Semester

Spring

Date of Graduation

2022

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Wildlife and Fisheries Resources

Committee Chair

Christopher Rota

Committee Co-Chair

Michael Strager

Committee Member

Michael Strager

Committee Member

Petra Wood

Abstract

Nearctic-Neotropical migrant birds experience a wide range of environmental conditions throughout their annual cycle; thus, it is particularly challenging to evaluate the spatial factors that may influence population growth. The Canada Warbler (Cardellina canadensis) faces substantial range-wide population declines, but little study has been conducted regarding elements occurring across the entire year that drive demographic rates. The aims of this research are (1) determine the relationship between Canada Warbler population demographic rates and environmental conditions along an elevation gradient in the central Appalachian Mountains and (2) ascertain the nonbreeding season location and migratory routes used by the central Appalachian population, which is near the southern extent of the entire breeding range. Research occurred from 2019 – 2021 at six study sites ranging in elevation from 526 – 1282m spanning an approximate 130km north-south gradient within the Monongahela National Forest, West Virginia, USA. To determine the relationship between demographic rates and environment, I assessed adult annual survival and daily nest survival. I uniquely color-banded 203 adult male Canada Warblers in 2019 and 2020, and resighted marked birds in 2020 and 2021. I modeled survival in response to predictor variables including elevation, rhododendron coverage, available stream length, topographic position, and aspect. I implemented a spatial Cormack-Jolly-Seber model with Bayesian methods and compared models using DIC criteria. To determine nest survival, I located nests and monitored their outcomes using motion-sensitive game cameras. I modeled daily nest survival as a function of elevation, rhododendron coverage, other shrub coverage, topographic position, and aspect using Bayesian methods and compared models using DIC. I found that elevation was the best predictor of adult survival, which increased from 0.573 (95% credible intervals (CI) = 0.333 – 0.820) at 555 m to 0.702 (95% CI = 0.493 – 0.871) at 1255 m, although the slope coefficient of the elevation effect overlapped 0. I located 12 nests in 2021, of which 9 fledged successfully. The intercept-only model was the best predictor of daily survival, which, exponentiated over the 19-day nesting period, resulted in a posterior mean nest survival of 0.604 (95% CI = 0.527 – 0.696). To elucidate the migration ecology of the population, I deployed 32 light-level geolocator tags on adult males in 2020 and retrieved tags in 2021. I recovered 13 (40.1%) geolocators, of which 10 provided data on post-breeding (fall) migration routes and nonbreeding season sites, and nine provided data on pre-breeding (spring) migration routes. The nonbreeding sites were clustered nonrandomly in Colombia, indicative of potential population connectivity. Post-breeding migration was largely overland through Mexico and Central America, with potential trans-Gulf flights by some birds. Pre-breeding migration routes by each individual were significantly (t = -4.75, df = 8, p = 0.001) further east than the post-breeding route, based on the minimum (westernmost) longitude recorded during migration (mean difference = 232km), consistent with a pattern of anticlockwise loop migration. Overall, my research documented critically lacking information on region-specific relationships between demographic rates and environmental conditions and provides the first insight into the migratory ecology of a population of Canada Warblers near the southern extent of their breeding range. My results fill crucial ecological knowledge gaps for an imperiled species and serve as a foundation for full annual cycle demographic modeling.

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