Survey techniques used for monitoring deer and deer damage – a brief summary

Monitoring deer – the what, the where and the how (many).

Australia doesn’t have a lot of data on deer. Until now we haven’t really needed it. Deer numbers were small. They posed no threat to primary producers, no threat to the environment and the native animals who live there, no threat on our roads.

But in the last few years this has changed. Their numbers have increased exponentially and now we are beginning to see just how destructive they can be.

So now the scientific community are playing catchup: how many deer are there? What species are there and where are they? How do they move and behave in the Australian landscape? What do they eat, what weeds do they distribute, what effect are they having on our waterways and peatlands, what diseases do they carry, and pass on, … there is a long list of unknowns, few knowns.

Government agency and environment groups are becoming increasingly active in their efforts to gain some of this data. Below is a precis of some of the more common methods being used:

Animal surveys:

Camera-trap surveys

Camera traps are motion and/or infrared sensitive cameras which are strategically placed and left in situ to take images of animal movement in their vicinity. They are usually left in place for periods of weeks, after which their images are downloaded and visually assessed for species types, numbers and locations.

Camera-trap surveys will usually be trying to ascertain one of three types of information:

Relative abundance

• Easy, relatively cheap
• Checks for population change over time ie long-term studies
• Prone to error and miscalculation

Occupancy

• More complex
• For emerging populations
• Calculates % of area inhabited, not numbers of deer

Density

• Highly complex, much more expensive, requiring complex statistical analysis
• Measures the number of deer in a given area ie stocking rate
• Good for determining the impact of control measures
• Better suited for smaller sized sites

Advantages

• very effective
• easily repeatable
• can use citizen science
• cheap in the long term, especially if citizen science is engaged
• good for smaller populations and denser forests

Disadvantages

• need good cameras (>$300 each) and a lot of them, sometimes 60 or more
• initially expensive, especially for larger areas
• visually processing images is very time consuming and can exhaust volunteer enthusiasm

Future

• visual recognition software almost at the stage where it can identify individual species which will aid in processing images. This will significantly reduce cost/time & volunteer fatigue
• within camera IT becoming available which can communicate when species are present remotely and either send an alert or close an enclosure gate etc

Aerial surveys

Aerial surveys are done either by helicopter or drone. Helicopter surveys can be either manned (ie. visual only), use infrared cameras or both infrared & visual; drone surveys use infrared cameras only. Drones can be either the vertical or horizontal launch types.
Surveys are normally done at dawn or dusk when the deer are more active and come out of the bush. This also allows better differentiation between the heat signature of the animals and the cooler background. Sometimes this is not possible in more populated areas due to concerns of disturbance, and surveys may need to be extended into the mornings and afternoons.

The data gathered is then assessed and mapped to give an indication of the location and density of the deer population. This is increasingly being aided by species recognition software.

Aerial surveys are becoming increasingly popular as their costs decrease and the technology improves.

Advantages

Helicopter over drone:

• more economic over larger areas
• can be manned and therefore allow visual comparison to the IR camera
• better over hilly country
• tend to disturb animals and cause them to move, allowing greater chance of seeing them through denser canopy
• cover greater area in a shorter time

Drone over a helicopter:

• they can fly lower and closer to houses; good for more populated areas
• cause less disturbance to land owners

In general, aerial surveys are of greatest benefit over large areas, with large numbers of animals and with open vegetation.

