On bias due to observer distribution in the analysis of data on natal dispersal in birds

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Abstract
Natal dispersal, the displacement from site of birth to site of reproduction, is an important process. It determines the spatial scale of population dynamics as well as the genetic structure of populations. Although some inferences can be made about dispersal from the measurement of genetic parameters, direct data on individuals marked at their site of birth and recorded at their site of breeding are scarce. In principle, such data could be collected on a large scale through bird ringers concentrating on the recapture of breeding birds. However, the analysis of such data has pitfalls. The raw frequency distribution of observed distances is strongly affected by the spatio-temporal distribution of observers. A strategy for reducing these effects of observer distribution on the observed dispersal pattern is proposed and tested by way of a simulation model. Whereas the results presented are preliminary, there are prospects to obtain a description of dispersal which is relatively independent of the limitations on its observation.