Thesis

Nest site selection and influence of woodpeckers in a burned forest of the Sierra Nevada

Understanding how woodpeckers re-occupy burned areas is important as they provide a keystone function by creating habitat for other organisms. This thesis research investigated the possible influence of three species of Picoides woodpecker on re-colonization by birds and mammals in a burned forest and compared nest site selection and factors influencing nest presence of woodpeckers. Woodpecker nests were found in 2009 and 2010. Woodpecker cavities found in 2009 were monitored for use by small mammals and birds, resulting in indices of recovery that describe the quantity and quality of secondary cavity use. White-headed woodpeckers had highest indices of cavity utilization, although Black-backed and Hairy woodpeckers were important to some secondary cavity users. Factors influencing nest site selection were compared with ANOVA and Kruskal-Wallis tests, with significant differences found in mean tree height and decay, and density of small and large snags, and canopy closure. Logistic regression was utilized to determine the factors with the greatest influence on nest presence. These were found to differ among the woodpecker species, although percent scorch of nest tree was important for all species. Densities of medium and small snags were positively associated with presence of Black-backed and Hairy woodpecker nests, respectively. Nest presence of White-headed woodpeckers was positively associated with decay and negatively associated with tree height and canopy closure. Differences in mean nest characteristics and factors influencing nest presence may explain differences in secondary cavity use, suggesting that cavity height, snag density, and decay play important roles in determining secondary cavity use in burned forests. Woodpeckers play an important role in post-fire habitats by rapidly colonizing burned areas and creating cavities that are used by many other species that rely upon them for nesting, denning, roosting, and resting. Understanding how wildlife species respond and recover from fires is critical for conservation and management of forest ecosystems.

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