Evolution of Black Grouse (Tetrao tetrix) populations in Europe: an overview | Evolution des populations du tetras lyre Tetrao tetrix L. en Europe. Un essai de synthese

The Black Grouse population of south-eastern Belgium is relatively isolated from other populations scattered over western and central Europe. It has nevertheless succeeded in maintaining small numbers and so far in avoiding extinction. During the three past decades, numbers of cocks censused in spring in the Hautes-Fagnes have fluctuated within limits characterized by an exceptional peak of two hundreds in 1971-72 and a floor of some twenty-five male individuals in the mid-sixties as well as now, with less pronounced recoverings and lowerings meanwhile. The situation of that local population is very similar to what has been observed in populations elsewhere in Europe : more or less regular fluctuations and a long lasting decline trend. We have therefore investigated the bulk of European papers published on the population ecology of tetraonid species. The aim is to update a previous review published in 1982, by comparing our local situation with other ones as well as with the global situation on the continent, in order to identify key factors affecting populations numbers, and finally, to precise research targets and improve conservation tools. Fragmentation and modifications of the habitats turning from open landscapes to more wooded ones, and disturbance by human activities - exploitation of peatland or of boreal and alpine forests, overgrazing in moorlands and development of recreational activities - are considered to be the main factors affecting level and survival of populations, particularly sensitive while nesting and wintering. Important charges of domestic or wild ungulates sheep, cattle, red deer, boar - have negative effects. Tetraonid populations are considered able to resist interactions with predators - fox, raptors, corvids - but this is to be considered cautiously as far as very small relictual populations are concerned. Considering these different influences, any management programme aiming to enhance the populations of Black Grouse in Europe should pay attention to several actors to preserve or restore the quietness of the birds during all critical stages of their life cycle, and essentially during courting, nesting and over wintering. Finally, effects of short-term and long-term variations and evolution of climate are to be investigated over decades.