Twig selection on mountain birch <i>Betula pubescens</i> by winter‐feeding willow grouse <i>Lagopus lagopus</i> in a subarctic forest

In a subarctic forest at Kvaløya, northern Norway, willow grouse Lagopus lagopus fed snow level by clipping bits of twigs from mountain birch Betula pubescens during winter. Birch has two types ending in terminal bud: long with smooth bark, and short rings thicker bark. The selected ringed above despite surplus the forest. Ringed had more bark cm −1 twig length higher relative bark/wood ratio than twigs. Smooth growth nodes that increased diameter inwards tip. Because non‐linear relation between area circumference circle, decreased for each node. Although being able to clip much twigs, 90% clipped were ≤ 2 mm diameter. It is concluded optimally on winter selecting minimize fibrous wood intake.