Bird's detectability and number of visits to the area
Bird counting methods usually are based on 1-3 visits. As a rule strong bias of results were indicated (Verner 1985). This bias is not very important if one is interested in counts of a single species. The problem arises when one is interested in communities of birds. If different species show different patterns of activity then the ability of an observer to detect those species must differ. Thus, a small number of visits will lead to over estimations of the number of some species and under estimation of other species. In this paper we investigate the influence of detectability on the optimal number of visit. We developed a simulation model of transect counts and used data collected during two years of transect study on avifauna of the Bieszczady National Park as an imput data for the simulations. Then we compare the simulation outcomes with the field data.
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