Thesis (M.S.)--University of Missouri-Columbia, 2003. / Typescript. Includes bibliographical references. Also available on the Internet.

Thesis (M.S.)--University of Missouri-Columbia, 2003. / Typescript. Includes bibliographical references. Also available on the Internet.

Thesis (M.S.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on November 1, 2007) Includes bibliographical references.

Understanding species-habitat relationships is fundamental to the conservation of a species. This is especially important when the species is considered endangered. The Golden-cheeked Warbler is a habitat specialist that breeds only in oak-juniper woodlands (considered a climax forest) of central Texas. The warbler was listed as endangered under the federal Endangered Species Act primarily because of habitat loss and fragmentation. Conservation measures include the preservation of existing habitat and attempts to manage and enhance areas that once supported the warbler to return to the climax oak-juniper woodlands. My objectives were (1) to quantify the vegetation structure and species composition by vegetation volume of occupied warbler habitat across the breeding range in Texas and (2) to quantify the habitat use by the warbler in categories of behavior, substrate, height, and tree species. Instantaneous, focal animal behavioral observations were collected for three breeding seasons at six sites across the range of the warbler. Warbler behavior and microhabitat use were compared to availability of vegetation volume by height class and tree species. I found that Goldencheeked Warbler habitat varied by vegetation volume, canopy height and tree species among all sites. The warbler preferred twigs and foliage and the upper two height classes of the habitat structure for all behaviors. Tree species use did not match availability at any sites. The one consistent species result was the warbler used Ashe juniper significantly less than it occurred at all sites. Other major species were used disproportionately to the species occurrence at each site. Some tree species were used more often than they occur in the habitat while others species were used less than they occur in the habitat. Preferences for height class and tree species use were not significantly influenced by vegetation volume. Some other factor not measured such as prey availability may be the cause. Because warbler habitat characteristics and use vary across the range, any efforts to manipulate vegetation to become habitat must consider regional characteristics of Golden-cheeked warbler habitat.

Noise pollution can mask or distort bird songs, which inhibits mating success, predator detection, and parental response to begging calls. Road noise can cause lowered density and reproductive success in songbirds. I examined the impact of construction noise on reproductive success and territory selection of golden-cheeked warblers (Dendroica chrysoparia) at 3 sites: adjacent to road construction, adjacent to road-noise only, and a control with no noise or construction activity. I also examined birds' responses to experimental playback of construction noise to determine if warblers alter behavior in the presence of introduced road construction noise, if they have habituated to construction noise, and whether habituation is hindering their reproductive success. I used the Vickery reproductive index to evaluate productivity and automatic recording units to assess the levels of ambient noise in each site. From 2007-2009, productivity was stable in the road-noise only site and showed more annual variation in the construction and control sites; productivity was nearly identical in the latter 2 sites in 2008 and 2009. There was no significant difference in productive territory locations based on distance from road. Ambient noise was similar in the construction and roadnoise only sites but significantly different from the control. To examine habituation and territory placement, I (1) used construction noise playback to individual birds and evaluated occurrence of behavioral response as a function of distance from the roadway, and (2) established broadcast stations that simulate construction noise to determine impacts on territory selection. Of 88 surveys, 6 birds responded to construction noise playback. I conducted 18 control surveys and observed 1 behavioral response. All birds that responded were located greater than or equal to 140 m from the road. I established 3 broadcast stations per season in 2008 and 2009. In each year I placed broadcast units on the edges of randomly chosen territories identified during the previous field season. There was not a significant difference in mean territory shifts for broadcast and non-broadcast unit territories, and territory shifts did not show patterns in directionality or in reproductive success. Results suggest that construction noise does not appear to affect behavior or reproductive success of golden-cheeked warblers.

