This report considers the comparative results of three autumn seasons‟ study (2008 – 2010) within the scope of the potential impact of the Saint Nikola Wind Farm (SNWF), constructed in summer 2009, on migrating birds. Data from visual observations and radar study are analysed.
In 2010, the occurrence of autumn migrants was strongly correlated with a very short period when strong westerly winds occurred. Outwith this exceptional period, numbers of migrants were low, but rose dramatically during the short period of strong westerly winds. Spatial and temporal dynamics in the numbers of different species passing through the wind park territory during autumn migration is presented.
SNWF does not appear to lie on a regularly used part of the Via Pontica migration corridor for diurnal migrants, especially those species that rely on thermals to migrate. This is probably due to SNWF‟s proximity to the Black Sea and the geography of the Kaliakra Cape. The Via Pontica migration corridor is probably fairly broad in extent in Bulgaria but most of the migratory traffic is likely to the west of SNWF and Kalikra, presumably because birds try to avoid the Black Sea and the risks associated with an absence of thermals over the sea. These arguments are illustrated by analysis of data across several spatial and temporal scales regarding a common migrant, the white stork.
As a consequence, it is reasonable to conclude that few autumn migrants are typically recorded at SNWF and, when numbers are relatively high, they are strongly associated with westerly wind conditions, probably because these winds drive birds from their preferred route. Such westerly winds are unusual during autumn.
Therefore, the risk of collision mortality posed by SNWF is intrinsically low because: a) it lies away from the main Via Pontica migration corridor; and b) presence through vagrancy is further limited by the rarity of conditions that drive vagrant migrants towards SNWF (i.e. strong westerly winds).
This intrinsically low risk, through the behavioural ecology of autumn migrants, is reduced still further by the turbine shut down protocol at SNWF. This mitigation measure, to reduce collision risk, was enacted during a short spell in autumn 2010 when unusual westerly wind conditions probably pushed several migrant birds away from the their preferred migration route.
No collision victims of key migratory species were recorded during the brief period of concentrated potential vulnerability in 2010. This was likely a result of the low intrinsic risk of collision posed by SNWF and/or the turbine shutdown system that was enacted.
Data to date indicate that SNWF does not constitute a major obstacle or threat, either physically or demographically, to important populations of diurnal autumn migrants