Habitat
No living being can exist without suitable habitat. However, the term ‘habitat’ is often used without clear definition. Habitat for ringtails is more than just a few trees.
The entire range of present resources and conditions and their interactions form habitat. (Richardson et al, 2015, Chauvenet et al, 2015) Vegetation and its role as provider of food and shelter, predators, parasites, competitors are all part of the complex web that forms a specific habitat. (Chauvenet et al, 2015, Armstrong and Ford, 2015)
Even though our ringtail is a highly specialised feeder, it survives in a wide range of habitats – woodlands, forests, urban areas – and their highest numbers seem to occur in the urban or peri-urban context and on private land and not in the so-called conservation estate.
Land conserved by government agencies was usually not selected because of its high habitat values but because of the lack of more lucrative uses such as farming, logging or mining. However, it is not very likely that these residual areas could make a major contribution to the conservation of species.
Those areas with high habitat values for ringtails are too lucrative for protection no matter how critical they would be for the survival of this endangered species.
Protection of areas with low habitat values gives a false impression of progress in biodiversity protection as we equate the number of protected hectares with a high number of surviving animals while it might only be enough for a very limited number to survive. (Pressey and Ritchie, 2014)
The mere protection of an area without any further actions like predator control will also not stem the loss of biodiversity.
While National Parks, Nature Reserves and State Forest have the advantage of secure tenue, private land and even suburban areas that are intensively used by humans can play an important role in biodiversity conservation and can provide adequate habitat for western ringtail possums.
Shedley identified areas of remnant vegetation that contained suitable habitat but found that only 6.6% of the pre-European extent of ringtail habitat remained and of that 0.86% was contained in secure conservation estate. (Shedley and Williams, 2014)
After the devastating fire that badly affected Yalgorup National Park, this will have further reduced and now only the Tuart National Park and Locke Nature Reserve contain fairly high numbers of ringtails while numbers in and around the Perup Nature Reserve seem to be very low.
It is also questionable how secure this conservation estate really is as not all of it is for instance exempt from prescribed burns that can – as happened in the case of Yalgorup National Park – get out of control and damage what they set out to protect.
However, most occupied areas dominated by the preferred peppermint tree (Agonis flexuosa) occur outside reserves or National Parks anyway. (Jones et al, 1994a)
A common feature of all occupied sites apart from coastal areas is their association with creeks, swamps or drainage lines. (Jones et al, 1994a) Dominance of peppermint trees (apart from in some inland areas) and good canopy connectivity are other main features.
Currently there are 2 broad types of habitat available for ringtails: woodland/forest and urban/peri-urban areas.
Woodland/Forest
Fertility of the soil in south-western Australian forests and accordingly the nutrient concentrations in the dominant tree species are very low. (Wayne et al, 2005)
The most fertile and productive alluvial soils close to waterways could have supported high numbers of ringtails, however logging and clearing for agriculture have decimated high value habitat drastically and this selective clearing also caused extensive fragmentation of remaining potential habitat. (Jones et al, 1994a)
Soil nutrients and moisture gaining and retention capacity are low in those areas that are not good enough for agriculture. This lowers food quality and limits carrying capacity.
If the animals are restricted to pockets of peppermint-dominated habitat with high connectivity, events like fire (prescribed and wild) and predation can quickly lead to unsustainably low numbers. (Clarke, 2011)
There is agreement that canopy connectivity is of major importance, maybe of greater importance than vegetation density or canopy cover, however this would depend on other habitat values such as food quality and predation. (Shedley and Williams, 2014)
Perup which has only low canopy continuity (Jones et al, 1994a) seemed to the exception from the rule, however the area suffered the largest decline in ringtail numbers.
If canopy continuity is lacking, the animals will have to decent more often to the ground and travel farther on the ground which makes them highly vulnerable to predation. (Jones et al, 1994a, Clarke, 2011)
Ringtails translocated mainly from urban/peri-urban development areas to woodland can clearly adapt to other food sources even if they originated from an almost exclusive peppermint habitat. Judy Clarke showed in her research that ringtails tend to utilise the predominant vegetation strata – be it peppermint, mixed peppermint-other vegetation or myrtaceous dominated patches. (Clarke, 2011)
Translocation to non-peppermint areas (Karakamia, Perup) seems possible but if the population survives, densities stay very low (see translocation).
Urban / Peri-urban
Regarding population growth and ensuing development, the coastal stretch from Dunsborough/Busselton to Bunbury is one of the fastest growing areas in the whole of Australia. Decline of ringtail habitat in our backyards particularly through infill subdivision of old large lots is accordingly steep. (Jones et al, 2007)
Nevertheless, the greatest ringtail population density can currently be found in this Bunbury to Dunsborough coastal strip. (Shedley and Williams, 2014)
There are a few advantages to a life in our urban backyard: there are a variety of eatable plants in addition to from peppermint, backyard plants are often well watered and fertilised and some people even hang water containers into trees for possums in summer or provide boxes as shelter.
With some effort we can clearly sustain a species in our artificial ecosystems.
However the disadvantages are just as pronounced: gardens rarely ever have touching tree canopies and ringtails have to come down to the ground to travel from one tree to the next where a significant number of pets are roaming free – some of them day and night.
Food is rarely plentiful and most often not adequate for a specialised folivore. Exotic plant species now outnumber native plants in Australia and our gardens are rarely dominated by natives.
Fence lines and roofs make good walkways, but fences are often not high enough to be secure and as ringtails –unlike cats – cannot retract their claws and therefore sound far louder on a colour-bond roof than their size would warrant, are often unpopular as they cause nightly disturbances.
