We experimentally tested whether old nest material could decompose fast enough to clear tree holes between the consecutive seasons. To mimic the nest material we filled litter-bags with either 1 g of cellulose, or with 0.5 g of dog moulted hair. In August 2009 we placed pairs of these bags in 23 tree holes used by breeding birds in a deciduous forest in SW Poland. For reference, we placed the same sets of bags in the litter, at 23 random sites in the forest. The bags were removed in March 2010. After seven months of exposure almost all cellulose (median 92%) and most of hair (median 57%) disappeared from bags in the holes. These values were as high as (for cellulose) or even higher than (for hair) as in the litter samples. Additionally, some bags disappeared from almost every second hole, which suggests their removal by larger animals. The high decomposition rates alone would suffice to clear holes between consecutive seasons but, in the study area, this process was apparently enhanced by mechanical cleaning.