Why pandas roll in poo in winter

Scientists have reported seeing some unusual giant panda behaviour: some of the creatures appear to have a penchant for rolling in fresh horse manure in winter. The theory is that the muck contains chemicals that deaden the panda’s ability to feel the cold. Katie Haylor explains...

Katie - Using infrared cameras to observe a year of giant pandas in the wild, scientists in China have documented around 40 incidences of these bears sniffing, wallowing in and rubbing horse manure - yep, horse manure -  all over themselves, particularly in the colder months. So to reflect on this rather - at least to my ears - unusual finding, I spoke to Anglia Ruskin behavioural biologist Claudia Wascher.

Claudia - It is quite unusual to actually see a species rolling in the faeces of another animal. Individuals avoid going close to faeces because potentially these materials can have parasites, which animals can get affected with, or bacteria. So yeah, it is quite unusual.

Katie - Now I'm no panda expert, but I wouldn't have thought they spend that much time around horses. But it seems the ancient trading routes that cross the bears' habitats have brought these animals in close proximity. And timing is important here because it seems the fresher the faeces, the better.

Claudia - So they have compared how often does this behaviour occur when there is fresh manure compared to all older ones, and it is most frequent in the first couple of days.

Katie - Lovely. So why on earth are pandas giving themselves a horse poo spa treatment?

Claudia - They think that there is a specific chemical component in the horse faeces which is an adaptation to cold. So basically rubbing in the horse faeces would then make the pandas feel less cold.

Katie - In addition to that beautiful monochromatic fur the theory is that pandas are cleverly seeking out additional ways of staving off the chill at colder times of the year, mostly in November through to April.

Claudia - Don't think about it like having another coat on or having a pullover on. But it is more of a reaction. Similar to if you would eat a hot pepper, you would feel warm because there are certain chemicals in the food, which cause a chemical reaction, which causes the sensation in your body. And this is a similar case.

Katie - Claudia is talking about beta caryophyllene, or caryophyllene oxide. Chemical analysis showed that they're particularly prevalent in fresh horse manure. And tests with giant pandas at Beijing zoo suggested that they seem to prefer hay with these chemicals on, compared to controls. And because this poo rolling seemed to be temperature dependent, the scientists wondered if these chemicals could have a role in how animals sense temperature.

Claudia - They have chemically extracted this component from the horse faeces and have then injected mice either with this chemical component, or with a saline solution. And then they have looked in the mice, what kind of behaviours they display in response to cold. And the mice showed more behaviours which are expected as an adaptation to cold; so more shaking behaviours with the controlled substance. And this hints towards that the mice injected with this chemical component would feel less cold.

Katie - So what are these chemicals getting up to? The authors did some laboratory work to delve into this question. And I asked Claudia to summarise this.

Claudia - This chemical component actually responds to a specific channel within the nervous system. What basically happens is that the sensation of cold is a specific sensation, which means that certain parts of the body respond to a certain environmental condition. So nerve cells in the skin, activation in these nerve cells would cause us feeling cold. These nerve cells are inhibited by this chemical component.

Katie - So the authors reckon that on a molecular level, these chemicals are blocking receptors involved in cold sensation. Fair play to giant pandas! It seems rather clever to make the most of the surrounding environment like this. Others are less convinced. In the Science journal magazine this week, the University of Glasgow's Malcolm Kennedy points out that perhaps the pandas are just curious about this horse manure. And that if this lack of feeling chilly were to stop pandas seeking shelter against the cold, this could be highly problematic. Turns out that rubbing stuff all over oneself is not without precedent and the animal kingdom.

Claudia - There's a whole group of self anointing behaviours where vertebrates or different groups of animals rub themselves in some sort of biological substance. Faeces of other species, soil materials, plant materials. They are usually very poorly investigated. This is one of the first studies like this, which I'm also seeing opens up a lot of avenues for future research.