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The very public private life of male emus

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Associate Professor Dominique Blache, from the School of Animal Biology and Institute of Agriculture at the University of Western Australia, describes some of the fascinating behaviour of emus.     
Emus are fascinating birds because of their behaviour, physiology and level of adaptation to Australian conditions. They also have extreme incubation behaviour.
Males tend the eggs in a nest made of a few leaves, feathers and bits of wood. They sit on the eggs for 54 days without eating. In this eight-week period they shut down all unnecessary functions that cost energy, concentrating on just sitting. They do stretch their legs two or three times a day looking around the nest.
At this time most males are willing to accept eggs into their nests from almost any female. Female emus are attracted to the male because they want to lay their eggs in a nest when the season starts in May. Females can lay an egg every three days, gradually adding them to a nest but all of the eggs in that nest will hatch at the same time.
Amazingly it is thought that the eggs synchronise hatching, not the male emu. In a 49 hectare research enclosure, one male was observed trying to incubate 25 eggs, each of which weighed 400-500gm.

His body was not big enough to cover all the 25 eggs at the one time although he continued to try to solve the problem. In fact, only one did not hatch. Such large clutches are not likely to happen in the wild since fewer emus are likely to be in a small area. During the egg-sitting the males lose up to 25% of their bodyweight, a lot for a 45-50kg bird. This is mainly due to loss of fat, the famous emu oil, which comes from a very big mass of fat carried on their tails. They metabolise this fat to get nutrients while they sit on the eggs.

There were up to 18 nests in the research program's enclosure and these were all observed for the study each day. While laid over several weeks, all the chicks in the same nest would hatch on one day and by the third day they had all left the nest with the adult. Typically, in many nests, one unfertile egg was left and this was often the first one laid in the nest, and possibly was unfertilised. A male stays with the emu chicks for over a year and competes actively with other males to keep maximum numbers of young emus with him when he is walking around. 

The most aggressive (or parental care driven) males will pinch young ones from other males. While there are few predators for adults there are several for chicks. Therefore, it has been hypothesised that adding extra chicks to be cared in the one group, reduces the chances of the carer male's own chicks being predated, thus keeping his own gene pool safer. 

In the safe surroundings of the research program territory, some males managed to collect large groups of young from both the previous and the present year. The largest group recorded was 35 chicks gathered by an enthusiastically dominant male! However, in the wild only about 1-2 chicks survive the harsh conditions into adulthood. In the research enclosure the situation is biased so survival can be as high as 80-90%. The chicks mature for a year and then have to wait for six months for the next breeding season. The chicks will then gradually separate from the males as they also have to compete in that breeding season.

Females are the ones who select their mates. The calling of female emus in the breeding season is a special low frequency sound that can be heard from a long distance. Females have a special design in their windpipe that release puffs of air into a large balloon-like sac in front of their necks. This produces a drumming sound and is a call for a male. 

It also warns off other females. The females can exhibit intensive aggressive behaviour when selecting their partners. Emus jump on each other and fight in a way that is close to martial arts and may continue for hours. They gather as much speed as they can and spring with folded legs that are flung out just before impact. This really does hurt and can be damaging, which is why people who work with emus wear protected clothing.

Associate Professor Dominique Blache was interviewed for A Question of Balance by Ruby Vincent. All images from Dr Blache. Summary text by Victor Barry, September 2016.

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