Loggerhead Shrike Habitat Selection in South Carolina

• Main Author: Froehly, Jennifer L
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2018
• Subjects: Ecology; Wildlife Conservation; Wildlife Management
• ISBN: 9780438055049; 0438055047

The loggerhead shrike (Lanius ludovicianus) is a species of concern throughout its range due to severe population declines over the past seven decades. Grassland habitat loss and fragmentation is widely viewed as contributing to the decline. Habitat associations have primarily been studied up to the territory scale, with few studies assessing shrike habitat selection at landscape scales. In Chapter 1 we conducted roadside passive-active point counts for loggerhead shrikes in the coastal plain of South Carolina to evaluate support for several competing hypotheses of how land use and habitat fragmentation at multiple spatial scales influenced the occupancy of loggerhead shrikes. Detection probability increased with fair weather and temperature, and decreased with noise. High probability of detection (p=0.49, SE=0.08) indicated support for the application of passive point counts in future loggerhead shrike monitoring. Occupancy was best predicted by percentage of pasture at 1 km, where predicted occupancy increased from 2%, when there was 0% pasture in a 1 km radius, to 98%, occupancy when there was 43% pasture in a 1 km radius. There was considerable model selection uncertainty, and our model averaged occupancy estimate was low ( =0.17, SE=0.05). Extrapolation of our averaged model suggested that only 8% of the South Carolina coastal plain was occupied by loggerhead shrikes in the 2016 and 2017 breeding seasons. Our results highlight the importance of habitat beyond breeding territories, and highlight the need for higher concentrations of pasture and grassland at a 1 km scale in order to increase the proportion of area in South Carolina occupied by shrikes. Identification of factors that influence habitat selection of a nest site can also help managers effectively conserve a species. The Loggerhead Shrike could potentially benefit from fine scale management for nesting habitat, especially where fragmentation and private land ownership impedes conservation at the landscape scale. In Chapter 2 we examined how habitat characteristics at the nest tree and territory core scales influenced nest site selection by Loggerhead Shrikes in the coastal plain of South Carolina. We found 41 Loggerhead Shrike nests and measured characteristics at the nest site and at available sites to model selection factors at the tree and territory core scales. At the territory core scale, we found that low vegetation density heterogeneity, high vegetation height heterogeneity, shorter distances to powerlines, and lower shrub density increased selection. Diameter at breast height increased selection at the tree scale. Overall, Loggerhead Shrikes appeared to select for nest site characteristics that enhanced foraging ease and success, and limited predation risk. For the purpose of increasing optimal nesting habitat for Loggerhead Shrikes, we suggest that private landowners in South Carolina increase grassy habitat on their property and retain large trees in suitable nesting locations.