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)

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.

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)

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>

Friday, March 3, 2017

Haast's Eagle (Harpagornis moorei)

The Haast’s Eagle (Harpagornis moorei) was the largest and most powerful bird of prey known to have ever existed and was the top predator of New Zealand throughout the Quaternary. It was large-prey specialist whose primary prey items were the flightless moa (Dinornithiformes), which could weigh up to 200kg.

Haast's eagle (Harpagornis moorei) skull collected 25 Apr 1983,
Eagle Roost, New Zealand. Gift of Phil Millener, 1983.
CC BY-NC-ND licence. Te Papa (S.022473)

The Haast’s Eagle was first described by German geologist Julius von Haast in 1872. He named the bird Harpagornis moorei after the owner of the Glenmark Estate where the eagle’s bones had been found, George Henry Moore. The genus name Harpagornis is derived from the Greek words “harpax”, meaning “grappling hook” (a reference to the bird’s huge talons) and ornis, meaning “bird”. Other names for this species include “New Zealand Eagle” and “Giant Eagle”. A second, smaller species (H. assimilis) was described by Haast in 1874, but is now known to represent the male morph of H. moorei. The Poukai, a large and aggressive bird described in centuries-old Maori folklore, is widely accepted to be synonymous with the Haast’s Eagle.

Habitat & Distribution
Haast’s Eagle fossils have been found throughout South Island but is not known to have lived on the smaller North Island. It inhabited forest, woodland, and shrubland habitats from sea level up to the subalpine zone. Genetic evidence shows that Haast’s Eagles evolved from Australian Little Eagles (Hieraaetus morphnoides) during the early Pleistocene, demonstrating what is perhaps the most rapid evolutionary size increase yet documented. In response to an abundance of large prey and lack of substantial competition from other predators, these birds ballooned to over 20 times in mass within the span of perhaps a few thousand years.

Little Eagle (Hieraaetus morphnoides) in flight over South
Queensland, Australia. This species is regarded as the direct
ancestor of the Haast's Eagle which evolved in New Zealand
during the Pleistocene. Wiki.

Physical Attributes
Haast’s Eagle is the largest and most powerful bird of prey ever known to have existed. Adult females had a weight range of 10 to 18kg (22 to 40lbs) while the smaller males had a range of 9 to 12kg (20 to 26lbs). The wingspan was short compared to the size of the body, but was still a respectable 2.6 to 3m (8.5 to 10ft). Although this wingspan is matched or exceeded by several modern birds including several eagles and vultures, it should be noted that their bodies are proportionally much smaller with longer wings, making them much less massive. Haast’s Eagles flew in a manner similar to modern large, forest eagles such as the Crowned Eagle (Stephanoaetus coronatus), Harpy Eagle (Harpia harpyja), and Philippine Eagle (Pithecophaga jefferyi): utilizing constant flapping with occasional spurts of gliding. The shortness of its wings made the energy-conserving soaring flight employed by most large birds impossible, but instead enabled greater speed and agility at the cost of higher rates of energy expenditure. Based on its body proportions, Haast’s Eagle is interpreted as an ambush predator capable of short bursts of very rapid and agile flight, enabling it to maneuver through closed environments and chase terrestrial prey animals which were equally agile.

Comparative morphology of the feet and talons of the Haast's Eagle and with
its closest living relative the Australian Little Eagle. 

The Haast’s Eagle skull was more similar to that of a vulture than to other eagles: it was relatively long and low with sealed nostrils to prevent the airways from being clogged while feeding within large carcasses (other eagles feed by pulling at the exterior of a carcass and do not immerse the beak and head into the prey's body cavity the way vultures do, therefore this added nasal protection is not needed). The postcranial skeleton was more powerfully-constructed than those of other eagles. In particular, the bones of the legs and feet were tremendously robust and capable of exerting massive gripping strength. A strong pelvis and huge leg muscles enabled them to spring into the air from the forest floor, absorb the impact of landing and colliding with prey, and grapple with struggling animals. The talons, which measured up to 8cm long without their sheathes, were deeper at the bases than those of other eagles for greater durability and strength: the bones of several moa have been found with high-impact puncture and gouge wounds in their pelvises which could only have been left by this eagle’s talons.    

