2.2. Bird survey
Birds were surveyed using a point-counting method with three bird survey rounds covering the whole breeding season: end of April, end of May and middle of June. Surveys started at sunrise within 4 h, restricted to good weather conditions (no rain or storm). For each plot, sampling took 5 min in which all birds were registered via listening and sighting while standing still in the middle of each plot. Sampling was limited to 5 min, which was enough
time to register even inconspicuous bird species, but not too long to risk double counting. We took special attention not to count the same bird individual more than once. Birds flying through were not counted. For later analyses, bird species were classified according to their nesting site as tree-, shrub- and ground breeders (Table A.1 in Supporting information; Bezzel, 1993). Within one day we surveyed four forest stands. The order in which the foreststands were sampled was changed in consecutive censuses for the following survey round. In total, 48 plots were surveyed three times.