I read somewhere they can account for 90% of the deer. It was in one of the many articles out there on this topic. Granted, there will always be a +/- factor in deer but this is the best thing out there and it is pretty darn good. The plane doesn't disturb the deer so at least they are not running from the plane from one flight path to another and being counted repeatidly.

The did this same count at Raystown where deer sightings were low, according to hunters, during the season. They found something like 50 deer per forested square mile after the seasons were over.