Disadvantages

• drones, by regulation, must fly within line of sight of the operator. This means multiple sites will be required in hilly areas, meaning one survey with helicopter the survey may take several days of work with a drone. This can increase costs markedly
• helicopters especially can be noisy and greater care must be taken around built-up areas
• not reliable yet in differentiating deer species
• cost – neither are cheap, though, because less working hours are required in set-up and monitoring, they may well prove competitive over time. At the moment the costs of helicopters and drones is similar, though very dependant on topography, tree cover and residential density. Drones are becoming increasingly competitive though due to improving technology

Future

• IR camera technology is continually improving, resulting in better definition & image refresh rates, allowing better species recognition and faster flying speeds
• Improvement in drone technology is allowing better control & the transport of heavier equipment over longer distances.
• Drones are getting cheaper, decreasing overall costs
• Species recognition software is continually improving, allowing better identification and separation of species

Direct visual surveys

Just what it says – simply people observing deer in their own surrounds, logging the data, including date, time & location and other observations. It can be with or without binoculars or, if after dark, with a thermal imaging scope.
With proper scientific input, this data can be quite valuable. Not all surveys require advanced technology nor large amounts of expertise. This makes visual surveys a good mechanism for engaging the community.

The DeerScan app is an example of a direct survey technique, where members of the community can use the app to record sightings of deer. These records can include other signs of deer as well, including finding deer scat, wallows, tree rubbings or even hearing deer. CDMC are registered as a Group within DeerScan. For more information on DeerScan and how you might be able to help us monitor deer, read the article on DeerScan under Get Involved on our website.

Some other methods of recording animal sightings, including deer, is the Atlas of Living Australia or iNaturalist, which are available free to all.
Radio trackingWhat are theyThis requires the placing of a radio tracking device on each animal. The device emits a signal which can then be used to locate the animal. Some of these need to be tracked using a hand held aerial, whereas others can be picked up and located by satellite.

Advantages

• Satellite-linked devices can give information about animal movements to gain a better knowledge about the movement of deer through the district and deer behaviour – where they eat, where they rest, deer social interaction
• Much of this can be done from the comfort of a desk, with a daily location map on your computer screen

Disadvantages

• Very expensive: the devices are not cheap and putting them on the deer is very expensive, requiring capture & sedation of the deer
• The devices may influence deer behaviour subsequent to the trapping
• Animal welfare issues – deer are easily stressed and can damage themselves when being trapped

Radio tracking would be a wonderful tool to add to the deer knowledge base, as there is scarce information about the behaviour of deer in our landscape. Understanding this would be a wonderful help in planning for better techniques in controlling deer. Unfortunately it is extremely expensive and due to animal ethics reasons are usually conducted by a university or other scientific organisation.

Faecal pellet surveys

Not the most romantic of surveys, but highly effective. In this technique, regular counts of faecal pellets are conducted at nominated sites over a regular timeframe. This is then compared over time to see if the counts decrease or increase.

Advantages

• Very cheap
• Little expertise required
• Good for monitoring changes of deer population over time
• Good use of citizen science

Disadvantages

• Not a good indicator of deer numbers
• Not reliable in differentiating deer species
• Need scientific help to set the study up

Note: The use of DNA analysis of faecal samples can also be very valuable in identifying species, population sizes (variation found between samples) and the origins and movement of deer over time. It is not commonly done due to expense and the expertise required.

Vegetation surveys

There are three major categories of these:

• Monitoring which species are present and in what quantities
• Monitoring the regrowth rates of species – ie How many saplings are surviving? How many new plants are coming through?
• Monitoring the damage being done to existing vegetation

Advantages

• They give some of the most important information ie exactly how much damage is being done. What are happening to the existing species? Is biodiversity being affected?
• Very accurate and repeatable studies
• Give a good indication over time of the state of the environment
• Give a good indication of the impact of deer
• Are very useful when monitoring the environmental effects of an animal reduction program
• Give useful parameters when applying for government grant monies to control deer, where you can actually demonstrate the environmental value of reducing deer numbers

Disadvantages

• Vegetation surveys are quite technical and require a lot of expertise both in setting them up and assessing them
• Not so good for citizen science due to expertise required
• Expensive
• Take years to get meaningful results

Other

There are several other areas of measuring deer impact, such as loss of farm income, monitoring costs of deer mitigation, costs of deer vehicle collisions. Too many to cover in this article.

If you have further information in this area, or questions relating to any of the above, we would love to hear from you. Please email us at info@cardiniadeer.org.au