Date of Award

5-1-2023

Document Type

Thesis

Degree Name

Master of Science in Coastal Marine and Wetland Studies

Department

Coastal and Marine Systems Science

College

College of Science

First Advisor

Christopher E. Hill

Second Advisor

Derek P. Crane

Third Advisor

John J. Hutchens

Abstract

Loggerhead shrikes, Lanius ludovicianus, are a declining grassland songbird native to North America. Land-use change has been associated with the decline of grassland bird species. However, the process of urbanization creates novel short-grass habitats reminiscent of shrikes’ natural habitats. Loggerhead shrikes have been observed living in developed areas, particularly in Southeastern coastal states. Understanding the long-term impacts of urban-dwelling on loggerhead shrike populations is vital to identifying whether urban areas offer refuge or act as an ecological sink for shrike populations.

In chapter one, I quantified the use of space by shrikes in urban habitats within Horry County, South Carolina. I calculated home range sizes using minimum convex polygons and kernel density estimators. I used the detection histories of a banded population of shrikes to calculate the average population density of my study area. I also calculated internest spacing of shrike nests using a three-year dataset of nesting locations. I found that compared to their rural counterparts, shrikes in urban areas maintain smaller home ranges (1.6-6.1 ha), are more densely populated (2.9 shrikes per km2) and maintain close internest spacing (median distance to neighboring nest: 354 m). These results indicate that loggerhead shrikes are actively taking advantage of the habitats provided by developed areas and that those habitats provide better resources than more agricultural sites.

In chapter two, I compare the foraging behavior of shrikes in urban and rural areas. I observed shrikes foraging within both land uses during 30-minute periods throughout both the breeding and non-breeding season. I recorded perch parameters (type and height), foraging style (aerial or terrestrial attempt), ambient temperature, prey type, as well as outcome of foraging attempt. I used a MANOVA to compare the forage behavior of urban and rural shrikes. Using a generalized linear mixed model, I investigated how aspects of foraging behavior impact foraging outcome. The foraging strategy of shrikes in urban areas was consistent with that of shrikes in rural areas. Shrikes in urban areas used anthropogenic perches more often than natural, though this may be a reflection of availability rather than choice. Shrikes in my study foraged at an average rate of 16 attempts per hour with an 80% capture efficiency. The top-ranked model predicting foraging outcome included four predictor variables: foraging style, perch type, perch height, and ambient temperature. Foraging success was greater from tall perches, natural perches, in warmer temperatures, and during terrestrial foraging attempts. Results from this study indicate that while the urban matrix alters habitat structure, urban shrikes are able to forage as successfully as their rural counterparts.

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