Apart from a lot of anecdotal evidence of deer in the Cardinia Creek catchment, little is known of the current situation of deer in these valleys. We all hear of increased sightings, gardens destroyed, orchards trashed, farmers’ livelihoods impacted, deer collisions on the roads and environmental damage in our bush.
The Cardinia Deer Management Coalition (CDMC) was established because of concern for the impact of deer locally and with the intent on doing something about it. One of the ways we have been doing this is to facilitate efforts by local landowners who would like to control deer on their properties. However, a frustrating issue we have is not knowing how many deer we already have nor exactly where they are. This makes it difficult to know whether all the effort locals expend in controlling deer is likely to be effective or not.
To find this out the CDMC applied for a Federal Government Environmental Wellbeing grant to conduct an aerial survey of the catchment. We were successful, with the government committing $22,000.
Why an aerial survey?
There are many different types of survey available, including vegetation surveys, camera trap surveys, faecal scat monitoring, direct observation, deer damage observations, even monitoring motor vehicle insurance claims. (For more on these surveys, see Deer survey techniques, in this section.)
We chose an aerial survey as it enables us to get a quick result over a very large area of difficult terrain. Camera trap surveys were also considered, however they can be difficult to set up, requiring expertise we don’t currently have and they can be very time consuming in maintaining the network of cameras and processing the images. We may well use them in the future however, in small targeted areas.
The survey design and analysis is being done by Dr Tarnya Cox and the flights will be conducted by Heli Surveys. Tarnya Cox is a Research Scientist with the Vertebrate Pest Research Unit of the NSW Department of Primary Industries and has done numerous thermal imaging surveys, including some for DELWP in Victoria.
Heli Surveys (https://www.helisurveys.com.au/thermal-surveys), likewise, have extensive experience in this field, including in New Zealand and a recent deer survey in a periurban forested area on the outskirts of Brisbane. The desired outcome is the plotting and counting of deer in representative areas of the catchment. This should allow us to calculate the overall population with a reasonable degree of accuracy and provide a better understanding of the major congregation areas of deer and their preferred habitat.
Understanding the total deer population is vital to help us understand firstly the scope of the problem and the level of control measures that will be required to reduce their population. Secondly, our aim is to repeat the survey at intervals to see if the control measures being used locally are achieving a reduction in numbers. And thirdly as an aid in gaining an understanding of the relationship between deer density and environmental damage.
The survey will take place between Menzies Creek / Clematis in the north to Inglis Road in the south and from Narre Warren East / Harkaway in the west and Dewhurst / Officer in the east. The helicopter will fly along a series of approximately 20 transects and take two to three hours. There may be a small component of drone survey performed at night.
The timing of the survey will depend on the weather, and of course Covid-19 may yet throw a spanner in the works. At the time of writing, the expected timeframe is during the last week of July, however this could extend out by four to six weeks.
The helicopter, crewed by a pilot and camera operator, is equipped with both a high resolution, high refresh-rate thermal imaging video camera and a normal video camera which are aimed to the side. These capture a continual image as the helicopter moves along predetermined transects at a height above ground of approximately 150 metres. (To see a video of the efficacy of a thermal compared to an ordinary camera, check out the Heli Surveys website.)
The transects are parallel and about 500 metres apart, ensuring animals do not get counted twice. The line of the transects are designed to get a representative cross section of the habitat types across the valleys, while avoiding flying near or over houses where possible.
The flights are normally carried out around dawn and dusk and preferably in the cooler months. This enhances the ability of the thermal camera to pick up the contrast between the heat signature of the animal against a cooler background and, for deer, the animals are more likely to be actively foraging for food at this time. Sometimes these times are not possible, especially in more populous areas, as pilots are reluctant to fly close to houses in the very early morning.
If a drone is used, these usually fly lower and slower and mainly at night.
Once the flights are complete, the data from the cameras will be downloaded and the analysis will be undertaken to determine and plot the locations and numbers of deer and other species. These results may then be used to determine an estimation of the total deer population across the catchment.
Although the camera technology has improved markedly over the past few years, it is not yet possible to reliably differentiate between fallow and sambar, but will be able to differentiate between deer, farm animals and marsupials such as kangaroos, wallabies and wombats. We believe we will also be able to identify koalas in the canopy in what may well be Cardinia shire’s first ever koala survey!
If you have any questions or would like further information about this survey, please email the CDMC on: email@example.com
The truth is that we don’t really know much about deer in Australia. We know roughly where they are, we know what species there are and we know a bit about their biology. They have been a sleeping giant but were recently described in NSW as probably the greatest emerging feral threat in Australia. It all seemed to come out of the blue, because they have been here since the 1860’s. And because they seemed harmless, not much study has been done on them. That is changing now as a number of groups and universities are joining together to find out what we are up against, how much damage they are doing and how much worse is it likely to get. Environmental scientists have been raising concerns for years, but the recent change seems to be largely to do with the fact that deer are coming out of the bush and into farms and private properties and on to our roads. They can’t be ignored any more. The Cardinia Deer Management Coalition are keen to be involved in research into deer for a number of reasons. Firstly we would like to know how many deer are in our valley, what their distribution is and how they move through the landscape. Where are their refuges. And this for each of our two species: fallow and sambar. Knowing this will give us an indication on how many deer will need to be culled annually before their numbers start to decline. Secondly, we would like to know how much damage is being done. Anecdotally the amount is huge. This information comes from scientists and rangers in DELWP, Parks Vic, from Melbourne Water employees and from the Landcare networks and farmers. But it is yet to be quantified. How many plants and of what species are being eaten out, how many are under threat? Is regrowth being destroyed faster than it can recuperate? Thirdly we need to be able to monitor whether the deer numbers are increasing or decreasing. How do we do this? There are a number of techniques ranging from the use of camera traps, to radio tracking, to assessing damage caused by deer to monitoring faecal counts. Currently Melbourne Water are monitoring a trial in the Dandenongs where they are comparing an open area to a deer exclusion area (native herbivores can get in) to a total herbivore exclusion area. Hopefully the results of this will be coming out this year. DELWP have recently been conducting a trial of aerial (helicopter) shooting in the Alps to see whether it is efficient and cost effective. This data is being reviewed at the moment. The CDMC are currently discussing with local councils, Parks Vic and Melbourne Water the feasibility of conducting aerial surveys in our valley. This is a fairly new area with respect to deer, but hopefully something might come of this. CDMC hope in the future to get involved in some form of Citizen Science, where our community gets to help collect the data that might help us to save our environment. Watch this space. The future of deer control? It is widely acknowledged that hunting deer will at best slow the progress of the deer invasion. Even with the past and proposed changes in legislation relating to the hunting of deer we are not likely to get close to culling the about 45% per annum we need just to keep the numbers static. Scientists from a number of sources such as the various universities, Arthur Rylah Institute, Invasive Species Council, Centre for Invasive Species Solutions, DELWP just to mention a few, are researching into various aspects of the deer risk and potential methods of control. The goal of any animal vertebrate control programme is that it should be humane, effective, efficient and affordable. The two emerging technologies currently gaining most press coverage are targeted poisoning and genetic control. Of the two, targeted poisoning is closer to potential use, but still has a few hurdles to jump. Genetic controls are in their infancy and likely to be 10 or more years away.