KWAK RGM & MEIJER R (1985) Species-specific acceptance levels in the mapping method. LIMOSA 58 (3): 97-108.

In the usual guidelines for the mapping method, the acceptance levels for obtaining territories from species maps are fixed. The same levels are used for all species. In 1976-78, the Research Institute for Nature Management (RIN) conducted a survey in a large number of study plots (fig. 1) in order to quantify the registration efficiency of territorial species on single visits throughout the year. The registration efficiency only applies to standard fieldwork conditions, i.e. census visit in the early morning (one hour before to four hours after sunrise); fair weather; 30-40 minllO ha per visit. The survey threw light to large differences in registration efficiency between species (tab. 1). We may therefore assume that in species with a high registration efficiency, a relatively large number of registrations per territory is obtained during a number of visits. On the other hand, in species with a low registration efficiency, relatively few registrations per territory took place. Accordingly, the use of a fixed acceptance level will result in an incomparable number of territories from species to species, particulary in cases with a low number of visits (less than 15). By using the species-specific registration efficiency for scaling the acceptance levels, this serious shortcoming can be avoided. To separate adjoining territories, contemporary contacts are needed. We consider one contemporary contact as sufficient to acknowledge a territory. Therefore no species-specific approach is needed in this respect and so this aspect is neglected in this study. With the aid of the registration efficiency throughout the year, the number of visits required to gather at least 1, 2, and 3 registrations in 90% of the territories can be calculated. The calculation method is shown in fig. 2. The results are given in tab. 1; fig. 3 presents two examples. Calculations are also made for a period of four weeks with the highest registration efficiency (app. 2). The number of census visits needed to reach the 90% level increase strongly as the registration efficiency declines (fig. 4, 5). When taking into account the species-specific registration efficiency, the acceptance level to obtain 90% of the territories should be just as high. The acceptance levels are therefore derived from the data in tab. 2 and app. 3. When these acceptance levels are compared to the levels used in Great Britain and FR Germany, they are often relatively low. In order to exclude migrants recorded during the census no single registrations made before the date limit are included (tab. 2). Species-specific acceptance levels are, in our opinion, a useful and necessary addition to the international recommendations for the use of the mapping method

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