Since there is a thread recently on aerial surveys I thought I'd jot down some words on how aerial population estimates (known as "density estimates") work, a bit of the science behind them, and why they are so expensive.
I'll just deal with moose density estimates for now.
Most density estimates are usually done in early November after the first snowfall because we need snow on the ground to see tracks and for the contrast needed to spot moose as well. We also need to do it while bulls still have their antlers. So what we have to have for an accurate density estimate is good flying weather and that snow on the ground.
What was typically done first was to use larger faster planes (Cessna 185s or 206s or equivalent) to stratify certain areas within a unit. This stratified random sampling and spotting determines low-density and high-density moose areas based on the amount of moose spotted. We don't want to fly just the high density areas, or the low density areas, but a mix of both. So after that is done those areas are mapped out for the actual survey, and coordinates chosen for line transects to fly.
Now comes the super cubs with spotters (or equivalent slow-flying aircraft), typically there are several aircraft involved in the survey. This requires hiring extremely experienced pilots, and also having experienced spotters. Both pilots and passengers do the spotting and counting, and they also try to determine bulls, cows, and calves/yearlings. So the day arrives and the planes head out. Prior to a newer method we used what is known as the Gassaway method (named after the Alaskan biologist who perfected it). The Gassaway method involved flying a certain amount of time over individual survey units (SUs), around 4 minutes per square mile, and counting moose. Recognizing that with that amount of time over an SU not all the moose there may be spotted, Gassaway method involved re-flying some of the SUs for longer and recounting to come up with a "sightability correction factor" (SCF). This SCF was then taken into account afterwards and utilized in the data to correct for errors and improve the "confidence interval" (CI), which is basically a margin of error. Most reports you read will have a 90% CI, or a 95% CI. The higher the CI the less margin of error.
Now all this usually involved flying over several days by several aircraft. A typical moose density estimate for a certain area can be done for around $30,000-40,000 at the cheapest. If we want to cover larger areas and not extrapolate as much it can cost a lot more. If it's done right, in good conditions, the resulting data is very sound. There are times when a survey was all planned and pilots and aircraft in place, and the weather turned crappy (high winds, poor visibility), but we have still done them. The results from those estimates can be pretty meaningless, as spotters are puking in the back seat, planes have to fly higher, it is turbulent etc etc. I think we realize now it is best to call off surveys when we don't have the right conditions, rather than spend all that money for unsound data. Unfortunately though, this can prevent surveys for a year or more if we don't get the snow we need and the right flying weather at the right time.
We do things a bit differently now. We mostly use the GSPE (geo-spatial-population-estimate) method. This method was perfected by another ADFG employee, a biometrician. They are like the math geeks <grin>. The new GSPE method recognized that instead of re-flying certain survey units to correct for any missed moose, that if we spent a longer time flying each SU, there was no need to come back and re-fly and recount, so the GSPE method typically requires 8 minutes over each square mile chosen to survey.
Now even using highly experienced pilots for this, it isn't without risk. Many of you have heard of a "moose stall." That is when circling to look at moose or count them the plane can go into a stall. We've lost some extremely good pilots and biologists this way, though it has been rare. We've had some planes go down with no injuries. The most important thing when we do these surveys is to hire the most experienced pilots we can get, and often these pilots are guides and/or air-taxi operators with very high time in their specific aircraft.
That's the basics. I would like folks to recognize that we can do very accurate density estimates from the air, but that the results don't always agree with what hunters are seeing on the ground. And in many cases hunters then don't "believe" what ADFG is saying because the area they hunt either doesn't have that many moose or an area they are familiar with has less moose than in the past. What we need to recognize is that it is impossible to gauge a population based on what you are seeing in a specific place, or even if you are a pilot and fly the same exact line out to your cabin and in the past saw more moose than you see now, that somehow means the ADFG data is flawed. These are fairly large areas we are talking about and we need to take in the whole area rather than a few specific places.
This kind of thing happened quite a bit in the 20A and surrounding areas; hunters didn't believe there were as many moose as ADFG data showed. It's good to question data and ask how we arrived at it, and what the confidence intervals are etc. I think, however, that there is a wave of hunters who are discounting good data out of hand more and more, and this is causing some difficulties. Most of it is education related I think; if hunters knew more how these surveys were conducted and the science behind them I think they'd trust the data more. Which is why I'm typing this up this morn. I could have some of the particulars wrong, this is all from memory, but wanted to get the basics down. If you got this far then you get a gold star <grin>.