IMPROVING ESTIMATES OF WHITE-TAILED DEER ABUNDANCE FROM HELICOPTER SURVEYS

Abstract

Aerial strip counts of large mammals consistently underestimate numbers (Caughley 1974; Beasom et al. 1981, 1986; DeYoung 1985; Bartmann et al. 1986). If precision is acceptable and bias is constant, this may be acceptable in some research applications, such as estimating rate of increase (Sinclair 1972). In management, however, the absolute size of the standing crop must be known before optimum harvest rates can be established (Caughley 1974: 922). The less desirable alternative is to begin harvesting at a conservative rate and monitor the population for ill effects while increasing harvest pressure slowly through time. Caughley (1974:930) concluded ... no complete technical solution [to undercounting] is available through refinement of techniques and advocated development of a correction factor for each situation. However, the negative bias in aerial surveys can be reduced by refinement of the estimation technique. This bias decreases as strip width decreases, but greater accuracy may result in loss of precision (e.g., Burnham et al. 1985). We evaluated 2 methods of improving estimates of abundance obtained during helicopter surveys of white-tailed deer (Odocoileus virginianus) in brush-dominated habitats. The first used reduced strip width, and the second used a correction equation based on frequency distributions of groups encountered in belts paralleling the flight line. Mark-recapture estimates derived from marked deer sighted on repeated helicopter surveys served as base counts against which improvement in estimates of abundance was assessed.