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    Game Population Surveys in Arizona - Desert Rat - The Premier Hunting and Fishing Blog of the Southwest!

    Game Population Surveys in Arizona

    I found this description of how they (AZGFD) do game population estimates over on my friend Amanda’s great message board at CouesWhitetail.com. This was graciously posted by Jim Hinkle from AZGFD and I found it very informative! ~DesertRat

    Jim Hinkle, Big Game Management Supervisor for AGFD asked me to post this since he has seen questions in this forum about how surveys are done. Thanks Jim for taking the time to write this up!!

    If you guys have more questions after you read this, I am sure he would be glad to try and answer them.


    Game Surveys and Management

    I’m told there is great interest by members of this web site regarding how Arizona Game and Fish Department (AZGFD) conducts game surveys and how that information is used to prescribe harvest and permit numbers. While it would take a book length dissertation to cover the full theory, practice, and statistical considerations of assessing wild populations, I will attempt to cover the basics within this post.

    The bottom line for those of you whose personalities, professions or avocations lead you to seek absolutes; be prepared – absolutes are rare in game management! We cannot count all our wildlife nor can we absolutely know how many animals our hunters are taking. Everything we do relies upon estimates. I know that doesn’t make some of you feel very warm and fuzzy, but it is the truth. We do the very best we can given the tools at our disposal and the financial and human resources we have to use them, but we will never possess the precision that many of our critics would like.

    Herd Counts (not really)!
    The most important rule of surveying game populations is:


    This is why we call them surveys, not counts.

    No matter how many helicopters or observers you have, you will never be able to count all the deer, elk, etc. in the state. Why? Because the state is just too big and many of the habitats are difficult to observe in (think mixed conifer forest or ponderosa pine with a juniper-oak understory). Also the critters don’t enjoy being counted so they do things to frustrate game surveyors like hiding or leaving the country before they can be seen.

    So if you can’t count them all, what do you do? You count a portion or subset of them and measure a population parameter other than total number. The population parameters that we and other states have found most useful for the antlered and horned mammals are male to female and young to female ratios. It works like this. Give a couple of wildlife managers a helicopter, a pilot and enough Jet A fuel to fly around for a few hours. The WMs map out a survey route ahead of time that uses either a series of line or block transects to cover a portion of the various habitat types in their unit. They go fly around counting and classifying (is it a male, female or young-of-the-year?) everything they see and generally have a great time when they’re not puking. They come back to earth with filled out survey sheets of their observations. Those observations are then totaled into an annual survey for the unit.

    How and When
    Throughout my 25-year career I have surveyed every big game species, except buffalo, by every method possible. I have conducted hundreds of hours and thousands of miles of foot, horseback, vehicle, fixed-wing aircraft and helicopter surveys. My mule tracks are all over the Blue Range Primitive Area. Without a doubt, helicopters are the most effective method for observing the most animals in the shortest amount of time. Period. Fixed-wing aircraft work almost as well for pronghorn (flat open country) at a third of the cost of helicopter time, which is why we do our pronghorn surveys with airplanes. Foot, vehicle and horseback surveys which we still employ in certain circumstances simply require too much man-power time to be our primary survey technique.

    We do surveys for herd animals during their breeding season, so that we have the best chance of observing mixed-sex groups. When one of the main goals of your survey is to measure the male to female ratio, you want the boys to be with girls and not off hiding out in bachelor groups playing cards and smoking cigars. For deer this means we survey in very late December and January. Elk during late August and early September. Pronghorn during late July and August. You get the picture. The other benefit of surveying during the rut is that young of the year are still small enough to be easily distinguished, but they are also old enough to be running with the herds and past the point of the greatest mortality. Most mortality in fawns, calves or lambs occurs within the first few weeks of life. Once they are several months old, their chances of surviving to adulthood is much greater. Surveying young of the year at several months old gives us a better idea of what will survive and recruit to adulthood vs. what was born.

    Comparing Apples to Apples
    So now you have your survey numbers, but not total population count, so what do you do with the numbers? To explain, let’s use an example. Assume you have a herd of pet deer on a farm. Within your herd you have 10 bucks, 50 does and 25 fawns. You neighbor also has a deer herd. His herd has 12 bucks, 70 does and 25 fawns. Which herd is in better shape? Tough to tell from the raw numbers, so we convert the numbers into standard ratios based on the number of does. Bucks divided by does multiplied by 100 equals the number of bucks per 100 does. Fawns divided by does multiplied by 100 equal fawns per 100 does. Trust me on the math. Converting our two deer herds into standard ratios yields:

    20 bucks: 100 does: 50 fawns for farm #1 and,

    17 bucks: 100 does: 36 fawns for farm #2.

    Biologically speaking, farm #1 has a healthier deer herd, even though farm #2 has more total deer. Why is farm #1 better? Keep reading.

