoft ME, Walter R, Scofield RP, Haile J, Holdaway RN, Bunce M, Jacomb C (2012). "Ancient DNA analyses of early archaeological sites in New Zealand reveal extreme exploitation of moa (Aves: Dinornithiformes) at all life stages". Quaternary Science Reviews 52: 41-48 <Full Article>

Allentoft ME, Bunce M, Scofield RP, Hale ML, Holdaway RN (2010). "Highly skewed sex ratios and biased fossil deposition of moa: ancient DNA provides new insight on New Zealand’s extinct megafauna". Quaternary Science Reviews 29: 753–762 <Abstract>

Huynen L, Gill BJ, Millar CD, Lambert DM (2010). "Ancient DNA reveals extreme egg morphology and nesting behavior in New Zealand’s extinct moa". Proceedings of the National Academy of Science 107(37): 16201-16206 <Full Article>

Wood JR, Rawlence NJ, Rogers GM, Austin JJ, Worthy TH, Cooper A (2008). "Coprolite deposits reveal the diet and ecology of the extinct New Zealand megaherbivore moa (Aves, Dinornithiformes)". Quaternary Science Reviews 27: 2593–2602 <Abstract>

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>

Gemmell NJ, Schwartz MK, Robertson BC (2004). "Moa were many". Proceedings of the Royal Society B doi: 10.1098/rsbl.2004.0234: <Full Article>

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>