Since 1990, wildlife biologists in Great Smoky Mountains National Park (GSMNP) have used capture and on-site release as the primary management technique to reduce recurrence of nuisance activity by American black bears (Ursus americanus). On-site release involves the capture and immobilization of bears that frequent developed areas, collection of biological data, and subsequent release in the area of capture. Although several studies have documented the effectiveness of this technique to reduce recurrence of nuisance activity, survival of bears after on-site release has not been thoroughly examined. We monitored 17 black bears (9 males and 8 females) that were radiocollared and released on-site in GSMNP between May 1997 and December 1998. We estimated short-term survival (May-Dec) using the Kaplan-Meier staggered entry procedure. Survival of black bears released on-site in GSMNP was 0.88 (95% CI = 0.70-1.00). We suggest that on-site release of nuisance black bears is an appropriate technique to reduce recurrence of nuisance activity while maintaining an acceptable survival rate in GSMNP.

We conducted a mark-recapture experiment to examine population dynamics of the fulvous harvest mouse (Reithrodontomys fulvescens) and plains harvest mouse (R. montanus) in response to low-level nitrogen amendments (16.4 kg N/ha/y) in an old-field grassland. The experimental design consisted of 16, 0.16-ha plots with four replicates of each treatment combination (fenced, nitrogen amendment; unfenced, nitrogen amendment; fenced, control; unfenced, control). We predicted that densities, survival, and transition probabilities would be greater for both species on nitrogen-amended plots because of greater aboveground biomass (i.e., enhanced concealment from predators). We observed no distinct patterns in survival or transition probabilities of R fulvescens or R. montanus with regard to treatments. Although population densities of R. fulvescens did not exhibit any distinct patterns with regard to treatments, densities of R. montanus tended to be highest on nitrogen plots, but lowest on nitrogen-fenced plots during winter 1999-2000. As low-level nitrogen amendments continue to be applied, we predict survival and densities of R. montanus and R. fulvescens on control plots, especially fenced plots with no nitrogen amendment, will eventually exceed those on nitrogen-amended plots as a result of higher plant species diversity, food availability and better quality cover.

The contribution of small mammals to nitrogen cycling could have repercussions for the producer community in the maintaining or perhaps magnifying of nitrogen availability. Our objective was to model nitrogen outputs (deposition of feces and urine) of small mammals in an old-field ecosystem and estimate the amount of fecal and urinary nitrogen deposited annually. To address this objective, we used models from laboratory studies and combined these with data from field studies to estimate dietary nitrogen and monthly and annual nitrogen outputs from fecal and urine deposition of five rodent species. The models accounted for monthly fluctuations in density and biomass of small-mammal populations. We estimated that the minimal amount of nitrogen deposited by rodents was 1.0 (0.9-1.1) and 2.7 (2.6-2.9) kg Nha(-1) year(-1) from feces and urine, respectively, for a total contribution of 3.7 (3.5-4.0) kg Nha(-1) year(-1). Hispid cotton rats (Sigmodon hispidus) accounted for >75% of the total nitrogen output by small mammals. Our estimates of annual fecal and urinary nitrogen deposited by rodents were comparable to nitrogen deposits by larger herbivores and other nitrogen fluxes in grassland ecosystems and should be considered when assessing the potential effects of herbivory on terrestrial nitrogen cycles.

Mesopredator populations are increasing because of habitat fragmentation and elimination of keystone predators. An increase of mesopredators, such as the raccoon (Procyon lotor) and Virginia opossum (Didelphis virginiana), may change competitive interactions within the trophic level of medium-sized carnivores and omnivores. We conducted live-trapping during 1998-2001 in north-central Oklahoma and compared population parameters of opossums living in areas with and without reduction of raccoons during 2000-2001. The equivalent of 6.2 raccoons/km(2) was removed from the treatment area. Capture rates of opossums were higher in the non-removal area for most of the study period, but population estimates and,density did not vary by treatment. Survival rates of opossums varied by sex and season, but not by treatment according to modeling of opossum survival. Habitat partitioning, prey switching by opossum predators, food supply, study scale, and environmental and demographic stochasticity may have masked effects of interspecific competition on population dynamics of opossums on the study site.

