Nestling food of three hole-nesting passerine species and experimental increase in their densities in Mediterranean oak woodlands

Abstract

We studied nestling food of three species breeding in Mediterranean oak woodlands that collect food in different niches of trees: blue tit (Cyanistes caeruleus; foliage-gleaner), great tit (Parus major; bark–foliage-gleaner) and nuthatch (Sitta europaea; bark-gleaner) in 2013–2014. Species-specific functions were compared using size and composition of preyed caterpillars, and nest-boxes were used in a before-after control-impact (BACI) design to test increase in breeding densities by providing nest-boxes. Our results demonstrate a high importance of caterpillars in the nestling diet of the three passerine species and suggest their complementary predation on early and late instars of the same Lepidoptera species. According to results of our BACI experiment, species’ breeding density increased by providing nest-boxes, with blue tit showing the highest difference in percentage change between manipulated and control plots (38.2, 26.8 and 14.3 % for blue tit, great tit and nuthatch, respectively). Overall, we highlight the combined functions of different tree-foraging guilds in caterpillar predation and propose nest-box provision as a management method to prevent defoliator outbreaks in Mediterranean oak woodlands.