Wildlife Research and Management - Wildlife Research
Date Published: September 10, 2008
Number of Pages: 7
Author(s): Clifford G. Rice
I developed an estimate of the number of mountain goats in Washington based on aerial surveys conducted 2004-2007 and expert guessing for areas not surveyed. To determine geographic units for estimation I started with 2007 WDFW hunting units, added areas not covered in 2007 units from 2002 units, and then added ad hoc polygons for areas not included by either. For surveys, I adjusted counts and calculated 90% confidence intervals based on our sightability model and averaged across years for units with multiple surveys. For non-surveyed locales, I solicited opinion (guestimates) as to best guess, likely minimum and likely maximum for designated ad hoc units.
In some cases units were partially surveyed, where I generally added the survey estimate and the guestimate for the remaining areas, but in some cases the guestimate included the surveyed area, in which case I used the guestimate for that unit. For the total estimate range, I took the simple expedient of adding the upper and lower confidence intervals from the surveys with the likely minimum and likely maximum guestimates.
I summarized unit level estimates in 2 hierarchical groupings, Area and Zone. Survey estimates and guestimates were added separately within each Area and Zone. For surveys, I added the variances and recalculated confidence intervals based on the total variance. For guestimates, I simply added likely minimum and likely maximum guestimates. Hence, precision increased with broad scale estimation for surveys, but not for guestimates.
Rice, C.G. 2008. Status of Mountain Goats in Washington. Unpublished report. Washington Department of Fish and Wildlife.