Autumn at Grimsö - Hazel grouse survey

23 November 2021

In late autumn, work at SITES station Grimsö mainly comprises of digitalization and compilation of data from the earlier peak season, and lab work to specify ticks sampled from voles etc. However, outdoor activities still run in autumn, one of which is the hazel grouse survey.

The hazel grouse (Bonasa bonasia) survey at SITES Grimsö started in 1987 as part of a conventional research project. This quite anonymous species is strongly connected to specific habitat features and the data obtained during the initial project showed to be interesting, and unique for Sweden. Thus, the annual counts continued as a monitoring program after the initial project ended. The hazel grouse is included in some of the national bird monitoring programs, but the large-scale and long-term survey designed only for hazel grouse at Grimsö, is rare also at the international level.

The survey is conducted as territorial mapping in part of the research area, and the method includes the use of a whistle imitating the territorial song of a male hazel grouse. A systematic and dense network of whistle points are applied throughout the study area, so all territory holders, either just the male or a male and female together, are found. In the last Decades, hazel grouse have shown strong declines in southern Sweden, which is also mirrored in our survey. This highlights the importance of long-term and detailed data which improves the understanding of causes and effects behind population trends.