Because of its recent extinction, descriptions of the eagle’s life appearance can be gleaned from the oral traditions passed down by the Maori. The Poukai is described as a black and white bird with lighter-tinged feathers, and reddish feathers covering its head and neck. This description, along with the modern Little Eagle as a point of reference, was used to produce the life reconstruction below. Ancient rock paintings depicting large, eagle like birds are also thought to represent this species.

Ecology & Behavior
The Haast’s Eagle is one of only two known birds of prey which evolved to be the largest and most dominant predator within its environment, the other being the modern Philippine Eagle which also evolved on islands without large mammalian competitors. Unlike its smaller relative, however, Haast’s Eagle was adapted to actively hunt prey items much larger than itself and had a prey base consisting of terrestrial vertebrates weighing 10 to 200kg, with a possible preference for items of intermediate size within this range. Most common among its prey were the 7 species of moa with which it coexisted on South Island. Haast’s Eagles were best suited for “perch-hunting”, a method which entails flying from one perch to another to scan the surrounding area for potential prey. Prey is then ambushed from above and seized from behind or from the sides at speeds of up to 80km/h (50mph). Damage patterns on moa skeletons show that the eagle typically attacked by striking the pelvis with enough force to puncture the bone. An impact in this part of the body would paralyze, knock over, or impair the movements of a bipedal prey item depending on its size before it was dispatched by having its neck crushed in the eagle’s talons. Hunting methods would have varied depended on the type of prey and on the environment. Modern eagles, for example, are known wait for prey at water sources, knock animals off cliffs (video), and even engage in cooperative tactics when hunting in more open areas (video): such adaptability was possible for the Haast’s Eagle as well. Haast’s Eagle fossils have also been found in natural predator traps where they attempted to kill or scavenge prey animals before becoming trapped themselves.

Comparison of the spread of both feet of the Haast’s Eagle
to the pelvises of North Island Giant Moa (Dinomis novaezealandiae),
Heavy-footed Moa (Pachyomis elephantopus), and Upland Moa
(Megalapteryx didinus). Damage patterns on moa skeletons show that the
 pelvis was the preferred point of initial contact, which would result in
severe injury and immobilization. Figure 12.20 from Holdaway,1991.

In general, modern eagles select prey animals that they can kill or restrain quickly and transport out of reach of terrestrial competitors. Because of its status as top predator and owing to the sheer size of its prey, however, Haast’s Eagles could afford to remain on the ground near their kills for days until the carcass was fully utilized. Such large kills raise compelling questions about this bird’s social behavior: a particularly large moa carcass would probably decay beyond consumption before a single eagle could fully utilize it. Therefore, Haast’s Eagles may have lived and hunted in pairs, which is a behavior adopted by modern eagles. Like other large eagles, Haast’s Eagles probably laid 1 or 2 eggs at a time with both parents participating in the incubation and feeding of the offspring, which would have grown rapidly over the next few months after hatching. The unique hunting method which these birds employed may have necessitated extended periods of juvenile dependency beyond the typical one year it takes for modern large eagles to make their first kill, potentially remaining within or near their parents’ home range until they reached sexual maturity at 6 to 8 years of age.

Haast’s Eagle fossils are rare, suggesting that they had relatively low population densities like modern forest eagles. One study estimated that the available land area of South Island could have supported a total population of 3,000 to 4,500 breeding pairs. This combination of low population density and slow reproductive rates is ideal within a stable island environment, but it also left the eagle highly vulnerable to ecological disturbances. The extinction of the Haast’s Eagle is directly attributable to the over-exploitation of its preferred prey and the controlled burning of its habitat by Maori settlers about 500 years ago. Tools fashioned from the eagle’s bones have been recovered from archaeological sites, although it is unlikely that humans hunted these birds directly. Rather, Maori oral tradition suggests that they would have been understandably fearful of it. Like a big cat or a Polar Bear, the Haast’s Eagle was the top predator of its environment and thus would not have been fearful of humans upon first exposure. It also specialized in hunting bipedal animals up to 200kg, and likely saw humans as a potential food source rather than a threat. Indeed, the Maori have described the Poukai as a man-eating bird that would spring upon unwary humans from the trees (which has been depicted in the scene from episode 3 of the documentary Monsters We Met embedded below). Nonetheless, the ecological damage caused by human activity caused the rapid decline of this eagle across South Island. It is also eluded to in Maori oral traditions that the last individuals survived longer in the less habitable montane regions before these isolated populations also became extinct.

