The Lower Rio Grande Valley (LRGV) of Texas is an ecologically diverse region in the United States and marks the northernmost extension for many tropical species of plants and animals. Since the early 1900s, 95% of the native Tamaulipan brushlands have been cleared due to agricultural practices and urban development. The plain chachalaca (Ortalis vetula) is a medium sized bird endemic to the native brushlands of the LRGV. In 2003, I trapped and radio-tagged 29 birds (16 males, 13 females) to evaluate the effects of fragmentation on the population dynamics (i.e., survival, mortality, and movements) of this brushland species. My study objectives were to estimate (1) seasonal survival of chachalacas by sex, and (2) ranges, core areas, and movements using radio telemetry. Mammalian predation (43%, n = 6) and unknown (43%, n = 6) deaths accounted for the majority of mortality observed. I found no difference (P > 0.05) in estimated 8-month survival (December 2003-July 2004) between males (S = 0.364, SE = 0.132) and females (S = 0.405, SE = 0.153). In comparing seasonal survival for all birds (males and females combined), I observed a difference (P < 0.05) in survival between the nesting (S = 0.414, SE = 0.103) and breeding seasons (S = 0.917, SE = 0.079). Female ranges (x‾ = 117 ha, range = 42–177 ha) and core areas (x‾ = 23 ha, range = 5–46 ha) during the nesting season were larger than male ranges (x‾ = 41 ha, range = 31–46 ha) and core areas (x‾ =10 ha, range = 7–14 ha) during the same period. During the breeding season, female ranges (x‾ = 59 ha, range = 10–188 ha) and core areas (x‾ = 9 ha, range = 2–33 ha) were similar to male ranges (x‾ = 48 ha, range = 4–130 ha) and core areas (x‾ = 9 ha, range = 1–23 ha). Mean distances between seasons were similar for both sexes (females, nesting, x‾ = 486, breeding, x‾ = 345; males, nesting, x‾ = 184, breeding, x‾ = 292), though females distances generally were greater. Dispersal defined as movement off the Santa Ana National Wildlife Refuge was observed for 3 birds. In 2 cases, a radio-tagged female and male were observed crossing the Rio Grande River (approximately 100-m wide) to habitat in Mexico. Study results suggested mammalian predation may limit the growth of chachalaca populations. Though land use changes such as agricultural uses may not directly limit chachalaca populations in providing cover and food, concentration of populations in remnant native brushlands may serve as ecological “sinks” to the species. Greater range and movement data observed in my study may be attributed to suboptimal habitat (i.e., increased fragmentation) for plain chachalacas.

Understanding the salt marsh ecosystem in the Guadalupe Estuary is needed because wetlands in this system support the endangered whooping crane (Grus americana). The marsh plant research and monitoring described herein were based in the salt marshes at Aransas National Wildlife Refuge (ANWR), which are utilized by the cranes each winter. Past research indicates that the Carolina wolfberry (Lycium carolinianum) contributes 21-52% of crane energy intake early in the wintering period (Chavez 1996). Beginning in Fall 2003, vegetation transects were sampled along an estuarine gradient at ANWR. Species diversity and composition was similar at the three sites, with all sites containing the same 6-7 common species. While Spartina alterniflora is only a minor part of this vegetation community, it dominates the few low inter-tidal, fringe areas present. Species composition exhibited little variability from Year 1 to Year 2 of the study. Densities and biomass of L. carolinianum were not significantly different between sites or years. L. carolinianum, while important to salt marsh ecology, accounts for only a small portion of the overall productivity. Based on correlation coefficients, L. carolinianum was found in association with some of the common species in the vegetation community, indicating that its growth and survival requirements are typical to the salt marshes at ANWR. Also beginning in Fall 2003, I repeatedly sampled L. carolinianum in permanent plots along the estuarine gradient. L. carolinianum exhibits strong temporal patterns. Leaf production peaked in early spring and again just prior to peak berry abundance. Flowering of L. carolinianum occurred in October and November. Peak berry abundance coincided with the cranes’ arrival in late October and early November. Berry production occurred in October, November, and December; berries were virtually non-existent in the marshes for the remainder of the year. Stepwise regression showed stem diameter alone was a good estimator of aboveground biomass of this species in ANWR marshes, accounting for 94% of the variability (p<0.001). Changes in aboveground biomass followed no distinct patterns in the year of monitoring, perhaps due to the woody stem of the plant. Spatial patterns in L. carolinianum were not explained by water quality parameters alone; it is suggested that soil properties may help to account for the spatial variability.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 221-235). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 221-235). Also available on the Internet.

Thesis (Ph. D.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains vii, 125 p. : ill., map. Includes abstract. Includes bibliographical references (p. 90-96).

Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains vii, 73 p. : ill. (some col.), maps (some col.). Includes abstract. Includes bibliographical references (p. 71-73).

Graduation date: 1993

Thesis (M.S.)--Georgia Southern University, 2007. / Title from PDF title page (viewed on Feb. 19, 2008). Electronic version approved: December 2007. Includes bibliographical references (p. 35-37).

Thesis (M.S.)--Western Washington University, 2008. / Includes bibliographical references (leaves 112-121). Also issued online.

Thesis supervisor: You-Kuan Zhang. Includes bibliographic references (p. 158-172).