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Breeding Atlas >> Overall paterns of changes in bird distribution in the period between atlases
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Overall paterns of changes in bird distribution in the period between atlases |
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The main objective of an atlas such as the new Catalan Breeding Bird Atlas is to provide information on the distribution of the bird species present in a given region and the ecological factors determining their distributions (Gibbons et al. 1993, Schmid et al. 1998). However, given that a previous atlas dating from the 1980s exists, there were two additional but equally important aims for the present atlas: to quantify the temporal changes in bird distribution occurring in the period between the two atlases. Changes in species' distributions in the period between the two atlases were calculated after taken the sampling effort per 10 km square into account and comparing the number of squares occupied in the two different periods.
Mean index of distribution changes indicating the significance of change according to the habitat categories of the species. The change index = (range2nd atlas - range1statlas)/((range2nd atlas+ range1st atlas)/2). This index allows distribution increases to be measured and is symmetrical around 0, with a maximum decline in the case of extinction as -2, and a maximum increase in the case of colonisation as +2. Whiskers represent standard errors.
Changes in distribution do not show any homogeneous pattern and, rather, were dependent on the habitat selection of the considered groups. Whereas species from shrublands, forests, urban environments, cliffs and especially wetland and river habitats showed a tendency to expand their distributions, farmland and steppe species showed range retraction. On the other hand, we did not detect any significant effect of migratory behaviour on the overall changes in species distribution.
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Catalan Winter Bird Atlas 2006-2009
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