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In fine feather


 
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Professor Shane Maloney, Head of Anatomy, Physiology and Human Biology at the University of Western Australia, continues his focus on emus, this time with his colleague Professor Graeme Martin, from the University of Western Australia’s Institute of Agriculture.     
Emu feathers are very interesting for several reasons. Emus through a process called neoteny, basically retain their chick feathers through to adulthood. The emu feathers remain fluffy and, because emus don’t fly, their wings don’t fold either. The fluffy feathers are great for insulation against high and low temperatures.
Emu feathers are dual feathers. A feather branches not far along from the skin, forming a Y-shape with the quill going into the skin. This is a special characteristic within the ratite family (think ostrich, cassowary and rhea) and the feathers also don’t have barb structures.
In emus, the selection pressure was to keep the chick feathers as insulation rather than to develop flight feathers. 

 
Flight feathers have a single shaft with feather elements that come out from both sides. Each flight element has little barbules, the adjacent elements acting like Velcro producing a very structured, flattened feather. This means the feathers can stand the resistance of air and this push provides lift. Birds that fly spend a long time preening that coat of feathers. An aquatic bird like the penguin also spreads oil from a gland near the base of their tail into the feathers using its beak, thus providing waterproofing.

 
Emus have adapted incredibly to thermal environments living in the western NSW rangelands where it is hot and dry to the NSW snowfields. 
    
Indeed, emus forage in the arid zone when the temperature can be as high as 45°C and all other animals seeking shelter and shade. Given that emus are black this didn’t make much sense to Professor Maloney so he investigated further.
He exposed emu pelage (soft covering) to different wind speeds and different amounts of sunlight to see if he could find how a black-coated bird could survive in those conditions. 

Emu at Research Station Shenton Park (image from Shane Maloney)
ion Schenton

 
The wind tunnel used to make measurements of insulation and effects of sunlight on feathers (image from Shane Maloney).
The shape of the emu’s coat is similar to an umbrella over its back. The solar radiation is absorbed by the interlacing black feather tips, far away from the skin.
It only takes a couple of metres per second of wind speed for that heat to be transferred to the air. 

 
Because emus never stop walking when they forage they are exposing themselves to enough wind speed to basically remove nearly all of the heat intercepted from the sun. Emu feathers provide about 30 to 40mm of insulation. In the cold emus can erect those feathers, creating a larger 60mm layer of insulation.

Like most animals emus have different temperaments. When emus attack they come head on, jump up in the air and kick frontwards, the middle toe having a large, damaging toe nail.

Worth avoiding! The powerful middle toe nail on an emu's foot. (note the emu shown is anaethetised and not restrained but supported by the leg rope. Image from Shane Maloney)

 

Emus will probably cope with climate change, their thermal regulatory capacity being good. They will, however, have other challenges like the changes in habitats and whether their food will be maintained, even though they are omnivorous. For now though, emus remain in fine feather.

Professors Shane Maloney and Graeme Martin were interviewed for A Question of Balance by Ruby Vincent in July 2016. Summary text by Victor Barry August 2016

 

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Emu run through The very public private life of male emus

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