HomeStereotypical behaviour as seem among Bank voles.What is necessary for a Bank vole to make stereotypies?The vole has to have been born in captivity and after that spend some time in little impoverished cages without many opportunities to amuse oneself. Wildcaught Bank voles do practically never engage in stereotypies (as defined below); I have noticed these types of behaviours among only 2-3 out of several hundreds, and that only after around a year in captivity. How do these stereotypies look like?The stereotypies are easy to recognize. According to my subjective opinion they can be classified as Backward Somersaultings, High Speed Jumping (typically in the same corner), Running following a fixed route (also known as "Pacing") and finally the "windowscreen wiper". The first three types is practically self-evident; the "windowscreen wiper" is performed in a rearing position - preferable on the same spot -front legs bent and paws close to the neck. Now the vole sways quickly from side to side while brushing against the side of the cage and looking out, or up. This type of stereotypy can be continued for several minutes in a row, up to half hours. Intermediate types of stereotypes do occur and to give a couple of examples then I have had voles which started out doing a backward somersault - clinging for a moment in the lid and then make the final twist to land again on all four legs. Immediately thereafter the procedure is repeated. Another vole started out with a couple of backward somersaults and then continued with 7-8 rounds of running in circles after which the procedure was repeated. However, most bank voles did only indulge in one of the "classical" types. A minority made a switch starting with one type and then using another months later to another and still fewer had two types (or more) stereotypies on their repertoire. Performing in these types of stereotypies must keep the voles fit since it was quite normal for them to continue in this monotone, repeated and apparently purposeless behaviour for half, sometimes even whole hours. Other fellow researchers in stereotypies have written papers concerning the so-called "Wire-gnawing" among regular lab-mice (see e.g. Würbel et al., 1996) and "Bar-biting" among Bank voles (See e.g. Garner and Mason, 2002) which of course is the one and same activity. These researchers has considered this behaviour as stereotypic. I must disagree for the following reason: Sharpening of the teeth or Attempts to escape could be two perfectly valid motivations for such behaviour. I have spend on average 2-4 daily hours for 5 years observing and maintaining my vole colony and during that time observed only a very few of my Bank voles bar-biting (approximately 1-2%.) Should Sharpening of the teeth therefore be the prime motivation I would expect the behaviour to be much more frequently observed so I lean towards the more simple motivation: Attempts to escape. Bank voles do that all the time if they see an opportunity (e.g. a badly placed lid; a crack in the cage) so in short, I do not consider bar-biting a type of stereotypic behaviour among Bank voles but a rational behaviour with the purpose to escape captivity. Lastly it might be in place to mention polydipsia (Excessive drinking). Bank voles do that in frequent numbers when captive, but it is not a type of stereotypy. To my knowledge this phenomenon among Bank voles was first published by two Danish researchers (Sorensen & Randrup, 1986) using Danish Bank voles, and has only recently been published by researchers using Bank voles from other countries (Niklasson et al., 2003b). Sorensen and Randrup hypothesized that stereotypies were a mean to deal with stress and frustration and those who failed developed polydipsia and died. Later it turned out that polydipsic Bank voles were in fact suffering from diabetes mellitus (see here) but I remember clearly that even at the time I started my thesiswork at University of Copenhagen, Denmark (1995) the polydipsia was regarded a type of stereotypy; a phenomenon most likely related to SIP in rats. Visible signs of a stereotyping vole:Backwards somersaults leave a thick layer of dust everywhere in the cage, on the sides; on the lid and even the top of the food pellets is covered. The spot on the bedding where the vole takes of and land is clearly marked. Only faint marks on the side can be seen - occasionally - since Bank voles doing backwards somersaults usually did them various places in the cage and not always had to touch the side. High Speed Jumping usually takes place in a corner and produces some dust. Where the vole brush against the side