A special clientele: rehabilitated western ringtail possums
Success rates for relocation of captive bred animals is particularly low – our animals are not captive bred but mostly raised in captivity. The difference might be marginal or important and depends on the point of view. Captive breeding programs would concentrate on healthy animals with a high chance of reproducing well and producing healthy offspring. Pairing of particularly well suited animals, genetic analysis prior to any effort, expert supervision, constant vet involvement and highest hygiene standards can be delivered in a professional breeding program, but not in a home-based care facility. Young animals usually come into care at a stage when they have already had the natural treatment by their mothers (pap, amino-globulins etc.) in the most important early pouch stage.
There is however the risk that without early assessment of the viability of the animal, we might be ‘breeding’ weak and even potentially diseased animals that were rejected by their mothers for that reason.
Even for scientifically led translocations frequently only animals from rehabilitators are available. This will be increasingly so as the EPBC documentation and the recovery plan regard translocation as the least preferred option and development applications that necessitate translocations are not as easily approved as in the past.
Ringtails from rehabilitators are mostly hand-reared, less frequently injured adults or displaced possums picked up during habitat removal with no refuge near-by.
Behavioural adaptation to captivity can hardly be avoided but might compromise the success of a program.
As rehabilitators we tend to anthropomorphise (attribute human qualities and traits) our animals and treat them accordingly - sometimes to a degree that they are too humanised to be releasable into a life in a natural environment. However, a bias towards anthropectomy (Andrews and Huss, 2014) – the denying of human qualities to other species - could be equally harmful for a healthy development. (Andrews, 2015)
In an experiment with rats it was discovered that offspring of stressed mothers still developed normally into young adulthood but showed memory lapses and anxious behaviour later in life. The older they got the worse their memory deficits became and these developed at a much faster rate than in rats raised for the first weeks of their lives in a stress- free environment.
The stress transferred by their mothers in early life had damaged the hippocampal network, lowered the numbers of synapses and damaged synaptic connections and even reprogrammed the expression of specific genes. (Brunson et al, 2005)
Other research using ‘attentive mothers’ that frequently licked their offspring confirmed the finding that these early environmental factors program gene expression and thus regulate an animal’s lifelong stress response. A second group of mice was taken from their mothers and not handled apart from the most unavoidable interactions.
The more care a young rat received, the lower the level of stress hormones in their bloodstream. They were less fearful, more exploratory, learned faster and retained what they have learned for longer.
Interestingly when young rats received ‘attentive behaviour’ instead from humans, they also did not suffer from this deprivation manifesting in elevated cortisol levels and hippocampal damage. (Meaney, 2001)
This research was regarded as relevant for humans who are most likely more different to rats than ringtails would be.
As so often a healthy balance between the provision of ‘motherly care’ and acceptance that this is a wild animal, not a human baby would be desirable.
Ringtails are very susceptible to stress and sudden severe stress and mild but chronic stress can both kill them (unfortunately personal observation). It would therefore be desirable to give them a ‘stress-proof’ upbringing.
No research so far has been conducted into which personality and behavioural traits are best suited for long survival in a natural environment. Anxious, guarded behaviour might be advantageous if food is scarce and predation pressure high. A low profile and quick response to stress might increase chances of survival.
Apart from the overall fitness of the animals their digestive health and nutritional status might determine whether they are successful in their lives after release.
Scientific methods are in place to minimise bias and to develop and test hypotheses. Community led research is clearly at a disadvantage as it can at best develop hypotheses based on fairly subjective observations.
Observation and captive feeding trials show no clear distinction between those raised on high quality browse from areas with the largest viable colonies and those who were raised on browse from areas that are not frequented by wild ringtails but the latter might have been substitute-fed with fruit/vegetable etc.
Diet suggestions in the literature for captive animals usually include a variety of unnatural foods and might tempt rehabilitators to follow their professional example. (e.g. Jackson, 2003)
The literature even provides an example for a diet devoid of tree foliage, however the low fibre level was inadequate to promote and maintain normal gut motility and function. (Hume and Barboza, 1993)
In the earlier stages most ringtails would follow normal growth patterns and look healthy.
However, zoo animals will never have to fend for themselves and find their own food; they will not need adequate gut bacteria to live on a poor leaf diet and all deficiencies can be remedied by supplements and vitamins.
An animal that has not adapted to a fully natural diet might not be able to withstand release stress and the challenges in a new environment which alone usually lead to weight loss. If it cannot survive the critical establishment period, and therefore not breed, release has failed.
Poorer survival and success rates of rehabilitated animals compared to wild translocated ringtails in official research (Clarke, 2011) could have resulted from these issues to a higher degree than from behavioural adaptation to captivity.
Releasing in spring could soften the impact as the food is plentiful and most nutritious, however even this advantage would not be sufficient if gut function is inadequate.
