Date of Award

5-2022

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Forest Resources

Advisor

Amber Roth

Second Committee Member

Cynthia Loftin

Third Committee Member

Aaron Weiskittel

Abstract

The Rusty Blackbird (Euphagus carolinus) has experienced a steep population decline since the 1970s, with qualitative accounts suggesting that the species’ numbers have been falling prior to the 1950s. The reason for this decline is still not fully understood, though recent work suggests that habitat destruction and disturbance in the breeding and wintering ranges are likely causes. The species is a habitat specialist that relies on spruce-fir stands located near wetlands for breeding in the boreal and Acadian forests of North America. Historically, the natural disturbance regime in the Acadian region included biotic agents such as beaver and spruce budworm, though over the last century anthropogenic change due to commercial logging has become more commonplace. Rusty Blackbird response to intensive commercial forestry practices within their breeding range has yet to be assessed fully. I examined Rusty Blackbird nesting and fledgling habitat selection and survival in intensively managed forests that contained practices such as precommercial thinning and regenerating clearcuts in Maine and New Hampshire. Fledglings were affixed with VHF-radio transmitters and tracked via radio telemetry. Nest and fledgling use points were compared to paired, random points to determine habitat and harvest metrics that were preferentially selected. We used resource selection functions (RSFs) in the form of general linear mixed models (GLMMs) to compare used to available points at multiple spatial scales. Similarly, we ranked daily survival rates (DSR) models to identify what habitat characteristics were associated with nest and fledgling survival. We found that adult Rusty Blackbirds selected nest sites with ~50% wetland cover and an average canopy cover of ~40% in a 30-m radius around the nest at the stand scale, and by basal area at the within-stand scale. At the among-stand scale, nest DSR increased in stands with lower average canopy heights and lower cover of precommercially thinned stands in 30-m radii around the nest. At the within-stand scale, nests had higher DSR when placed higher in trees and not in precommercially thinned stands. Fledglings selected areas with wetland cover of greater than 25% and average canopy heights of 50-75% in the first two weeks following fledge, and selected for stream sides and average canopy heights of ~60% after the first two weeks since fledge. While our fledgling sample size was small (n=35), fledgling DSR decreased in stands with lower average canopy heights. Overall, nest and fledgling survival (65% and 71%, respectively) was high in northern New England, though our results suggest that precommercially thinned stands may act as ecological traps for nesting Rusty Blackbirds.

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