Population trends and fluctuations in Swedish woodpeckers

Sven G Nilsson,Ulf Wiktander,Ola Olsson,Sören Svensson

doi:10.34080/os.v2.22398

Abstract

This is a quantitative study of population changes in four non-migratory woodpeckers in Sweden. Data were collected during five periods from late autumn to spring and during the breeding season, mainly using point counts. Most analyses are based on the proportion of the routes (each with 20 points) with observation of the species in each year. From 1975 to 1991 there were no population trends in the Great Spotted and Black Woodpeckers, but decreases in the Green and Lesser Spotted Woodpeckers. The mean annual decrease was about 2% in the Green and 4% in the Lesser Spotted Woodpecker. There was no trend in winter weather over this period, and only for the Black Woodpecker we found associations between mild winters and numbers recorded. The Great Spotted Woodpecker population increased in years with a high spruce seed supply. In southernmost Sweden frequency of observation was higher for the Green and, in winter, for the Black Woodpecker than further north, while the reverse was true for the Great Spotted Woodpecker. No regional difference was found for the Lesser Spotted Woodpecker.

Highlights

Woodpeckers are most common in old, unmanaged forests where, in Europe, up to eight species can occur in the same forest (e.g. Tomialojc et al 1984)
Data from different seasons and regions were consistent in indicating no trend in populations of the Black and the Great Spotted Woodpeckers (Fig. 1 and 2)
The analysis indicates a positive effect of spruce seed supply on the size and rate of change of the Great Spotted Woodpecker population (Table 4)

Summary

Introduction

Woodpeckers are most common in old, unmanaged forests where, in Europe, up to eight species can occur in the same forest (e.g. Tomialojc et al 1984). In many managed forests in Sweden, only the Black Woodpecker Dryocopus martius and the Great Spotted Woodpecker Dendrocopos major occur The Middle Spotted Woodpecker Dendrocopos medius, dependent on old, open oak-dominated forests in Sweden, decreased over the last hundred years and disappeared in 1982 (Pettersson 1985). The White-backed Woodpecker Dendrocopos leucotos requires extensive forests with many old deciduous trees and snags (Aulen 1985). It has contracted considerably from its fonner breeding range (Aulen 1986). In 1988, its population was estimated at 80 - 110 pairs (Aulen et al 1989)

Methods

Results

Conclusion