Data in Brief: Twig selection on mountain birch Betula pubescens by winter-feeding willow grouse Lagopus lagopus in a subarctic forest

In a subarctic forest at Kvaløya, northern Norway willow grouse (Lagopus lagopus) fed at snow level by clipping bits of twigs from mountain birch (Betula pubescens) during winter. Birch has two types of twigs ending in a terminal bud: long twigs with a smooth bark, and short twigs with rings of thicker bark. The grouse selected ringed twigs above smooth twigs despite a surplus of smooth twigs in the forest. Ringed twigs had more bark cm-1 of twig length and a higher relative bark/wood ratio than smooth twigs. Smooth twigs had growth nodes that increased in diameter inwards from the tip. Because of the non-linear relation between the area and the circumference of a circle, the bark/wood ratio decreased for each node. Although being able to clip much thicker twigs, 90 % of smooth twigs clipped by grouse were ≤ 2 mm in diameter. It is concluded that willow grouse fed optimally on birch in winter by selecting twigs to minimize fibrous wood intake., Please see the README document (\"README_Dataset_WillowGrouseFeedingEcology.md\") describing the data content and the published article for description of methods used for collecting the data: Klemetsen, A. & SmalÃ¥s, A.. 2023. Twig selection on mountain birch Betula pubescens by winter-feeding willow grouse Lagopus lagopus in a subarctic forest. Journal of Wildlife Biology. Accepted manuscript. Doi: https://doi.org/10.1002/WLB3.01065.,挪威北部克瓦略亚（Kvaløya）的亚寒带森林中，柳雷鸟（Willow Grouse，Lagopus lagopus）在冬季会通过啄断山桦（Mountain Birch，Betula pubescens）的细枝，在雪层高度处取食食物。山桦的枝条均带有顶芽，可分为两类：一类为树皮光滑的长枝条，另一类为带有增厚树皮环纹的短枝条。尽管森林中光滑树皮枝条的供给充足，柳雷鸟仍优先选择带环纹的枝条。 带环纹的枝条每厘米枝长的树皮量更高，且树皮与木材的相对占比也高于光滑枝条。光滑枝条的生长节点直径从枝梢向内逐渐递增，由于圆的面积与周长呈非线性关系，每个生长节点处的树皮/木材占比会随之降低。尽管柳雷鸟具备啄断更粗枝条的能力，但它们啄取的光滑枝条中，90%的直径≤2毫米。 研究表明，冬季取食山桦的柳雷鸟会通过选择性采食枝条，最大限度减少纤维状木材的摄入，从而实现最优觅食策略。 有关本数据集的内容说明及数据采集方法的详细细节，请参阅README文档"README_Dataset_WillowGrouseFeedingEcology.md"，以及以下已录用待刊的发表论文：Klemetsen, A. 与 Smalås, A. 于2023年发表的《亚寒带森林中冬季取食的柳雷鸟对山桦Betula pubescens枝条的选择》，刊载于Journal of Wildlife Biology，DOI：https://doi.org/10.1002/WLB3.01065。