Comparison of Variable Circular-Plot and Spot-Map Censusing Methods in Temperate Deciduous Forest

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Abstract
Breeding land birds on 10 paired 10 ha tracts in 5 separate stands of mature oak-hickory forest in the South Carolina Piedmont were censused by the Spot-Mapping method (SM). Eleven Variable Circular-Plot (VCP) counting stations, 5 placed systematically in each SM tract and an additional one located at random, were placed in each stand. Four techniques for summarizing VCP data provided density estimates for comparison with SM results at the tract, stand, and overall scales. VCP recorded 50 of 55 spp. encountered by SM, failing to tally only species that were visitors or were extremely difficult to detect. VCP yielded both over and underestimates of SM densities at all spatial scales. VCP results were more similar at larger scales and less similar to SM values at smaller scales, although long confidence intervals at smaller scales masked imprecision. No summarization technique for VCP data was clearly superior; each worked better for species with certain characteristics affecting detectability. Results of comparable accuracy were obtained by VCP in 20% of the time required by SM.