Compulsive Digging

 

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This article first appeared in the September 1997 issue of the NGS Journal.

Anyone who keeps Mongolian gerbils knows the problem: the gerbils constantly dig in the corners of their cage. This is not just normal digging behaviour - because of its characteristics it can be described as so-called stereotyped digging. I have a simple method that can prevent gerbils from developing this behaviour.

Stereotyped behaviour is often subject of scientific studies. Animals in captivity sometimes show movement patterns consisting of one or more elements of behaviour that are constantly repeated. This behaviour is dependent on the environment in which they are confined. For example horses often develop weaving behaviour (swaying of the head) when kept in boxes. The repetitive to-and-fro walking of tigers, lions etc. in zoos is a result of not having enough space. It has been hypothesised that stereotyped digging behaviour in gerbils is influenced by cage size, too.

[Picture] Christoph Wiedenmayer, a Swiss psychologist, has proved that this is not the case and that another factor is relevant for the development of stereotyped digging in gerbils. For his dissertation he studied the cause of this behaviour in gerbils at the University of Zurich. This has now been published as CAUSATION OF THE ONTOGENETIC DEVELOPMENT OF STEREOTYPIC DIGGING IN GERBILS: Wiedenmayer C, 1997, Animal Behaviour, 53(3), 461-470

In his first experiment, he kept gerbil families in standard laboratory cages of different size. Digging behaviour was not affected by cage size - all gerbils in all cages developed stereotypies. He therefore assumed that a lack of adequate stimuli that control digging in the wild could be responsible for this behaviour.

In search of these adequate stimuli he looked at - what is the motivation, the goal for a gerbil to dig? In their natural habitat, gerbils dig burrows which consist of different chambers connected by tunnels. So he deduced that the burrow is the goal of digging, a goal that can not be achieved in standard laboratory cages.

In the wild gerbils grow up in a burrow which is dug by their parents. Christoph Wiedenmayer found out that when gerbils grow up in a burrow they will use it and don't dig much. There is no need to dig because a burrow is already there!

The result of his further experiments is quite simple: if gerbils grow up in an environment with a "burrow" they won't develop stereotyped digging behaviour. The essential fact is that the "burrow" must have a tunnel with a chamber connected to it. When the gerbils were only given a shelter without a tunnel, stereotyped digging occurred. In the end he used transparent plastic tubes (length 20 cm, diameter 5 cm) and plexiglas shelters (13 x 13 x 10 cm). A hole in the back wall of the standard laboratory cages led through the tube to the plexiglas chamber. All gerbils that grew up in this setting didn't show stereotypies. His aim had been to find a simple and not too expensive method to improve housing conditions for laboratory animals.

After having read his work I wanted to try it myself with one of my gerbil families. As I don't have laboratory cages and didn't like the thought of just giving my gerbils a house with a tunnel, I decided to let them construct their own burrow system.

[Picture] I keep most of my gerbils in aquariums. For my experiment I used a tank of 100 x 40 x 40 cm. I put a large layer of wood shavings mixed with hay and some cardboard tubes into the cage. About 2/3 of the cage was filled with this mixture. I chose hay and cardboard tubes to make it easier for the gerbils to dig tunnels that can't collapse. I put one pair of gerbils into this cage and observed their behaviour and that of its offspring for several months. The breeding pair soon started to dig a lot in the wood shavings. They dug tunnels and chambers, but they also dug in the corners. Of course my starting pair of gerbils hadn't grown up with a burrow! Even though they had the opportunity to dig in the middle of the cage they still showed stereotyped digging in the edges. It seems that once developed it can't be forgotten!

The two gerbils worked hard and built up a nice burrow system which changed from day to day. Some tunnels were kept constantly the same, others were abandoned or enlarged. Due to the tubes and other obstacles under ground they constructed a few "chambers" that never changed.

Soon the first litter was born. I didn't see the pups - they were hidden deep in the burrow - but I could tell from the behaviour of the mother (and her shape) that she must have given birth. A few days later I had the luck to see the babies, though: the mother decided to move them to another chamber that was situated directly at the front pane. They were 5 healthy little pups. During the next three weeks the mother moved them several times and I rarely saw any member of the family on the surface.

After the pups were weaned I observed them to see if they would start digging in the corners or not (the parents still dug in the corners from time to time). As expected the young gerbils never dug in the corners. I left the cage uncleaned for about three months (!) because I didn't want to destroy the burrow. In the meantime, the second and even the third litter were born. Obviously I had chosen a very friendly family for they never fought. (Maybe because they had a burrow?)

All gerbils that have grown up in this cage never showed stereotyped behaviour. They spent most of the time under the surface, though.

So I ended up with one breeding pair still digging (from time to time but much less than before!) in the corners and a lot of young gerbils with "normal", healthy gerbil-behaviour. When I finally cleaned the cage I wanted to know if the gerbils would nevertheless start to dig in the corners when they had no burrow any more. So I put a normal layer of wood shavings in the aquarium (4 -5 cm high). The gerbils still had access to shelter (one big cardboard tube and one flower pot, not connected), but all gerbils that had lived in a burrow for their whole lives were very frightened in the first time and didn't like to come out of the shelter. They got used to it in the end - but they also started to dig in the corners. It lasted a long time until they began with corner-digging, and it was not very much, but they DID. So it is not sufficient to provide a burrow during growing up but also for the rest of their lives in order to prevent stereotyped digging permanently.

As I said before, it is also sufficient to give your gerbils a "reduced" burrow consisting of a small house connected to a tunnel. So you don't need to put a lot of wood shavings etc. in the cage if you don't want to. From my own observations I can tell that my gerbils spent a lot of time with digging and changing their burrow. They were kept busy and I had the impression that it was the most "natural" environment I ever could give them (in a glass tank). Even though they were under ground most of the time one or two tunnels always led along the front pane and I could watch them quite often.

The only disadvantage of this is that whenever a gerbil dies you can't tell. It is almost impossible to count them in such an environment. So it can happen that a young gerbils dies and you don't know - ending up with a nasty smell when you finally clean the cage.

My experimental family has its burrow back - I couldn't stand watching my young ones digging in the corners. They got new shavings and new tubes and have started to build a new burrow. Luckily, they only dig tunnels and not in the corners any more!

I recommend this method to everyone who wants to make an end to stereotyped behaviour and to give his gerbils an environment as natural as possible.

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Last updated 14 September 2009