Inter-analyst variation was studied using the results of 15 mapping visits conducted by the author in 1992 in a 30-ha study plot in the oak forest in Moscow, Russia. During field work, special attention was paid to obtaining simultaneous records of singing birds. The average speed of the survey was 2.0-3.8 hours/10 ha. Identical sets of maps concerning 14 passerine species have been interpreted by five highly experienced European analysts and six Russian ornithologists with no previous experience of themapping method. Additionally, several ornithologists having previous experience in studying territorial behaviour of the Chaffinch Fringilla coelebs or Great Parus major and Blue P. caeruleus Tits evaluated maps of respective species. Within each of the four groups, the analysts showed a very high degree of mutual discrepancy. The coefficient of variation of estimates for 14 species varied from 21% to 87% among experienced analysts and from 45% to 90% among inexperienced ones. For each of 14 species, variation tended to be higher in the latter group. However, variances of estimates of experienced and inexperienced analysts differed significantly only for one of 14 species. Proportions between species were similarly reflected by different persons. The effect of "geographical" experience on the interpretation of results was not obvious.
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