A painting of what King Island used to look like, showing a large colony of elephant seals lying on the beach, which minature emus move among them.

It is thought that the tiny emus on King Island likely spent most of their time on the beach and in coastal scrub ©Julian Hume

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Giant egg of extinct miniature emu discovered in Australia

When Europeans first settled on then-uninhabited King Island off the southern coast of Australia at the start of the nineteenth century, they found it was home to a tiny subspecies of emu that reached just a metre in height.

These miniature birds were living in the coastal scrub that encircled the island, but within just eight years the miniature emus were extinct. Now researchers have found the only known egg of this extraordinary bird. 

A number of the islands scattered to the southeast of Australia, including Tasmania, Kangaroo Island and King Island, were once home to different subspecies of emu. Because of the limited size of the islands, these birds - now all extinct - shrank to become smaller than the mainland emu.

The smallest of these islands was King Island, which subsequently had the smallest emu.

Very little is known about the King Island emu, because within less than a decade of it being recorded by Europeans, all the wild birds of its species were wiped out of existence, with only two individuals surviving in Paris until they both died in 1822.

But new research carried out by Dr Julian Hume, an avian palaeontologist at the Museum. His colleague Christian Robertson has documented the existence of the only known egg from these birds, revealing that the tiny emu laid eggs roughly the same size as their mainland cousins.

The research has been published in the journal Biology Letters.

A rapid extinction

Before the arrival of European settlers, King Island supported eucalyptus forests in the interior and was surrounded by scrub land that led down to sandy beaches. These long beaches were home to a large colony of elephant seals, the primary attractant for these first settlers.

After setting up sealing stations, the population of people on the island grew and they started to burn off the scrub. It was a combination of humans hunting the emus to eat and the destruction of the emus' habitat that led to the birds' extinction on the island by 1810. 

A drawing of the King Island emu amongst green vegetation showing its short stature.

The King Island emu was around half the size of the mainland emu, which is thought to have been an adaptation to the small size of the island © Wikimedia commons

But just before their extinction, a number of individuals including adults and chicks were rounded up and shipped to France. Only a male and female survived the long voyage, and they lived in Paris until 1822, when both died within months of each other.

This tragically short period between when the King Island emu were first formally described and when they went extinct means that very little is known about this unusual bird and its ecology.

Julian and his colleagues have been trying to fill in some of these blanks after a wealth of fossilised emu bones and shell fragments were found in the sand dunes of King Island, before the fossil site was destroyed by the building of a golf course in 2015.    

Small birds, big eggs

But local naturalist Christian Robertson had also been collecting and recording fossils on King Island - and it turned out that he had also discovered an almost complete King Island emu egg.

'He found all the broken pieces in one place, so he painstakingly glued them back together and had this beautiful, almost complete King Island emu egg,' Julian told Live Science. 'It is the only one known in the world.'

Four large dark brown-gray eggs in a row on a white background. The far right egg is cracked and only partically complete.

The only known King Island emu egg (far right) is only slightly smaller than the mainland emu egg (far left) despite the dramatic differences in the size of the birds ©Hume and Robertson 2021

By comparing this single King Island emu egg with the only known Kangaroo Island emu egg, a handful of Tasmanian emu eggs and 38 mainland emu eggs, Julian and Christian were able to show that even though the miniature emus were about half as big as their larger mainland, they actually laid eggs of a similar size and volume.

This suggests that as the birds reduced in body size, it must have been advantageous for them to have simultaneously retained the larger size of their eggs. This is also seen in New Zealand's kiwi birds, whose egg can weigh as much as 25% of an adult female's body weight.

The extraordinarily large size of the kiwi's egg is thought to be an adaptation so that the hatchling is already large and independent.

Julian suspects that this may also have been the case with the miniature emus. They may well have produced relatively large chicks to give them a better chance against native predators that lived on King Island, such as the carnivorous quolls.