My Graduate Students' Thesis Abstracts - Revised 9 Jan 09
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 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.
Grace E. W. Bockoven
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,
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.
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.