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Temporal and spatial variation in habitat quality : breeding ecology of the chestnut-backed chickadee in uncut and partial cut forests in British Columbia Mahon, Carmen Lisa

Abstract

I examined how partial cutting influenced the use and selection of habitat by chestnut-backed chickadees (Poecile rufescens). My objectives were: (1) to examine the variability of nest survival and identify the contributions of year, harvest treatment and habitat characteristics, and predator activity at 3 spatial scales, (2) to compare use and selection of nesting habitat in uncut, partial cut-mature, and partial cut-old sites at 3 spatial scales, and (3) to identify the influence of habitat structure or annual differences in food abundance and predation pressure on reproductive output. I found that nest predation rates fluctuated between years: 56% in 2000, 64% in 2001, 10% in 2002, and 12% in 2003. Survival models revealed that only the covariate year reliably predicted nest survival time at the stand and nest patch scales, while year and nest height predicted survival time at the nest tree scale. I found no effect of harvest treatment in the stand, nest patch, and nest tree models. Squirrel population density, space use, and activity near nest areas did not differ between years. Indirect effects on nest survival may have occurred due to temporal changes in habitat quality for squirrels. Chestnut-backed chickadees exhibited flexibility in resource selection when selecting nest sites. I found no correlation between the density of breeding chickadees and structural characteristics at the stand scale, but found selection of similar resources at the nest patch and nest tree scales. When selecting nest trees, chickadees in my system used a variety of tree species, conditions, sizes, nest site locations, and cavity types. Reproductive output showed no consistent pattern across sites, and was highly variable among years. Chickadee foraging patterns differed between years suggesting annual changes in prey abundance and type, although reproductive output did not decrease with a decline in primary prey. Predators had the greatest impact on the daily mortality rate of nesting chickadees. Indices of predator density did not differ among years; a functional response by predators due to changes in their food supply may have strongly influenced annual reproductive output of chickadees in this population.

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