Koalas Feed Their Babies Poop—Here’s Why

Koalas (Phascolarctos cinereus) are one of the most recognizable and adorable animals on Earth. They live in eastern and southeastern Australia in forests and semi-open woodlands, where you are most likely to spot them in eucalyptus trees. Here, they both feed and hide out from predators. These are unusual little animals with an even more unusual way of nurturing their young. Let’s uncover how mother koalas help their babies’ gut health in a less-than-appetizing way!

A Surprising Diet Choice

Koalas are herbivores (specifically browsing folivores) and feed almost exclusively on the leaves of the eucalyptus plant (gum trees). Sometimes, they will also eat the soft stems, flowers, and occasionally bark. In southern parts of their range, Eucalyptus viminalis and Eucalyptus ovata are preferred, but in the north, Eucalyptus punctata, Eucalyptus camaldulensis, and Eucalyptus tereticornis are the top choices. Some eucalyptus plants are avoided altogether. Only two other animals, the greater glider and ringtail possum, are so reliant on these plants.

As diets go, the eucalyptus plant is not a great choice. The leaves are not very nutritious and provide little protein, but are very fibrous and hard to break down. What’s more, they are poisonous to most other animals. As a defensive mechanism against leaf-eating animals, the leaves contain lignins, tannins, and some other toxic oils. Interestingly, the plants growing on less fertile soil produce more toxins than those in fertile areas.

Eucalyptus Adaptations

The koala’s body has overcome the challenges in their diet using several adaptations. When feeding, they are very picky about which eucalyptus plants they feed from. They avoid those on less fertile soils to prevent exposure to lots of toxins. Having selected a single leaf, they chew it thoroughly using their specialized broad, highly cusped molars. Their stomach is small but has a cardiogastric gland, which increases acid and enzyme production to break down the tough fibers.

Koalas have a slow metabolic rate and a six-foot-long caecum (part of the large intestine), so the leaves are retained for a long time. This gives the body more time to break them down and extract energy. Because koalas sleep for between 18 and 22 hours a day, their energy requirements are also minimal.

Toxin Destruction

The koala’s digestive system can detoxify the eucalyptus leaves. It contains specialized bacteria that break down the fiber so that it can be absorbed. More importantly, these bacteria can metabolize the toxins of the leaves so they do not harm the koala. Usually, they produce very dry fecal pellets, but mother koalas produce a very different type of poop when they need to.

Koala Reproduction

Koalas are marsupials, which means they are a particular type of mammal that carry and suckle their young on milk in a pouch on the mother’s abdomen. While koala joeys can technically be born at any time of year, most births in the wild occur between October and May, with a peak from November to January, depending on the region. Not all mothers give birth every year; some only breed every two or three years. There are just 35 days between conception and birth, and baby koalas are born very tiny – they weigh just 0.03 ounces and are ¾ inch long. They are also very vulnerable, with no hair or ears, and are totally blind. Most are single births; very rarely does a mother have two babies. Despite this seemingly helpless state, the joeys make their way from the birth canal to the pouch, where they locate the two teats which swell to fill their mouth and prevent them from being dislodged. There is also a strong muscle at the entrance to the pouch that the mother contracts to stop them from falling out.

Healthy Bacteria

Joeys stay within the pouch for six or seven months, feeding and growing. Their eyes and ears develop, and they grow fur. At around 22 weeks, their little eyes may be spotted peeping out of the top of the pouch. This is when the Mom starts to do something a little strange! To make the transition from milk to eucalyptus leaves, the joey’s developing intestines need a little help. So, the mother feeds them a substance called pap, which she produces in addition to milk. It is a special type of poop and is essentially partially digested leaves produced by her caecum. The joey leans out of the pouch downwards and backwards to feed on the pap.

In this form, the joey’s immature digestive system is able to obtain energy from the leaves. Just as importantly, pap contains the bacteria needed for the joey to successfully and safely digest the eucalyptus leaves. These bacteria populate the young koala’s intestines and get them ready for a life of eating eucalyptus leaves!

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