Browsing by Subject "habitat use"
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Item Blue Crab Population Ecology and Use by Foraging Whooping Cranes on the Texas Gulf Coast(2012-02-14) Greer, Danielle MarieIn 2002, a proposal was submitted to divert water from the confluence of the Guadalupe and San Antonio Rivers to San Antonio, Texas. To investigate the potential impacts of diverting water from the Guadalupe Estuary, my research focused on the foraging ecology of the crane and population ecology of the blue crab, a documented crane food. During winters 2004-2005 and 2005-2006, I examined diets and optimal foraging patterns of territorial adult cranes at Aransas National Wildlife Refuge, Texas. To identify foods of greatest benefit to cranes, I used currencies of optimization to evaluate foraging gain, cost, and efficiency. Foraging benefit differed among foods, depending on the foraging currency used and resource targeted (e.g., energy). Wolfberry fruit, snails, and insects were consumed in the highest quantities, required the least foraging effort, and were generally associated with the highest foraging efficiency. Blue crabs and clams were important sources of protein and biomass. During September 2003-October 2005, I used novel artificial settlement substrates and modified methods of standard deployment to investigate the spatio-temporal patterns of blue crab terminal settlement and recruitment rates. Monitoring rates in shallow bay habitat and ponds of the interior salt-marsh revealed megalopal crabs were developmentally advanced when arriving to study sites and the extent to which young crabs infiltrated the salt-marsh increased with age. Such findings suggested sites represented optimal terminal settlement habitat and consequently critical nursery habitat. Model selection indicated water temperature before and during embryonic development was the best predictor of megalopal settlement, whereas juvenile recruitment was most influenced by recent precipitation. I studied the size-specific abundance patterns of blue crabs in and around mature salt-marsh. Using drop-trapping and throw-trapping methods, I collected monthly samples in several habitats during October 2004-March 2006. Interior-marsh habitats contained fewer but larger crabs than bay habitat. Crabs contributing greatest to biomass were smallest (11-30 mm carapace-width) in bay habitat, larger (31-80 mm) along interior-marsh pond edges, and largest (41-130 mm) in interior-marsh open water. Model selection revealed crab density was most influenced by micro-site characteristics (habitat, water column structure type and structural complexity). Overall, shallow bay provided important nursery habitat for young blue crabs and interior marsh ponds were important for dispersing juvenile and adult crabs.Item Ecology of Wintering Black-capped Vireos in Mexico(2013-11-06) Powell, Robert AndrewThe black-capped vireo (Vireo atricapilla) is an endangered Neotropical migratory songbird that has received considerable attention in its breeding range, but relatively little attention in its winter range in Mexico. To address information needs regarding winter ecology of the black-capped vireo, I conducted research in Mexico focused on investigations of the winter distribution, habitat use, and migratory linkages between breeding and wintering sites. Over 3 winter periods in 2002?2004, I identified and described the geographic distribution for the black-capped vireo at study sites across 8 states in western Mexico and determined if differential migration occurs among different classes of individuals. I documented winter occupancy in the 5 most northern Mexican states surveyed (Sinaloa, Durango, Nayarit, Jalisco, and Colima), and identified a strong association between sex/age class and winter latitude with adult males occupying habitat at more northern latitudes relative to females and juveniles. During two winters in 2003-2004, I conducted field research at study sites in Mexico to evaluate patterns of winter habitat use by black-capped vireos and determine which habitat characteristics may influence vireo use of winter patches. Winter habitat use by black-capped vireos was best predicted by increasing values of slope and foliage cover, and by decreasing values of canopy cover and tree diameter. Vireo use plots characterized as thorn forest had greater foliage density, greater shrub density, less canopy cover, and smaller tree diameter than plots classified as tropical deciduous or semi-deciduous forest, suggesting that thorn forests may be most suitable for vireo occupancy during the winter months. I also used stable carbon, hydrogen, and nitrogen isotopes in black-capped vireo feathers obtained across 3 states in the breeding range and 8 states in the wintering range to determine if vireo feathers collected on the wintering grounds could be used to assess breeding origins and to determine if a relationship exists between breeding and wintering latitudes such as chain or leapfrog migration. Feathers collected at both breeding and wintering sites displayed considerable variability in isotopic composition for all 3 isotopes analyzed, and thus did not provide sufficient information to establish migratory linkages between breeding and wintering sites.Item Spatial Ecology of and Public Attitudes toward Monk Parakeets Nesting on Electric Utility Structures in Dallas and Tarrant Counties, Texas(2014-07-29) Reed, Janet ElaineMonk parakeets (Myiopsitta monachus) were introduced to the United States (US) where they established naturalized populations. They often build their bulky twig nests on electric utility structures, causing economic damage. From May 2010?February 2013, we examined the spatial ecology of and public attitudes toward monk parakeets nesting on electric utility structures in Dallas and Tarrant counties, Texas, US. As nest sites, monk parakeets selected electric switchyards and substations constructed with multiple flat surfaces and acute-angles, within small fenced areas, with large canopy trees and taller anthropogenic structures within 100 m. Multi-scale analysis of urban land use-land cover (LULC) suggested the surrounding landscape had little impact on nest-site selection. Monk parakeets used canopy LULC more often than pavement, grass, buildings, or water. They traveled farthest from their nests during winter. Flock sizes were highly variable, yet largest during nonbreeding season. They foraged on a broad range of native vegetation and exhibited a diverse diet of flowers, fruits, acorns, grass blades, wild dry seeds, leaf buds, insect larvae, and commercial bird seed. We evaluated sociological variables as predictors of opposition to managing monk parakeets nesting on electric utility structures. Most survey participants were affluent, well-educated, older Caucasians who were unknowledgeable about, inexperienced with, and unsure about the impacts of monk parakeets. They indicated least opposition to nest removal and structural modification. When opposing, they would most likely do so socially and through petitions. Participants were influenced by their desire for monk parakeets to feed at their bird feeders or nest in their yard, people and groups important to them, and their perceived ease of opposing. Our results suggest LULC manipulation and food-based strategies are not reasonable for controlling urban monk parakeets. We recommend an outreach program explaining monk parakeet biology and the impacts of their nesting habits. We suggest targeting affluent areas adjacent to electric structures with nests and the predictors driving participants? behaviors. To provoke least opposition, we advise nest removal and structural modification. We recommend electric companies conduct cost-benefit analyses exploring feasibility of modifying construction elements preferred by monk parakeets and redesigning new construction to reduce risk of future nesting on electric utility structures.