Date of Award

5-2003

Level of Access

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Wildlife Ecology and Wildlife Conservation

Advisor

Malcolm L. Hunter, Jr

Second Committee Member

Raymond J. O'Connor

Third Committee Member

Alan White

Abstract

I investigated effects of small-gap timber harvests on bird communities at nine sites (10 ha each) within the Penobscot Experimental Forest (PEF), grouped into three replicated "blocks" (three sites each). Blocks were randomly treated with three treatments: 10% harvest, 20% harvest, and no harvest (i.e., control). I examined how treatments affected breeding songbird abundance, richness, and site-fidelity over four consecutive summers, including 1-3 years before and after each site was harvested. Ability to detect treatment effects was limited by the small number of replicates, but power analyses indicated that given the experimental design and observed variability, there was a high (>go%) probability to detect 20-30% differences in overall abundance among treatment groups. There was no evidence that treatments caused changes of this magnitude, or affected densities of individual species, avian richness, or which species were most abundant before versus after treatment. Annual variations in densities were much stronger than differences between treatment groups. Of 96 male Hermit Thrushes and 74 male Ovenbirds captured within sites, an average of 62% and 28% of respective males were recaptured annually. Of these, 90% of male Hermit Thrushes and 94% of male Ovenbirds were recaptured on the same site in successive years, regardless of the site's treatment status. However, there was a significantly higher tendency for Hermit Thrush to disperse to new sites if they were previously captured on treated versus control sites. In Chapter 3 I argue that annual fluctuations in bird densities may be driven largely by predator (i.e., red squirrel, Tamiasciurus hudsonicus) population dynamics. Previous research has shown that avian nest-predation by red squirrels strongly affects local breeding productivity of birds, and that red squirrel populations are regionally synchronous. I examined four lines of evidence that are consistent with the premise that squirrel population fluctuations can affect bird populations over large areas. Squirrel populations in the PEF peaked in 1995 and crashed in 1996, while bird densities decreased from 1995 to 1996, then increased sharply from 1996 to 1997. Breeding Bird Survey data showed a similar pattern of avian population change (especially for coniferous-forest birds) from 1995- 1997 at much larger scales.

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