The comeback: The raven (Corvus corax) recolonizes Central Europe
The raven is the largest passerine (song bird) worldwide.
It is respected and known as an intelligent fellow by some but hated as a “pest bird” by others. Due to the latter, it has a horrific history. Ravens were poisoned, shot or clobbered to death and a increasing decline in range and numbers of free ranging ravens was documented. Finally, in 1927 it was extinct over large areas of Central Europe. Last nesting activities were e.g. in Luxembourg as early as the end of the 18th century and in 1919 in Belgium. In Germany, the raven originally was a breeding bird in all larger forest areas. Since the middle of the 18th century a continuous decline in numbers was documented and around the turn of the century the raven was completely missing in Baden Württemberg, Hamburg, Palatinate, Saxony, Silesia, Westphalia and Thuringia.
At the middle of the 19th century the raven was extinct in western Central Europe !
Last refugia were found in northern Germany, Eastern Poland and in the Alps.
After the end of the aggressive persecution and when first conservation activities took place, population expansion to its former ranges began. The source for the recolonization came from the last refugia (see above). Although the ravens are rapidly recolonizing it`s former distribution areas, the process of recolonization is not yet finished. The data set concerning the actual raven distribution in Central Europe is quite good but the origin of the immigrated birds is not certainly known. Therefore, the idea of that survey was to detect cryptic genetic variation in Central European ravens as a result of geographical isolation. The formerly disjunctive distribution might have led to genetic differentiation among the three relict populations. As the origin of the newly established populations is situated in these refuges, one might retrospectively assign the actual populations to their source populations and make the recolonisation process more obvious.
In connection with the dissertation of Sascha Rösner at the university of Marburg (faculty of biology, ecology of animlas), which is supported by the animal foundation Wolfgang Bösche, we would like to answer the following questions:
- is there cryptic genetic variation in the raven populations of Central Europe ?
- where do the recently recolonizing ravens originate from ?
- how important are large forested areas for the recolonization process of the ravens ?
- how will the recolonization process continue in future ?
- are there similar processes of recolonisation and establishment in other large vertebrates ?
The results of our study might help to better understand the ecological process of recolonization patterns in other species …