Evaluation of the welfare and reproductive biology of captive tigers using non-invasive techniques: Behaviour and hormone monitoring

Tigers are such an iconic species that their inclusion in any large zoo around the world is almost a certainty. Since they are wide-ranging carnivores, zoos cannot come close to providing the space their wild counterparts enjoy. As such, many captive tigers suffer from poor welfare, often evident even to the untrained eye, with the stereotypic pacing to which many zoo visitors are familiar. However, it has been suggested that for many captive species the complexity of the enclosure is more important than enclosure size, though this varies between species. Little is known for tigers, with research in this area hampered by the low numbers of tigers housed in most zoos. When multi-institutional studies are conducted to combat this hurdle, they face a multitude of additional variables from managerial to climatic, with the effects of many unknown and often unaccounted for/ignored.
To determine the factors most influential to captive tiger welfare there is a need to develop better tools with which to measure their welfare. Only then can we determine what exactly contributes to negative welfare states and work to remove their influence. Perhaps more importantly, we can also determine what factors may promote a positive welfare state. To do this, I took a multi-faceted approach, applying physiological and behavioural measures of welfare in captive tigers.
I tested a variety of enzyme immunoassays (EIAs) for use in quantifying faecal glucocorticoid metabolites (FGMs) as biomarkers of physiological stress. Furthermore, I produced a guided walkthrough for other researchers to perform their own EIA validation experiments. Without lab equipment with built in programming (which can be expensive), the statistical techniques required can be challenging for non-statisticians. By providing R code and an interactive spreadsheet, researchers can simply copy and paste the raw data output and follow my simple steps to perform all the necessary calculations for a full comparative biological validation. After validating an EIA for tiger FGMs that was both highly sensitive and robust, allowing for the accurate analysis of FGMs in tiger faeces even after short term exposure to the elements, I used it for a longitudinal analysis.
I collected faecal samples (1 – 2 per week) from seven Sumatran tigers in three zoos around Australia for over a year. In doing so I showed that Australian temperate climates influence Sumatran tiger FGMs as the seasons change, with seasons most similar to that of the tropical, less changeable, Sumatran climate predicting the lowest FGM concentrations. Of particular importance was the amount of precipitation, with rainier seasons correlating with lower FGM concentrations. Furthermore, cold weather appeared to be more likely to coincide with a physiological stress response in tigers, with lower maximum temperatures being the best predictor of a faecal sample containing peak FGM concentration.
In addition to this, I conducted an observational study at a facility that housed 12 tigers (the single largest collection in Australia at the time). I created an extensive ethogram including 51 behaviours and used an information-theoretical approach to create explanatory models from a large number of potential explanatory variables (both managerial and individual). From this I showed that the greatest predictor of low pacing prevalence was the presence of olfactory cues from conspecifics, followed by the presence of a pool, with the effects being greater for larger pools than smaller ones. Furthermore, these same variables predicted the opposite for patrolling behaviour, considered to be natural behaviour and thus indicative of a positive welfare state. Indeed, it is often postulated that pacing in wide-ranging carnivores is a direct result of the prevention of performing exploratory behaviours. Additionally, tigers in oestrus and those exposed to the scent of a tiger in oestrus further increased their patrolling, but when in smaller and less complex enclosures (e.g. small or no pool, no conspecifics or scents of conspecifics) it also caused an increase in pacing.
The results of my experiments lead to several management suggestions, in particular regarding the ways in which water and olfactory enrichment could be used to improve captive tiger welfare. For instance, the fact that higher precipitation predicted lower FGM concentrations may indicate a possible benefits of novel enrichment practices such as the use of sprinklers to simulate rain. This may have a dual effect due to the release of odoriferous particles from the substrate from falling water. Tigers clearly benefit from the presence of smells they find interesting, in particular those from conspecifics, and the placement of such scents in various locations around the tigers’ enclosure could lead to more use of the enclosure and more exploratory behaviours being performed. Similarly, rather than large expenditures (which for some zoos are not possible) to create large central swimming pools, the construction of multiple pools spread throughout the enclosure may be more beneficial even if they are smaller. This comes from the observation that the size of pool did not predict a difference in comfort behaviours performed (e.g. lying in water, lying on back, self-grooming), and the small differences in the effects on pacing and patrolling may be closed due to the added bonus of providing a greater number of valuable resources (i.e. water sources) to more areas of the enclosure. Although some enrichment practices can be labour and/or cost intensive to continually provide, the best form of olfactory enrichment possible may simply be to rotate tigers through enclosures as they will provide all the olfactory stimulus required (e.g. through marking). The tiger that paced the most in the study did so in an enclosure that no other adult tiger ever visited (and he also performed very little patrolling), but when the same tiger would visit an enclosure that housed multiple tigers it hardly paced at all and patrolled extensively. Furthermore, scent from a female in oestrus may greatly affect the results. However, an important caveat to consider with these last two suggestions is that if the enclosure is not complex and/or large enough, then the increased drive to patrol may result in an increase in pacing. And the individualities of tigers must also be considered, for some the scent of conspecifics may be seen as a threat, resulting in diminished welfare. It is therefore important, as with any management change, to monitor the effects on all individuals to ensure the desired result, an improved welfare state, is achieved.