My Graduate Students' Thesis Abstracts - Revised 9 Jan 09

Lisa Beckstrom
Marek Smith
Beth Bockoven
Eric Harrold
Jim Mason
Elaine Corvidae

Jennifer Rettew
Cori Cauble

Lisa Beckstrom.

LISA J. BECKSTROM. Habitat Selection of Neotropical Migratory Birds and Changes in Riparian Forests Along the Catawba River Basin in Mecklenburg County, North Carolina.   

            In this study, point counts were used to document and compare habitat use of Neotropical migratory birds in the Piedmont of North Carolina during fall and spring migrations and, for some species, during their breeding cycle.  Although species richness and avian abundance were higher in bottomland hardwood habitats during both migration events, they differed significantly among habitats only in spring.  While there was no significant difference among habitats in the breeding season, avian abundance and species richness were higher in mature pine-hardwood.  A Stepwise Regression analysis revealed that there was no one indicator variable common to both migration and the breeding season, except for number of pines which negatively affected migratory species richness and avian abundance.

            Since both bottomland and non-bottomland forested riparian habitats were used by migrants as stopover sites, a Geographic Information System (GIS) was employed to measure current and predicted future (1996 - 2045) spatial distributions of these habitats along the Catawba River basin in Mecklenburg County, North Carolina.  Both habitats were already largely fragmented with greater than 95% of bottomland patches within 100 m of hydrological features measuring less than 5 hectare (ha).  Patch size was not predicted to significantly change for bottomland habitats, but it was predicted to decrease for non-bottomland riparian forests.

Marek Smith.

MAREK K. SMITH. Surviorship, Dispersal and Diet of Captive-reared and Wild-reared Barn Owls (Tyto alba pratincola) in the Southern Piedmont of North Carolina.

Little is known about the post-release success of orphaned Barn Owls (Tyto alba pratincola) reared in captivity or the effectiveness of captive-rearing processes in preparing nestlings for the wild. Within a ten-county area of North Carolina in 1977-98, 15 captive-reared and 10 wild-reared juvenile Barn Owls were radio-tracked from their release or natal sites, respectively. Diurnal roost sites were located and pellets were collected. Telemetric contacts ranged from less than 1 d to 116 d. Short-term survivorship was similar among groups with only two documented deaths, one captive-reared owl and one wild-reared owl. Captive reared owls dispersed at significantly greater rates than wild-reared owls and both groups dispersed in random directions. Prey composition was similar among groups with meadow vole (Microtus pennsylvanicus), short-tailed shrew (Blarina brevicauda), and hispid cotton rat (Sigmodon hispidus) comprising the majority of prey items. Within-species tests of prey size did not differ among groups, but captive-reared owls did take smaller mammalian prey overall. Although the higher rates of dispersal of captive-reared owls indicated low site fidelity to release sites and potential inexperience in locating prey, the results of this study suggested that captive reared owls can adapt to the diversity of prey in the natural environment and survive in the immediate weeks post-release.

Beth Bockoven


Grace E. W. Bockoven
Western Carolina University (May, 1999)
Director: Dr. Jerry West

          As the USFWS prepares to delist the Peregrine Falcon, it is important to understand why the Southern Appalachian Recovery Region (northern AL & GA to northern VA & WV) has not met the recovery goal of 20-25 nesting pairs for three consecutive years even though the reintroduction program is at least 15 years old. A nest site habitat availability and suitability model was created using an Arc/Info Geographic Information System (GIS). The locational data for 54 historical nest sites (pre-1964) and currently active nest sites (since 1980) were overlaid with digital map layers of 17 variables. Mahalanobis distance statistic was calculated for each pixel. This statistic is a measure of dissimilarity where higher values represent habitat that is least like the conditions of the sample sites. This map layer can be used to predict habitat that peregrines might use. Potential nest sites were evaluated with the model in an effort to concentrate monitoring efforts by wildlife agencies. Peregrine eggs were collected and analyzed for organochlorine concentrations and eggshell thickness. Organochlorines (p,p' DDE, PCBs 1254 & 1260, Dieldrin and Mirex) detected in this study were below the levels associated with population decline. The amount of eggshell thinning (0.34 mm) was well below the 17% threshold level above which population declines in peregrines are expected. Pellets, feathers and bones found at eyries were examined to determine the peregrine's prey base. Peregrines in western NC fed heavily on year-round resident birds in the orders Passeriformes and Charadriiformes. The data indicate that the peregrines mainly hunt birds that frequent open habitat and water. The results from this study indicate that there are not any clear factors limiting peregrine falcon productivity in the Southern Appalachian Recovery Region. This region should be de-listed along with the rest of the national peregrine population.

ERIC S. HARROLD. Barred Owl (Strix varia) Nesting Ecology in the Southern Piedmont of North Carolina. (Under the direction of Dr. Richard O. Bierregaard Jr.)  

          An improved understanding of the essential structural habitat components critical for occupation by Barred Owls was obtained from a comparison of habitat structure in relatively unmodified rural sites to sites in suburban residential areas with high human densities. This study showed that suburban landscapes can contain features characteristic of old forests including an open understory, large
trees, and dense canopy cover. Older residential areas in Charlotte are best described as a wooded landscape in which the dominant trees are planted oak trees >50 years of age. The home range size of owls in suburban Charlotte, North Carolina is smaller than that of owls of northern populations occupying natural forest habitats. Owl home ranges were located in areas consisting primarily of residential land use. Comparison of data obtained from suburban and rural nests suggests that owls are selecting similar prey in these environments. Birds were the most commonly occurring categorical prey item for both suburban and rural sites. The presence of Barred Owls in highly modified suburban environments suggests that the species is more adaptable with respect to tolerance of human activity than reported in previously published studies

JAMES SCOTT MASON. The reproductive success, survival, and natal dispersal of Barred Owls (Strix varia) in rural versus urban habitats in and around Charlotte, North Carolina. (Under direction of Dr. Richard O. Bierregaard Jr.)