there will of course be no dust, so a clear mark, shaped like am upright vole, can easily be spotted. Most voles which jump repeatedly will loose some hairs on the skull/nose since they could touch the lid with their heads in our cages (Height: 13.5 cm) Running following a fixed route do not produce a significant amount of dust, but the route is easy to see after a while. The Windowscreen wiper does not produce dust but a slightly greasy spot in the shape of a "V" or "Y" is seen on the side of the cage. Frequency and onset age of stereotypers in F1Roughly one third of the first generation (F1) of Danish voles born in captivity will develop one or another form of stereotypies. The average age of onset is 2 months (High Speed Jumping) and three months (Backwards somersaulting) (Schoenecker et al., 2000). Gender bias in stereotypies:Females seem to develop stereotypies more frequent than males (38% vs. 23%) but there do not seem to be any gender related differences in the proportion of voles that prefer one or the other type of stereotypies - at least not in an unselected Danish F1 generation (Schoenecker et al., 2000). As far as I can analyse data from Meers and Ödberg (2006) it would seem that Belgian Bank voles (descendants of imported English C. glareolus britannicus) exhibit the same female proneness to develop stereotypies (Schönecker, 2007). That females show an increased proneness towards development of stereotypies (p< 0.05) is most likely related to the fact that 2-3 times more males than females develop diabetes in captivity (p< 0.001) (Schoenecker et al., 2000). Indication of a genetic basis of stereotypies.I managed in one single generation to reduce the frequency of stereotyping Bank voles down to 8% using selective breeding on non-stereotyping F1 generation. If I instead used stereotyping F1 I ended up with roughly seven times more stereotypers in F1 so the conclusion was easy to draw: Stereotypies among Bank voles is something which is easy to breed up or down (Schoenecker and Heller, 2000). It would seem this demonstration in reality reflects a rather universal phenomenon, which has been observed among ordinary pet shop owners/keepers (Personal communication) and among researchers studying mink (Jeppesen et al., 2004) and African striped mice (Schwaibold & Pillay, 2001). Furthermore something could indicate it would be possible to breed selectively on the type of stereotypy. The pups is naturally looked after by the mother until weaning and after that it turns out that the pups end up performing her preferred type of stereotypy in 83-94% of the cases (Schoenecker and Heller, 2000). Two factors could be playing a part here: Imprinting ("learning") and "stereotypic genes" (or more likely "segregating units") but so far the answer to that is still unresolved. An indication of the importance of the last factor can be seen below. Preferred type of stereotypies among different strains of Bank volesWhile Danish Bank voles from Zealand clearly prefers Backwards somersaults (80%) to Jumping (Sorensen and Randrup, 1986; Schoenecker et al., 2000) then the opposite propensity is evident among Belgian (Ödberg, 1986; Meers and Ödberg, 2006) and Swedish voles (Grethe Sørensen (1987). Grethe Sorensen was the first to point at this difference since, as she noted in her preliminary observations to her 1987 paper, Bank voles from the Northern Sweden (Norrland) made a lot of Jumping stereotypies while voles from Southern Sweden (Skane - right opposite Zealand) even though kept in the same types of cages and in the same room as the northern voles, only made a few Jumping stereotypies. Grethe Sorensen consequently suggested that this Jumping stereotypy could be a characteristica for certain geographical localized strains of Bank voles. Bank voles from the United Kingdom seem to have the same distribution between Backward Somersaulters and Jumpers as the voles from Zealand, Denmark (see e.g. Cooper and Nicol, 1991; 1996). A probable explanation on these country-related differences is rather simple: Bank voles from both United kingdom and the Danish islands have effectively been isolated from the continental strains for thousand of vole-generations so the phenomenon of genetic drifting combined with random mutations could in my opinion explain the observed differences. To pinpoint such "segregating units" is a quite other matter, and so far all I can do is to point to all the exciting areas of basic research that still awaits future scientists with these interests, good time and proper fundings. Last updated the 22. November 2006
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