King Island emu
Kingdom
Phylum
Class
Family
Genus
SPECIES
Dromaius novaehollandiae minor

The King Island emu (Dromaius novaehollandiae minor ) is an extinct subspecies of emu that was endemic to King Island, in the Bass Strait between mainland Australia and Tasmania. Its closest relative may be the extinct Tasmanian emu (D. n. diemenensis ), as they belonged to a single population until less than 14,000 years ago when Tasmania and King Island were still connected. The small size of the King Island emu may be an example of insular dwarfism. The King Island emu was the smallest of all known emus and had darker plumage than the mainland emu. It was black and brown and had naked blue skin on the neck, and its chicks were striped like those on the mainland. The subspecies was distinct from the likewise small and extinct Kangaroo Island emu (D. n. baudinianus ) in a number of osteological details, including size. The behaviour of the King Island emu probably did not differ much from that of the mainland emu. The birds gathered in flocks to forage and during breeding time. They fed on berries, grass and seaweed. They ran swiftly and could defend themselves by kicking. The nest was shallow and consisted of dead leaves and moss. Seven to nine eggs were laid, which were incubated by both parents.

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Europeans discovered the King Island emu in 1802 during early expeditions to the island, and most of what is known about the bird in life comes from an interview French naturalist François Péron conducted with a sealer there, as well as depictions by artist Charles Alexandre Lesueur. They had arrived on King Island in 1802 with Nicolas Baudin's expedition, and in 1804 several live and stuffed King and Kangaroo Island emus were sent to France. The two live King Island specimens were kept in the Jardin des Plantes, and the remains of these and the other birds are scattered throughout various museums in Europe today. The logbooks of the expedition did not specify from which island each captured bird originated, or even that they were taxonomically distinct, so their status remained unclear until more than a century later. Hunting pressure and fires started by early settlers on King Island likely drove the wild population to extinction by 1805. The captive specimens in Paris both died in 1822 and are believed to have been the last of their kind.

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Appearance

The King Island emu was the smallest type of emu and was about 44% or half of the size of the mainland bird. It was about 87 cm (34 in) tall. According to Péron's interview with the local English sealer Daniel Cooper, the largest specimens were up to 137 cm (4.5 ft) in length, and the heaviest weighed 20 to 23 kg (45 to 50 lb). It had a darker plumage, with extensive black feathers on the neck and head, and blackish feathers on the body, where it was also mixed with brown. The bill and feet were blackish, and the naked skin on the side of the neck was blue. The 2011 genetic study did not find genes commonly associated with melanism in birds, but proposed the dark colouration could be due to alternative genetic or non-genetic factors.

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Péron stated there was little difference between the sexes, but that the male was perhaps brighter in colouration and slightly larger. The juveniles were grey, while the chicks were striped like other emus. There were no seasonal variations in plumage. Since the female mainland emus are on average larger than the males, and can turn brighter during the mating season, contrary to the norm in other bird species, the Australian museum curator Stephanie Pfennigwerth suggested that some of these observations may have been based on erroneous conventional wisdom. Hume and Robinson also suggested female King Island emus were larger than the males, and that Cooper could have mistaken brooding males for females when he stated the males were larger.

Subfossil remains of the King Island emu show that the tibia was about 330 mm (13 in) long, and the femur was 180 mm (7 in) long. The pelvis was 280 mm (11 in) long, 64 mm (2.5 in) wide at the front, and 86 mm (3 in) wide at the back. The tarsometatarsus averaged 232 mm (9 in) in length. In males, the tibiotarsus averaged 261 mm (10 in), whereas it averaged 301 mm (12 in) in females. In contrast, the same bones measured 269 mm (10.5 in) and 305 mm (12 in) in the Kangaroo Island emu. Apart from being smaller, the King Island emu differed osteologically from the Kangaroo Island emu in the intertrochlear foramen of the tarsometatarsus usually being fully or partially abridged. The outer trochlea was more incurved towards the middle trochlea in the Kangaroo Island bird, whereas they were parallel in the King Island emu.

The King Island emu and the mainland emu show few morphological differences other than their significant difference in size. Mathews stated that the legs and bill were shorter than those of the mainland emu, yet the toes were nearly of equal length, and therefore proportionally longer. The tarsus of the King Island emu was also three times longer than the culmen, whereas it was four times longer in the mainland emu. Additional traits that supposedly distinguish this bird from the mainland emu have previously been suggested to be the distal foramen of the tarsometatarsus, and the contour of the cranium. However, the distal foramen is known to be variable in the mainland emu showing particular diversity between juvenile and adult forms and is therefore taxonomically insignificant. The same is true of the contour of the cranium, which is more dome-shaped in the King Island emu, a feature that is also seen in juvenile mainland emus.

