Nest Survival of Chickadees in Managed Forests: Habitat, Predator, and Year Effects.

We examined the influence of year, habitat, and predators on nest survival by monitoring 69 natural cavity nests of the chestnut-backed chickadee (Poecile rufescens) across a range of uncut and partial cut stands in northwest British Columbia during 2000-2003. We considered 3 spatial scales of habitat: 1) the stand (19-24 ha of uncut and partial cut stands), 2) the nest patch (a 0.03-ha patch centered on nest trees), and 3) the nest tree. At each scale we hypothesized that nest survival time of chickadees differed among years, as a result of harvest treatment, habitat characteristics, and predator activity. Nest predation rates fluctuated among years: 56% in 2000, 64% in 2001, 10% in 2002, and 12% in 2003. We identified the red squirrel (Tamiasciurus hudsonicus) as the dominant nest predator. At the stand and nest patch scales, only the covariate year reliably predicted survival time: Risk 1.81 (Year 2001) for both models. At the nest tree scale, we found the most support for a model with year and nest height: Risk 1.67 (Year 2001) -- 0.08 (Nest Height). All models indicated that for chickadees nesting in 2001, the probability of nest failure increased by more than 5 times. We found no effect of harvest treatment in the stand, nest patch, and nest tree models. Since squirrel density, space use, and activity near nest areas did not differ among years, we suggest that squirrels undergo a functional response and consume food items like eggs and nestlings following low mast years and cones following high mast years. Resource fluctuations that alter the availability and quality of food for red squirrels may result in strong variability in chickadee nest survival Studies that do not consider such temporal variation may conclude that sites with low nest survival are sink habitats. Managers and researchers may need to consider longer term and/or multitrophic level studies to examine interactions among birds, their predators, and the environment. [ABSTRACT FROM AUTHOR]

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