Musing on Emus

As Gondwana was breaking up 100 million years ago, after half a billion years of comprising one mighty southern land, many of the most familiar elements of our living world were developing, including mammals, flowering plants and birds. Only those groups whose ancestors already existed then would be expected to occur right across the Gondwanan lands today. Family Proteaceae - Proteas, Banksia, Notros - is one such. Another comprises the most ancient of living birds, the ratites, the giant southern flightless birds.

In addition to African Ostriches (above, Western Cape) and South American rheas (Darwin's Rhea below, Seno Otway, far southern Chile), living ratites include the Australian-New Guinea cassowaries and emus and the New Zealand kiwis. Ones that didn't survive human depredations include the New Zealand moas and the Madagascan elephant birds.

Presumably the ancestral ratite (which certainly could fly) continued to get larger to outgrow its enemies, and perhaps to see better in a grassland habitat. Once the apparently magical 15kg weight limit for flying birds had been passed it had to forego the powers of flight, but there was then no limit to its size; an Emu can weight 55kg, an Ostrich 150kg and the elephant birds half a tonne! The word ratite comes from the Latin for a raft; with the loss of flight came the gradual loss of the unnecessary great flight muscles, and their attachment point - the protruding keel. The resulting flat breastbone was seen by earlier ornithologists as raft-like. 

Already spread across Gondwana, they developed in different directions once they became isolated after the break-up. (However I should mention that a 2010 paper, using mitochondrial gene sequencing, claimed that the group was too young to have arisen thus, but that each group flew to its current location and subsequently each one independently lost its flight powers. I certainly can't comment on the chemistry, but this does seem such an improbable scenario that I'm waiting for some corroborative evidence before I accept it.)

All that aside, Emus are intrinsically wonderful birds, and not hard to find in inland Australia as well as in some places much nearer the coast. The name itself is not, as commonly supposed, of indigenous origin, but from the Portuguese ema, referring apparently to a crane, but more generally to any large bird (it is still used for the rhea). The sailors who reported it were Dutch, but Portuguese was then the lingua franca among European sailors in the East Indies, perhaps because the early maps were in Portuguese.

Emu Dromaius novaehollandiae, Shark Bay, Western Australia.

Emus are great nomads, walking hundreds of kilometres following rains and food sources, which at different times of year may comprise grasshoppers, seeds, caterpillars or fruit. This led them into conflict with European settlers whose farms they seemed to threaten. In Western Australia the Great Emu War of 1932 was fought between migrating mobs of over 20,000 emus, and the Australian army with machine guns and grenades, called in by the state government. Jock Marshall in his pioneering conservation work The Great Extermination reports "History does not record the name of the CO emus, but he must have been a good chap". It seems that perhaps only a dozen emus were killed, and the government had to withdraw the military to save them from further embarrassment.

Unusually among birds Emus are polyandrous - ie one female, several blokes. In June (early winter) she lays up to 20 dark green eggs in a scrape on the ground; each can weigh three quarters of a kilo, so the cost is immense. Understandably, she plays no further part in the chick rearing, but if she feels so inclined she can go off and do it all again with someone else.

Emu nest, south-west Queensland.

He sits on the eggs for eight weeks, in a semi-torpor to save energy, living off his fat reserves without eating, drinking or defecating, but turning the eggs over at regular intervals. In the south-eastern high country this also meant being covered in snow at times. 

The stripey chicks can walk within hours of hatching, and run and swim in a week. 

Emu chicks near Cue, Western Australia.

As they get older they lose their stripes but can still be distinguished from their father by their dark heads and necks.

Immature Emus, Currawinya National Park, Queensland.

He looks after them for 18 months, so he only breeds every other year; the female of course doesn't have that restriction.

A familiar night sound to campers in 'the outback' is the resonant booming of Emus, enabled by a unique cleft and an inflatable pouch in the trachea. It can be heard up to two kilometres away.

Another characteristic is the feathers; haystack-like, they seem to have no cohesion, and indeed they don't. Unlike more modern birds they don't have barbules to lock the feathers together; further, the aftershaft, which forms a woolly base to feathers in most birds, is the same length as the main shaft in an Emu, so the feathers appear to be double.

Emu plumage, which characteristically flops about while it is running.

Emus are in some ways the archetypal Gondwanans (ignoring the prevailing view of their intellectual powers!); they are ancient and very special.

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