Patterns in raptor migration in relation to weather: Implications for migration monitoring
More than 800.000 raptors of ca. 30 species migrating over Batumi every autumn. Ten species observed in numbers constituting >1% of their world population (see Verhelst et al. 2011). Several others in (one of) the highest concentration known to ornithologists anywhere in the world. The list of arguments to show the importance of the Batumi bottleneck in an international context is quite impressive. So for the casual observer, the need for implementing a long-term monitoring of migratory raptors at the eastern Black Sea seems clear. However, many factors affect the efficiency and precision with which a monitoring can be conducted and therefore the reliability of the obtained results for interpretation by conservationists.
One of the most crucial, but also variable, factors determining flight paths of migratory birds is weather! Wind, rain, atmospheric stability, … may all affect migrating birds differently, and the effect will depend on the movement strategies employed by any species. For monitoring purposes this is important as regional but also local weather conditions may cause migrating birds to choose another route, where they are not picked up by counters.
For these reasons one of the first crucial steps in any migration monitoring program should be to assess the impact that weather has on the counted species in order to determine for which species the huge efforts that are required are actually worthwhile. Thus, for Batumi we need to determine:
- for which species the route along the eastern Black Sea coast is ‘crucial enough’ to assume that a relatively constant part of trans-Caucasian migrants will use it in any given year and
- how local routes close to Batumi may shift out of sight of the observers as a result of local weather conditions.
These research avenues are now (2011-2012) being pursued in a cooperation of thesis students and researchers affiliated with BRC and MEDRAPTORS.