The wintering bird community in the Eucalyptus globulus plantation of Arminza (Vizcaya) was studied during two consecutive winters. During the mild winter of 1989-1990, around 39 birds/10 ha were counted in this plantation. A half of these birds (21 birds/10 ha) fed on eucalypt trees. The main substrata they used were flowers (53,5 % of birds feeding on the eucalypt trees), sprouts of growing leaves (26,9 %) and capsules (13,7 %). The remaining substrata showed minor importance as feeding places: trunks (0,6 %), branches over 5 cm diameter (0 %), branches of 1-5 cm diameter (0,9 %) and developed leaves twigs under 1 cm (4,4%). This unbalanced distribution of birds on the Eucalypt trees was related to the food distribution. Flowers had many invertebrates (mainly Tysanoptera and Diptera) and nectar, both foods being useful resources for several species (Sylvia atricapilla, Phylloscopus collybita, Parus caeruleus and Parus major). The sprouts of growing leaves, infested by bugs (Homoptera), were mainly used by Regulus ignicapillus and the seeds in Eucalypt capsules were exploited by Carduelis spinus, Parus major and P. ater. During the cold winter of 1900-1991, eucalypt trees did not flourish and bugs vanished. This decrease in food resources was related to the sharp decrease in the abundance of the wintering avifauna (9 birds/10 ha).
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