Every simplification of habitat could from a ringtail’s point of view be seen as degradation. The pruning (to death) or removal of trees below powerlines or the compaction of soil (e.g. paving around trees) and light or noise pollution are just a few examples.
Some of the valued (by ringtails) food resources in urban backyards are for instance: New Zealand Christmas tree, blue ceanothus, lilly-pilly, wisteria, roses, geranium, grevillea, wattle (such as flinders ranges), bottlebrush flowers and very fresh young shoots and leaves of peach trees and (preferably older leaves of) apricot trees. Their favourite food – Agonis flexuosa – is becoming rarer as our backyards get smaller.
Urban consolidation favours units or small lots that cannot accommodate mature trees and the lack of any tree retention program let alone any compliance monitoring and enforcement for those few residential lots with some environmental measures in place (e.g. building envelops) leaves hardly any chance for longer term persistence of ringtails. Tightening of fire regulations and a ‘one rule fits all’ approach adds to the problem.
The importance of urban public reserves for ringtails is well documented (Harewood, 2008), however, the management of dogs in public spaces is currently redefined in Busselton and there is a push towards opening up reserve areas for unrestrained dogs (dog exercise area) as a trade-off for some dog-free beaches. Particularly in the hot summer months, ringtails sheltering in the sedges under trees in some locations are at risk of dog attack.
Reserves and Public Open Spaces for new subdivisions seem to be created only with human interests and needs in mind.
The City of Busselton’s almost compulsive urge to clear all ground cover – preferably with big machinery that demands wide spacing between trees and no connectivity of vegetation – adds to the significant risk of predation and/or heat stroke in summer.
The assumption of Shedley and Williams that dense understorey may not be particularly important to ringtails if the upper canopy is continuous and provides adequate food resources and protection because some small urban reserves with only grass or degraded understorey still have a high density ringtail population (Shedley and Williams, 2014) is puzzling.
Firstly, continuous canopy is very rare in Busselton/Dunsborough reserves but secondly the severe shortage of acceptable habitat will necessarily lead to overcrowding of any area that provides some food and protection.
The City owned Kookaburra Caravan Park in Busselton has been a prime example of an area overrun by ringtails to a degree that they overgraze and eventually kill the most palatable mature trees – if they were not removed when they become dangerous for campers. The high numbers were not a testament to the great habitat but to the extreme lack of any good habitat in that area.
The population has suddenly halved in 2016 after two dry winters.
Dense understorey is also particularly important in our hot summers and the number of animals suffering from heat stress will increase with decreasing density of understorey.
In the above mentioned assessment very high ringtail densities were found in the smallest patches while larger patches contained higher numbers but at lower densities. (Shedley and Williams, 2014) Habitat quality is clearly the key to ringtail perseverance not size of the area. However, the areas with formerly large stretches of habitat and mature vegetation are lucrative for subdividing and only the tiniest patches remain. Dispersal opportunities are very limited due to fragmentation. If there is nothing suitable close-by, the resident population will remain and fight it out.
We however completely agree with the authors’ conclusion that retaining small suitable remnants of ringtail habitat is of crucial importance and that their long term sustainability is questionable unless they are linked to other habitat patches. (Shedley and Williams, 2014)
In important areas with unavoidable fragmentation, those links are often provided by planting corridors between separate areas of habitat. As new plantings will take years to mature and become true habitat and as those strips are usually too narrow to ever provide breeding habitat, it is questionable how effective these actions can be.
Those peri-urban habitat areas close to the town sites of Busselton/Dunsborough with soils that support the best food but without the extreme limitations and dangers of suburbia might be the most important for ringtail conservation and the area around Locke Nature Reserve (Siesta-Kealy area) seems to be the best researched and with the largest current population.
A huge advantage of this area close to the Busselton town side is that peppermint stands here had only low fire impacts over the last up to 6 decades and mature trees are retained.
Highest ringtail density can be found in those ‘older-growth’ areas. (Jones et al, 2007)
Opposite the Nature Reserve which seems to be rarely used by humans, there is a long stretch of camp sites. Ringtail density is high everywhere.
If the food supply is plentiful and of high quality, ringtails do not travel far and are unwilling to come to the ground. Kaori Yokochi observed this highly sedentary behaviour and a high fidelity to canopies in the nature reserve and the camp sites alike. In the camp areas the animals tended to remain in clumps of trees with continuous canopy. (Yokochi et al, 2015b)
Even narrow cleared stretches such as fire breaks limited the animals’ movements. Yokochi attributed the avoidance of crossing roads to the lack of canopy connection not to environmental issues such as noise or light disturbances. (Yokochi et al, 2015a)
These observations are in contrast to findings that even isolated trees sometimes have ringtails in them. (Shedley and Williams, 2014)
As some mature ‘paddock trees’ will provide good food, the need to feed might however override the unwillingness to come to the ground and even the fear of predators. If the spacing of trees is not too wide, they could also have a stepping stone function to get from one habitat patch to the other. (Gleeson and Gleeson, 2012)
Habitat suitability model
To be able to develop an effective strategy to conserve any threatened species we need to know which factors drive occupancy of habitats and survival of animals. If a species occurs in a variety of unconnected and ecologically diverse areas, the extrapolation of knowledge from one location to another can lead to errors that might undermine the conservation effort. (Bain et al, 2015)
Western ringtail possums occur in coastal areas in the west (Busselton) and the south (Albany) in addition to in inland habitats such as the southern forest (Manjimup). The habitat features of importance could be different for all 3 locations.
Some features such as predation might be comparable in all 3 regions however the effect on the species could still be different due to differences for instance in shelter availability and canopy connectivity. A habitat suitability model developed for one of the 3 regions that is then extrapolated to other regions might have a negative instead of the intended positive effect on the conservation of the species.