            This was the first known study to investigate the reproductive success, survival, and natal dispersal of Barred Owls (Strix varia) in the southeastern United States. Furthermore, this was the first study to examine the effect of urbanization on this species and to quantitatively distinguish between rural and urban habitat types. Within a four-county area surrounding Charlotte, North Carolina, 58 breeding pairs were tracked. Compared to other studies, the reproductive output of the Charlotte population was slightly lower; this may be attributed to differences in habitat among geographic regions. Urban Barred Owls had a higher reproductive output compared to their rural counterparts, which is likely a result of better quality habitat, an abundance of suitable nest sites, and a diverse prey base in the city. Using radiotelemetry techniques, a total of 11 young were tracked between 2002 and 2003. Vehicle collisions were a cause of juvenile mortality in urban Charlotte, but were not recorded in the surrounding rural areas. Rural young, on average, dispersed farther than urban young (4151 m versus 2714 m) and traveled farther between dispersal jump areas (1499 m versus 1210 m). These results suggest that habitat connectivity and quality may be better in urban areas because rural habitat surrounding Charlotte primarily consists of relatively unsuitable young pine/mixed hardwood forests, agricultural fields, and most recently, subdivisions.

ELAINE LEE CORVIDAE. Comparison of wing muscles in three birds of prey: correlation of functional and behavioral differences. (Under direction of Dr. Susan E. Peters and Dr. Richard O. Bierregaard Jr.)
Flight is energetically costly but essential to survival in birds.  Therefore locomotor structure, including skeletal and muscular characteristics, is adapted to reflect the flight style necessitated by different ecological niches.  Red-tailed Hawks (Buteo jamaicensis) soar to locate their prey, Cooper's Hawks (Accipiter cooperii) actively chase down avian prey, and Ospreys (Pandion haliaetus) soar and hover to locate fish.  In this study, wing ratios, proportions of skeletal elements, and relative sizes of flight muscles were compared between these species.  Oxidative and glycolytic enzyme activities of several muscles were also analyzed via assays for citrate synthase (CS) and for lactate dehydrogenase (LDH).  It was found that structural characteristics of these three raptors fit within prevailing aerodynamic theory.  The similarity of enzymatic capacity among different muscles of the three species shows low physiological diversity and suggests that wing architecture may play a greater role in determining flight styles for these birds.

JENNIFER ANNE RETTEW.  Factors influencing mortality in nestling Ospreys (Pandion haliaetus): an analysis of breeding strategies.  (Under the direction of Dr. R. O. Bierregaard) Defended 2006.


          Breeding strategies are important to the evolution of species because they allow individuals to maximize reproductive output while minimizing investment.  One such aspect of breeding strategy is nesting behavior.  In Ospreys (Pandion haliaetus), the female remains at the nest to guard and brood the nestlings while the male hunts.  A hierarchy is established among the nestlings through hatching asynchrony and sibling aggression.  Aggression occurs primarily in the presence of food, but can also be triggered by other stress.  Ospreys are territorial around the nesting site and chase away other Ospreys, as well as other species that present a threat to the nest.

            Brood reduction is an adaptive mechanism by which birds can adjust the optimal brood size in a given season to fluctuations in the environment.  In Ospreys, reduced prey delivery is the direct cause of brood reduction, with increased prey delivery causing an increase in survival of the nestlings.  Sibling aggression further contributes to the size hierarchy set up by hatching asynchrony in the nest, but does not directly influence mortality itself.  Sibling aggression occurs in nests with both high and low prey delivery and may be performed regardless of hunger levels.  Female Ospreys may supplement the prey available to the nestlings, leaving the chicks unguarded to hunt.  Nests with hunting females have lower mortality rates, indicating that increased parental feeding effort may act as a buffer to seasonal fluctuations in the environment.

LESLIE CORINN CAUBLE. The diets of rural and suburban Barred owls (Strix varia) in Mecklenburg County, North Carolina. (Under the direction of DR. RICHARD O. BIERREGAARD)

          The diet of Barred Owls found in unfragmented mature forests was compared to the diet of Barred Owls occupying suburban residential areas in Mecklenburg County, North Carolina. This study found a significant difference between the diets of rural and suburban Barred Owls, with the suburban diet comprised predominantly of avian prey (54.6%) and the rural diet consisting mostly of reptiles and amphibians (28.3%) and insects (26.5%). One rural and one suburban nest were matched based on age of owlets, date of recordings, and date of branching and were compared to control for the effect of seasonality. A significant difference was found between the age-date matched rural and suburban Barred Owl diets suggesting that seasonality is not greatly influencing the observed diet differences. A comparison was also made between the diets of Mecklenburg County Barred Owls and Barred Owls found in other areas of North America. A significant difference was determined between Mecklenburg County Barred Owl diets and diets reported for other North American Barred Owls. Results of this study suggest that Barred Owls living in suburban habitats are taking advantage of unique foraging opportunities found in residential areas. Suburban areas may have increased avian densities due to bird attractors which, when combined with an open understory, may account for the large numbers of avian prey items observed.

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