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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Tree preferences and niche use by foraging forest birds depending on forest stand tree composition
Auteurs :	Hans Utschick, Auteur
Type de document :	Article
Dans :	Ornithologischer Anzeiger (45(1) AUG 2006)
Article en page(s) :	1-20
Résumé :	Bird foraging studies in Mid-Swabia (Southern Bavaria) within mature forest stands (May 2000, Feb 2001) of varying naturality (forest reserves; pure deciduous stands, spruce-dominated mixed stands; Douglas fir stands) revealed general preferences for old broadleaved trees (especially oak) and larch (mainly during sprout of needles). On deciduous trees all parts (canopy and stem strata) were used intensively, while on spruce and douglas fir birds were abundant only in the lower tree parts (subcanopy, trunk with dead branches), mainly members of the stem climbing foraging guild and ubiquitous forest birds like the Chaffinch. In the upper spruce crown (not douglas fir) exterior strata supported only few coniferous species like Coal Tit or Goldcrest. In winter, interior and lower crown strata obviously offered more food then the outfreezing exterior and upper ones. In the mixed stands birds clearly preferred all leave tree species including those no more preferred in pure deciduous stands (maple, birch). Vice versa, spruce trees strongly attracted foraging birds only when embedded as a single or in small groups in mature deciduous stands, due to rich arthropod abundance (hide effect; most important in winter). Within the mature deciduous stands typical for nature reserves, birds on their foraging raids regularly included suboptimal food habitats (small trees, unfavourable canopy strata) usually avoided in younger or coniferous stands. Habitat patchiness was important, for birds preferred tree groups at gap margins. Probably, in winter there is an irradiation effect causing daily shifts in vertical niche use too. In the afternoon of sunny days more foraging birds used the upper strata of leave trees or larch than in the morning, but not so in evergreen coniferous trees like spruce.

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