Post-release feeding

A study about rehabilitator releases of ringtail possums in the eastern states states that often feeding was provided at least for the initial acclimatisation (1–2 weeks after release) but in some cases long-term and in situations such as drought.  Food provision was also the most common tool used for post release monitoring.  (Guy and Banks, 2011)

Feeding appears particularly important for relocated/released prey species. They can settle in far quicker as the pressure of finding food is reduced and familiarisation with the situation including the presence of predators is the only fundamental stressor.

Western ringtail possums from a care situation are used to being fed and being provided with the carer’s choice of leaves. Captive animals cannot in the true sense forage and their behavioural patterns (including feeding) are necessarily very different from those of free ranging animals. (Ellsworth et al, 2013)

Food resources on site might also be different to those formerly provided and adaptation could be slow. Weight loss, an aspect in early mortality figures in translocation research, is less pronounced when food is supplemented and the provision of food in one area (the release spot) is also likely to reduce wide, immediate dispersal – another factor in early mortality figures. 

A review of a wide range of studies investigating  effects of supplement feeding summarised the following results:

However, populations responded to supplementation more frequently and more significantly when conditions were poor than when they were fair or good and the supplementation did not influence the pattern of population dynamics.
The supplementation only resulted in parameters otherwise seen under good environmental conditions even though in reality, without outside help, conditions would be rated as bad. 
Consistently in all experiments food supplementation alone did not prevent major declines as they were based on a suit of issues and even with  presumably unlimited food supply populations did not steadily increase over saturation levels. (Boutin, 1990)

We only substitute  food in the early establishment stages until  the animals have settled in and do not come back nightly – or do not rest in the cage throughout the day  and feed before they move out to explore.  Supplementation would be worthwhile and valuable in drought conditions but then food in adequate quantities is unavailable to us. (also see 'Releases by carers/rehabilitators'; 'Habitat discussion')

Individuals and populations are ultimately limited by the food supply. The value of the food supply and its nutritional limitations can hardly be tested for every new release site.

Captive feeding experiments with browse from a prospective site could give some insights as the measure of intake would prove the suitability and digestibility (toxins) of the leaves. However, captive animals react differently for various reasons (e.g. reduced need due to reduced activity levels) and a freely browsing animal would eat the young tips in the tree canopy which we cannot reach and collect. Leaf quality also varies between trees and rejection of browse collected from one tree does not mean the quality at the release site is generally low.
Drought can also change the overall quality of browse and if no breeding/weaning quality food is available, populations can decline quickly even in habitats with large viable populations.

If the provided food is the main nourishment for releases for months, the habitat is clearly badly chosen and the introduction will most likely fail. In spring provided food is usually ignored quickly by the new releases as the fresh, natural browse is available.

Snow hare research found that food supplementation in a well populated area can cause immigrants to move into the new release area and can lead to either wider distances being travelled to reach this additional food or to competition with the newcomers and takeover.  (Boutin, 1990)

A study examining  behaviour in voles found that females allowed increased overlap of home ranges with extra food as long as the supply was plentiful but defended exclusive areas aggressively as soon as the food was in shorter supply and dominant individuals then attempted monopolizing the food source. (Boutin, 1990)

We so far know very little about the social behaviour of western ringtails and how resources are allocated among individuals. Resources might be made inaccessible to some members of the release group/population.  A dominant female’s home range overlaps with that of males and her dispersed recruits, however whether supplement feeding would lead to acceptance of a larger resident population is impossible to distinguish without being able to identify all or most individuals. Some of our footage hints at similar behaviour to the descriptions above though.

Food supplementation itself or the frequent appearance of prey species in one particular spot (the feeding station) could attract predation and that way make the individuals receiving food more vulnerable.

We almost exclusively limited supplement feeding to peppermint as this is not a preferred food source for common brushtail possums. A possible influx of brushtails which then tend to evict ringtails would be highly counter-productive. However, in late summer brushtail possums seem to move into ringtail dominated peppermint areas as other food sources get scarcer.

Another important benefit of food supply is the Increased detectability of animals. Cameras can be placed strategically and the likelihood of sightings increases many-folds.

The ultimate goal of any release project is a self-sustaining  population. However, the argument that food supplementation therefore counteracts this goal is weak at times when provision of predator proof fenced enclosures seems the only option of survival for prey species such as western ringtail possums.  Short-term or emergency (severe drought) food supplementation is still less labour-intensive and cheaper than this extremely expensive intervention which necessitates constant management and creates a myriad of long-term issues. (see "Sanctuaries") Populations relying on this level of management are not truly self-sustaining either.

We cannot determine the home ranges of our animals but for those few we can recognise we can say that they stayed in the release vicinity, retained a good body condition (subjective) and bred/raised offspring. It is highly doubtful that we achieved this exclusively by supplement feeding in the early stages.

use of lures