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San Antonio, TX, United States

Marshall M.E.,Texas A&M University | Morrison M.L.,East Wildlife Foundation | Wilkins R.N.,East Wildlife Foundation
Condor | Year: 2013

Vegetation characteristics affect avian reproductive success for a variety of reasons, including predators, nesting sites, song perches, and food availability. We investigated the relationship between habitat composition and prey availability and the effect these variables have on reproductive success in the Golden-cheeked Warbler (Setophaga chrysoparia). Our objectives were to determine differences in pairing and fledging success of Golden-cheeked Warbler territories in two distinctive vegetation types and to explore the relationship between reproductive success and tree species composition, arthropod density, and foraging effort. We sampled in 2009 and 2010 at Fort Hood, north-central Texas, within 347 territories of two vegetation types: post oak (Quercus stellata) habitat and Texas oak (Q. buckleyi) habitat. Pairing and fledging success of territories was significantly higher in Texas oak habitat. The birds' rate of movement was considerably higher in post oak habitat, indicating a difference in prey-encounter rate. Golden-cheeked Warblers clearly switched substrates on which they foraged from oaks in April to juniper in May. Arthropod sampling revealed a correlation between preferred foraging substrates and arthropod density. Our study of foraging indicates that the interplay between tree species and the arthropod communities they support is a crucial element driving the Golden-cheeked Warbler's reproductive success. © The Cooper Ornithological Society 2013.

Randklev C.R.,Texas A&M University | Wang H.-H.,Texas A&M University | Groce J.E.,Monash University | Grant W.E.,Texas A&M University | Wilkins N.,East Wildlife Foundation
Journal of Fish and Wildlife Management | Year: 2015

We assessed the influence of geology, land use, and other features on the occurrence of the rare freshwater mussel smooth pimpleback, Quadrula houstonensis, in the Leon River, Texas. Boosted regression trees were used to assess the relationships between the species’ occurrence and potential explanatory variables based on field data from 52 sampling locations. The individual variables that best explained prevalence for this species were downstream distance from reservoirs, percentage of shrubland within the riparian buffer, and percentage of alluvium and aquifer bearing rock-types. These results indicate that smooth pimpleback may be sensitive to flow modification and changes in land use that increase sedimentation. The application of similar modeling efforts to other rare species in this region could help in their management and conservation. © Citation of the source, as given above, is requested.

Collier B.A.,Texas A&M University | Farrell S.L.,Texas A&M University | Long A.M.,Texas A&M University | Campomizzi A.J.,Texas A&M University | And 4 more authors.
Auk | Year: 2013

Abstract.-Relating population density to spatially explicit habitat characteristics can inform management by directing efforts to areas with lower densities or focusing conservation and land protection on high-density areas. We conducted point-transect surveys for the endangered Golden-cheeked Warbler (Setophaga chrysoparia) and Black-capped Vireo (Vireo atricapilla) in the live-fire region of Fort Hood, Texas. We used mark-recapture distance sampling and combined a Horvitz-Thompson estimator with a habitat-based, resourceselection gradient to estimate spatially explicit density for both species. We detected Golden-cheeked Warblers at 120 locations (202, 197, and 89 detected by primary, secondary, and both observers, respectively) and Black-capped Vireos at 173 locations (241, 255, and 107 detected by primary, secondary, and both observers, respectively). For Golden-cheeked Warblers, the average (± SE) composite detection probability estimate within a 100-m point-sample radius was 0.57 ± 0.14, and for vireos it was 0.24 ± 0.02. Estimated mean density (singing males ha-1) was 0.14 ± 0.03 (95% confidence interval [CI]: 0.08-0.23) and 0.47 ± 0.05 (95% CI: 0.38-0.60) for Golden-cheeked Warblers and Black-capped Vireos, respectively. Our analysis suggested evidence of heterogeneity in the detection process for both species, as well as imperfect detection at distance g(0), both of which would bias estimated densities if ignored. Additionally, both species exhibited spatial variability in estimated densities, with those areas that had higher occurrence probabilities typically having higher estimated density. In the absence of spatially explicit density prediction, managers must treat all losses of potential habitat for endangered species uniformly, despite likely differences in conservation value. Our approach could be used to ascertain areas of changing density in relation to changing habitat conditions over time and space.© 2013 by The American Ornithologists' Union. All rights reserved.

Crimmins S.M.,West Virginia University | Crimmins S.M.,University of Wisconsin - Madison | Edwards J.W.,West Virginia University | Campbell T.A.,East Wildlife Foundation | And 4 more authors.
Northeastern Naturalist | Year: 2015

Management strategies designed to reduce the negative impacts of overabundant Odocoileus virginianus (White-tailed Deer) populations on forest regeneration may be influenced by changes in both population density and timber harvest. However, there is conflicting evidence as to how such changes in per capita resource availability influence home-range patterns. We compared home-range patterns of 33 female White-tailed Deer from a low-density population at a site with abundant browse to patterns of a sample of >100 females prior to a 75% reduction in population density and a doubling in timber harvest area. Home-range and core-area sizes were approximately 3 times larger than were found prior to population decline and timber harvest increase, consistent with predictions related to intraspecific competition. We also observed greater site fidelity than previously exhibited, although this may be an artifact of increased home-range sizes. Our results support previous research suggesting that White-tailed Deer home-range size is inversely related to population density and is driven, in part, by intraspecific competition for resources. Relationships among population density, resource availability, and home-range patterns among female White-tailed Deer appear to be complex and context specific.

Mellish J.M.,Texas A&M University | Sumrall A.,Texas A&M University | Campbell T.A.,East Wildlife Foundation | Collier B.A.,Texas A&M University | And 3 more authors.
Southeastern Naturalist | Year: 2014

Understanding the interrelationship of environmental and biological factors that influence population growth rates of invasive Sus scrofa (Wild Pig) is a requisite for population management of the species. Such information can be used to evaluate various types of population control to ensure that the most cost-effective damage-abatement methods are used. We developed a sex-and age-structured model to simulate general population dynamics of Wild Pigs in Texas. Our objectives were to estimate potential statewide Wild Pig population-growth rates for Texas, identify model parameters that most influenced population trajectories, and compare resulting model predictions with ancillary population-trend data. Our Wild Pig simulation model estimated a mean annual growth rate of 0.32 (SE = 0.01), and stochastic model projections of Wild Pig population sizes ranged from 3.6 million to 16.9 million after 5 years. To evaluate parameter sensitivity, we recast our simulation results into a Bayesian belief network, and evaluated input-parameter influence based on variance reduction using Shannon's measure of mutual information. Our results indicated that the most influential model parameters within our simulation were number of litters per female and number of piglets recruited into the population, while adult and juvenile survival had little influence on Wild Pig population size within our simulations. Overall, our results suggest that natural resource managers should focus efforts towards reducing Wild Pig reproductive success, as opposed to attempting to increase adult mortality, when conducting Wild Pig population-control campaigns.

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