ii Notice The U.S. Environmental Protection Agency through its Office of Research and Development funded, and managed the research described herein. It has been subjected to the Agency's peer and administrative review and has been approved for publication as an EPA document. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. All research projects making conclusions or recommendations based on environmentally related measurements and funded by the U.S. Environmental Protection Agency are required to participate in the Protection Agency Quality Assurance Program. This project was conducted under an approved Quality Assurance Project Plan. The procedures specified in this plan were used without exception. Information on the plan and documentation of the quality assurance activities and results are available from the Principal Investigator. iii Foreword The U.S. Environmental Protection Agency is charged by Congress with protecting the Nation's land, air, and water resources. Under a mandate of national environmental laws, the Agency strives to formulate and implement actions leading to a compatible balance between human activities and the ability of natural systems to support and nurture life. To meet this mandate, EPA's research program is providing data and technical support for solving environmental problems today and building a science knowledge base necessary to manage our ecological resources wisely, understand how pollutants affect our health, and prevent or reduce environmental risks in the future. The National Risk Management Research Laboratory is the Agency's center for investigation of technological and management approaches for preventing and reducing risks from pollution that threatens human health and the environment. The focus of the Laboratory's research program is on methods and their cost-effectiveness for prevention and control of pollution to air, land, water, and subsurface resources; protection of water quality in public water systems; remediation of contaminated sites, sediments and ground water; prevention and control of indoor air pollution; and restoration of ecosystems. NRMRL collaborates with both public and private sector partners to foster technologies that reduce the cost of compliance and to anticipate emerging problems. NRMRL's research provides solutions to environmental problems by: developing and promoting technologies that protect and improve the environment; advancing scientific and engineering information to support regulatory and policy decisions; and providing the technical support and information transfer to ensure implementation of environmental regulations and strategies at the national, state, and community levels. This publication has been produced as part of the Laboratory's strategic long-term research …

We examined the reliability of using nitrogen concentration of stomach contents from hispid cotton rats (Sigmodon hispidus) as an index of dietary nitrogen. Stomach contents of hispid cotton rats fed pelleted diets varying in nitrogen concentration were analyzed for stomach nitrogen. Regression analysis revealed a positive linear relationship between stomach and dietary nitrogen, but the relationship was not 1 : 1. Thus, inverse estimation of the regression equation can be used to adjust for a lack of a 1 : 1 ratio to obtain more reliable and accurate estimates of diet quality. Although we expected this relationship to be robust in its application to field studies, the pelleted diet model consistently underestimated dietary nitrogen during model evaluation experiments with natural forages. We conclude that the applicability of using nitrogen concentration of the stomach contents of cotton rats as an index to dietary nitrogen is dependent on the level of accuracy and precision required in estimating nitrogen concentration of foods consumed.

We conducted a mark–recapture experiment to examine the population dynamics of hispid cotton rats (Sigmodon hispidus) in response to low-level nitrogen amendments (16.4 kg nitrogen/ha per year) and exclosure fencing in an old-field grassland. The experimental design consisted of sixteen 0.16-ha plots with 4 replicates of each treatment combination. We predicted that densities, reproductive success, movement probabilities, and survival rates of cotton rats would be greater on nitrogen-amended plots because of greater aboveground biomass and canopy cover. Population densities of cotton rats tended to be highest on fenced nitrogen plots, but densities on unfenced nitrogen plots were similar to those on control and fenced plots. We observed no distinct patterns in survival rates, reproductive success, or movement probabilities with regard to nitrogen treatments. However, survival rates and reproductive success tended to be higher for cotton rats on fenced plots than for those on unfenced plots and this was likely attributable to decreased predation on fenced plots. As low-level nitrogen amendments continue to be applied, we predict that survival, reproduction, and population-growth rates of cotton rats on control plots, especially fenced plots with no nitrogen amendment, will eventually exceed those on nitrogen-amended plots as a result of higher plant-species diversity, greater food availability, and better quality cover.