Oak wilt is a fatal disease of oaks caused by the fungus Ceratocystis fagacearum. Loss or degradation of habitat due to the disease may negatively affect the federally endangered golden-cheeked warbler (Setophaga chrysoparia). To assess the impact of oak wilt on golden-cheeked warblers, I investigated its influence on habitat selection and quality. I used remote sensing to estimate the amount of potential golden-cheeked warbler habitat currently affected by oak wilt, to predict the amount of potential habitat likely to be affected in the near future, and to assess the current probability of warbler occupancy in areas affected by oak wilt historically. I also quantified vegetative characteristics to assess overstory vegetation and regeneration in areas affected by the disease. I found proportional occupancy and territory density in unaffected areas to be, respectively, 3.5 and 1.8 times that of affected areas. Pairing success was 27% lower for territories containing oak wilt but fledging success was not affected. I estimated that 6.9% of potential golden-cheeked warbler habitat and 7.7% of the total area within my study region was affected by oak wilt in 2008. By 2018, I predicted that 13.3% of potential golden-cheeked warbler habitat and 16.0% of the study region would be affected by the disease. Using historical imagery, I found that areas affected by oak wilt in the past are less likely to be classified as current potential warbler habitat than areas never affected by the disease. I found no differences between the understory vegetation of affected and unaffected areas but that oaks were more common in the overstory than in the understory, suggesting that species composition in affected areas may shift in the years following an outbreak of the disease. My results suggest that the presence of oak wilt negatively influences habitat selection and quality for golden-cheeked warblers, likely due to reduced canopy cover in susceptible oak species. Additionally, oak wilt frequently occurs in golden-cheeked warbler habitat and will continue to spread into warbler habitat in the coming years. Future management efforts should address the threat oak wilt poses to golden-cheeked warblers by incorporating applicable preventative measures.

The concept of habitat quality is fundamental to the study of ecology, and ecologists have long recognized the importance of vegetation structure and composition in the assessment of wildlife habitat. Vegetative characteristics affect productivity in birds for a variety of reasons (e.g., predator assemblages, nesting sites, song perches, food availability). I investigated the relationship between habitat quality and prey availability and the effect these parameters have on reproductive success in golden-cheeked warblers (Dendroica chrysoparia). My objectives were to 1) determine any differences in pairing and fledging success of warbler territories within two ecosites exhibiting two distinctive tree species composition 2) explore the relationship between tree species composition, arthropod density, and foraging effort, and the effect these parameters have on reproductive success in golden-cheeked warblers and 3) investigate the connection between preferred foraging substrates and changes in arthropod abundance within golden-cheeked warbler territories throughout the breeding season. I mapped individual warbler territories and searched for fledglings, observed foraging behavior, and collected arthropods in each territory to determine productivity, foraging effort, and food availability. I conducted these methods over two seasons in juniper-oak woodlands on Fort Hood, north-central Texas within 347 territories of two vegetative types: those marked by the predominance of post oak (Quercus stellata) and those marked by the predominance of Texas oak (Quercus buckleyi). Pairing and fledging success of territories differed substantially between the two vegetative types. Movement rates differed considerably between the two vegetative types, indicating a difference in prey encounter rate. Foraging data indicated a clear switch in preferred foraging substrates from oak species early in the breeding season, to Ashe juniper (Juniperus ashei) in mid-May. Arthropod sampling revealed a correlation between preferred foraging substrates and arthropod density. Results suggested that Texas oak was an important foraging substrate for golden-cheeked warblers, and territories that lack this tree species generally did not succeed in fledging young. My study can be used to indicate areas that should be targeted for conservation by local, state, and federal government because they provide high quality habitat based on warbler productivity.

Prescribed fire is a common tool used to restore native diversity, control invasive species, and reduce fuel loads. However, fire alone can be insufficient to restore pre-settlement vegetation; other factors such as differences in native and invasive species pools, deer herbivory, seed availability, and the spatial pattern of the fire can influence vegetation trajectories and restoration outcomes. Central Texas is a mosaic of savanna and mixed woodlands co-dominated by Quercus buckleyi (Texas red oak) and Juniperus ashei (Ashe juniper). In a savanna, I studied the joint effects of initial species composition (native-dominated or invasive-dominated) and disturbance (high-intensity fire, clipping, or control) on the ability of native species to establish, survive, and resist invasion by Bothriochloa ischaemum, an invasive C4 grass (ch. 1). Native savanna patches were resistant to invasion following high-intensity fire; fire can be used to selectively control B. ischaemum. In central Texas savanna and woodlands, under fire suppression and overabundant white-tailed deer, Quercus spp. are failing to regenerate, while J. ashei is increasing in abundance. To better understand vegetation trajectories following J. ashei removal in savanna, I studied the soil seedbank along a chronosequence of J. ashei invasion (ch. 5). In woodland, I studied the joint effects of prescribed fire and deer (ch. 2), clearing of J. ashei followed by high-intensity slash-pile burns (ch. 3), and wildfires (ch. 4) on the abundance and size of J. ashei and of hardwoods. Hardwoods resprouted vigorously after fire; J. ashei individuals of all sizes were killed by fire and slow to re-colonize. These management interventions failed to increase Q. buckleyi seedling abundance. It is likely that deer control is necessary to allow fire to have positive effects on the regeneration of oaks in this region, and wherever deer are over-abundant. However, deer can indirectly benefit hardwoods by reducing competition with palatable forbs (ch. 3). In general, these results show that fire suppression in central Texas oak-dominated woodlands is causing a shift not to more mesic-adapted species, as observed in the eastern US, but to J. ashei, which is at least as xeric-adapted as oak, a process I termed 'juniperization'. / text

