Monitoring options
Successful recovery of a threatened species hinges on adequate funding and long-term commitment. Without this, monitoring efforts are usually inadequate or inappropriate and cannot provide the information and evidence needed. (Fleming et al, 2014)
Monitoring of species at risk over a certain period of time is often part of the conditions for approval of clearing. After the funding from the developer ceases, monitoring is discontinued. This could jeopardise its usefulness if data has not been accumulated over an adequate time frame.
Monitoring is often included in the list of mitigations, even though it is not a measure that can reduce negative impacts on wildlife. It is a mere tool to inform management whether an action is required, whether it is effective or needs adjustment and to provide baseline data. (Gleeson and Gleeson, 2012)
Ongoing and frequent monitoring can reveal issues early in a process and provide the chance of a quick response.
Monitoring is a basis for ‘adaptive management’ – the progressive improvement of management through learning during the project. (Lindenmayer and Burgman, 2005)
An adaptive management concept enables the assessment of all available management options and the most appropriate option to be selected and if need be altered to accommodate a changing situation. Adaptive management is far more than ‘learning by doing’ or ‘trial and error’.
Monitoring western ringtail possums in the wild is fairly difficult as the most common method of ‘capture-mark-release-recapture’ cannot be used as they would rarely enter a trap on ground level and therefore estimates of population sizes derived on that basis would not be reliable. (De Tores et al, 2004)
Placing traps in trees, catching animals by hand or the use of a tranquilliser dart gun is labour intensive, expensive and often inefficient in addition to raising ethical questions. (Wayne et al, 2005b)
Trapping is labour-intensive and a time sensitive project as traps have to be checked and reset daily in the early morning to avoid unethically long times spent in the trap for any species caught.
Common brushtail possums are very trap-happy and some develop a taste for certain bait and get caught frequently while it would be rare to catch the same ringtail twice. No captures at all, even at high density sites, is a common and frustrating result. (De Tores and Elscott, 2010)
The ringtails’ elusiveness also limits the use of hair tubes that capture hair of an animal brushing past, which can then be identified by its species-specific characteristics.
So-called stag watching, the observation of potential habitat trees or dreys during the early hours of the evening when the animals appear from their shelter and start foraging has probably been superseded by increased use of cameras.
As ringtails are not very vocal, search for them listening for vocalisation is fairly frustrating, however particularly in the early evening hours it can be helpful when spotlighting. I often hear ringtails before I see them.
The search for tracks on sand plots is for obvious reasons not helpful for an arboreal species and marks on trees give evidence of the presence of brushtail possums but not ringtails.
Scat searches and counts are a highly useful method for surveys determining presence/absence of ringtails and the frequency of detection and the relative abundance of scats provides a lot of valuable information if you are trained to interpret them.
In scientific research projects scat detection rates were strongly related to those derived from spotlighting and proved to be a useful alternative as a measure of relative abundance. (Wayne, 2005a)
However, dense understorey vegetation can make detection difficult and a good understanding of ringtail ecology would help in the way that you know where to look for scats.
Scat deposition rates vary with the quality of the food trees and scat decay rates vary with season, weather, habitat and other factors, making it problematic for inadequately trained personal to interpret the findings reliably. (De Tores, 2009)
Scat counts were reportedly the most reliable method for detection and abundance estimates for Koalas in very low density habitats. As Koalas are as strongly arboreal as ringtails, this finding is relevant to ringtail research. (Mossaz, 2010)
Another type of scat analysis can also give some indication of ringtail presence. The scats of carpet pythons on Leschenault Peninsula still contained ringtail remains when the population had already decreased drastically. (De Tores, 2009)
Estimating ringtail presence and abundance based on drey counts is however highly unreliable (De Tores, 2009) as the animals might not build dreys in areas with a good supply of tree hollows and low abundance of brushtail possums. Areas with sheds, houses or other constructions that provide reliable shelter often only display a low number of dreys.
Spotlighting from cars or on foot along transect lines or within plots is still the most commonly used method for deriving population and abundance estimates as the strong eye-shine of the animals is easy to detect.
If covering large areas the use of vehicles is the only option, but the restriction to tracks and the choice of a sensible speed could lower the level of accuracy. The open vegetation structure in the Southern Jarrah Forest around Manjimup is for instance well suited to spotlighting.
Surveys on foot using a head torch provide an estimate of the minimum number of individuals sighted at one particular survey. (De Tores, 2009)
Single area counts are usually repeated on three non-sequential nights to allow for variations in activity levels due to sometimes unidentifiable reasons. (Jones et al, 2007)
It is highly unlikely that all animals present are seen in every survey even if the researcher is highly experienced and skilled. For abundance estimates to be reliable, it is also necessary to include information on the detection probability. (De Tores, 2009)
Ringtail possums are easier to spot then brushtail possums but the quality of a survey is highly dependent on the observer and differences can be significant. Training needs to ensure that spot-lighters are able to distinguish ringtails from brushtail possums when only a vague shape and/or eye-shine are visible.
The use of head torches maximises the chance of detecting possum eye-shine as the source of the light is very close to the head torcher’s own eyes and the angle of incidence is equal to the angle of reflection.
Halogen is preferable to LED lights but battery life is extremely short and it is hard to even find halogen head torches on the market these days.
LED bulbs are often extremely bright but the light still seems to have poor penetration of dense vegetation.
They are excellent to find your way through the bush but the high light intensity could lead to missing fainter eye shines.
Research in the jarrah forest found no significant difference in detection rates when using lights of 50 W to 100 W; however detection rates decreased below 20 W. The colour of light (white or red) also had no significant influence on detection. (Wayne et al, 2005b)
The impact of high-intensity light on the animals’ eyes such as short term blinding is however a welfare concern. (Kerle, 2001, Wayne et al, 2005b) Whether red light is less damaging to ringtail eyes has not been adequately researched (or published) yet.
