Jaroslav Koleček

Changes in bird distribution in a Central European country between 1985–1989 and 2001–2003

European birds have been significantly affected by dramatic environmental changes during the last decades. The effects of these changes on species richness and distribution in particular countries are still poorly understood because of a lack of high-quality, large-scale data standardized over time. This is especially true in Central and Eastern Europe. On a model group of birds in the Czech Republic (countrywide atlas mapping data), we examined whether long-term changes of species richness and distribution between 1985–1989 and 2001–2003 differed among groups of species defined by their habitat requirements, type of distribution in Europe, migratory strategy and the degree of national legal protection. Further, we investigated the effects of colonizers and local extinctions on these changes. Whereas the number of species in the whole country remained the same in both periods (208 species), species composition had changed. Increasing occupancy (i.e., number of occupied mapping squares) was observed in species of forest and wetland habitats, in short-distance migrants and in non-protected species. Southern species also positively changed their occupancy, but this pattern disappeared after the inclusion of six species dependent on extensively cultivated farmland that went extinct between mappings. The overall occupancy of all species together showed positive changes after excluding colonizers and extinct species. We suggest that the improvement of environmental conditions after 1990 caused the stability of or increased the distribution of common birds in the Czech Republic, and it was the disappearance of specific farmland practices that might have caused the loss of several species.

Differences between the Predictors of Abundance, Trend and Distribution as Three Measures of Avian Population Change

Abstract. Changes in bird populations can be described as simple changes in abundance or density of individuals or, in larger areas, as changes of distribution or population indices. Although these measures describe different aspects of population change, they are often used interchangeably when discussing the relationships between various predictors of bird population changes found in different studies. This hampers a meaningful comparison of results, because it is unclear which differences between studies are biologically relevant and which are just methodological artifacts, caused by the different nature of measures used to quantify population changes. We compared predictors of the three measures of population changes: (i) change in abundance, (ii) change in magnitude of population trend and (iii) change in distribution, using data collected in a single region, the Czech Republic, and over similar time periods. We also aimed to identify significant drivers of population changes of Czech birds, using a large set of predictor variables and virtually all species regularly breeding in the region. No significant predictors were common across the three measures of population change tested. Abundance increased mostly in forest birds, while the change in magnitude of population trend was positive in species with a higher level of legal protection and in r-selected species. Species extending their distribution include wetland birds, above-ground nesters and north European species. Although individual measures of population changes are positively correlated, their predictors are different. This limits possibilities of simple comparisons, but also offers a better insight into forces shaping bird population changes in time and space.

Intra-tropical movements as a beneficial strategy for Palearctic migratory birds

Migratory birds often move significantly within their non-breeding range before returning to breed. It remains unresolved under which circumstances individuals relocate, whether movement patterns are consistent between populations and to what degree the individuals benefit from the intra-tropical movement (ITM). We tracked adult great reed warblers Acrocephalus arundinaceus from a central and a southeastern European breeding population, which either stay at a single non-breeding site, or show ITM, i.e. move to a second site. We related ITM to the normalized difference vegetation index (NDVI) describing vegetation conditions and probably reflecting food abundance for these insectivorous birds. Three-quarters of birds showed ITM across the non-breeding range. We found no difference in range values and mean values of NDVI between the single non-breeding sites of stationary birds and the two sites of moving birds. The vegetation conditions were better at the second sites compared to the first sites during the period which moving birds spent at the first sites. Vegetation conditions further deteriorated at the first sites during the period the moving birds resided at their second sites. Our study provides evidence that birds probably benefit from improved conditions after ITM compared to the conditions at the sites from where they departed.

Magnitude and direction of population trends, ecological and life-history traits of 36 passerine species breeding in Europe between 2001 and 2012

Magnitude and direction of population trends (1 = 100%), ecological and life-history traits of 36 passerine species breeding in Europe between 2001 and 2012. Non-breeding niche position varies from 1 (closed forest) to 7 (open country) and non-breeding niche breadth expresses the difference between the values of the two main habitats; non-breeding habitat wetness scores from (1) dry to (3) aquatic habitats. Non-breeding regions: (1) west–central region, (2) west–east region, (3) central–south region, (4) ‘entire’ region. Breeding habitat: forest (F), wetland (W), urban (U) and open habitat (O). PC 1 expresses a gradient from ‘slower strategy’ (K-selected) species to ‘faster strategy’ (r-selected) species. PC 2 depicts a gradient from species allocating most of their energy to just one breeding attempt per season to species spreading their investments across multiple breeding attempts per season.