| Summary: | The longitudinal spread zone was investigated for 30 arctic shorebird populations from 10 different wintering communities in widely different regions of both the Northern and Southern Hemispheres. Information about total breeding and wintering ranges, migratory connectivity and subspecies was compiled from literature sources. The spread of the distributions was analysed in relation to the mean distance between the breeding regions and the corresponding winter regions. Correlations between the number of subspecies per species and the longitudinal and latitudinal extension of winter and breeding ranges were investigated. The spread of the breeding distribution in the Arctic was similar for shorebirds with shorter or longer migration distances. This indicates that total migration distance has neither a restrictive nor an expansive effect on breeding ranges, possibly because limiting effects are associated with certain segments of the migratory journeys that are similar irrespective of the total distance. in contrast, there was a positive correlation between the spread of winter ranges of shorebirds from the different breeding sectors and mean migration distance. This pattern may arise if populations and species from a given breeding sector use both near and distant winter regions along the same flyway system. Birds from the most remote breeding sectors at migratory divides between major flyways will show the widest spread to different winter regions. We expected population differentiation in a species, as broadly reflected by the number of subspecies, to be primarily associated with the diversity of winter regions occupied by the species. However, the number of subspecies per species was related to the size of both the wintering and breeding range. Since these two ranges were themselves strongly correlated it was not possible to make a distinction between their relative effects on subspeciation.
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