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 41,000,000-59,500,000 pairs, which equates to 81,900,000-119,000,000 mature individuals (BirdLife International 2015). It is therefore likely that the global population falls in the band 10,000,000-500,000,000 mature individuals.
In Europe, trends between 1980 and 2013 show that populations have undergone a moderate increase (EBCC 2015).
The species occupies lowland deciduous forest and woodland with low undergrowth, as well as parks, hedgerows, shelterbelts, overgrown cemeteries, large gardens and reedbeds. In the east of its range it is found in spruce Picea and pine Pinus forests of Siberian taiga. Frequently, it inhabits damp alder Alnus and willow Salix woodland and river valleys and in the south of its range it prefers habitats with at least some tall trees but, exceptionally, breeds in coastal scrub lacking tall trees. It breeds from April until early August and lays five to six eggs. The nest is a ball of dry grasses, leaves, moss, plant fibres and feathers, normally placed on the ground and well concealed in a bramble bush Rubus fruticosus, a patch of nettles Urtica, grass or other thick vegetation. The diet is mostly insects and their eggs and larvae but also includes other arthropods, small molluscs Gastropoda, seeds and berries (Clement 2015). Most populations of the species are migratory (Snow and Perrins 1998).
Fluctuations in the British population are believed to be likely due to droughts in the non-breeding quarters in the West African Sahel (Clement 2015). In Finland, the species suffers from habitat fragmentation, interspecific competition from Willow Warbler P. trochilus and Goldcrest Regulus regulus, and climate change (Lampila et al. 2009).
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
Although this species is not threatened locally it may benefit from protection and restoration of its habitat. Monitoring should be implemented to detect population changes.
Text account compilers
Ashpole, J, Butchart, S., Ekstrom, J. & Khwaja, N.
BirdLife International (2017) Species factsheet: Phylloscopus collybita. Downloaded from http://www.birdlife.org on 17/12/2017. Recommended citation for factsheets for more than one species: BirdLife International (2017) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 17/12/2017.