Darren Naish is a science writer, technical editor and palaeozoologist (affiliated with the University of Portsmouth, UK) who mostly works on Cretaceous dinosaurs and pterosaurs. He also studies such things as the 
The bipedal 'boxing' behaviour of babirusas is odd, but arguably odder is a unique sort of 'ploughing' behaviour they've recently been shown to practise. On being presented with an area of soft sand, captive babirusas (mostly males) have been noted to kneel down and push their head and chest forward through the sand, the result being a deep furrow. One obscure report from the 1970s suggests that Sulawesi people associated babirusas with the creation of straight-line furrows. Possible babirusa furrows were reported from south-eastern Sulawesi in 2002, but this behaviour has otherwise gone unreported from the wild and it wasn't documented among captive individuals until the 1990s [adjacent image from Leus et al. (1996)].
After studying babirusas kept at the Royal Zoological Society of Antwerp, Leus et al. (1996) found that males performed the behaviour most vigorously when placed in the enclosure of another male, and as they ploughed they made various snorting and growling noises, all the while producing lots of foamy saliva. The animals were also seen to 'mouth' sand, the implication being that they were testing it for sensory clues left behind by other babirusas. Ploughing behaviour almost certainly, therefore, has a scent-marking function (analysis of babirusa saliva does not reveal the presence of sexual pheromones, as is the case in wild boar, but an unknown substance suggested to serve this role was discovered). A viscous fluid discharged from an orifice near the eye is also known to be produced by babirusas, and while it again likely functions in sexual behaviour its exact function remains mysterious (Leus et al. 1996). In the adjacent image [from Leus et al. (1996)], the orifice is just about visible as a dark slit very close to the eye. It is leaking fluid, and this is running along the individual's face.
Ploughing behaviour is apparently unique to babirusas among Suidae, and its discovery implies that babirusas in captivity might have their behaviour enriched if they are provided with suitable areas of soft, plougable sand or soil.
By the way, I apologise for the twee title - it sounds like the sort of thing they'd use in the news section of BBC Wildlife (and, indeed, that might be where I saw it first). More on babirusas to come yet.
For previous babirusa articles see...
- The deer-pig, the Raksasa, the only living anthracothere... welcome to the world of babirusas
- Are anthracotheres alive and well and living on Sulawesi? No, but it was a nice idea. Babirusas, part II
- What's with the bizarre curving tusks? Babirusas, part III
- When babirusas fight (babirusas, part IV)
For other Tet Zoo articles on artiodactyls see...
- McGowan's mystery bovid
- The legend of Hogzilla
- Welcome.... to the world of sheep
- Return.... to the world of sheep
- Tet Zoo picture of the day # 23 [on entelodonts]
- Deer oh deer, this joke gets worse every time I use it
- Duiker, rhymes with biker
- Sable antelopes and the miseducation of youth
- Giant killer pigs from hell
- The plasticity of deer
- Over 400 new mammal species have been named since 1993
- Great Asian cattle
- Stuffed megamammal week, day 1: Khama
- Stuffed megamammal week, day 2: Eland
- Stuffed megamammal week, day 3: Okapi
- Death by lightning for giraffes, elephants, sheep and cows
- Dromomerycids: discuss
Refs - -
Leus, K., Bland, K., Dhondt, A., & Macdonald, A. (1996). Ploughing behaviour of Babyrousa babyrussa (Suidae, Mammalia) suggests a scent-marking function
Journal of Zoology, 238 (2), 209-219 DOI: 10.1111/j.1469-7998.1996.tb05390.x
Life Science
Environment
Comments
But lots of pigs churn up soil in a similar but not so dramatic way, and warthogs of course get down on their 'knees' to feed off the ground (though I'm not sure that they root in the ground that deeply) - so it looks like a case of 'exaptation' where cues left passively by rooting babirusas have become used by males to actively signal to each other. Veeeeeery cool.
Posted by: Bill | February 20, 2010 9:18 AM
Perhaps the babirusas were marking their territory. As in "okay, this side of the enclosure is 'your' space, and this side over here is 'mine'.
Posted by: Anonymous | February 20, 2010 6:26 PM
Hmmm, straight-line furrows. Babirusoid dinosaurs?
Posted by: tdh | February 20, 2010 10:24 PM
For those who saw the two messages that have been/are about to be deleted: all will become clear...
Posted by: Darren Naish | February 21, 2010 5:54 PM
Erm...
I've been holding off commenting because I hoped that what would become clear would become clear, but it isn't clear yet.
Is there system maintenance going on? Is there an ETA for its completion? Is just this posting under interdiction, or all of TetZoo?
Help?
Posted by: Owlmirror | February 21, 2010 10:59 PM
I have not seen our two males exhibit any plowing behavior, apart from wallowing. For a long time they were shifted into the same enclosure, but now the the son has his own exhibit.
I can say that babirusa enjoy swimming. They are apt to dive into the water when they are piglets. At any age, they will swim (feet unable to touch the bottom) to get peanuts thrown in the water of their enclosure's moat. Although it isn't their favorite thing, they will submerge their head to get at something especially good. Also, the younger the pig, the more apt he is to dive to the bottom the moat. I know longer work at Audubon Zoo in New Orleans, Louisiana, but I am still friends with the keepers. I know two piglets were born close to a year ago, but I do not know the sexes or if they have taken to swimming too. Anyway, I thought others may find this interested. Take care!
Posted by: Phil1078 | February 21, 2010 11:24 PM
I wonder if babirusas just like the FEEL of ploughing into soft stuff?
Our spaniel would do this, whenshe got on the beach.. rapidly dig a shallow trench then lie down in it. i figure she may have liked the ease of digging and the feel of cool damp sand on her hot little doggy underside.
Heck, give me a bed with clean crisp sheets, or a big furry rug, and I'm likely to root and sprawl, myself.
Posted by: Graham Peter King | February 27, 2010 9:53 PM