    What’s in a Ratio?
    So what do the ratios mean? The young to female ratio is representative of a population’s ability to maintain numbers or grow and is influenced by a variety of factors such as nutrition and predation. Generally speaking, for mule deer it takes about 40 fawns per 100 does measured in mid-winter to replace natural mortality. Herds with less than 40:100 are declining and herds with greater are growing. This fawn to doe measurement is an indicator of herd trajectory based largely on environmental factors (precipitation, forage quality/quantity, predation, disease, etc.). Hunt management has little to no effect on young to female ratios, especially for those species where only males are harvested.

    Conversely, male to female ratios are a reflection of what our hunt management has done to the herd. A deer herd in an un-hunted state would have buck to doe ratios of near 100 bucks per 100 does. Our harvests maintain these ratios at considerably lower levels. The keys to buck: doe ratios are 1) maintain enough bucks to ensure all of the does are bred (biological) 2) manage buck numbers to balance hunter opportunity with hunting experience (social).

    Research studies suggest that ratios as low as 5-10 bucks per 100 does are adequate to ensure that all does are bred. Low male to female ratios are not, nor likely have ever been a biological limitation in Arizona’s elk, deer, antelope or sheep herds. Socially, the effects of male to female ratios on hunting experience can be quite different. A deer herd managed for high buck: doe ratios, say 40 bucks per 100 does, would result in a superior hunting experience (high hunter success, high number of bucks observed, high number of older age class bucks) at a cost of limited hunter opportunity (only a few hunters are able to go). Our alternative management units like the AZ Strip and the North Kaibab are managed this way. Conversely, a deer herd managed for lower buck: doe ratios, say 10-20 bucks per 100 does, would result in near maximum hunter opportunity with the cost of a diminished hunter experience (lower hunter success, lower number of bucks observed, lower number of older age class bucks), which is how our standard management units are managed under the current Commission approved guidelines for hunting seasons. If you have never seen our hunt guidelines, they are posted on our website (see link below).


    The guidelines are the “recipe” for how we manage the hunted species in Arizona. The guidelines web page also does a good job of explaining how the guidelines are developed and approved. If you are dissatisfied with specific or general hunting experiences in Arizona, getting involved in the hunt guideline development process is the best way to influence positive change.

    A Simple Hunt Recommendation
    Armed with your new-found knowledge, let’s see if you can follow a simple deer hunt recommendation. Your unit has a current buck to doe ratio of 20:100 and a fawn to doe ratio of 40:100. Your target buck to doe ratio is 10-20:100. You are right at the top of the target buck to doe ratio range. With 40 fawns per 100 does you are replacing natural mortality, but not growing. Given that information, would you increase, decrease or leave harvest (permits) the same as last year? You got it…no change. If your buck to doe ratio was higher than 20:100, you could increase tags, especially if you had a fawn to doe ratio of higher than 40:100. Obviously if the buck to doe ratio was lower than 10:100 you would decrease tags. At the most basic level, it’s all about keeping the ratio within the target range.

    But Really, How many are there?

    Refer back to the rule, you can’t count them all. But you can count them in ways that lead to an estimate of how many there are. The method we are now implementing on most aerial surveys involves the use of a simultaneous double-count recording technique to estimate the observation rate of the surveyors (e.g. a 65% percent observation rate means that of every 100 animals that are within visual distance of the aircraft, only 65 are actually seen). Secondly, by GPS mapping our survey flight and animal observations, we can establish a number of animals observed per unit area and then expand it out to the area of the management unit. Combining the observation rate and density expansion works like this:

    We fly 100 linear miles of helicopter deer surveys and record every deer observed within 1/8 mile of the flight path (220 yards on either side of the ship). The exact distance from the flight path to the animal is easily verified using the helicopter’s GPS unit. So the total flight area is 100 miles long x ¼ mile wide = 25 square miles. Say we see 112 deer on this flight but using the simultaneous double-count method to determine our observation rate, it is determined that we only see 75% of the deer that are actually there (remember the rule!). So 112 deer observed divided by a .75 observation rate equals 150 deer estimated to be within the survey area. We then divide the 150 deer estimate by the 25 square miles surveyed and determine an average of 6 deer per square mile of habitat surveyed. If the deer are equally distributed within our unit, and our unit is 1000 square miles in area, we multiply 6 deer per square mile by 1000 total square miles and end up with a population estimate of 6000 deer. Simple, right? Not really. This is an over-simplified example but gives you an idea of what can be done. The simultaneous double count stuff is really quite complicated. Just so you know I’m not making this up, do a Google search for “simultaneous double count” and you will find several scientific publications documenting the use of this technique.

    That’s all I’m going cover for now. Post back with questions and I’ll do my best to answer. At some time in the future I’ll do other pieces on the hunter questionnaire program, use of long-term data sets and population modeling to further refine population estimates and assist in hunt recommendations.

    Good Hunting,

    If you’d like to ask a question or join in the conversation, you can view the thread HERE.

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