Bioavailable nitrogen is a limiting nutrient throughout the Eastern United States. Research demonstrates that exposure to large doses of nitrogen leads to deleterious environmental impacts. However, effects of chronic exposure to lower doses of nitrogen are not well known. Since 1998, we conducted an integrated multidisciplinary study investigating ecosystem feedback associated with chronic exposure to low doses of nitrogen. In this nitrogen-limited ecosystem, the ability of the soil system to adapt to new nitrogen inputs was degraded by the first winter season when soil nitrate concentration (indicated by extract concentration) increased 590%. Increased concentrations of nitrate were especially evident on fertilized plots (P<0.0001) but also were measured on plots that were only fenced to manipulate herbivore abundance (P=0.0443). Changes to the plant, macro invertebrate, herbivore, and microbial communities each reduced ecosystem nitrogen use efficiency thereby producing a selfreinforcing positive feedback loop leading to conditions favoring greater concentrations of soil nitrate. Because all of these effects occur together, it is unclear whether the results seen in soil nitrogen Jorgensen, Holub, and Mayer are Ecologists and Gonsoulin is a Microbiologist, U.S. Environmental Protection Agency, Office of Research and Development, National Risk Management Research Laboratory, P.O. Box 1198, Ada, OK 74820. E-mail: Jorgensen.Eric@EPA.GOV. Silva is a Soil Scientist and West is a Microbiologist, Oak Ridge Institute for Science and Education, Oak Ridge, TN 37831. Tunnell is a Range Scientist, Clark and Parsons are Wildlife Scientists, and Engle and Hellgren are Professors, Oklahoma State University, Stillwater, OK 74078. chemistry are from one or some combination of them working together. What is clear however is that changes to trophic feedbacks associated with chronic exposure to low levels of bioavailable nitrogen resulted in an annual mean nitrogen excess of 105.6%. Although it was not our goal to measure mass balance for all nitrogen loss pathways, we estimate that ecosystems similarly exposed to excess or new sources of nitrogen may be at risk and are capable of leaching essentially all new nitrogen additions during seasons of dormancy. These experiments demonstrate that even the relatively small amount of nitrogen deposited in precipitation has the capacity to change multiple aspects of ecosystem structure and function.

Along tire northern periphery of their range, populations of the hispid cotton rat, Sigmodon hispidus, are vulnerable to major reductions in density and occasional local extinctions as a result of severe winter weather. Between our sampling periods on 3 December 2000 and 14 January 2001, 3 independent winter weather events, in conjunction with the coldest month in the state since 1983, affected central and eastern Oklahoma. We recorded a drastic decline in the population of hispid cotton rats at the Center for Subsurface and Ecological Assessment Research in central Oklahoma following these winter weather events. Densities dropped from 58.6 cotton rats/ha on 3 December 2000 to 1.2 cotton rats/ha on 14 January 2001. Although hispid cotton rat densities were declining before these winter weather events occurred, we attributed the dramatic decrease to severe winter weather and below-normal temperatures. As of 19 November 2001, the population of hispid cotton rats at the site had not recovered. Abundances between January and November 2001 ranged from 0.6 to 2.6 cotton rats/ha compared with a range of 30.1 to 112.5 during the same period in 2000. Additionally, we present evidence of populations of hispid cotton rats being affected at a statewide scale as a result of the weather in December 2000. We suspect that severe winters, such as the events described, might slow the northward advance of hispid cotton rats and serve to indirectly regulate populations along the intermediate and northern fringes of its range.

Rehabilitation and release of orphaned bears into the wild offers bear managers an alternative to euthanasia or transfer of bears to captive facilities. Theobjective of our study was to estimate short-term survival of orphaned American black bears (Ursus americanus) rehabilitated and released into the Smoky Mountains. Between January 1998 and July 1998, we released 11 rehabilitated orphaned bears (6 males, 5 females) into the Smoky Mountains of Tennessee and North Carolina. Age of bears at time of release ranged from 11 to 18 months old. We monitored released bears via radiotelemetry from January 1998 to October 1998. Although we documented no mortality of bears, the fate of 2 bears in the study was unknown. Maximum survival (assuming 2 bears of unknown fate survived) to 180 days post-release was 1.00 (95% Cl = 0.22-1.00), and minimum survival (assuming 2 bears with unknown fate died) to 120 and 180 days post-release ranged from 0.90 (95% Cl = 0.69-1.00) to 0.77 (95% Cl = 0.26-1.00), respectively. Our results indicated that short-term survival (to 180 days) of rehabilitated orphaned bears was high and may be a viable alternative for managers dealing with orphaned bears.