Thesis (Ph. .)--University of Oklahoma, 1957. / Includes bibliographical (leaves 172-180).

A marked population of wintering Gray Vireos (Vireo vicinior) was studied for two seasons (1985-1986 and 1986-1987) on two study sites near Puerto Lobos, Sonora, Mexico. Eleven of the 15 individuals banded in the first winter returned to the same areas in the following winter. Territories were defended throughout the winter and averaged 0.9 ha in size (N = 9). Territorial interactions occurred frequently along boundaries as neighbors trespassed to forage on each others' territories. All birds appeared to defend individual territories. First year birds appeared to occupy marginal territories on the periphery of the best habitats. Fruit from the elephant tree, Bursera microphylla, became a dominant part of the vireo's diet as winter progressed and the fruit ripened. The importance of B. microphylla to the vireos' winter diet and the high degree of overlap between the winter range of the vireos and the distribution of the plant suggested a mutualistic interaction between them. Gray Vireos acted as the primary dispersers for the plant.

Over the last 50 to 150 years there has been widespread conversion of grassland to shrubland throughout the western United States. A major management concern on the Edwards Plateau is the encroachment of Ashe Juniper (Juniperus ashei). To facilitate brush management programs, I investigated relationships of two endangered species, the black-capped vireo (Vireo atricapillus) and the golden-cheeked warbler (Dendroica chrysoparia), with their habitats at the landscape level. GIS (Geographic Information Systems) and remotely sensed data, such as Landsat imagery, DEMs (Digital Elevation Maps), and DOQQs (Digital Ortho Quarter Quads) were used to evaluate vegetative and geomorphic features within both 100m- and 400m-radius areas surrounding occupied and (assumed) unoccupied sites. Stepwise-logistic regression was used to develop probability models for each species within a catchment and was then applied to the entire Leon River Watershed and evaluated for accuracy. Golden-cheeked warblers were identified in areas with mean juniper cover greater than 70%, mean departure from North (aspect), and maximum slope. For black-capped vireos, mean shrub cover, mean departure from North, and mean slope were important in habitat selection. Variables at the 400m spatial scale best identified areas of probable occurrence for both species, indicating that features of landscape surrounding a territory may play an important role in habitat selection.

Over the last 50 to 150 years there has been widespread conversion of grassland to shrubland throughout the western United States. A major management concern on the Edwards Plateau is the encroachment of Ashe Juniper (Juniperus ashei). To facilitate brush management programs, I investigated relationships of two endangered species, the black-capped vireo (Vireo atricapillus) and the golden-cheeked warbler (Dendroica chrysoparia), with their habitats at the landscape level. GIS (Geographic Information Systems) and remotely sensed data, such as Landsat imagery, DEMs (Digital Elevation Maps), and DOQQs (Digital Ortho Quarter Quads) were used to evaluate vegetative and geomorphic features within both 100m- and 400m-radius areas surrounding occupied and (assumed) unoccupied sites. Stepwise-logistic regression was used to develop probability models for each species within a catchment and was then applied to the entire Leon River Watershed and evaluated for accuracy. Golden-cheeked warblers were identified in areas with mean juniper cover greater than 70%, mean departure from North (aspect), and maximum slope. For black-capped vireos, mean shrub cover, mean departure from North, and mean slope were important in habitat selection. Variables at the 400m spatial scale best identified areas of probable occurrence for both species, indicating that features of landscape surrounding a territory may play an important role in habitat selection.

Solitary Vireos (Vireo solitarius alticola) were studied on an extensive mature forest landscape in 1994 and on three sites harvested using the group selection method in 1995. Pairing success was 88% on the unharvested site in 1994, however it was lower on the harvested sites in 1995 (53.8%). Low reproductive success was observed in both years (12% and 22% respectively). In 1995, the amount of opening within a 200 meter radius of the first observation point of a male was positively related to pairing success (p<0.05). This suggests that females may be cueing in on the increased number of shrubs in and around openings. / Master of Science

This study compared male response to playback and interspecific vocal imitation in two White-eyed Vireo populations, in southwestern Virginia and eastern North Carolina. White-eyed Vireos are hypothesized to imitate notes from other birds which transmit efficiently through dense habitat. Male White-eyed Vireos did not respond differently to playback of each other I s songs. The song repertoires between Virginia and North Carolina were not found to include strikingly different imitations despite the different sound environments. Degradation and attenuation of White-eyed Vireo song notes was also compared between the two locations. There was no statistically significant difference in degradation or attenuation of notes when compared to native or foreign habitat. Notes occurring more frequently in the population did not transmit more efficiently. Notes unique to North Carolina did transmit more efficiently in their native habitat, but this difference was explained by the relatively less dense habitat in North Carolina. / Master of Science