Stereotypies; are they always bad?

By Jemima Frame

A stereotypy is a repetitive (often purposeless) movement such as body swaying, or pacing, most commonly seen in captive animals. This abnormal stereotypic behaviour is generally an indicator of poor psychological wellbeing in the animals and is a behaviour which is frequently seen in zoos. It is thought that both the stress of being in an unusual environment, and the inability to perform some important species-specific behaviours contribute to the development of these stereotypies (Manteca & Salas, 2015). However, recent research has suggested that stereotypies are also associated with the animal’s reproductive performance, and it has even been suggested that they display better welfare than less stereotypic individuals.

Stereotypies are still a relatively misunderstood behaviour in zoo animals, with scientists not entirely sure what causes them. Stereotypies generally develop when animals are kept in suboptimal conditions, leading scientists to think that it is associated with poor welfare. However, further research has shown that in some cases animals with stereotypic behaviour have reduced cortisol levels and lower blood pressure, suggesting they have better welfare than less stereotypic individuals (Martin et al., 2020). It has even been hypothesised that some of the behaviours are completely natural and are just performed in a smaller area. For example, a male giant panda may pace back and forth while in captivity as a result of the territorial pacing that normally occurs during breeding season. The panda simply paces back and forth because the small enclosure prevents him from pacing for long distances in one direction. If this is the case, this stereotypical behaviour could be viewed as a good sign as it is an indicator of sexual motivation which leads to increased reproductive success.

The relationship between stereotypies and reproduction is still largely unknown, with some studies showing them to have a negative effect and some positive. There are arguments for and against the effect of stereotypies. On one hand they may be positively associated with reproduction as stereotypic animals are more active and therefore have better physical fitness, and they have found a coping mechanism that reduces stress, which in turn boosts the hypothalamic pituitary gland (HPG) axis function, therefore increasing reproductive output. On the other hand, highly stereotypic animals have higher stress levels therefore supressing HPG axis function, and they can act inappropriately which compromises courtship and maternal care (Martin et al, 2020). Stereotypic animals could also cause a biased offspring sex ratio. Sex allocation theory predicts that animals in good condition will bias offspring towards the sex with higher reproductive variance, which is males, while females living in stressful conditions will bias towards production of women. This effect is often mediated by glucocorticoids. This sex biased ratio allows us to understand whether stereotypic animals experience more or less stress than their fellow captive animals. If they experience more stress, they should have male dominated offspring, if they experience less they will have female dominated offspring (Robertson et al, 2006). 

A recent study into the role of stereotypies in reproductive performance in the giant panda Ailuropoda melanoleuca has been carried out (Martin et al, 2020). They found that male stereotypic pandas copulated more and produced more cubs, which is likely due to high levels of sexual motivation, and as mentioned before their pacing activity could be natural and not at all a sign of bad welfare. However, female stereotyping pandas showed behavioural incompetency in mating and cub rearing, suggesting they were poorly adapted to human care and will likely have fewer offspring survive. Stereotypic females also showed a trend towards producing female skewed litters, suggesting they were under stress and had poor welfare. Interestingly male giant pandas that had stereotypies were found to produce significantly more male-skewed litters compared to males with no stereotypies, further confirming the prediction that the stereotypies in male pandas were not a sign of poor welfare. These contradictory results suggested that when selecting breeding partners for maximum reproductive success, the optimal pairing would be a stereotypic male panda and a non-stereotypic female panda. These results are important as they provide the first experimental evidence that stereotypy performance is related to reproduction, and also highlight that stereotypies can have different effects on the different genders. 

Many stereotypes appear to arise out of frustration of not being able to perform a certain task, including foraging, ranging or mate searching, which cannot be carried out due to their enclosed confinement. Stereotypies may not always be a sign of poor welfare and, as shown in male giant pandas, can sometimes result in greater reproductive success. More research must be carried out to investigate further the full effects of stereotypies in animals, as well as determining which stereotypies in specific animals indicate poor welfare, instead of just generalising all stereotypies and assuming they all indicate bad behavioural health. Having this knowledge will enable zoos to better care for their animals and ensure they can provide optimal habitats for the animals they protect.

References:

Manteca, X. & Salas, M. (2015) Stereotypies as animal welfare indicators. Available from https://www.zawec.org/en/?catid=0&id=44 [Accessed 29/11/2020]

Martin, M. S., Owen, M., Wintle, N. J. P., Zhang, G., Zhang, H. & Swaisgood, R. R. (2020) Stereotypic behaviour predicts reproductive performance and litter sex ratio in giant pandas. Scientific Reports. 10 (1), 7263. Available from: doi: 10.1038/s41598-020-63763-5.

Robertson, B et al. (2006) Sex allocation theory aids species conservation. Biology Letters. 2 (2), 229-231. Available from: doi: 10.1098/rsbl.2005.0430.