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Damage caused by deer and evidence of deer
Deer are damaging and destroying some our most fragile and unique natural assets from the coast to the highest mountains. The Australian environment and natural ecosystems evolved in the absence of heavy hard hoofed animals (ungulates) and are therefore have not adapted to be resilient to these severe impacts.
Feral deer are now present in nearly if not all the national and state parks throughout the Victoria. Of particular concern is the impact they are having on Australia’s iconic Alpine Sphagnum Bogs and Associated Fens which are listed as endangered under the Environmental Protection and Biodiversity Conservation Act 1999 and listed as the threatened Alpine Bog Community under the Victorian Flora and Fauna Guarantee Act 1988 (Image 15).
Deer are potentially impacting Aboriginal cultural heritage sites and becoming an increasing problem in peri-urban settings.
Deer are also impacting grazing land, orchards, vineyards, dairy farms, pine plantations, pastures and market gardens (ISC 2023) and particularly when in large numbers, can severely impact agricultural land and productivity, and native bush through a range of activities including:
- Selective overgrazing of native plants: While deer are generalists that browse a wide range of plants, they also selectively over browse (often to the ground) preferred species, seedlings and saplings when they can find them (Image 1);
- Causing overgrowth of some native species: Deer find some plants such as Burgan Kunzea leptospermoidesunpalatable which can lead to unchecked growth of Burgan which provides harbour for deer (Image 2);
- Browsing: Deer have lower teeth which close on a hard upper gum plate with no upper teeth (Image 3). When they browse woody shrubs they leave a tag as they tear rather than bite vegetation. Evidence of deer browsing includes ragged torn stems and branches and browse lines on woody shrubs (Images 4 to 7);
- Over grazing: of a range of pasture grasses and native forbs and grasses;
- Damage to trees and shrubs: Tree bark stripping, stem breakage and shrub damage and destruction of foliage from antler rubbing to remove velvet and to scent/mark trees (Image 8, 9 & 10);
- Vegetation destruction and clearing: through stags fighting, thrashing vegetation, clearing vegetation and pawing and repeated urination in soil around selected trees (preaching trees). Deer stand on their hind legs and rub scent as high up as possible on preaching trees from glands on their head to attract females and ward off other males during the breeding season (referred to as the rut) (Image 11);
- Vegetation trampling: in bedding sites where leaves and litter are flattened and vegetation crushed;
- Soil disturbance: caused by:
- Creation of wallows (a depression containing mud, deer urine and often water created by deer rolling and trampling) used by Sambar and Red deer in Victoria, during the rut, results in soil disturbance, vegetation destruction, water fouling (from urine and faeces) pugging and unstable soil prone to soil erosion (Image 12, 13 and 16);
- Pugging (when wet soil is churned up and pushed down by hard hooves of heavy animals) particularly around and along the banks of creeks/streams, drainage lines, lakes and dams, preaching trees and rutting areas (Image 14 and 15). This results in vegetation destruction, soil compaction and in turn reduction in soil structure affecting plant root, water and air penetration. This can cause increased risk of erosion and opportunities for weed invasion. It can also reduce water quality due to dislodged sediments entering the water;
- Creation of tracks resulting in vegetation destruction and removal, soil compaction, and pugging (Image 15 and 17).
- Erosion and downstream sedimentation from wallowing, pugging and vegetation destruction;
- Potential spread of weed seeds: (e.g. English Broom) and propagules on land and in waterways, carried on fur, hooves and in droppings which may also invade bare ground created by deer;
- Increased nutrient load and potential spread of pathogens: from urine and faeces deposited on land and in waterways causing fouling of waterways and impacting water quality. Pathogens in deer faeces can contaminate and affect water supplies (HWS 2023).
- May provide vectors for the spread of livestock diseases: such as Foot and Mouth Disease posing a biosecurity risk for agriculture. The Australian Government Department of Agriculture, Water and the Environment (now the Department of Agriculture, Fisheries and Forestry) is funding a study titled ‘The role of wild deer in the transmission of diseases in livestock’ by the Centre For Invasive Species Solutions (2023), for updates go to: Transmission of diseases by deer; and
- Deer are increasingly becoming roadway hazards in both regional and peri-urban areas (Image 18 & 19). See the Invasive Species Council Website for videos of deer on roads.
Economic costs for the community
There are few if any studies that detail the economic costs of deer impacts on agriculture until recently when the Invasive Species Council commissioned Frontier Economics to produce a report on the economic, social and environmental cost of feral deer in Victoria titled: ‘Counting the doe: an analysis of the economic, social & environmental cost of feral deer in Victoria’ (FE 2022) which was released in June 2022 and is available at: Counting-the-doe-the-economic-impacts-of-feral-deer-in-Victoria. This report provides the latest detailed breakdown of economic, social and environmental costs of feral deer in Victoria. The key points of the report include:
Without adequate control, it is estimated that deer will number between 1.7 to 4.6 million deer by 2050.
Estimated costs to the broader community from unchecked feral deer over the next 30 years is estimated to be from $1.5 to 2.2 billion and broken down to:
- $245 m to $350 m in economic costs from lost gross margin due to grazing (assuming 10% of feral deer are grazing thereby reducing stocking capacity and therefore farm income).
- $106 m to $144 m in economic costs from resources spent managing feral deer (based on the assumption a farmer spends 20 days a year managing deer on their properties).
- $269 m to $365 m in economic costs from lost forestry production (assumed loss from feral deer grazing and trampling).
- $576 m to $825 m in economic costs from deer-related vehicle accidents (assumes all future feral deer related crashes on highways within Victoria can be avoided).
- $308 m to $474 m in social costs from reduced recreation, amenity and use values due to environmental degradation and deer-related accidents and safety concerns (assumes that Victorian national and state parks recreational use will be impacted by 1% due to feral deer).
The estimates amount to billions of dollars and do not include additional costs such as:
- Other costs of management (e.g. cost of materials and equipment such as fencing).
- The cost of water supply due to the need for increased water quality treatment (deer carry the parasite Cryptosporidium sporidiumand they are in greater abundance in water supply catchments than other host species).
- The risk of the spread of disease to humans, livestock and other animals.
- Negative impacts on indigenous cultural heritage through environmental damage.
- Negative impacts on biodiversity and restoration works.
- Negative effects on river and waterway health.
Therefore it is likely that the true economic, social, cultural and environmental costs imposed on the community as a result of feral deer in Victoria will be larger than the current estimates.
The analysis suggests that the cost of eradication all feral deer in 2022 could be $338 m to $581 m which is around a quarter of the cost of the potential benefits. The sooner action is undertaken to control deer, the lower the cost will be (deer numbers will continually increase requiring greater resources if control is delayed) and the sooner farmers will benefit.
On ground agricultural impacts of deer include repeated damage to farm infrastructure such as fencing (Image 20), harassment of stock, erosion of tracks under fences, extensive browsing of crops (Image 20) and pasture in competition with stock has been noted (Claridge 2016). One winery in Panton Hill, Victoria lost an entire Chardonnay crop in one night just after fruit set and heritage apple trees were damaged (FE 2022). Pasture may be destroyed through the creation of wallows turning grassed areas into mud.
