Long-term effects of forest management on territory occupancy and breeding success of an open-nesting boreal bird species, the Siberian jay

Abstract

In large parts of the world forests are intensively managed, affecting stand structure and biodiversity. Since re-growth of trees can be slow and management cycles can span over 100years, long-term longitudinal data are needed to assess the effects of forestry on organisms living in these habitats. Here, we draw upon 50years of population data of an open-nesting, sedentary bird species, typically of boreal forests, the Siberian jay (Perisoreus infaustus). Forests at the study site were managed by clear-cutting and re-plantation, and a management cycle spanning over 120years. We tracked changes in forest structure in the nest vicinity and the whole territory with the help of aerial images, and linked them to territory occupancy and offspring production in 13 territories. While territories were occupied in 77.2% of all instances, reproduction was only successful in 19.6% of all instances. Both parameters were positively influenced by a large proportion of unthinned forests older than 50years, which provide visual protection from nest and adult predators. Thus, it is crucial to assess both territory occupancy and reproductive output to understand the effects of forestry on bird populations. Moreover, our results suggest that in forests with slow turnover cycles, management which avoids thinning (such as green tree retention forestry) can promote population persistence of open-nesting bird species.