Justification of Red List category
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be increasing, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
In Europe, the breeding population is estimated to number 3,700,000-7,000,000 pairs, which equates to 7,400,000-14,000,000 mature individuals (BirdLife International 2015). It is likely that the global population falls into the range 10,000,000-500,000,000 mature individuals.
The population is suspected to be stable in the absence of evidence for any declines or substantial threats. The European population is estimated to be increasing (BirdLife International 2015).
During the breeding season this species is found in thick undergrowth, such as dwarf willow (Salix) clumps in damp valleys and riverine thickets, and in forests, principally of birch (Betula), willow, poplar (Populus) and pine (Pinus) forests with occasional spruce (Picea). At higher altitudes, it is also found in rhododendron (Rhododendron) thickets and in montane scrub above the tree-line. In Siberian taiga it frequently uses Alnaster fruticosus thickets. Breeding occurs from June-August. The nest is made mostly of grass stalks, bits of reeds, moss, plant fibres and horsetail (Equisetum) shoots and is placed on the ground in vegetation among tree roots, grass or reed clumps, tussocks or hummocks. Clutches are five or six eggs. It feeds mostly on small insects and other invertebrates. The species is migratory and winters in south-east Asia (Clement 2015).
The species is threatened by future climate change (Heikkinen 2006).
Conservation Actions Underway
CMS Appendix II. Bern Convention Appendix II. There are currently no known conservation measures for this species within Europe.
Conservation Actions Proposed
Research into causes of declines in Europe and into appropriate measures for mitigating climate change threat.
Text account compilers
Ashpole, J, Butchart, S., Ekstrom, J., Khwaja, N. & Symes, A.
BirdLife International (2023) Species factsheet: Phylloscopus borealis. Downloaded from http://datazone.birdlife.org/species/factsheet/arctic-warbler-phylloscopus-borealis on 07/12/2023.
Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from http://datazone.birdlife.org on 07/12/2023.