LINE-TRANSECT SAMPLING FOR ESTIMATING BREEDING WOOD DUCK DENSITY IN FORESTED WETLANDS

Techniques for estimating wood duck density or abundance have not been well-developed. This study was conducted to (1) evaluate the feasibil ity of using line-transect sampl ing to estimate density of breeding w ood ducks in forested wetlands, (2) determine sample size required for obtaining estimates of breeding wood duck density at various levels o f precision, and (3) evaluate whether wood duck behavior and field met hods are compatible with the assumptions of line-transect theory. Samp ling was conducted on Mingo National Wildlife Refuge in southeastern M issouri. I established 8.23-10.31 km of transects in forested habitat and sampled on 9 dates between 7 March and 2 April, 1989 and 1991. I a nalyzed sighting distance and sighting angle data using program DISTAN CE and a Fourier series model. Wood duck density estimates ((D) over c ap) ranged from 0.3-1.0 birds/ha, with associated coefficient of varia tion (CV[(D) over cap]) ranging from 24-52%. Based on precision of den sity estimates I determined that 30 km of transects would yield a CV(( D) over cap) of 20%, whereas a CV((D) over cap) of 5% would require ab out 480 km of transects. The level of precision required for density e stimates depends on the intended application of results. Managers and researchers should consider whether their study area will accommodate the necessary level of sampling. Density estimates from line-transect sampling will be useful in investigations of the breeding biology of w ood ducks, especially in regard to nest box management.