Direct and indirect weather impacts on spring populations of lesser spotted woodpecker (Dendrocopos minor) in Norway

摘要

In Norway, a positive relationship between spring numbers of lesser spotted woodpecker (Dendrocopos minor) and previous June temperatures has been interpreted as an effect of temperatures on woodpecker survival and reproduction during the breeding season. This article considers the possibility that woodpecker numbers are related to the abundance of the moth Argyresthia goedartella in the current year. Larvae and pupae of A. goedartella are important food for lesser spotted woodpeckers in early spring when few other surface-living invertebrates are available. The occurrence of this moth depends on the flowering of birch (Betula spp.) and alder (Alnus glutinosa), which in turn is influenced by June temperatures in the preceding year. Spring numbers of the lesser spotted woodpecker in two regions of Norway were compared with a trapping index of A. goedartella and weather variables assumed to influence the woodpeckers' breeding success and adult survival. The best multiple regression model included December temperatures and moth indices, supporting the hypothesis of a strong impact of A. goedartella on spring survival. Conservation strategies for the lesser spotted woodpecker should therefore focus not only on minimum areas of deciduous forests with decaying wood, but also on the availability of the moths' host trees, birch and alder.