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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.

Survival of juveniles during the postfledging period can be markedly low, which may have major consequences on avian population dynamics. Knowing which factors operating during the nesting phase affect postfledging survival is crucial to understand avian breeding strategies. We aimed to obtain a robust set of predictors of postfledging local survival using the great tit (Parus major) as a model species. We used mark–recapture models to analyze the effect of hatching date, temperatures experienced during the nestling period, fledging size and body mass on first‐year postfledging survival probability of great tit juveniles. We used data from 5192 nestlings of first clutches ringed between 1993 and 2010. Mean first‐year postfledging survival probability was 15.2%, and it was lower for smaller individuals, as well as for those born in either very early or late broods. Our results stress the importance of choosing an optimum hatching period, and raising large chicks to increase first‐year local survival probability in the studied population.

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