Inventaire et évolution des arènes de parade, dénombrement des tétras lyres (Tetrao tetrix) et évolution de leurs effectifs sur le plateau des Hautes-Fagnes : 1966-1997

Black Grouse is a most endangered species in central and western Europe, and the Hautes-Fagnes plateau in the Belgian Ardenne is probably its most western sanctuary on the continent. This Hautes-Fagnes plateau (summit of Belgium), a mixture of peat bogs and large forests, turned into moorland through traditional agricultural practices. Moorland reached its largest extent (17,500 ha) two centuries ago, then declined progressively down to 5,002 ha in the early 1960s, as new economic needs caused them to be drained and planted with spruce tree cultures. About 4,000 ha were saved in 1957 and 1964 as parts of the Hautes-Fagnes Nature Reserve, but the population of Black Grouse, a flag species for all plants and animals sharing the same habitats, had already suffered a sensible decline at that time. ln order to contribute to its conservation, we organized inventories and descriptions of thirty arenas where cocks gather in spring for Iekking (the very places to watch and count them), and these provided most valuable knowledge of the fluctuations of their numbers over the Iast thirty years and insight into the nature of risk factors.

Thanks to important recruitments in the late 1960s, the population grew up to 198 males in 1971, then it collapsed down to 42 cocks in 1976. During the next 20 years, it fluctuated between about 80 (e.g. 1977, 1987), and less than 40 (e.g. 1982, 1983, 1995). The latest surveys in 1996 and 1997 revealed less than 30 cocks. The present situation is thus more critical than in the mid l970s, and even made worse by the spontaneous evolution of some parts of the Nature Reserve from attractive moorlands to less attractive woodlands. Considering that this evolution partly originates from weather dependent variations of recruitment (see Loneux et al.), hard work and strict policies are urgently needed to restore Black Grouse’s habitat (see Keulen et al.) and to enhance their populations, bearing in mind that a stock of 50 cocks is the Iower limit to face hazards of any kind during low density periods. Such a Black Grouse centered management policy will also benefit to all plant and animal species inhabiting the same open landscape.