WINTER LINE-TRANSECT SURVEYS OF WOOD DUCKS AND MALLARDS IN MISSISSIPPI GREENTREE RESERVOIRS

We evaluated line-transect sampling from the ground and estimated dens ities of wintering wood ducks (Air sponsa) and mallards (Anas platyrhy nchos) in 3 greentree reservoirs in Mississippi. We also compared dens ity estimates from programs TRANSECT II and SIZETRAN, and we tested th e relationship between seasonal abundance of ducks and selected enviro nmental variables. We conducted 44 surveys between December and March 1988-1990. The Fourier series estimator in TRANSECT II fit all 16 data sets that met our minimum sample size (n greater than or equal to 20 individual ducks or flocks). No flock-size bias was detected using SIZ ETRAN, and there was no detectable difference in density estimates gen erated by TRANSECT II and SIZETRAN using the half-normal estimator. Wi th the Fourier-series estimator in TRANSECT II, wood duck and mallard densities ranged from 0.45-11.37 ducks/ha; coefficients of variation r anged from 15-60%. Generally, numbers of both duck species decreased w ith increasing precipitation and river levels. Line-transect sampling with 2 observers was feasible and economical (approx. $100/km(2)) for estimating densities of wintering waterfowl if forested wetlands could be waded and sample sizes exceeded 30.