Surveys for Western Ringtail Possums
Hi all. I’ve been busy doing surveys for Western Ringtail Possum (Pseudocheirus occidentale) lately and while it’s not the key time for them to be active, sometimes you need to find out what’s happening at a site to help plan ahead.
I’ve often been asked by clients, what’s involved in doing a survey and how do I know that I’ve searched enough for a particular species. In this post, I want to discuss the methodology and survey approach I use to answer these questions.
Like most things in biology, there really isn’t any definitive answer, but there are guidelines for survey intensity and type of surveys required. These are put out by the Commonwealth Government via their Survey Guidelines for Australia’s Threatened Mammals (DSEWPC, 2011) and the Western Australian Government via their technical guide Terrestrial Vertebrate Fauna Surveys for Environmental Impact Assessment (EPA/DEC, 2010).
Designing a survey is very much dependent upon the animal being targeted. The Western Ringtail Possum is an arboreal nocturnal herbivore that can build shelters called dreys (made from leaves) or is found in hollows away from the coast. In a future post, I’ll put some information about the species and its range and behaviours, but for the sake of this post, I’ll focus on surveying for them.
The first step is to look at the site where we need to survey and determine if it’s likely to be in an area where the species is found. The species is generally found in coastal areas between Bunbury and Albany on the south west part of Western Australia. Most of the time, when I’m contracted to survey for them, it’s because the site is within their known range. This is particularly the case in the Busselton to Dunsborough areas and surrounds.
Next is to plan for a day time (diurnal) search of the site to look for potential suitable habitat resources or signs of the species. With ringtail possums, they dreys are usually easily to find as long as the canopy allows for visual inspection. The other signs can include their scats and occasionally their fur.
These day surveys are best conducted along transects spaced at 50-100 m intervals in the areas of likely habitat. The speed of this approach varies according to the landscape being surveyed and the density of the vegetation, but the Commonwealth guide states that a suggested survey effort is for a smaller site (i.e. less than 5 ha) is two hours for every hectare.
In conducting the survey, it’s important to keep records of habitat type, and any signs found. Occasionally animals can been seen resting in their dreys. The location of these data need to be recorded. In Ecosystem Solutions, we use a Trimble Juno field computer loaded with ArcPad GIS software to record locations as well as the path of the transects followed.
Once the diurnal survey has been conducted, we have a better idea of the habitat areas and any signs of the animals within the particular site. Its time now to do a nocturnal survey using a spotlight. Spotlighting is a survey method that is used to detect nocturnal species while they are active.
This type of survey is done in a similar manner to the diurnal survey except that a spotlight is used and the survey is conducted at night. At Ecosystem Solutions we also use a head torch to light the path we are walking as well as assisting when the vegetation becomes too dense and a spotlight is not as effective. Ideally the spotlight is held at a level close to the observer’s eyes, to enable eye shine from an animal to be detected.
The distance that the species can be seen in these types of surveys varies depending up on the nature of the site itself and the surveyors’ experience. Previous studies has shown that observations are effective up to 50 m from a transect line, providing the canopy allows a clear line of sight. This means that 100 m transects are optimal, allowing for minimal overlap providing the vegetation canopy allows for that distance of visibility.
Weather condition are also know to influence the success of spotlight surveys, therefore we are careful to not conduct surveys in extreme temperature, or high rainfall or windy nights.
The approach is basically to use a hand held spotlight of approximately 30 watts power (can be up to 50 in tall forests). This allows detection without causing undue stress on the animals. More powerful spotlights can result the animals looking away from the light making them difficult to spot.
The spotlight should be held near the observer’s line of vision to maximise the chance of detecting eye shine (that is the light reflected from the animals eyes). By moving the spotlight beam at a slow consistent speed over the habitat areas, eye shine should be seen if the animal is present. Once eye shine is seen, binoculars should be used to confirm the species and to record any distinguishing features (sex, approximate age etc.).
The guidelines suggest at least two 200 metre transects be used per 5 ha site, with the transects selected to target the appropriate habitat areas or areas identified as likely habitat from the day survey.
The suggested speed is 10 metres per minute, hence a 1,000 m transect will take 100 minutes (1 hour and 40 mins).
The WA Department of Parks and Wildlife recommend at least two of these surveys be conducted, over non-consecutive nights, to enable a better picture of the numbers and key locations of the species to be determined.
Care needs to be taken to not shine the spotlight for too long on any individual animals or using too narrow a beam once an animal has been located. This is to ensure that the animal’s vision is not impacted as a result of the survey.
This is a very broad and rough summary of how we plan and conduct surveys for western ringtail possums. For other species, some of the details will change, however the principles are the same.
If you need any advice on surveying for ringtail possums or any other western ringtail possum issues, don’t hesitate to give me a call.
See you next post….cheers Gary
Note if you want the references to this post, give me a yell…