Phylloscopus bonelli is a widespread summer visitor to southern Europe, which constitutes >75% of its global breeding range. Its European breeding population is very large (>1,400,000 pairs), and was stable between 1970-1990. Although trend data were not available for the large Spanish population during 1990-2000, the species declined in a number of countries, and the large French population halved in size. Hence, this previously Secure species probably underwent a moderate decline (>10%) overall, and consequently it is now provisionally evaluated as Declining.

Breeds only in middle and lower middle latitudes of west Palearctic in warm temperate and Mediterranean continental and oceanic climates. At lower levels, often favours open deciduous woodland of oak, birch, beech, sweet chestnut, and other trees, provided canopy is thin and undergrowth suitable. Equally at home, however, in mixed or pure coniferous woods composed of pine, spruce, or larch, from foothills to 1000 m.

Egg laying May to early July in North-West Africa, April in France, end of April mid May in Switzerland, about mid May in Greece. Nest site is on ground, under overhanging vegetation, often in slight hollow in ground or bank. Nest is a domed structure with side entrance, largely of grass, with small amounts of leaves and moss, lined with finer material including some hair. 5-6 eggs are laid, incubation 12-13 says, by female only.

Mainly insects and a few other invertebrates. Feeding methods much as in other Phylloscopus. Most foraging done in tree crown, frequently on outermost branches and twigs.

This species has a large range, with an estimated global Extent of Occurrence of 1,000,000-10,000,000 km2. It has a large global population, including an estimated 2,700,000-6,900,000 individuals in Europe (BirdLife International in prep.). Global population trends have not been quantified, but the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e. declining more than 30% in ten years or three generations). For these reasons, the species is evaluated as Least Concern.

Migratory, wintering in narrow belt along southern edge of Sahara, mostly 10-17°N, from Sénégal and southern Mauritania east to Lake Chad basin. Probably heads west of south initially in autumn; high concentrations occur within Europe, but passage inconspicuous in North Africa, presumably due to overflying. In spring, however, locally abundant in North Africa; migration is apparently on broader front. Autumn migration begins mid-July, with main movement in August, continuing to early or mid-September. Arrives early in Sénégal, from first days of September, and northern Nigeria early October. Spring migration begins late February or early March. Arrives on European breeding grounds from early April in south, mid-April in north. Vagrant in north-west Europe. In Britain and Ireland, spring records are chiefly in south, suggesting overshooting; autumn records more widespread.

article number 1 Title
A phylogenetic analysis of the evolution of moult strategies in Western Palearctic warblers (Aves: Sylviidae)
Author(s): E. Svensson and A. Hedenstrom
Abstract: Adult birds replace their flight feathers (moult) at least once per year, either in summer after termination of breeding or (in the case of some long-distance migratory species) in the winter quarte..[more]..
Source: Biological Journal of the Linnean Society (1999), 67: 263-276
download full text (pdf)

article number 2 Title
Genetically confirmed interbreeding between western Bonelli's warbler ( Phylloscopus bonelli ) and wood warbler ( P. sibilatrix )
Author(s): Christian Dietzen, Clemens Hackenberg et al
Abstract: During May and June 2003, a mixed breeding pair consisting of a male western Bonelli's warbler (Phylloscopus bonelli) and a female wood warbler (P. sibilatrix) successfully raised six young in a broad..[more]..
Source: J Ornithol (2007) 148:8590
download full text (pdf)