What Happens to Old Nests in Natural Cavities?

Abstract

It is well known that old nest material accumulates in nest boxes and should be removed to keep the boxes usable. Perrins (1979) and M0ller (1989) proposed that the removal of old material, via reduction of ectoparasites, could improve conditions in the boxes. This in turn could have profound effects on nest-site choice, mating success, and reproductive efficiency of the individuals that use the boxes. Natural cavities are not cleaned by humans. Thus, by implication, conditions in them should deteriorate owing to the accumulation of old nest material. Indeed, Perrins (1979) stated that . . the nest material would slowly decompose within the chamber and presumably over a series of years the site might become filled with old nests. I have tried to find support for this statement in the literature, but so far I have failed to find any information on this issue. Therefore, it seems that the information presented below, which indicates that old nest material disappears rapidly from natural cavities, constitutes the first data on this subject. Study Area and Methods.-Data were gathered from 1992 to 1998 in the Bialowieza National Park in eastern Poland, within which the last surviving fragments of European primeval lowland temperate forest are preserved. The tree stands of the park have never been cut, and the entire area has been strictly protected as a reserve since 1921. Hence, one can still observe cavities and cavity nesters in conditions free of direct anthropogenic disturbance. The forest consists of several types of old-growth stands (see Tomialojd and Wesolowski 1990, Tomialojc 1991, Wesolowski and Tomialojd 1995), but most of the data were gathered in two types of chiefly deciduous stands. One was a stand of riparian trees composed mostly of alder (Alnus glutinosa), ash (Fraxinus excelsior), and Norway spruce (Picea excelsa); the other was a stand of upland deciduous forest composed of more than 12 species of trees, mainly hornbeam (Carpinus betulus), small-leafed linden (Tilia cordata), con-