Aves, p�le ornithologique de Natagora

Consultez les articles du Bulletin Aves !


Retour à la liste des articles

Aves, 29/2 | 1992 | 49-94

  Virelles: A pond rehabilited.
Philippart, B.

Article is available in pdf Download the French article in pdf (2.36 MB)

Article summary

The pond of Virelles, in the geographical region "Entre-Sambre-et-Meuse" (southern part of the Hainaut province) has been a nature reserve since 1983. At that time inadequate management, with solely the tourist industry in mind, has greatly depleted its biological interest. A management plan aimed at re-establishing this potential wealth was drawn up and it has been in operation since 1985. Basically this consists of clearing the undergrowth, scything the reedbeds and hayfields, and emptying, at regular intervals, the pond, harvesting the fish and thus drying it out for a prolonged lengh of time in the winter. Field results show that the management applied to each habitat is adequate : the persistance, extension or the reappearance of several species of plants or of animals, typical of these habitats, testifies to this. In the reedbeds and hayfields this concerns basically plants and insects; results concerning avifauna are less obvious and no doubt less rapid. As regards the mass of water itself, however, evolution has been spectacular from all points of view, limpidity of the water, vegetation, entomofauna, populations of fish and avifauna - both breeding, overwintering and passage birds. The pond was first emptied in the autumn of 1986. Several weeks of drying out and the elimination of many tons of large herbivore and bottom-feeding fish (Carp and Bream - Table 1) rendered, above all, a great limpidity to the water, and allowed the development, during the summer of 1987, of an abundant aquatic vegetation which hitherto was entirely lacking (Fig. 4). The Great-crested Grebe was the first species to react to these modifications: an increase in small fish, thanks to judicious restocking and the elimination of a great number of large fish, destroyers of spawn, enabling five broods to be raised successfully in 1987 whereas only one brood had been raised between 1983 and 1986. The number of broods attained in 1990 was 23 and the number of out-of-breeding-season visits by the Great-crested Grebe, as well as by other piscivores has greatly increased since 1987. (Fig. 6, 8, 17) The other species, namely the vegetarians reacted a little later, once the vegetation had developed enough but their increase was even more spectacular. The evolution in their numbers over the years that followed shows a good concordance vath that of the vegetation, itself linked to that of herbivore fish populations. (Fig. 11 - 12, 14, 18). The evolution of many species less linked to the expanse of water, or naturally less abundant in the region is more difficult to gage and to link to the management undertaken at Virelles. What, however, cannot be denied is that by taking over the management, wildlife protection associations have enabled it to be reinstated among the richest sites in Wallonia.

Articles published in the same bulletin