Riegel , J., Lafontaine, R.-M., Pasteels, J. & Devillers, P. 2001. Potential influence of the Siberian Chipmunk Tamias sibiricus (Laxmann) on the regression of the bird fauna of the Forêt de Soignes, Brussels. Summary Cahiers d'Éthologie, sous presse.

The Siberian Chipmunk, Tamias sibiricus, was introduced in the Forêt de Soignes in the seventies and has constituted in parts of the forest substantial populations, evaluated at 2000 individuals. Its presence has been increasingly suggested as a possible cause for the severe regression of the populations of several species of birds, in particular insectivorous passerines, which has been observed over the past decades in the entire forest. This decline has resulted in the local extinction of seven species, Phoenicurus phoenicurus, Anthus trivialis, Phylloscopus sibilatrix, Sturnus vulgaris, Oriolus oriolus, Cuculus canorus, Streptopelia turtur, and is presently affecting five additional ones, Sylvia borin, Sylvia atricapilla, Troglodytes troglodytes, Parus major, Erithacus rubecula. In order to gain a first insight in whether or not an influence of the chipmunk on this trend was likely, the abundance of birds was compared between areas with and without Tamias sibiricus, using an unlimited-distance point-count methodology. No significant differences were detected in the abundance indices of the entire avifauna or of selected species assemblages, those of ground nesters, hole nesters, seed eaters and sedentary species. The most likely interpretation of the results is that Tamias sibiricus has no impact on bird populations, although a sink situation with an effect compensated by immigration can of course not be ruled out by the method used. It is, however, highly unlikely in the particular situation investigated. A species by species analysis was also conducted; it can only be indicative as it is more susceptible to small differences of habitat between sampling areas. Significant differences were observed for a few species, to either the advantage or the disadvantage of the area colonised by chipmunks. For the most part, considering the species concerned, and the direction of the differences, they are not likely to reflect an influence of the chipmunk. Only the deficit of Troglodytes troglodytes in the area of presence of Tamias sibiricus could be relevant, although it may also be linked to the vagaries of recovery after a period of low population. In total, the presence of Tamias sibiricus does not appear to represent a serious management concern, a comment that could not be made about other, far more threatening, potential introductions that the pet trade could provoke.

Key words: exotic species, introductions, forest avifaunas, avian population trends, Tamias sibiricus, Brussels Region, Forêt de Soignes.