Trends of common birds inside and outside HNV
In the current assessment we have assessed for the first time the bird population trends inside and outside HNV. This assessment aims to show the importance of these areas to bird conservation. It is important to note that agri-environmental measures (AEM) are implemented in HNV areas. This suggests that the conclusions made for population trends in HNV are closely related to the species’ trends from areas where AEM are implemented. The direct trend correlation between HNV and AEM areas is possible after a study for specific physical blocks.
Results show that trends of all 38 species included in the common birds index for Bulgaria decrease with slower rate in HNV areas in opposed to those outside them.
Fig. Common bird index inside and outside HNV (38 species)
These results suggest the potential of HNV areas for positive impact of AEM on birds. To check the significance in the differences of the trends inside and outside HNV we used TRIM and WALD-TEST for significance of variables. Results show that 9 out of 38 species have statistically significant differences in their trends inside and outside HNV.
Looking at the species trends inside and outside HNV areas per habitat type we can conclude that the most visible is the difference in the trends of forest birds. Those inside HNV are increasing insignificantly and those outside HNV are decreasing. Species from “other” habitat types inside HNV areas have identical trends with those for the whole country and outside HNV are in significant decline. This is due to the fact that high proportion of the species in the group are from urban environment where the majority of them are in decline.
Amongst the species from the farmland bird index only 4 out of 17 show statistically significant differences in their trends between areas inside HNV and outside them. These species are Skylark (p=0,022), White Stork (p=0,0009), Common Starling (p=0,0494) and Goldfinch (p=0,0478). The most significant is the trend difference for Skylark which is stable inside HNV and steeply declining outside it. For the other species there are certain variations which do not allow us to be precise in our conclusions regardless of the statistical significance.
Fig. Farmland bird index inside and outside HNV 2005-2013
The higher values on the graph for farmland bird index outside HNV suggest that we still cannot be precise in our conclusions for the role of HNV for farmland birds. Nevertheless the fact that there are significant differences in the trends suggests that we need more specific studies.
Fig. Forest bird index inside and outside HNV 2005-2013
Forest bird species that show significant differences in the trends inside and outside HNV are the Wood Pigeon (p=0,0008) and the Blackbird (p= 0,0075).
Fig. Index of birds from ‘other' types of habitats inside and outside HNV 2005-2013
The species from “other” habitat types significant differences in the trends inside and outside HNV show three species: Common Cuckoo (p=0,0161), House Martin (p=0,0296) and Magpie (p=0,0439). All three of them show better state inside HNV than outside it.
The number of species that show statistically significant differences in the trends inside and outside HNV is still not enough to fully confirm the positive role of HNV. However data suggests that the monitoring scheme is a suitable tool for showing the effect of HNV and AEM implemented there on biodiversity.