Ardea
Official journal of the Netherlands Ornithologists' Union

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Scheffer M. (1987) An automated method for estimating the number of bird territories from an observation map. ARDEA 75 (2): 231-236
In breeding bird censuses observations of birds showing territorial behaviour are marked on a map during several control visits. At the end of the season the number of territories of each species is estimated from these maps. A method for automated interpretation of the observation maps is proposed. The method is based on an average linkage clustering algorithm. The results of the method are compared with those of manual interpretations of the same maps by a group of ornithologists, as well as with territory numbers estimated by the person who did the observations in the field. Interpersonal variation in estimated territory numbers was large within the group of ornithologists. Differences between the computer interpretations, the mean numbers estimated by the group, and the field worker's interpretation of the maps were much smaller. The average deviation of the computed territory numbers from those estimated by the person who did the field work was 5% in a large set of data from both farmland and woodland. It is concluded that the results of the proposed method are similar to those achieved by manual interpretations. The large interpersonal variation in interpretation of observation data can be removed by means of the automated approach. To execute the described analysis a computer program written in FORTRAN 77 is available at cost price.


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