Habitat fragmentation and isolation can result in decreased occupancy and reproductive success within songbirds, particularly for species inhabiting urban environments where suitable habitat may be limited. The golden-cheeked warbler (Setophaga chrysoparia) is a federally endangered songbird that inhabits oak-juniper (Quercus spp.- Juniperus spp.) across central Texas. Past research on this warbler has indicated decreased patch occupancy near urban areas and negative reproductive effects associated with decreased distance to edge and decreased canopy cover. A rural study indicated warblers occupy patches ≥3 ha, and warblers in patches ≥20 ha are more likely to successfully fledge young. There are no thresholds yet identified for this warbler within urban environments, where effects of habitat fragmentation on reproductive success are more pronounced than within rural environments. I monitored patch occupancy, territory establishment, pairing success, and fledging success of warblers in an urban environment. I determined minimum patch-size thresholds for productivity measurements, and also monitored effects on productivity from canopy cover, woodland composition, distance to and size of the nearest habitat patch, and distance to the nearest habitat patch >100 ha. I compared my results to those from a similar study conducted in a rural system. I compared territory size and territory density between an urban and rural system. Warblers occupied 24% (n = 63) patches surveyed; the smallest patch occupied was 3.5 ha. The smallest patch with an established territory was 10.7 ha, and 10% (n = 63) of habitat patches had at least one established territory. Warblers successfully fledged young in 3 patches, the smallest of which was 26.5 ha. I found patch-size was predictive for territory establishment and pairing success with warblers requiring 13 ha (95% CI: 10.0 – 16.8 ha) and 19 ha (95% CI: 15.7 – 22.6 ha) habitat patches, respectively. I found a minimum threshold of approximately 66% canopy cover (95% CI: 65.2 – 66.4%) required for patch occupancy, and found no warblers established a territory in a habitat patch >25 m from the next nearest patch. I found higher minimum thresholds within an urban system for territory establishment and pairing success than those seen within a rural system. I suggest preserving warbler habitat patches >22 ha that are in close proximity to other habitat patches. This will help to enhance warbler habitat within urban areas and maintain reproductively viable habitat patches, while not halting development completely.

Preservation of large tracts of habitat is often recommended for long-term population viability of area-sensitive species. Large tracts may not always be available. Smaller patches, though not able to contain a viable population individually, may contribute to overall regional population viability if within the small patches pairs could successfully reproduce. By definition, area-sensitive species should have a minimum patch size threshold of habitat below which they will not likely reproduce. Two potential causes for positive relationships between patch size and production are inverse relationships between patch size and brood parasitism and patch size and food availability. My objectives were (1) to determine the minimum patch size thresholds of reproductive success for golden-cheeked warblers (Dendroica chrysoparia), black-and-white warblers (Mniotilta varia), and white-eyed vireos (Vireo griseus); (2) to determine whether thresholds for occupancy, territory establishment by males, or pairing success were indicative of thresholds of reproduction; (3) to determine whether the proportion of pairs fledging brown-headed cowbird (Molothrus ater) young was related to patch size, and (4) to determine the affects of patch size on food availability (i.e., arthropod abundance). The Vickery index of reproductive activity was used to determine reproductive activity of each male or pair and to quantify parasitism occurrences. I collected arthropods using branch clipping to assess the relationship between patch size and arthropod abundance. I found minimum patch size thresholds of reproductive success for golden-cheeked and black-and-white warblers, but not for white-eyed vireos. Minimum patch size of reproductive success was between 15 and 20.1 ha. Minimum patch size thresholds for occupancy, territory establishment by males, and pair formation were not consistent with thresholds for reproductive success. I found no relationships between patch size and cowbird parasitism or patch size and arthropod biomass. Conservation practices for target species based on thresholds of occupancy, territory establishment, or pair formation may not address issues of reproduction. The ability to identify thresholds of reproductive success for target species could be useful in conservation and management in multiple ways including setting goals for retention and restoration of a target species’ habitat patch size.