of the aircraft were manned, the path width 

 distance was called 2 nm. 



Example: Let N = 350 



L = 2,034 nm 

 W = w nm 



350 0.086 animals/nm^ 

 2,034 X 2 



2 

 This density of 0.086 animal s/noi , when extrapolated 



to the area surveyed (25,000 nm ), yields an estimated 



abundance of 2,150 animals in the SCB. 



Formula #1 is fundamentally the same as Eberhardt 1968, the estimator 

 used by U.S. Fish and Wildlife Service in their Alaskan bird surveys, and 

 the uncorrected or raw estimator referred to by Wiens et al. 1977. The 

 only difference between these estimators is in path width utilized by 

 each investigator. It is also the estimator we initially utilized until 

 sufficient data were assembled for us to question the validity of a 2 nm 

 wide observed path width. 



Other investigators have utilized an inverted form of this formula, 

 mistakenly believing that the resultant computations yielded animal 

 density per unit2area squared, when in actuality their formula yielded 

 the number of nm traveled to locate one animal. 



Formula #2 . Animals observed/linear nm: 



= ammals/nnear nm 



transect length 



where N = number of animals observed; 



where L (transect length) = linear distance flown in nm. 



Example: Let N - 350 

 L = 2,034 nm 



/. 350 = 0. 172/1 inear nm 



2,034 



This formula is useful only as a relative index of abundance and may be 

 used under circumstances where the path width is unbounded or when obser- 

 vational conditions "^ery substantially during a transect or from transect 

 to transect. However, the denisty figure obtained should not be extra- 

 polated to area-wide population estimates, since path width is not avail- 

 able. This method of computation has extremely limited applications, but 

 is presented for comparison's sake and since it has been utilized by 

 investigators in the past. 



B-71 



