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We recognized that not all mountain goats will be seen during helicopter surveys, and that the chance of not seeing animals varies with the situation. We investigated this by checking whether or not particular mountain goats were seen during surveys flown in 2003-2007, where we had mountain goats wearing collars or where observers on the ground kept track of mountain goats during the aerial survey. In each instance, we kept track of the conditions (such as the size of the group, weather, and characteristics of the terrain) and whether or not that mountain goat was seen during the survey. Therefore, we could evaluate and predict the conditions under which mountain goats were likeyly (or not likely) to be missed during a survey, and based on the conditions for a survey, estimate how many mountain goats were probably missed.
As a consequence, we now have a formal and statistically sound method for estimating population size based on helicopter surveys. Because we understand the factors leading to mountain goats being missed during surveys, we can adjust survey counts to produce a population estimate for a given area. This is known as applying a sightability model. The amount of adjustment varies with each survey, but may be as low as 5% (Goat Rocks), or as high as 55% (northeast Olympics).
- J. Bernatowicz
- J. Bohannon
- M. Davison
- R. Deol
- G. Falxa
- S. Fitkin
- B. Hall
- E. Holman
- L. Leschner
- T. McCall
- P. Miller
- R. Milner
- W. Moore
- R. Spencer
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