ABSTRACT

Cavity nesting birds depend on the availability of tree cavities for breeding, but the structure of the surrounding environment may also impact cavity occupancy. Here we investigated the effects of forest structure on occupancy rates of excavated cavities and similar-size nest boxes by cavity nesters in managed southern boreal forests in Finland. We recorded the occupancy over five breeding seasons (2017–2021) and derived forest structure parameters from high-resolution thematic raster maps. We found a high occupancy rate in nest boxes (81%), but lower rates in natural cavities excavated in forest interior, forest edges and retention trees (42-46%). The analyzes focusing on Paridae only revealed that the occupancy rates in nest boxes were decreasing with increasing amounts of Norway spruce and deciduous tree foliage biomass, and tree height, but increasing with the proportion of Scots pine. In forest interior cavities, we found a negative effect of stand age but a positive effect of the proportion of spruce. We conclude that the benefits of nest boxes can be maximized by considering specific forest parameters when deploying them. In excavated cavities the occupancy rates are likely more dependent on the varying internal quality than on the forest structure.

摘要

洞穴筑巢的鸟类依赖于树洞的可用性进行繁殖，但周围环境的结构也可能影响树洞的占用。在这里，我们研究了森林结构对芬兰管理的南部北方森林中洞穴筑巢者挖掘的洞穴和类似尺寸巢箱的占用率的影响。我们记录了五个繁殖季节（2017-2021）的占用率，并从高分辨率专题栅格地图中得出了森林结构参数。我们发现巢箱的占用率较高（81％），但在森林内部、森林边缘和保留树中挖掘的自然洞穴中的占用率较低（42-46％）。重点分析Paridae仅显示，巢箱的占用率随着挪威云杉和落叶树叶子生物量和树高的增加而减少，但随着欧洲赤松比例的增加而增加。在森林内部空腔中，我们发现林龄有负面影响，但云杉比例有正面影响。我们的结论是，在部署巢箱时考虑特定的森林参数，可以最大限度地发挥巢箱的好处。在挖掘的洞穴中，占用率可能更取决于内部质量的变化，而不是森林结构。