Long-term bird monitoring
The results of BRC 2008 and 2009 are further discussed in an international context of breeding populations and bottleneck areas in the Black Sea basin in an upcoming publication. A link to this article will be submitted upon publication. In summary the Batumi bottleneck is a key component in the flyways of many of the Eurasian migratory raptor species. Average recorded numbers for 10 of these exceed 1% of the estimated world population.
Taking into account the difficulty to conduct large-scale monitoring on these species’ breeding grounds, the Batumi bottleneck provides a unique opportunity to detect trends in raptor populations originating from the huge landmass of East-Europe and West Siberia.
In contrast to monitoring schemes at other bottlenecks, the BRC explicitly chooses to monitor only a selection of species. In this way we aim to increase the quality of data obtained through ground-based counts, to reduce the necessary count effort and to make it more realistic that the monitoring will be continued in the future.
A first step in the selection of priority species for monitoring was based on the proportion of their estimated world populations (BirdLife 2010) that migrates through the Batumi bottleneck, using a threshold of 1%. Three species, for which the counts approach 1% were also included (Table 3).
Note that the 1% treshold is also the main criterion used by BirdLife to identify Important Bird Areas (IBA´s) for conservation. The fact that nearly 10 species reach this threshold indicates just how crucial the eastern Black Sea route is for the protection and conservation of migratory raptors in Eurasia.
It should also be mentioned that for some species of concern to conservation like Steppe Eagle and Imperial Eagle the BRC counting season does not cover the entire migration season, probably not even the migration peak. If it would, the population coverage by BRC would most likely increase severely.
Table 3: First step of species selection for monitoring: proportion of world population migrating through Batumi.
In a second step, we aimed to maximize the efficiency of count effort (Table 4). Several considerations led to the exclusion of species from the list. First of all, we assessed the difficulty of collecting high-quality data for each species. Identification difficulties form one of the main obstacles in reliable data collection, because observer skills vary between years. This was a main argument that led to the exclusion of both Sparrowhawk species. A second consideration was that late species would be harder to monitor, because it has proven extremely difficult to find sufficient volunteers/observers after mid-October. Species for which the last day with >1% of seasonal migration falls after October 12th (Julian date 285) were excluded from the monitoring scheme.
Table 4. Second step of species selection: assessment of count difficulty.
In this way we selected 7 key species, which will determine the design of the Batumi montoring scheme. In practice this means that BRC ensures the necessary count effort to monitor these species on a yearly basis, i.e.: sufficient observers for a predefined duration of the season with daily counts. Start and end dates for counts for each of these species are based on data collected during the 2008 and 2009 surveys.
Besides these 7 species, a number of secondary species will be registered. These include large Aquila species other than Lesser Spotted Eagle – A. pomarina. This is because counting A. pomarina logically implies that the similar looking A. nipalensis and A. clanga need to be excluded during identification, which in turn constitutes most of the work for counting these species. Short-toed Eagle but mostly Osprey and vultures generally migrate in much lower numbers than priority species whilst they are relatively easily identified and therefore require no substantial additional effort. Furthermore, the potential inclusion of some late-season species will be discussed as soon more data become available.