References & Further Reading
Scofield RP, Ashwell KWS. (2009) Rapid somantic expansion causes the brain to lag behind: the case of the brain and behavior of New Zealand’s Haast’s Eagle (Harpagornis moorei). Journal of Vertebrate Paleontology, vol 29, no 3 <Abstract>

Bunce M, Szulkin M, Lerner HRL, Barnes I, Shapiro B, et al. (2005) “Ancient DNA provides new insights into the evolutionary history of New Zealand’s extinct giant eagle”. PLoS Biol 3(1): e9. doi: 10.1371/journal.pbio.0030009 <Full Article>

RN Holdaway, TH Worthy (1997). “A reappraisal of the late Quaternary fossil vertebrates of Pyramid Valley Swamp, North Canterbury, New Zealand". New Zealand Journal of Zoology 24(1): 69-121 <Full Article>

Brathwaite DH (1992). “Notes on the weight, flying ability, habitat, and prey of Haast’s Eagle (Harpagornis moorei)”. Notornis (Ornithological Society of New Zealand) 39 (4): 239-247 <Full Article>

Holdaway RN (1991). "Systematics and palaeobiology of Haast's eagle (Harpagornis moorei Haast, 1872) (Aves: Accipitridae)". Ph.D. thesis, Department of Zoology, University of Canterbury, Christchurch, New Zealand <Full Article>

Wednesday, March 1, 2017

March of the Moa Part 1: Evolution and History on New Zealand

The moa (Dinornithiformes) are a group of flightless birds which lived on New Zealand from the middle Miocene and survived until the late 14th to early 15th century: around the time Europe was transitioning out of the Middle Ages and into the Renaissance period. They were the largest and most influential vertebrates within New Zealand’s terrestrial ecosystems and there were 9 species within 6 genera and 3 families by the arrival of the first human settlers 700 years ago. More information is known about moa than arguably any other completely extinct animal group with everything from complete skeletons and eggshells to preserved soft tissues containing ancient DNA being collected. This post will, therefore, serve as the first entry in a 5-part series summarizing our current understanding of these great birds.

Skeleton of the South Island Giant Moa (Dinornis robustus)
on display at the Yorkshire Museum, England. Wiki.

Prior to 2010, it was believed that moa were most closely related to Australian emus and cassowaries among modern birds. It has since been realized, however, that the closest living relatives to moa are the tinamous (Tinamidae): a family of small South American ground birds which resemble gamefowl. It is a mystery how these South American birds, which are relatively poor flyers, managed to cross the 12,304km (7,645.2 miles) of open ocean to reach the islands of New Zealand. Perhaps they arrived by island-hopping or by rafting over the course of millions of years. Another possibility is that tinamous, or a close relative, already existed on New Zealand by the early Oligocene when there was less distance between New Zealand and Antarctica with only a shallow sea separating them, while Antarctica itself was still connected to South America. This latter hypothesis is supported by the presence of meiolaniid and pleurodire turtles, mekosuchine crocodiles, and mystacinid bats living in New Zealand during the early Miocene, all of which share South American or Australian origins and are unlikely to have arrived by crossing deep ocean. Once established in New Zealand, however, ancestral moa underwent a remarkable adaptive radiation taking on the role of mid-sized to large terrestrial herbivores in the absence of mammalian competitors. 

An Elegant-crested Tinamou (Eudromia elegans), one of many species
of volant, ground-dwelling birds from Central and South America. Tinamou
are the closest living relatives of the moa. Wiki.

