Numerous species choose to live in groups for some obvious benefits – a lowered risk of being predated upon, or the ability to relax while someone else keeps an eye out for danger for a change. Let’s face it, we all need friends sometimes. It isn’t always easy to function as a team, however, and there are even some real dangers to associating in groups. For one, the risk of catching an infectious disease is higher in a group. It can also be harder to survive in a group if your food resources are patchy or scarce. Thus, species make nuanced decisions on whether to choose group-living, and they modify their diets, physiology, ranging patterns, reproduction, and even their social lives to accommodate their group.
One of the more spectacular examples of a group-living animal that has manipulated its sociality to fit its environment is the African Ice Rat (Otomys sloggetti robertsi). Researchers have recently discovered that these rats are social in their underground burrows but (and this is where things get odd) completely solitary and even aggressive with each other when they forage above ground.
The African Ice Rat is active during the day, forages mainly on plant material, and unlike other rats that live in alpine conditions, does not hibernate. It is found in the South African Drakensburg and Maluti Mountains, where temperatures can drop to just below zero Celsius (32 degrees Farenheit). It frequently snows.
So how do they survive in their harsh environment without sleeping through the winter?
Their thick, short fur and elongated small intestines (for increased absorption of nutrients from food) can only take them so far. In fact, their basic physiology is pretty much the same as that of rats that live in warmer conditions.
Researchers from the delightfully named University of Witwatersrand in Johannesburg suspect that they keep warm, adorably, just like we like to – by huddling.
Ice Rats live in groups of multiple males and females (2-10 of each sex) in elaborate underground burrows. Researchers excavated some burrows to discover that each burrow can cover an area of 98-1200 sq-metres above the ground, but consists of an intricate maze of connected passages with multiple entrances, sometimes two floors, and a couple of shared nesting chambers. The cost of building an Ice Rat mansion is so high that it is economic to pool resources and share it with others.
In the cold winter, they emerge from their burrows to bask above ground, with their limbs retracted and backs oriented toward the sun. The rest of the time they are huddling below ground, in the company of their burrow mates.
Fascinatingly, when they are above ground, they are excessively solitary – researchers watched one colony for 613 hours and observed only 31 instances of interaction. Of these, 26 were aggressive. Apparently, when ice rats meet each other above ground, they engage in, of all things, boxing! Some times they even indulge in protracted chases of their own room mates.
Despite this antagonistic behaviour towards their underground friends, the members of a colony overlap in their aboveground activities spatially. This suggests that although they practice temporal avoidance, they do use the same resources, a likely outcome of patchy resource distribution above ground.
To make things more interesting, the researchers went one step further and conducted displacement experiments on the rats.
First, they trapped individuals above the ground and temporarily placed them in a cage back inside their colony. In other cases, they placed individuals from a different colony (effectively, strangers) within the focal group’s colony. Then they sat back and watched the members of the colony respond.
Surprisingly, the rats were equally antagonistic to the strangers and their own colony members when encountered inside the colony area. Although they adopt a much more social attitude when under the surface, their best friends are just strangers to them when it comes to sharing foraging territories outside the burrow.
We’ve certainly all heard of people who are friends one instant, and enemies the next, but these rats are superlative modulators of sociality. Remarkably, they do it to avoid feeding competition above ground, while still relying on each other for shared protection during adverse weather and breeding seasons. They don’t even appear to hurt each others’ feelings!
Hinze A., Rymer T. & Pillay N. (2013). Spatial dichotomy of sociality in the African ice rat, Journal of Zoology, 1469-7998. DOI: 10.1111/jzo.12028
Hinze A., Pillay N. & Grab S. (2006). The burrow system of the African ice rat Otomys sloggetti robertsi, Mammalian Biology – Zeitschrift für Säugetierkunde, 71 (6) 356-365. DOI: 10.1016/j.mambio.2006.05.002
Rymer T.L., Kinahan A.A. & Pillay N. (2007). Fur characteristics of the African ice rat Otomys sloggetti robertsi: Modifications for an alpine existence, Journal of Thermal Biology, 32 (7-8) 428-432. DOI: 10.1016/j.jtherbio.2007.08.003
More on Ice Rat Research:
Take a look at Andrea Hinze’s thesis on the African Ice Rat.
The New Scientist gets some insight from Neville Pillay, a member of the research team on this project. The article links this study to the idea that “under the right circumstances, even seemingly nice people can behave abominably,” which is certainly catchy but exaggerates the “aggression” observed. The behavioural changes documented by this research seem to be driven by ecological constraints, and not some inherent capability for aggression.