The aim of this paper is to describe the seasonal variation in responses by Green Woodpecker Picus viridis, Great Spotted Woodpecker Dendrocopos major, Nuthatch Sitta europaea and Short-toed Treecreeper Certhia brachydactyla, to playback. The study was carried out in the province of Bologna, at altitudes ranging between 100 and 1,100 m a.s.l.. Between February and May 1996 through 1998 1,299 field playback experiments were carried out in 419 series of 1-4 species, the order of which was chosen at random. As regards D. major, we stimulated it first with drumming and then with vocalisations. Drumming and calls were played for two minutes from a tape recorder (100, with a control period of three minutes. Three out of four species showed a marked seasonality in their response to playback: P. viridis Chi-squared = 39.07, df = 9, P < 0.0001; D. major Chi-squared = 42.34, df = 9, P < 0.00001; S. europaea Chi-squared = 33.41, df = 9, P < O.OOI. An analysis of the individual components of Chi-squared shows that: in March P. viridis responds more frequently than expected (highest value in the second 10-day period), while in May it responds less frequently than expected. D. major responds more than expected in the third 10-day period of February, in March and in the first and second 10-day periods of April (highest value in the second 10-day period of March) whereas less than expected in May. S. europaea responds more often than expected in the third 10-day period of February and in the first 10-day period of March and less in May. As far as C. brachydactyla is concerned, there is no significant link between response and season, probably due to the longer breeding period (2 clutches per year).
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