The exact timing of when the moa ancestor first arrived in New Zealand is up for debate, but the earliest definitive moa fossils are known from the early to late Miocene Saint Bathans Fauna. By this period, moa were already large-sized, flightless, and had similar skeletal anatomy to that of their more recent relatives, implying that their origin and arrival to New Zealand was much earlier than this. The radiation of the 9 Holocene species occurred primarily in South Island and was influenced by the accelerated uplifting of the Southern Alps during the late Miocene (6mya), an event which altered New Zealand’s climate and created new biomes which encouraged the evolution of new species to exploit themSouth Island, the larger of the two main islands of New Zealand, has three main habitat zones:
  1. The colder highlands of the Southern Alps run from the north to the south of the island, influencing the rainfall and vegetation on either side.
  2. The land to the west of the Southern Alps is densely-forested with high rainfall,
  3. To the east of the mountains lay drier woodlands, shrublands, and grasslands which comprise much of the lowland area.
North Island experiences high rainfall and is dominated by deciduous forest habitat much like the western lowland area of South Island, while the land closer to the southern coast is drier and more open. The more diverse range of habitats of South Island combined with its larger land area (150,437km² to North Island's 113,729km²) explains why moa diversity is highest on South Island: 7 of the 9 species lived (5 of which being endemics) lived on South Island while just 4 species (with 2 endemics) inhabited North Island.

New Zealand split from the supercontinent of Gondwana during the late Cretaceous
and is currently situated about 1,500km east of Australia and 5,000km north of Antarctica.
 Because of its remoteness, it was the last habitable landmass to be colonized by humans.
Most of its endemic animals descended from taxa that colonized it during the
late Mesozoic or early Cenozoic when it was still relatively close to larger landmasses. 
In later Cenozoic times, volant birds from Australia periodically flew here and 
radiated into new endemics.

Genetic evidence suggests that the 9 Holocene species of moa radiated from a common ancestor during the late Miocene with the Upland Moa (Megalapteryx didinus), the sole member of the family Megalapterygidae, being the most basal. The two species of Dinornis within the family Dinornithidae were the largest and tallest of the moa very slender skeletons and elongated limbs adapted for mobility. The family Emeidae is the most diverse, containing the remaining 6 species within 4 genera: 3 species within Pachyornis and the genera Anomalopteryx, Euryapteryx, and Emeus containing a single species each. Contained within this family are the smallest, as well as some of the most heavily-built moa.

Reconstructed skulls of the 9 species of moa shown to scale, alongside
silhouettes of each species. Restored skulls are drawn from specimens from 

the online collections of Museum of  New Zealand Te Papa Tongarewa. 
Scale bar in lower left corner equals 3cm.

Part 2: Anatomy & Action
Part 3: Paleoecology
Part 4: Behavior
Part 5: Extinction

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>

Allentofta ME, Hellerd R, Oskamb CL, Lorenzena ED, Halec ML, Gilberta TP, Jacombg C, Holdawayc RN, Bunce M (2014). "Extinct New Zealand megafauna were not in decline before human colonization". PNAS 111(13): 4922–4927 <Full Article>

Brassey CA, Holdaway RN, Packham AG, Anne´ J, Manning PL, Sellers WI (2013). "More than one way of being a moa: differences in leg bone robustness map divergent evolutionary trajectories in Dinornithidae and Emeidae (Dinornithiformes)". PLoS ONE 8(12): e82668. doi:10.1371/journal.pone.0082668 <Full Article>

Hand SJ, Worthy TH, Archer M, Worthy JP; Tennyson AJD, Scofield RP (2013). "Miocene mystacinids (Chiroptera, Noctilionoidea) indicate a long history for endemic bats in New Zealand". Journal of Vertebrate Paleontology 33(6): 1442-1448 <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>

Morten A, Rawlence N (2012). “Moa’s ark or Volant ghosts of Gondwana? Insights of nineteen years of ancient DNA research on extinct moa (Aves: Dinornithiformes) of New Zealand”. Animals of Anatomy 194: 36-51 <Full Article>

Worthy TH (2011). "Terrestrial turtle fossils from New Zealand refloat Moa's Ark". Copeia 1: 72-76 <Full Article>

Tennyson AJD, Worthy TH, Jones CM, Scofield RP, Hand SJ (2010). "Moa’s Ark: Miocene fossils reveal the great antiquity of moa (Aves: Dinornithiformes) in Zealandia". Records of the Australian Museum 62: 105–114 <Full Article>

Buncea M, Worthy TH, Phillips MJ, Holdaway RN, Willerslev E, Hailef J, Shapiro B, Scofieldi RP. Drummond A, Kamp PJJ, Cooper A (2009). "The evolutionary history of the extinct ratite moa and New Zealand Neogene paleogeography". Proceedings of the National Academy of Science 106(49): 20646–20651 <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>