Évolution saisonnière de l’avifaune dans une futaie de Chênes en Bourgogne

Abstract

A study was made of the phenology of the bird populations of two different and distinct vegetation types, which represent two extreme succession stages resulting from the shelterwood system of management of Quercus pedunculata forests in Burgundy. Bird populations were counted throughout the year along line transects. The avifauna of old, sub-climax, shelterwood remains remarkably stable throughout the year. About half of the nesting birds are sedentary species, and there are few winter migrants or transients which pass through during the course of spring and autumn migrations. On the other hand, the bird fauna of young, bush shelterwood is characterised by marked seasonal variations. There are very few sedentary, breeding forms and many species (particularly Thrushes and Finches) are recorded during the course of spring and autumn migrations, as they are generally in other open habitats. The young shelterwood also provides an important area for several winter visitors, such as Reed buntings, Siskins, Blue tits and Great tits. In both habitats, birds numbers reach their lowest levels in winter, with January the month when the smallest populations are recorded. This corresponds with the availability of food. Traps show an almost total absence of flying insects (that is to say, insects available to birds) from the end of November to the beginning of February, whilst in winter there are none of the berries so abundant in the bushy habitats in autumn. The two habitats support comparable numbers of birds during the breeding season, though in winter many more birds are found in the old shelterwood than in the younger succession stage. The winter visitors to the young shelterwood are too few to make up the numbers lost by the departure of the warblers and other insectivores, which constitute the summer populations. This difference is attributable to the availability of food, which remains higher in the older shelterwoods (hibernating insects, dry fruits) than in the younger succession stages. Many species remain in the older shelterwoods throughout the winter, showing a poly-phagous feeding behaviour which can be considered to reflect their evolution in this type of habitat. The existence of different plant communities, with different phenologies, in the same forest area helps many species which benefit from the different kinds of food resources provided by such an heterogenous habitat during the course of the year.