Digging and Burrowing

In contrast to the brown rat's cousin, the black rat (Rattus rattus), the brown rat will typically live and take cover close to the ground or even underground. The image to the right (excuse my sketch work) gives a basic impression of a brown rat burrow. An ability to dig and burrow allows the brown rat to build underground connecting tunnels that can serve basic needs such as housing a rat colony, providing a retreat from danger, and supporting the growth of a colony with nests for rearing young kittens. With rats being the adaptive and flexible little things they are these habitat tendencies can become blurred. A black rat will happily take over a burrow in the absence of the more aggressive brown rat while a brown rat will venture upwards in a building and happily climb up and accommodate a set of staggered stacked boxes that have become a permanent storage feature. Both the brown rat and black rat have found that living close to humans brings it rewards. Our buildings, as shown below, along with our food sources that are often close by are readily taken advantage of.

Display permission kindly given by Gerd Rossen. More amazing images are at  http://www.digital-nature-photography.com

The domestic brown rat that people keep as a pet is most often called a fancy rat. Since its domestication it has undergone selective breeding to develop attributes that would make it a 'good' pet. Breeding rats that display a calm and docile disposition gives us a tame animal but it can also 'remove' or reduce the frequency of other behavioural traits associated with its wild cousin. To test if my own rats still retain digging and burrowing behavioural traits I filled a fish tank with a simple hay burrowing medium and watched to see if their digging and burrowing instincts remained.

The video below shows that my domestic brown rat (Rena) still retains her digging and burrowing instincts even after hundreds of generations of selective breeding. Sally, on the other hand, wasn't amused in the slightest.

The digging process is very interesting to observe. In the video above we can see Rena's tendency to begin digging from a corner or edge that is next to an upright surface. She first lowers her nose to sense the ground with her whiskers and then pulls handfuls of the digging medium (finely chopped hay) under her body or depending on her angle of attack to the side of her body. Her body appears arched when she's stationary and straightens as she moves forward with the digging process. She is able to sense an accumulation of hay beneath and kicks her hind paws to clear the pile from under and behind.

The evolutionary process that has taken place so far to develop this digging and burrowing behavioural instinct has come about through natural selection over an unimaginably long period of time. What we see today as a smooth sequence of coordinated movements would have built over descending populations of predecessors. Animals that introduce new variety into their population that in some way enable them to be better adapted than their competitors have a better chance of survival. The combination of coordination, sequencing of physical and mental abilities, and use of all other parts that make up the 'vehicle' that hold the rat's genes is a marvel of evolution. I wonder what further digging and burrowing changes lie in store for rats as they continue to evolve.

As Sally wouldn't take part in the diggy diggy experiment I got her to pose for a photograph so I could get a close up of her paw. Getting a rat to pose is one thing. Getting a lower end digital camera to take a decent macro picture is another. While it's a little blurred in places the picture on the left captures the hindpaw and claws pretty well.

Here's an early under construction image of my rat's 'burrow'. The cage on the left houses their bed, food, and water. The tubing and plastic container on the right give them a place to scamper while I'm out. It's easy to release the rats, while I'm at home, simply by removing the metal grill cover on the plastic container. I'd like to give my rat's more freedom when I'm out but I just know they'd trash the room and gnaw their way through everything. This compromise allows them to explore their natural behaviour while keeping their natural gnawing behaviour in check.

In addition to the above, Rat Behavior and Biology (Anne's rat page), is well worth a look for a more comprehensive and detailed examination of wild brown rat burrows.

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