Vital for any deer manager is getting to know the size and structure of deer numbers on your ground. John Johnson explains how to get the most accurate data from a baited camera trap survey
A camera trap survey is arguably one of the most powerful deer population monitoring tools you can use that doesn’t require the assistance of a professional wildlife biologist or scientist. On your own, you can estimate deer density, sex ratio, buck age structure, fawn recruitment and more information that will guide you in achieving better management of the deer on the areas you manage and stalk.
There are two techniques used when carrying out a survey, baited and un-baited. This article covers the fundamentals of a baited survey. A typical baited scenario camera trap survey involves the use of one camera per 100 acres over evenly spaced, baited sites for 14 days. The accuracy of your results depends on how well you run the survey.
I have included a step-by-step guide based on the original research conducted in 1997 by Harry Jacobson and James Kroll, and simplified by biologists in the USA who conducted similar surveys. Even with this guide, you will still have a lot of questions as you work your way through your first camera trap survey. It is impossible to explain everything in a short article on a subject that has been developed over several years.
To answer those questions, the Quality Deer Management Association in the USA has published a book, Deer Cameras: The Science of Scouting, which includes four chapters devoted to helping the reader run successful camera trap surveys. If you are serious about monitoring and improving the local deer population through good management, I strongly recommend that you incorporate camera trap surveys into your population monitoring plans. This, of course, doesn’t replace the other records that are kept by any good deer manager.
It must be stressed that this type of survey uses a bait to attract the deer into range of the cameras. There is no justification for using bait as an attractant to cull deer and this is classed as an illegal act.
Once the camera trap survey has been undertaken and you have your numbers, you will have an estimate of the deer population that has been separated into bucks, does and fawns. Use these data to produce estimated deer density, buck to doe ratio and fawn to doe ratio. Sort unique bucks by estimated age to evaluate age structure.
Repeat the survey annually or as regularly as possible, using the same method, timing and camera sites, allowing you to monitor trends in herd characteristics.
This may sound more difficult than it really is, but it’s important to think through the details before you launch a camera trap survey, or your results may be compromised. The truth is, camera trap surveys are fun, and they can produce valuable information even for your hunting strategies.
Implementing a baited camera trap survey
Conduct camera trap surveys in pre-season (after antlers are completely grown) or post-season (as soon as the season ends but before antler casting begins). Avoid timing a survey when natural food sources are common – such as a heavy acorn crop with fallow – as this will compete with your bait. In general, maize is the best bait to use, or mineral supplement blocks if they work well on your ground. The timing is critical as antlered bucks provide the key information in the final calculation.
Determine the number of cameras needed. On properties smaller than 1,000 acres, use one camera per 100 or fewer acres. On larger properties, use one camera per 160 or fewer acres. Note: If you can’t afford or borrow enough cameras, rotate the cameras you have across the survey sites until each site has been monitored on 10 to 14 days. If you do this, be sure to start the cameras at the same sites at the same time each year and rotate to new sites in the same order each year to keep survey results comparable across years.
Using a map or aerial photo of your area, mark off a grid that divides it into one block per camera needed. Select a camera site close to the center of each block based on ease of access and deer activity. Identify each grid with a number or letter (placing a numbered or lettered sign at each site so that it will appear in the photos will help you later to organise images and data by location).
Clear ground level debris at each camera site to allow for clean images of deer. Orient the camera facing north to avoid backlighting caused by sunrise or sunset.
Locate the camera approximately 12 to 20 feet from the bait, with the bait in the centre of the image. This setup may vary with the make and model of camera.
Set the delay, between triggers, for no less than five minutes to keep the number of images manageable. There is a pre-programmed “Feed” mode setting on Reconyx cameras.
Once each site is ready, “pre-bait” it for between seven and 10 days. Turn cameras on during this phase and monitor photos to ensure the cameras are working, camera set-up is good and they are capturing good quality images.
After seven to 10 days, if the deer are responding to your bait and the traffic at each site is strong, begin the next phase: the active survey.
Maintain the survey phase for 10 to 14 days. In research, 14 days captured 90 per cent of all unique deer and 10 days captured 85 per cent of unique deer.
With the size and availability of high-capacity data cards, it should not be necessary to visit the camera during the survey period. Wear gloves when handloing the camera to to reduce the possibility of leaving your scent on it.
Collect cameras and compile images. Count the total number of bucks, does and fawns. “Fawns” are all deer under a year old, including button bucks. “Total” counts include known repeats of individual deer. Do not count deer you cannot identify as a buck, doe or fawn.
Study photos closely to count unique bucks based on recognisable antler or body characteristics. For example, you may have 100 total buck images but only 10 unique bucks in total. Your ratio of unique bucks to total bucks is therefore one in 10, or 10 per cent (0.10).
Multiply your ratio of unique-to-total bucks by the total of does and fawns to come up with an estimate of unique doe and fawn numbers. For example, if you have 200 total images of does and multiply it by your 0.10 ratio, you get an estimate of 20 unique does.
Apply a correction factor to your estimates. If you ran the survey phase for the full 14 days, multiply each of your buck, doe and fawn estimates by 1.11 to adjust for deer you may not have photographed. If you ran the survey phase for 10 days, multiply by a correction factor of 1.18. The results are your adjusted estimates.