The water content in leaves is important but it is the overall food quality (high nutrient levels, low secondary metabolite levels) that determines whether animals need access to fresh water or can survive on the little that is in their food and naturally available in their environment. The assumption that ringtails only need water in heat is incorrect as they drink at any temperature if water is available.
The myth that ringtail possums do not need to drink should be dispelled by now. Ringtails are mammals and all mammals have fluid requirements to keep their metabolism active.
However, we give our hand-reared youngster at least 10% of their body weight in daily milk replacers. This is clearly necessary as our milk replacers are far less potent than mothers’ milk and only a larger amount seems to provide all nutrients. In the late stages this can be up to about 50 ml of milk replacer – an amount no ringtail mother would ever be able to produce in 24 hours.
Are we ‘training’ drinkers? This could also influence the animals to eat less leaves as they can not only get their fluids but also their general nutrient requirement in a more easily digestible form from milk. Whether this over-supply of fluids while in care might influence feeding habits later in the wild has never been researched.
Adolescent ringtails (particularly males) seem to reach a point in time (after weaning) when some otherwise healthy and normally behaving animals start to drink unusual amounts of water. The percentage of ringtails that show this behaviour is unknown.
We tend to give our charges soft, young leaves, often regrowth which if it comes from young trees can be quite high in toxicity. Some animals then drink excessive amounts of water but still eat well which in my opinion hints at an attempt to water toxins down or flush them out. However, in some cases, leaves are completely rejected. This observed browsing resistance by western ringtail possums has also been noted in research into common ringtails. If levels of some compounds (mainly macrocarpal G) exceeded a certain threshold, animals refused to eat the leaves. (Foley et al, 2004)
Whether a diet with consistently high toxic plant compounds can lead to heavy drinking, which in turn might then lead to kidney or bladder disease, would need research.
In my view, it is an indication for high toxicity as the reason for the drinking, if water intake is drastically reduced after A. flexuosa was substituted with the cultivar A. flexuosa nana, which is reportedly low in toxins. However, heavy drinking can also be habitual and an indication for boredom. As the perceived necessity for a high water intake would render an animal unreleasable, it should and could be investigated by rehabilitators how much the animals in their care have drunk per night over an extended time frame, in the various seasons and in relation to the food the animals consumed.
Animals come into care for a reason that might not always be immediately evident. Old, at times badly healed, fractures and consequences of former injuries – e.g. arthritis after burns - were sometimes discovered when checking for other issues, but could still have played a role in the animal’s needing care. The combination of parasitism, emaciation and dehydration with no definitive disease process seems a common reason for presentation at a vet or rehabilitator and for early mortality in translocation research (Clarke, 2011) but has not been investigated.
Disease organisms can be transmitted at the human, domestic animal and wildlife interface, which could serve at an incentive for more investigations even if costly. It is obviously unrealistic to expect all animals to be comprehensively checked by a vet.
Surprisingly, several haematological and serum biochemical parameters showed differences for wild and captive ringtails in translocation research. Only glucose and ALP (Alkaline phosphatase which is for instance elevated in jaundice and bone disease (Blood et al, 2007)) were higher in captive animals than in wild ones. All other values were lower. (Clarke et al, 2013)
Judy Clarke hypothesised that captive animals that cannot forage for themselves might be provided with diets lower in protein and available nitrogen while supplementation with fruit and flowers increases their blood glucose level. I would add that our milk replacers also lead to high blood glucose levels as several juveniles displayed glucose levels of +4 when routinely vet checked. They were not diabetic and glucose levels normalised with time.
Enzymes elevated during stress are likely to be elevated in all translocated ringtails, however particularly in wild animals that are not used to being handled. (Clarke et al, 2013)
CK (creatine phosphokinase), an enzyme found in the heart, brain, skeletal muscle and other tissues which rises in the blood when muscle or heart cells are injured, are significantly higher in healthy ringtails than in domestic animals (at least twice the value of a dog, three times the value of a cat - http://www.2ndchance.info/normaldogandcatbloodvalues.htm) which unfortunately might not be common knowledge for all veterinarians.
At least prior to release health screening would be important to minimise the risk of pathogen transmission between sites and species.
Parallel endocrine and infection investigations and research in to the influence of stress and disease have rarely been conducted for translocations but captive animals might provide useful surrogates for experimental studies of stress and wildlife disease in a cost efficient way as long as stressors that are imposed by captivity itself are identified and acknowledged. (Hing et al, 2016)
Stress related disease in possums can manifest in a variety of symptoms such as anorexia, diarrhoea or lesions and it can exacerbate latent infectious disease (Ladds, 2009) and should be a priority area for research. Our western ringtail possum is not only a prey species evolved to not show stress to ‘predators’, but also a frequent topic in human-wildlife conflict and also highly attractive to humans. Apathy and stoicism can easily be misinterpreted as a ‘relaxed, friendly nature’.
Well organised cooperation between rehabilitators/shelters , DBCA and vets/veterinary training institutions could provide a good starting point for investigations.