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Distribution

Geography

King Island emu habitat map

Biome

King Island emu habitat map
King Island emu

Habits and Lifestyle

Péron's interview described some aspects of the behaviour of the King Island emu. He wrote that the bird was generally solitary but gathered in flocks of ten to twenty at breeding time, then wandered off in pairs. They ate berries, grass and seaweed, and foraged mainly during morning and evening. They were swift runners, but were apparently slower than the mainland birds, due to being fat. They swam well, but only did so when necessary. They reportedly liked the shade of lagoons and the shoreline, rather than open areas. They used a claw on each wing for scratching themselves. If unable to flee from the hunting dogs of the sealers, they would defend themselves by kicking, which could inflict a great deal of harm.

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The English Captain Matthew Flinders did not encounter emus when he visited King Island in 1802, but his naturalist, Robert Brown, examined their dung and noted they had chiefly fed on the berries of Leptecophylla juniperina. An account by English ornithologist John Latham about the "Van Diemen's cassowary" may also refer to the King Island emu, based on the small size described. In addition to a physical description, he stated that they gathered in groups of 70 to 80 individuals in a given location while foraging, behaviour that was exploited by hunters. Hume and colleagues noted that most emu subfossils from King Island were found on the drier, leeward west coast of the island, and though probably due to preservation bias, they suggested that the emus were restricted to coastal and more open inland areas, and not found in the dense interior forests. An 1802 report by the English surveyor Charles Grimes also supported this, stating there were "plenty on the coast–but not inland". The tall, dense eucalypt forests of the island have since been destroyed.

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Lifestyle
Seasonal behavior

Diet and Nutrition

Mating Habits

Péron stated that the nest was usually situated near water and on the ground under the shade of a bush. It was constructed of sticks and lined with dead leaves and moss; it was oval in shape and not very deep. He claimed that seven to nine eggs were laid always on 25 and 26 July, but the selective advantage of this breeding synchronisation is unknown. The female incubated the eggs, but the male apparently developed a brood patch, which indicates it contributed as well. The non-incubating parent also stayed by the nest, and the chicks left the nest two to three days after hatching. The eggs were preyed upon by snakes, rats, and quolls. Péron gave the incubation period as five or six weeks, but since the mainland emu incubates for 50 to 56 days, Pfennigwerth pointed out that this may be too short. He stated a mother emu would defend its young from crows with its beak, but this is now known to be strictly male behaviour.

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Hume and Robertson compared the eggs of all emu taxa in 2021, and found that the eggs of the island dwarf emus were within or close to the size and smallest volume and mass ranges for mainland birds, with seemingly thinner eggshells. The egg of the mainland emu weighs 1.3 lbs. (0.59 kilograms) and has a volume of about 0.14 gallons (539 milliliters), while those of the King Island emu weighed 1.2 lbs. (0.54 kg) and had a volume of 0.12 gallons (465 mL). The egg mass of the mainland emu accounts for 1.6% of its body mass, whereas the egg mass of the King Island emu accounted for 2.3% of its body mass, even though it was 44% lighter than the mainland bird. Hume and Robertson attempted to explain these findings, and noted that emus and other ratites have precocial juveniles, that is, relatively mature and mobile when they hatch, and appear to have laid their eggs at the same time.

Hume and Robertson suggested the evolutionary advantage for the small emus in retaining large eggs and precocial chicks was driven mainly by limited food resources on their islands. Their chicks had to be large enough to feed on seasonably available food, and possibly to develop thermoregulation sufficient for them to deal with cool temperatures, as is the case for mainland emus and kiwis. The large egg-size and smaller clutch of small emus may have been evolutionary steps towards K selection. The precocial juveniles may also have been an adaptation to predation, and while King Island did not have large carnivores, there was a now extirpated population of very large tiger quolls which could have preyed on emu chicks. If the size of the clutch of King Island emus was large, and not the result of more than one female laying eggs in a single nest, this bird must have devoted an amount of energy to reproduction that was proportionally higher than that of mainland birds. Among living ratites, the rhea is morphometrically similar to the King Island emu, and has a similar breeding strategy.

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Population

References

1. King Island emu Wikipedia article - https://en.wikipedia.org/wiki/King_Island_emu
2. King Island emu on The IUCN Red List site - https://www.iucnredlist.org/species/22728643/94992893

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