Habitatansprüche des Kleinspechts(Dendrocopos minor) in Wäldern der Nordost-Schweiz

Summary

Despite the widespread distribution of the Lesser Spotted Woodpecker, many aspects of the species' biology are poorly known, particularly regarding its habitat requirements in central European forests. Recent studies suggest population declines in many areas of its range, making the need for appropriate management guidelines urgent. In 1997, we examined which habitat factors affect the presence of the Lesser Spotted Woodpecker in decidous lowland, non-riverine forests of northeastern Switzerland and evaluated the usefulness of playback tapes for censusing the species. Selected on the basis of prior knowledge of the species' distribution, 27 forests were searched for Lesser Spotted Woodpeckers using playbacks from March to early May. The species was still present in 17 of these formerly occupied forests, while 5 new registrations were made in previously unoccupied forests. Ninety percent of the registrations occurred between 16 March and 24 April, and the woodpeckers responded to the playbacks most often with call series. The habitat structure of forests with Lesser Spotted Woodpeckers was compared with that of forests where the species had been absent both during previous censuses and in 1997, and which had a similar tree species composition, forest structure and elevation to the occupied forests. Logistic regression analysis identified four habitat variables as significant predictors of the species' presence/absence. Accordingly, forests were most likely occupied by the Lesser Spotted Woodpecker if more softwoods, but fewer snags (with a DBH ≥15 cm) per area were available, if the distance to lakes and rivers was small, and the elevation was low. Therefore, the distribution of the Lesser Spotted Woodpecker seems to be affected by variables reflecting both forest structure and relative position of the forests within the landscape. We conclude that the Lesser Spotted Woodpecker will benefit from protection and promotion of softwood in all forest types, resulting in increased habitat connectivity. Moreover, censuses using playbacks can be efficiently conducted during a short period in March/April.

Zusammenfassung

Viele Aspekte der Autökologie des Kleinspechts(Dendrocopos minor) sind schlecht untersucht. Dies gilt in besonderem Maß für seine Habitatansprüche in den Wäldern Mitteleuropas. Ein Ziel der vorliegenden Arbeit bestand deshalb darin, in ausgewählten Wäldern der Nordost-Schweiz die für den Kleinspecht relevanten Habitatstrukturen zu identifizieren. Ausserdem wurde die Eignung von Tonband-Klangattrappen für die Kartierung untersucht. Für die Habitatanalyse wurden in 21 der 22 Wälder mit Kleinspechten und in einer Kontrollgruppe von 21 Wäldern ohne Kleinspechtvorkommen verschiedene Habitatvariablen erhoben. Mit einer logistischen Regression wurden die Variablen ermittelt, die am meisten zur Unterscheidung der beiden Gruppen beitragen. Es resultierten vier Variablen als Prädiktoren für das Vorkommen von Kleinspechten: 1) Weichhölzer begünstigen die Anwesenheit des Kleinspechts; 2) besiedelte Wälder weisen eine geringere Entfernung zu einem Gewässer auf; 3) Kleinspechte kommen hauptsächlich in tieferen Lagen vor; 4) Die untersuchten Kleinspecht-Wälder weisen im Vergleich mit den Kontrollwäldern weniger stehende tote Bäume mit BHD ≥ 15 cm auf. Die Erhebung von Kleinspecht-Beständen mit einer Klangattrappe kann während eines kurzen Zeitraums im März/April effizient und zuverlässig durchgeführt werden.