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Thread: Estimating nummers of deer - a guessing game?

  1. #1

    Estimating nummers of deer - a guessing game?

    Some advice please....

    Our local DMG is doing a deer impact survey and deer count for a local landowner.
    The site is approx. 800 Acres of 80% woodland, 20% fields for sheep/cattle, organically farmed and sympathetic towards conservation objectives.
    The site is more or less round, surrounded by other farms with arable fields and sheep/cattle.
    Our group has divided the site in 8 sections.

    I spent 2 hours around on the boundary of one of the sections and, at my sitting up position, could see approx 1/2 Mile of the boundary, where I counted 7 Roe deer I could all see at the same time.

    In my Report to the Project Manager I stated that, on the assumption I could only see 50% of the deer present in that 1/2 mile of boundary, it was a reasonable estimate that there could have been some 25-30 deer per mile of boundary grazing in the surrounding fields at that moment. As the total boundary is some 7 Miles I estimated some 175 Roe deer on the site. Not believing my own (logical) figure I reduced my estimate to some 100 animals.
    And I haven't started about the Muntjac yet, of which there are many many more..

    I did, btw, get an estimate from the D.I. who looked at the deer impact on the site. Based on the 10% of the woodland surveyed, the estimate was 300-500 deer.

    I am now asking the more experienced members of this site to pick some holes in those assumptions and come up with some (structural) comments please.

    Thank you
    • Do not be seduced by the marketing-men....

  2. #2
    Is there going to be a cull done? If so a simple way to get relative abundance is through a "change in ratio". You have already counted 7 deer this time. You would need to do several more counts from the same location for the same duration & in similar situations as this. Having more locations & keeping these indices will give more rigour. Let say your indices of "relative abundance" averages 7 deer. Once you do a cull you will get a "hard' number which isn't relative. Lets say you shoot 50 deer here. Then you need to go out & see how the ratio changes & use this to establish "absolute abundance". If your next indices of "relative abundance" shows 3.5 deer then you have halved the ratio & it can be assumed that there were 100 deer before the cull & now 50 remain. If the new "relative abundance" shows 5 then there was likely 175 deer before the cull & 125 remain.

    I like culls & "change in ratio" because the data is cheap to get & accurate, however there is several other ways of establishing "absolute abundance" including "capture, mark, recapture" or doing transects to establish dencity & using an algorithm to establish the "absolute abundance" from the indices.

    The most important thing to remember is the error bars. Above you have stated 300- 500 deer these are the error bars, this is often as good as it gets or needs to be. What is important in wildlife management is trends. If next year the figures are 350- 600 then thats all I need to know to see how things are trending, same as if its 200- 400. I also need to know what key processes are in play to cause the trends.

    It shouldn't be a guessing game when censusing wildlife.

    Cheers Sharkey

  3. #3
    you may as well stick a wet finger in the air IMO!!

    300-500 deer
    so basically 400 +/- 25%
    a spread of 50% accuracy....does that sound scientific to you?
    (I can see a deer but it might be two? or it might not be a deer at all it could be a log!!!""

    part of the problem with population surveys involving covered ground is they are wholly based on assumptions:

    assumptions that deer are evenly distributed
    assumptions that habitat can be classified as capable of holding more or less organisms based on the constituent plants/trees/cover
    assumptions that you can survey 10% of the land and extrapolate the density across the whole area
    assumptions that you boundaries are the same as the deer's
    assumptions that the deer you count today are not being counted across the "boundary" by the nest estate/farm tomorrow
    assumptions that deer ****e is evenly distributed
    assumptions on the immigration and emigration of certain sex or age animals in and out of your control area
    assumptions that the person counting the deer is competent/capable/unbiased (get two people to count deer in the same area without corroborating and look at the difference in numbers recorded!!)

    I spent years counting wildlife of various shapes and sizes and evaluating various methods from dung/print/slot counts in transects, to physical sightings and capture/mark/recapture and the numerous "algorithms" that are used to give an overall figure.

    They are wildly inaccurate. Wildly

    Unless you have completely open ground and a plane/helicopter with video and pattern recognition software you are guessing at best.

    As Sharkey says the only absolute figure you have is actual sightings.
    The only way to determine a more accurate absolute figure is apply your actual cull figures to the initial sightings/sex and age ratios

  4. #4
    Then there is Fallow Deer!

  5. #5
    Attempting to count any form of wildlife is, as Bewsher says is almost an impossibility. You only have to look at the badger cull to see what even the so called experts who set out the targets came up with. I suppose with deer a thermal imager might give a slightly more accurate figure but by and large it's guessology!
    I once was asked to do a roe survey in my own area which I know very well, I came up with a pretty improbable figure which I thought was a gross over estimate. Looking back I can see what it was an under estimate.

  6. #6
    Counting deer is extremely difficult to do in some areas, and also fairly pointless!
    The most important thing to do is to establish what 'impact' they are having on the landscape.
    If the impact is too great, then you have too many deer, its that simple! Working out which deer are having the greatest impact will give you a good start point. Target those first. This is most likely to be Muntjac which are best 'managed' on a 'shoot on sight' policy anyway. Calculating a cull plan is difficult without having a good idea of numbers, but if you cull them with a 60:20:20 split (60 Young:20 Mature:20 Old) until impact is acceptable, then you won't go far wrong.

  7. #7
    Just remember the % you have to shoot to maintain the current population at the same density (if that is what you want), might be wise to report a number that reflects your ability to meet the numbers required. Remember, its just a plan, and the plan can change.

    As mike tyson said, "everyone has a plan until they get a punch in the mouth!"

    ive counted deer on unknown ground, and formulated plans based on numbers seen and counted on numerous visits, using different counting techniques, including lamp and nv surveys. it all comes back to the holding capacity of the ground at the end of the day. Base your figures on that, and you wont be far wrong.

    couple of points you should note...

    moon phase, your deer are behaving differently at the moment

    time of year, in a month or so your going to get a heap of young animals turn up looking for a place to live

  8. #8
    I need to agree with MS its not about the amount of deer but the negative impacts they make on and around the area you are going to control. Those are the areas were you should pay particular attention. Regards the numbers on the ground while they do seem high to me they do not surprise me. So if they are at very high level I would take the DI estimate they are the scientific approach in your area.

  9. #9
    Everyone has made some very valid points and it really is a pointless and futile task and as others have said it would be more relevant to guage the effect/damage there having on there ecosystem rather than just there sheer numbers

    Just been in counting the deer on an estate where i run a shoot. Not heard the results yet.
    Combinations of transects counting dung combined with lamping, night vison and Thermal imaging, this was done by a proper company that specilsess in deer counts amongst other things

    U are probably better off walking varoius areas/rides of ur woods and accessing vegetation or relative abundance of certain types of vegetation preferably the stuff really like to graze/browse on, or set up some quadrants where u do it in more detail and go back to the exact same area each year and measure any changes compared to ur cull/numbers of deer seen.
    1 local deer manager done this for 1 big forest block for the last 30 odd year, sadly don't think it is still carried on

  10. #10
    Measure impacts not numbers. Simples.

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