BIJLSMA RG (1981) Western Bonellis Warbler Phylloscopus bonelli as breeding bird in the Netherlands. LIMOSA 54 (2): 57-62.

In the Netherlands up to 1979 only twelve records of Bonelli's Warblers have been accepted by the Rarities Committee. Surprisingly, from 1974 onwards a small number of singing males were found on the SW. Veluwe. This paper gives some data on the SW. Veluwe population and discusses the status of the Bonelli's Warbler in the Netherlands.
      During 1974-80 1, 2, 5, 1, 1, 2 and 4 territories respectively were found on the SW. Veluwe (c. 200 km2, of which c. 110 km2 contains suitable habitat) (figure 1, 3). In seven territories the males remained unpaired, sometimes despite persistent singing activities. Nine pairs were located; of these at least six. succeeded in fledging 3-6 young (27 young in sum). Taken all territories into consideration from 1974 onwards, the boundaries were 0-5000 m apart (average 1300 m). In only three of these territories Bonelli's Warblers were recorded in more than one year (figure 3).
      Eleven of the 16 males were located in mixed forest with full-grown stands or solitary trees of Pseudotsuga, Quercus (both robur and rubra), Fagus and Betula with numerous clearings and with well-developed patchy undergrowth on a soil with pronounced micro-relief (figure 2). The other males were found in old Pseudotsuga or Picea forest mixed with scanty growth of Quercus and/or Betula, old pine forest with some undergrowth of Quercus rubra and Prunus serotina. One territory was located in pure old Quercus rubra. Clearings, dead branches on the ground and soil relief were found in all these sites.
      The birds were feeding restlessly in the upper parts of mainly deciduous trees, usually on the outer branches and sometimes hovering at the end of twigs like Regulus regulus. Aphids were primarily taken in April and May, small caterpillars predominated thereafter (mainly Tortrix). Small moths (Lepidoptera), spiders (Arachnida), Neuroptera and Ephemeroptera were taken as well. Caterpillars larger than 2 cm were hold with the left leg and hammered to pieces before eaten.
      It is suggested that the Bonelli's Warbler is more common in the Netherlands than the scanty information indicates. During the Atlassurveys (1973-77) two more probable and one possible breeding case(s) were recorded (Bijlsma 1979) whereas the author found another pair (presumed breeding) in 1980 some 20 km north of the SW. Veluwe. Unacquaintance with the species probably results in under-recording. Western Bonelli's Warbler Phylloscopus bonelli

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