© Marcel Burkhardt
The White-backed Woodpecker in managed forests
The White-backed Woodpecker is considered a typical species of “primeval forests” and inhabits semi-natural forests with many deciduous trees and lots of deadwood. However, these findings were gained mostly in forests that had not been used commercially for some time. Little is known about the habitat needs of this specialised woodpecker species in central Europe’s managed forests.
Before the intensive use of forests from the 15th to the 19th century, the White-backed Woodpecker presumably was widespread in Switzerland and other parts of central Europe. Today, it is the rarest and most threatened woodpecker species in central Europe. The extension of its range in Vorarlberg, Liechtenstein and eastern Switzerland since the 1970s opens up interesting prospects for nature conservation in woodlands. This project is concerned with the following aspects:
1. Habitat selection and saproxylic beetles
The study aims to identify the site characteristics and forest structures of the forests, most of them managed, inhabited by the White-backed Woodpecker in Vorarlberg, Liechtenstein and eastern Switzerland. This involves determining the relationship between the occurrence of the species and factors such as altitude, exposure, slope inclination, canopy cover, tree species composition and proportion of deadwood. The study also investigates whether the occurrence of the White-backed Woodpecker is related to the abundance of saproxylic beetles (beetles that feed on decaying wood). The research is being conducted in collaboration with the University of Natural Resources and Life Sciences (BOKU) in Vienna, the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) in Birmensdorf, the School of Agricultural, Forest and Food Sciences (HAFL) in Zollikofen, and the University of Zurich.
2. Range use
To date, there are no published studies using radiotelemetry to examine the range needs of the White-backed Woodpecker. Therefore, in a second part of the project, we attempt to determine range sizes as well as the habitat structures that are actually used by the species. To do this, White-backed Woodpeckers are caught and equipped with small radiotelemetry transmitters so that the locations and activities of the woodpeckers can be recorded on a regular basis. The use of telemetry makes it possible to locate the birds at all times, thus collecting objective data on range use and size. Knowledge of the range size of individual birds is an important step towards understanding the space requirements of populations.
The study on habitat selection and saproxylic beetles was conducted on 60 sites, each 1 km2 large, in Vorarlberg, Liechtenstein and eastern Switzerland. Before the start of the study, White-backed Woodpeckers were found in about half of the 60 one-kilometre squares; the species was presumed to be absent in the other half. The presence of the species was checked twice in each one-kilometre square using playbacks. After leaf out, we mapped various habitat structures, selected based on the literature and expert opinions, in all 60 one-kilometre squares. To estimate the abundance of saproxylic beetles, exit holes were counted on a 20 cm strip surrounding lying and standing deadwood.
To investigate range needs, the woodpeckers are caught using high nets and playbacks. The birds are then ringed, measured and fitted with small radiotelemetry transmitters weighing 3 % of their body weight. The transmitters are attached to the two central tail feathers and come off again in summer or autumn the latest, when the birds moult. First observations show that the transmitters do not interfere with flying or any other activities. Each bird is tracked several times a week and then watched for several hours.
On the global Red List of the IUCN, the White-backed Woodpecker is classified as “least concern”, but with a negative population trend. On the Red List of Swiss breeding birds, the species is classified as “vulnerable”, on Austria’s Red List as “endangered”. In addition, the White-backed Woodpecker is found in Annex I of the EU’s Directive on the conservation of wild birds, and in Annex II of the Bern Convention. Studies on the ecology of this specialised woodpecker species are therefore highly relevant for nature conservation policy.
The study will deliver important information for a better understanding of the factors influencing the occurrence of the White-backed Woodpecker. Unlike other studies of this species, our project is conducted in partly managed forests. The results will show whether the habitat needs identified in this study match previous findings. In particular, we hope to gain information on threshold values for the species’ occurrence in managed forests with respect to availability of deadwood (standing and lying), tree age (living trees) and tree density. These are important data to ensure that potentially suitable habitats are managed in ways that accommodate the White-backed Woodpecker’s needs. This would not only help to protect the White-backed Woodpecker, but, thanks to its role as an umbrella species, also contribute to the conservation of many other organisms that inhabit deciduous forests rich in deadwood.
In 2015, White-backed Woodpeckers were recorded in 20 of the 60 one-kilometre squares. Initial analyses on habitat selection show that the species’ occurrence probability in a one-kilometre square increases with the average diameter of living trees as well as of standing and lying dead trees. The abundance of saproxylic beetles and a moderate altitude also appear to be conducive to the occurrence of the White-backed Woodpecker.
In spring of 2016, three females and three males were caught and fitted with transmitters in both Vorarlberg and Liechtenstein. The birds roamed widely, which is consistent with earlier observations. Gathering information about the woodpeckers’ activities proved to be extremely difficult, however, as the birds could only rarely be observed, despite the tracking devices.
Thibault Lachat, School of Agricultural, Forest and Food Sciences (HAFL), Zollikofen
Hanna Kokko, Department of Evolutionary Biology and Environmental Studies, University of Zurich
Sabine Hille, Department of Integrative Biology and Biodiversity Research, BOKU, Vienna
Ueli Bühler (expert on White-backed Woodpeckers, Canton of Grisons)
Habitatwahl des Weißrückenspechts (Dendrocopos leucotos) in Vorarlberg, der Ostschweiz und dem Fürstentum Liechtenstein
Einflüsse von Habitat und Totholzkäfern auf das Vorkommen des Weissrückenspechts im Raum Vorarlberg, Liechtenstein und Ostschweiz. Jahresbericht 2015.