Nature's nappies

Author
by Alice
Publish date
14 November 2013
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Here at the Melbourne Museum Discovery Centre we are inundated with a wide variety of interesting enquiries. We recently received this stunning photograph from a keen bird enthusiast in Camberwell, wondering what was being fed to the young chicks.

Wattlebird with faecal sac. Wattlebird with faecal sac.
Image: Jim Love
Source: Jim Love
 

Interestingly, the parent wattlebird pictured is not actually feeding this infant but cleaning up after it. 

The black and white material in the parent’s beak is what is called a faecal sac, a mucous membrane that contains the excrement and uric acid (the bird equivalent of urine) of the young nestling. The thick membranous exterior of the sac is strong enough for the parent to pick up with their sharp beak to carry away and dispose of without puncturing it. They are just like a disposable nappy for birds!

Faecal sacs are usually excreted by the chicks shortly after feeding takes place, but this varies from species to species. In the case of the wattlebird the production of a faecal sac is almost instantaneous after feeding. This immediate reaction ensures that whichever parent feeds the chicks, will also be there to carry away the waste at the same time. You can see this occurring in the image below, where the parent is extracting the sac from the nestling’s cloaca as it is being produced.

Wattlebird with faecal sac. Wattlebird with faecal sac.
Image: Jim Love
Source: Jim Love
 

Parents remove faecal sacs from the nest for a number of very important reasons.  Not only do they allow the nest to remain clean and hygienic for the young nestlings, but their removal also deflects the attention of predators by eliminating the scent and sight of the faecal matter. Different species dispose of their faecal sacs in different ways, some preferring to drop them into bodies of water to completely erase their scent while others simply drop them nearby.

Some species of birds will even eat the contents of their baby’s faecal sacs for the first couple of days after hatching. In very young nestlings the bacteria required to digest their food are still under development, hence their excrement is rich in partially digested food. This allows the parents to feed more worms and insects to their young as they can substitute their own meals for the nutrients in their baby’s droppings. 

Wattlebird with faecal sac. Wattlebird with faecal sac.
Image: Jim Love
Source: Jim Love
 

Not all species of birds produce faecal sacs. Young water birds such as ducklings and goslings leave their nests as soon as they hatch, often never returning, and therefore do not have to worry about continual housekeeping. While other birds including eagles, herons and some sea bird species that nest high in trees and on cliffs, will simply back up to the verge of their nests and excrete off the edge.

I will leave it to you to decide whether you think faecal sacs are disgusting, strange or just plain fascinating. Personally, I wish that all human babies were this easy to clean up after!

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Ella 16 November, 2013 15:55
Nature always finds amazing, not always tasty... but sustainable solutions. Thank you Alice!
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