Weggler, M., J. Bühlmann, R. Ayé, M. Müller, W. Müller, Y. Schwarzenbach & G. Pasinelli
(* = Kurzbeitrag)
Starke Bestandszunahme des Mittelspechts Dendrocopos medius im Kanton Zürich und Konsequenzen für Schutzempfehlungen.
(von 1994 bis 2006 vergeben)
Bestand, Bestandsentwicklung, Bestandserholung, Anteil besiedelter Waldobjekte, Besiedlungsgrad, Wachstumsrate, Waldgrösse, Kartierungsmethode, Habitat, Nahrungsangebot, Klimaerwärmung, Schutzempfehlungen
Strong increase of the Middle Spotted Woodpecker Dendrocopos medius population in the canton Zurich and consequences for conservation measures. For the fourth time since 1978, the population of the Middle Spotted Woodpecker Dendrocopos medius was monitored in 2012 with the same method. Population size increased from 106 pairs in 2002 to 221 pairs in 2012 considering the same study forests in both years. Taking into account other forests not systematically monitored previously, total population size in the canton Zurich in 2012 was estimated at 381 pairs. The annual population growth rate was thus at least +7.6 %. Of the 76 forests monitored in both 2002 and 2012, Middle Spotted Woodpeckers were found in 53 forests (70 %) in 2012 as opposed to 22 (29 %) ten years before. The strong increase in occupancy was due to forests up to 30 ha being substantially more often colonized than during the previous population counts. In contrast, forests larger than 30 ha were occupied to the same extent as before. The study forests colonized for the first time and recolonized, respectively, from 2002 to 2012 collectively contributed 75 % to the net increase of 115 pairs.
Applying a single-season site-occupancy model to data from Middle Spotted Woodpecker population counts done with playback, we found that detection probability averaged 0.557 (0.493–0.619, 95 % confidence interval) and did not differ between the two annual sampling occasions conducted from mid-February to early May in 2012. Across all study forests, occupancy, here reflecting playback stations with observations of the Middle Spotted Woodpecker, was 0.428 and thus higher than the naïve estimate of 0.341.
For decades, the population trend of the Middle Spotted Woodpecker in the canton Zurich was negative. Yet, the causes for the recent reversal in population trend are unknown. We hypothesize that habitat and food availability have improved as a consequence of global warming (increased stock in deciduous forests, increased amounts of dead wood and ivy Hedera helix), forest management (increased stand age) and the conservation measures applied since the mid-1990s (particularly the promotion of oaks). We recommend to proceed with the conservation measures applied so far and to extend them also to small, relatively isolated forests, which have to be considered potentially suitable habitats for the Middle Spotted Woodpecker, given the recent patterns of increase in population size.
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