Bird numbers during winter 1986 to 2020 in a coniferous forest in Schleswig-Holstein were depending on migration progress, food supply, and tree development

Abstract

For 35 years, the line transect method was used to count winterbirds in a coniferous forest in Schleswig-Holstein over a 9.2 km stretch. Censuses were conducted on three
days between November and February. The dominant tree species was the Japanese Larch but also Spruce were quite often. The maximum number of individuals on this route was 392 specimens per km, with an average of 92 specimens. This is a comparable high diversity. Highest species abundance between eleven dominant, subdominant, and influent species had been found within Coal Tits Parus major and Goldcrests Regulus regulus with more than 20 % each. They were followed by Eurasian Siskin Spinus spinus, Eurasian Blue Tit Cyanistes caeruleus, Common Crossbill Loxia curvirostra, and Common Redpoll Carduelis flammea, also dominant species. European Crested Tit Lophophanes cristatus, Goldcrests, Eurasian Blue Tit, Coal Tit and Eurasian Jay Garrulus glandarius had a presence of 100 %. Nine of the eleven common species showed strong changes in population density: six with positive and three with negative development. The numbers of Eurasian Blue Tit, Goldcrest and Common Redpoll were strikingly higher at the beginning than at the end of the project.

In the course of the aging of the trees and continued economic interventions, the living conditions change. In particular, mass changes of the caterpillar Coleophora laricella and the seeds of Larch and spruce have major effects, as well as changing migration habits. Occasional invasions, of up to three bird species per winter, shape
the overall numbers on a large scale. Therefore, a special bird community is only temporary. The total number of birds per count day varies by a factor of nine.  However, the typical coniferous community is stable in the long term.

Some similarities of the Loher Gehege with other coniferous forests are obvious: dominance structure and species composition are totally comparable. But the age of the trees and their diversity are responsible for the different density of individual bird species.