Date of Graduation
Davis College of Agriculture, Natural Resources and Design
Wildlife and Fisheries Resources
Mountains are important areas for avian diversity and conservation since they have steep elevational and environmental gradients. In the central Appalachian Mountains, several songbird species have trailing edge populations that are restricted to high elevations. Climate change and other factors can cause species distributions to change, which is of particular concern for birds in restricted trailing edge populations. Additionally, the Canada Warbler (Cardellina canadensis) breeds throughout the Appalachian Mountains and is species of conservation concern due to range-wide population declines. For this project, I used avian point count data from the central Appalachian Mountains to: (1) evaluate the spatial and temporal dynamics of a group of songbirds, and (2) assess fine-scale environmental correlates of the Canada Warbler. To assess avian dynamics, I used a 26-year (1993-2018) historic dataset of 5922 point count surveys conducted in the Monongahela National Forest, West Virginia to model colonization and persistence rates for 16 songbird species in a Bayesian framework. Colonization and persistence rates were modeled as a function of year, elevation, and harvest, with interactive effects between year and elevation. I then derived equilibrium occupancy for each species to evaluate the change in occupancy over the 26-year period and across the elevation gradient. Five species expanded upwards, 3 species expanded downwards, 1 species contracted downwards, 1 species shifted downwards, and 6 species had no directional change in equilibrium occupancy. None of the 16 species contracted upwards and there was little evidence of climate-induced elevational movement. Varying responses along the elevation gradient are likely due to a combination of several factors, including changing forest conditions and regional population trends. Spruce restoration and regeneration of northern hardwood and spruce forests are likely driving the upward and downward expansions observed in 5 species, which suggests that climate-induced movements may be alleviated by more direct changes to forest conditions. In chapter 2, I evaluate Canada Warbler space use and environmental correlates using 840 point count surveys conducted in 2017 and 2018. I assessed Canada Warbler occupancy in a multi-species occupancy modelling framework that accounted for potential interactions between Black-throated Blue Warbler (Setophaga caerulescens) and Hermit Thrush (Catharus guttatus). I found that Canada Warblers were more likely to occur in mid-elevations, in areas with high Rhododendron (Rhododendron maximum) stem density, closer to riparian areas, and in northern hardwood forests. Canada Warblers were also positively associated with Black-throated Blue Warblers. Conservation actions for Canada Warblers in its southern breeding distribution should span across a range of elevations in northern hardwood forests. Additionally, protection of riparian areas, especially those with dense Rhododendron thickets, will likely benefit Canada Warblers in their Appalachian distribution.
Dimmig, Gordon W., "Avian Occupancy Dynamics and Canada Warbler (Cardellina canadensis) Environmental Correlates on a Central Appalachian Elevation Gradient in West Virginia" (2019). Graduate Theses, Dissertations, and Problem Reports. 3778.