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

• Main Authors: Klemetsen, Anders, Smalås, Aslak
• Format: Other/Unknown Material
• Language: unknown
• Published: Zenodo 2023
• Subjects: Lagopus lagopus; birch; Selective Feeding; sub-Arctic; Kvaløya; Northern Norway; Subarctic
• Online Access: https://doi.org/10.5061/dryad.s7h44j1bd

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.