A MEDITERRANEAN BIRD DISPERSER ASSEMBLAGE - COMPOSITION AND PHENOLOGY IN RELATION TO FRUIT AVAILABILITY

This study deals with a fleshy-fruited plant-bird dispersal system at a site in Mediterranean France, characterized by Quercus ilex coppices, shrublands and old fields. Among the 19 bird dispersers recorded, 14 were of small size (< 25 g), with Sylvia atricapilla, Erithacus rubecula and S. melanocephala accounting for 86.6 % of those caught in mist nets. The importance of small-sized dispersers seems to characterize the Mediterranean shrublands and evergreen woodlands in the whole of the temperate systems. The highest numbers of dispersers occurred from October to January. The seeds of 38 fleshy-fuited plants (native, cultivated and alien) were collected in seed traps. Seed rain occurred throughout the year except in May, with a maximum fruiting period extending from September to early December and the greatest number of native species being dispersed in October. When we compare our data to those collected in Spain, England and Sweden a shift of the peak of fruit availability in relation to latitude (the higher the latitude the earlier the peak) is very likely in Europe. Such a shift is obvious in the United States. We suggest that 1) this shift is the result of climatic constraints on plants rather than that of the selective pressures of dispersers, and 2) that the coincidence between high fruit availability and dispersers' abundance can simply result from the opportunist behaviour of frugivorous birds.