A comparative analysis of fruit feeding among Mediterranean passerine birds

We analyse fruit feeding ecology of Mediterranean passerines in a regional, trait-based framework, with emphasis on their role as seed dispersers in Iberian scrub and woodland habitats. We compiled ecomorphological traits for 146 species (N> 6000 individuals), including body mass, gape width, and gut morphology and transit rates, from mist-netted birds, museum specimens, and published trait sources, also including data on digestive traits. Fruit use was quantified from standardized focal watches and camera-trap records at fruiting plants, providing estimates of visit frequency, duration, fruit intake rates, and fruit handling behaviour under natural field conditions. Species were classified along a trophic gradient from non-frugivores to pulp consumers, seed dispersers, and seed predators, and we used canonical discriminant analyses to examine how morphological and digestive traits distinguish these groups. We further quantified the fit between gape width and fruit diameter to assess morphological constraints on fruit size use. Frugivorous and seed-dispersing species occupy a distinct multivariate trait space, characterized by wider gapes, modified digestive anatomy, and faster transit rates relative to non-frugivores of similar size, and show higher per-visit fruit ingestion rates tightly constrained by gape-fruit matching and handling mode. Our results underline the functional distinctiveness of Mediterranean avian frugivores and illustrate how trait syndromes and foraging behaviour jointly shape patterns of fruit use and the structure of plant-frugivore interaction networks in Iberian Mediterranean ecosystems.