When light is shone into their eyes ringtails also tend to turn their head and you might miss them. (Thompson and Thompson, 2009)
In general, enough time needs to be spent scanning the vegetation for their eye shine while on the other hand, spotting needs to be done fast enough so that the animals haven’t turned away yet or moved on.
Unless areas to be monitored are small, transect lines need to be established to make long-term monitoring manageable and a comparison of data meaningful.
In the period between October and April when populations are at their largest because youngsters are still with their mothers the figures will be the seasonally highest. (Wayne et al, 2005c)
The best survey time for ringtails in my experience is shortly after sunset when the animals leave their shelter to forage. Research agrees in so far as surveys early in the night were deemed the most successful with numbers declining later in the night. Observer fatigue could however also be a reason for this. (Thompson and Thompson, 2011)
Rain and/or wet foliage clearly decrease detectability as eye shine is harder to spot because of all the reflections through moistness. Possums are also more likely to stay in a shelter during heavier down-pours.
Very cold nights usually lead to fewer sightings and the same applies to very windy nights.
While Western Australian research could not determine a significant influence of the lunar cycle on detections, the numbers of common ringtails detected in South East Australia decreased during the full moon phase. (How et al, 2004) As this was associated with predator avoidance it might apply to western ringtails as well.
Our western ringtails are most prolific in residential areas; however, obtaining reliable numbers is almost impossible as private property can usually not be accessed and the animals have lots of hiding opportunities such as roofs. Estimates derived from spotlighting will most likely be far too low.
The most often used survey technique in scientific research is nowadays the so-called distance sampling – a technique based on the information-theoretic approach. It has become the widely accepted methodology for estimating population sizes (density or abundance). (Buckland et al, 2001, De Tores and Elscott, 2010)
Randomly positioned transect lines in representative habitat types are traversed and the study animals GPS-recorded along the way. Perpendicular distances from each animal to the line are measured and recorded accurately. The animal has to be detected with certainty and at their initial location. The average probability of detection in relation to the distance from the line also has to be determined using appropriate analytical programs. (Clarke, 2011)
This is completely out of reach for any non-professional researcher. Training requirements would also be far too intensive.
Proponents of the technique claim superiority of distance sampling over ad hoc techniques such as survey counts that only produce a figure for individuals observed; however in small patches of remnant vegetation and for small populations the method is hardly employable.
According to research into the value of distance sampling as a tool to estimate abundance of the other strongly arboreal Australian mammal – the koala - it turned out to be inferior to presence-absence sampling using scats in a low density koala population. "Results from this study highlighted the poor level of accuracy obtained from this method, particularly for low density populations, resulting in the inability to estimate koala population size with any confidence". (Mossaz, 2010)
In general, distance sampling seems to have a tendency to over-estimate while spotlighting counts usually under-estimate. The ‘fight‘ between researchers which method is superior is not helpful in the quest for the best possible information about a species at any given location.
Monitoring using camera traps is – at least in the long run - highly cost-efficient and less labour-intensive than other methods. (Welbourne et al, 2015)
It is an effective way of detecting the presence of a species and it provides a general index of abundance
Even though another study found that camera traps under-sampled small mammals compared with traps (Welbourne et al, 2015), this will not be relevant for ringtail possums as they rarely ever enter traps.
Camera traps are clearly advantageous for long-term monitoring projects, attempts to learn about some behavioural traits or presence/absence determination of an elusive species. The physical survey effort and the number of survey nights needed could otherwise be prohibitive.
Camera traps are also ethically superior to survey techniques that require the capture of animals unless handling (chipping, DNA collection etc.) is required.
Estimation of population sizes by camera trap is however very difficult and there are so far no published rules available.
No matter which monitoring tool is used, it always helps if the animal can be attracted to the trap or camera. Trapping (including camera trapping) seems to be more successful with lure/bait – no matter whether the animal can actually consume it or not – than without bait.
The literature distinguishes between bait and lure. My interpretation would be that a bait is to be taken (and is mostly poisoned) while a lure is only meant to attract animals to the location. However, the terms are often used interchangeably.
For an overview of species present, peanut butter and oats seems to be the universal bait which can also be used for ringtails. Surprisingly common ringtail possums could also be attracted by truffle oil and mealworms while bait without a smell was mostly ignored. In this research common ringtails were even recorded when the trap with the bait was placed on the ground. (Paull et al, 2011) Common ringtails might display less canopy fidelity than our western ringtails.
It is controversial whether bait used as attractant should be accessible to be eaten. I would argue that in that case you would attract the same animals more often (coming back for seconds) than if you use a bait holder which would let the animals smell and see it but not directly access or ingest the bait contained within. An empty bait holder as a control would show whether the animals are attracted to the object or just the smell.
If the aim is to monitor a specific animal, species- specific bait could reduce captures /photos of non-target species, e.g. lots of rats. (Paull et al, 2011)
Discussion:
It seems that in general and not only for ringtails, the most important issue is not the method of monitoring but the frequency, duration of the project, the documentation and reporting.
For ringtails released in the AWC sanctuary, Karakamia, monitoring every 1-2 years had been recommended (Clarke, 2011), so that changes – in particular decline – can be detected early. This however seems not to have happened. The rapid population decline at Leschenault Peninsula stayed unnoticed due to lack of regular monitoring. (De Tores et al, 2004)
Monitoring radio-collared animals gives the broadest range of information, however also carries specific problems, especially high costs, premature collar failure and animal welfare concerns.
Detection probability including likelihood of observer error is extremely hard to quantify, impossible for non-scientific personal. A good understanding of the species’ ecology and behaviour seems a major requirement, however for our western ringtails gaps in knowledge are generally severe.
