Cavity occurrence and use by hole-nesting birds in Pyrenean managed oak forests

• Author(s): Penado, Andreia de Barros Mendes
• Date: 2009
• Persistent ID: http://hdl.handle.net/10451/1426
• Origin: Repositório da Universidade de Lisboa
• Subject(s): Aves; Nidificação; Quercus pyrenaica; Teses de mestrado
• Document Type: Master thesis
• Language: English
• Advisor(s): Robles Diez, Hugo; Rebelo, Rui Miguel Borges Sampaio e
• Contributor(s): Repositório da Universidade de Lisboa

Description

Tese de mestrado, Biologia (Biologia da Conservação), 2009, Universidade de Lisboa, Faculdade de Ciências

Resumo alargado em português disponível no documento

This study examines cavity occurrence and use by hole-nesting birds in managed Pyrenean oak (Quercus pyrenaica) forests in the southern Cantabrian Mountains (NW Spain). In 2007, cavity occurrence and use were assessed in 12 plots (6 in old forests, 6 in young forests), covering a total area of 97ha. Overall, 720 cavities from 466 trees were assessed. Generalized Linear Mixed Models (GLMMs) results showed that cavity trees were significantly larger than non-cavity-trees. Besides, cavity-trees were decayed in a significantly higher proportion than non-cavity-trees. Large decayed trees provided woodpeckers with suitable substrate for excavation, and were also a source of nonexcavated natural cavities. For nesting, birds preferred living trees, longer cavity depths, cavities with narrower entrances, woodpecker-created cavities and smaller diameter trees. The smaller holes may be preferred to avoid the access of medium and large sized predators. Similarly, deeper cavities may prevent predators from reaching them to remove chicks. Even if woodpecker-created cavities were preferred by birds, most of the cavities were not created by woodpeckers and only a small proportion of woodpecker-created cavities were used by birds (12%), so the role of woodpecker as keystone species in this area could not be confirmed. The preference for living trees may be related to cavity microclimate stability, as living trees heat and cool more slowly than decayed trees, leading to more stable temperatures. The preference for cavity-trees with smaller diameter may be due to the presence of large decayed trees unable to hold a nest. Taking into account that cavity-trees had larger diameters than non-cavity-trees, and that trees occupied by birds were smaller than non-occupied cavity-trees, many birds occupied medium-size trees. Nest-entrance tended to be oriented to East-Southeast, perhaps because such sunny orientations help to warm young and keep the cavity dry. Cavity and nest densities were higher in old forests in relation to young forests, perhaps because old forests provide higher availability of large decayed trees, which are important sources of cavities. Overall, occupation was low (19%), which may be due to the presence of a high proportion of low quality cavities which were unsuitable for nesting. Alternatively, intra- and interspecific territoriality may lead to low occupation rates of cavities