Abstract
One of the most controversial issues concerning wind turbines and photovoltaic farms is their negative impact on bird populations. The basic problem is the cumulative effect whereby birds, attracted by the water-like appearance of photovoltaic panels, may collide with the rotating blades of wind turbines. The paper analysed bird populations during four periods of their activity. The density of bird species of high, medium and low collision risk (HCR, MCR, LCR) at six photovoltaic farms was determined, including buffers of 200 and 1,000 metres from the installations. The results show that the structure of the avifauna occurring within and in the immediate vicinity of photovoltaic farms is variable and depends on both the nature of the specific installation and the phenological period. No bird mortality was observed during the 2-year study period. However, the potential expansion of photovoltaic farms to include wind farms may have the effect of increasing collision hazards, particularly during spring and autumn migration periods, as significantly higher densities of HCR birds were found during these times than during other periods. The study also indicated that LCR birds were abundant during the breeding period and post-breeding dispersion. They were significantly more densely distributed within a buffer of 200 m than 1,000 m from the installation. This confirms the attractiveness of photovoltaic farms for this group of birds, which may influence the possibility of not only cumulative impacts, but also synergistic impacts when photovoltaic farms are extended with wind farms.