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RESEARCH PRODUCT

Variation in Great Tit Nest Mass and Composition and Its Breeding Consequences: A Comparative Study in four Mediterranean Habitats

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Bird nests are structures whose properties affect breeding performance. Thus, the vast majority of bird species build their own characteristic nests, selecting appropriate materials to do so. However, in habitats where the availability of "ideal" materials is low, some ability to use alternative ones would be necessary, even at the cost of having breeding success reduced. The Great Tit (Parus major) breeds under widely different environmental conditions. Its nests are althought to be composed mainly of moss, although very few studies have quantified nest composition. Our target here was describing Great Tit nest mass and composition in four different Mediterranean habitats, and exploring their fitness consequences. We recorded the basic breeding parameters, collected nests after fledging, and decomposed a sample of them, in four eastern Spanish populations: Pina (pines and oaks), Mariola (pines), Font Roja (holm oaks), and Sagunto (orange trees). Nests were heavier in Sagunto and Mariola and lighter in Font Roja, and those from Sagunto had the lowest amount of moss. Clutch size decreased as moss mass increased in the four sites. In Sagunto, hatching success increased as moss mass increased. In all habitats, nestling condition was lower when the amount of sticks and feathers was higher. We conclude that Great Tit nest mass and composition varies considerably between habitats, and the amount of different materials could affect different breeding parameters.